1

MC LC

LI NI U ................................................................................................................. 3 Chng 1: C S CHP X-QUANG TNG SNG TRUYN HNH ........................ 5

1.1 TNG QUAN ......................................................................................................... 5 1.1.1 Tia X ................................................................................................................ 5 1.1.2 ng tia X .......................................................................................................... 6 1.1.3 S hp thu tia X ................................................................................................ 7

1.2. NG DNG X- QUANG, LCH S CHP, CHIU X- QUANG ......................... 9 1.2.1. Chiu v chp X quang .................................................................................. 10 1.2.2. Cng dng v hn ch .................................................................................... 11

1.3 MY X- QUANG TNG SNG TRUYN HNH ............................................... 12 1.3.1. My X quang tng sng .................................................................................. 12

1.3.2. V tuyn truyn hnh X quang ....................................................................... 15 1.4. S lc v vic ng dng vi x l trong thit b X- quang .................................... 18 1.5. Kt lun ................................................................................................................ 20

Chng 2: S KHI V CHC NNG CA MY XM-1550 ........................... 21 2.1. Thnh phn chc nng .......................................................................................... 21

2.1.1. Tnh nng k thut ......................................................................................... 25 2.2. S NGUYN L V HOT NG CA MY ......................................... 27

2.2.1. Bng X quang ............................................................................................. 27 2.2.2. Khi cao th ................................................................................................... 33

2.2.3. B t ng iu chnh nh sng...................................................................... 38 2.2.4. B to nh ...................................................................................................... 54

2.3. Kt lun ................................................................................................................ 69

Chng 3: VN HNH BO DNG V CCH KHC PHC MT S HNG HC THNG THNG ............................................................................................. 70

3.1. CC THAO TC VN HNH MY .................................................................. 70 3.1.1. Nhng ch v an ton .................................................................................. 70 3.1.2. Cch thc t ng phim............................................................................. 70 3.1.3. Cch thc vn hnh bng iu khin thao tc bng tay ................................... 71 3.1.4. Vic vn hnh gi chn, tay g v gi vai ............................................. 71

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3.1.5. M bng X- quang ......................................................................................... 72 3.1.6. Cc thit b v dng c bung ti ................................................................... 72

3.2. BO DNG ...................................................................................................... 76 3.2.1. Lm sch mn tng sng ................................................................................ 76 3.2.2. Qu trnh bo dng nh k .......................................................................... 76 3.3.3. Mn hnh tng sng v vic sa phim ............................................................. 79

3.3. CCH XC NH CC HNG HC CA KHI ............................................. 80 3.3.1. Cc m li ...................................................................................................... 80 3.3.2. Mt s hng hc v cch khc phc ............................................................... 82

3

LI NI U

Cc thit b y t l cng c c lc khng th thiu c ca cc thy thuc trong cc bnh vin t tuyn huyn, tuyn tnh, n tuyn trung ng. Trong nhng nm gn y, cng ngh chn on hnh nh c nhng bc pht trin vt bc vi s xut hin ca cc k thut chn on hnh nh mi nh CT, MRI. Bn cnh s xut hin ca cc k thut chn on hnh nh mi, k thut chn on hnh nh xut hin u tin l X quang cng khng

ngng pht trin v ngy cng hon thin hn. My X-quang ni chung v my X-quang tng sng truyn hnh ni ring, gip chn on a ra cc phng php iu tr thch hp gip vic hi phc sc khe ca ngi bnh c nhanh chng .

Thit b X quang l thit b to nh v cu trc bn trong ca i tng nghin cu trn c s ng dng tnh cht l ha ca tia Rnghen (tia X). Thit b X quang c ng dng rt rng ri trong cc lnh vc: thm d a cht, kim tra cht lng sn phm, trong nghnh hi quan Trong y t, n l mt cng c ch yu chn on v iu tr bnh. Thit b X quang l loi thit b kh t tin so vi thit b khc trong bnh vin. ngoi ra cc thit b phc v n cng kh tn km nh: phng t my, bung ti, ba tng quang, catxet do i hi k thut vin, bc s s dng vn hnh phi c trang b nhng kin thc c bn c kh nng lm ch thit b. i vi k thut vin, k s lm cng tc lm bo dng, sa cha li cng phi c hiu bit cao hn v phn tch mch, o c, vn hnh thnh tho. Hin nay Vit Nam c rt nhiu my X-quang ca nhiu nc sn xut vi nhiu mu m chng loi khc nhau. Trong ti ny ti cp ti my

X-quang tng sng truyn hnh XM-1550 y l loi my c s dng rng ri ti cc c s y t t trung ng n a phng. V cu to c bn ging vi my X-quang tng sng truyn hnh khc. c nhiu tnh nng thay th cho

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php bc s c th thc hin cc k thut x-quang can thip vo bnh nhn bng quan st trn mn hnh kt hp thao tc trn bnh nhn.k thut vi x l c ng dng lm cho cc qu trnh x l ca my c t ng ha, chnh xc,an ton, tin cy c ci thin ng k so vi cc my X-quang th

h c. Mch in c thay th nng cp thng dng cc loi IC tch hp ln c vi iu khin lm cho mch in c cu to gn nh hn v kch thc khi lng ca my gim i rt nhiu v iu quan trng hn l tc x l ca mch nhanh hn, n nh v c chnh xc cao. Chnh v vy ti

tm hiu lm ti my X-quang tng sng truyn hnh XM-1550. ti ny gm 3 phn chnh: Phn 1: C s chp X-quang tng sng truyn hnh. Phn 2: S khi v chc nng ca my XM-1550. Phn 3: Vn hnh bo dng v cch khc phc mt s hng hc thng thng.

n c thc hin di s hng dn ca Thc s Phm Phc Ngc - ging vin B mn in t Y sinh -.Khoa in t Vin Thng. Mc ch

ca n l nghin cu nguyn l hot ng ca my v phn tch hot ng trn s chc nng ca my.

Trong qu trnh lm n, bn thn ti nhn c s gip to ln ca thy Phm Phc Ngc tn tnh hng dn ti hon thin n.

Cho php ti c by t lng bit n chn thnh n thy!

H ni ngy 6 thng 9 nm 2012.

Ngi thc hin: Trnh Quang Ni

5

Chng 1 C S CHP X-QUANG TNG SNG TRUYN HNH

1.1 TNG QUAN 1.1.1 Tia X Tia x c mt nh vt l ngi c tn l Roentgen (1845-1923) pht minh nm 1895 .Bn cht tia X l loi bc x in t c bc sng trung bnh khong 8-10 cm.tia X pht ra do cc in t c c vn tc ln c phng ra t in cc m v p vo in cc dng ng nng ca chng b bin i 99% bin thnh nhit nng v mt phn nh thnh bc x tia X T nguyn l trn y pht sinh ra tia X cn c : + mt ngun in t:c to nn t pha in cc m ca mt tc n,khi c mt ngun in c hiu in th rt ln chy qua .Hiu in th ny c c nh mt bin p nng ln hng vn vn.Mt my X quang thng thng c cng sut t 45-70 kv ,cc my c cng sut ln in p c th t 50-120 kv .Cht lng ca tia X tc l sc m xuyn ca tia X ph thuc vo hiu in th ca dng in .S lng tia X c to ra ph thuc vo cng dng in i qua .ng i ca cc in t t cc m sang cc dng nm trong mt bng thy tinh chn khng. +cc dng cn gi l i cc ni pht sinh ra tia X .c cu to bng mt bng kim loi chu nhit cao c tc dng hm cc in t c gia tc . Nhng tnh cht c bn ca tia X: -Xuyn qua vt cht

-Tia X lm pht sng cht hunh quang t trong bng ti -Tia X trc tip lm en phim nh ging nh nh sng -Tia X c tc dng sinh hc -N c to ra bi mt n chn khng nng lng cao

6

Tuy nhin, c nhng vn m Roentgen ch khm ph ra,v phi mt 50 nm sau cc nh khoa hc mi nh gi y l tia X c th nguy him nu khng s dng hp l v c th gy ra bnh ung th Lc tia mm :khng c tc dng to nh gy hi cho c th . Qua nhiu nm thit b X quang khng ngng c hon thin -ci thin cht lng hnh nh

-nng cao tng phn gia cc m khc nhau -ci thin kch c phn gii

-lc tia cng

Gim ti mc thp nht liu lng ti ngi bnh.

1.1.2 ng tia X ng tia x n gin l mt it ng chn khng kn bng thu tinh bao

gm mt catt khi nung nng pht ra cc electron v mt ant chn cc tia electron . Catt c nung bng si t, mt ant v mt ng thu tinh

chn khng kn . in p V F ngun si t sinh ra dng I F chy xuyn qua

li si t, t nng tm kim loi ca catt. Electron trong catt c nung nng bt ra khi tm kim loi ca catt i vo trong chn khng. in p ant

VA ln cc electron ny to thnh dng tia I B . in p V A trn ng tia

l rt ln, c th ln n trn 100 kV. in p cao ny y electron ti vn tc cao. Gn 1% cc electron trn khi ti ant va chm vi cc nguyn t v sinh ra cc tia X. Sau cc tia X i xuyn qua ng vo trong khng kh. 99% cc electron cn li to thnh nng lng nhit.

hiu cc tia X c sinh nh th no u tin phi xem xt n cc dng tia in t. in t c thot ra khi catt t nng nh chuyn ng nhit em n cho chng nng lng ln thot ra khi lc lin kt nguyn t i vo trong ng chn khng. Gi tr ca nng lng gi l chc

nng lm vic E H gi tr ny ph thuc vo kim loi lm catt . Gi tr ca

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dng tnh bng ampe sinh ra bi bi s chuyn ng nhit, I B nhn c t vic nghin cu c hc lng t nh sau:

I B =C0ACT2e-11600 Tw /E

(1.1)

y AC

l din tch catt tnh theo m2, v C0 l h s vt cht ca catt. Gi tr ca C0 i vi vt cht khc nhau s c gi tr khc nhau.

(I) Khi in p V A cn thp to ra khng gian tch in hnh thnh xung quanh catt trong ng chn khng, dng in t c theo c s ca vt l lng t tnh theo cng thc sau:

I BE =2,33(10-6)AC

d

VA2

2/3

(ampe) (1.2) y d l khong cch tnh theo m t catt ti ant, v AC l din tch

catt tnh theo m2. Trong mt ng tia x c thit k ph hp, d nh sao

cho I B

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b dy vt cht hp thu ngang bng vi kch thc ca cng bc x . Ni mt cch khc, phn s ca nng lng tia x b hp thu t l vi b dy vt cht hp thu n. nh lut Lambert c bt u bi cng thc ton hc sau:

dsd

= (1.3)

y l mt khi lng trung bnh , s l khong cch xuyn qua vt

cht, v l hng s t l c gi l h s suy gim khi c n v o l

cm2/g. K hiu d c trng s thay i khc nhau ca cng tia X theo khong cch. gii phng trnh 1.5 ta ly tch phn 1.5 s cho kt qu:

=0e-s (w/m2) (1.4) y 0 l cng tia x ti m v l cng tia x l ra t m b dy s.

Cc gi tr ca theo n v cm2/g cho bi hnh 1.3, minh ho cc gi tr quan h i vi xng v m. Mt tiu biu ca cc m sinh hc l gi tr xc nh tu thuc vo cc m khc nhau. N l gi tr biu kin ch ra rng nghin cu xng bc s nn s dng in p ant thp, thng l 60 kV, v iu ny lm cho n d dng phn bit n vi c. Theo mt cch khc ,nu bc s mong mun lm m xng phn bit m c nm di t lp m,

th nn s dng in p ant cao thng l 200 kV. Hn na cc gi tr l xp x bng nhau. V vy, tht kh nhn c cc gi tr ln ca tng phn gia cc m mm khi s dng x quang.

R rng cng tia X pht ra t nc l ln hn nhiu so vi t xng. iu ny c ngha l xng hp thu nng lng tia x nhiu hn nc. Hn na s khc nhau v cng tia X trn phim s to ra nh c tnh cht

tng phn tt.

1.1.4 tng phn m tng phn ca nh trn phim gia 2 m c xc nh trong cc

iu kin ca cc cng tng i ca cc tia x thu c trn phim. 1 l

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cng ca cc tia x thu c t m 1 v 2 l cng ca cc tia x thu c t m 2. tng phn gia 2 m c xc nh bi phng trnh :

C12=10log

2

1 (dB) (1.5)

y nhn vi 10 v t s 1/2 l t s nng lng. Kt hp vi cng thc (15.6) ta c:

C12=10 loge

es

s

222

111

0

0

(dB)

y s1 l b dy ca m 1 v s2 l b dy ca m 2 .Bin i phng trnh ny ta c :

C12=10 (log e) ( s222 - s111 ) Hoc

C12=4,3429 ( s222 - s111 ) (dB) (1.6) T phng trnh ny chng ta kt lun rng tng phn gia 2 m

ph thuc vo h s suy gim khi, mt v b dy ca chng. Thc t C12 tng cng vi s chnh lch gia cc tham s trn.

1.2. NG DNG X- QUANG, LCH S CHP, CHIU X- QUANG Thit b X quang l thit b to nh v cu trc bn trong ca i tng

nghin cu trn c s ng dng tnh cht l ho ca tia Rnghen (tia X). Thit b X quang c ng dng rt rng ri trong cc lnh vc: thm d

a cht, kim tra cht lng sn phm, trong ngnh hi quan... Trong y t, n l mt cng c ch yu chn on v iu tr bnh. Thit b X quang l loi thit b kh t tin so vi thit b khc trong bnh vin. Ngoi ra cc thit b phc v n cng kh tn km nh: Phng t my, bung ti, ba tng quang, catxet... do i hi k thut vin, bc s s dng v vn hnh phi c trang b nhng kin thc c bn, c kh nng lm ch thit b. i vi k

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thut vin, k s lm cng tc bo dng sa cha li cng phi c hiu bit cao hn v phn tch mch, o c, vn hnh thnh tho.

Tri qua hn mt th k pht trin, thit b chp X quang c nhiu th h v cng vi s tin b ca khoa hc k thut ni chung, n cng ngy cng c nhiu chc nng chn on phc tp hn, p ng yu cu thc tin mt cch hiu qu.

1.2.1. Chiu v chp X quang C hai phng php thm khm bng tia X l chiu v chp. Hai

phng php ny khc nhau v nguyn tc, c nhng u nhc im nht nh v b sung cho nhau.

a. Chp X quang Hnh nh c ghi li trn phim dng cho vic chn on. Phng php

ny c nhng u im sau: - C th t c phn gii cao nh p dng nhng tham s k thut

thch hp nh tr s in p kV, dng in mA... - C th thay i i quang trong phm vi rng bng cch s dng

cng chiu x thch hp.

- Khng b g b bi thi gian. - Gim liu tia i vi ngi bnh do thi gian chp rt ngn. - Gim liu tia i vi ngi vn hnh do c th ng ngoi khu vc nh

hng ca tia.

- Cui cng, c th lu tr nh lu di, tin li cho vic theo di, nh gi s tin trin ca cn bnh...

b. Chiu X quang nh X quang c ghi nhn v nh gi bi ngi vn hnh. Nhng u

im ca phng php ny nh sau: - Vic chn on nhanh chng tc thi.

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- C th nh v ngi bnh t th thch hp nht sao cho hng chiu v kch thc chm tia X to c nh tt nht.

- C th iu chnh tc thi cng sut pht x ph hp vi tng i tng thm khm.

- Thch hp vi vic quan st nhng t chc ng nh s co bp ca tim v cc mao mch ln.

- Thch hp vi vic quan st v thc hin cc th thut nh tho lng, b xng, ly d vt.

Nh vy c th ni hai phng php trn c nhng u nhc im nht nh so vi nhau, chng c ng dng trong nhng thm khm cc i t-ng khc nhau v trong cc hon cnh khc nhau tu theo ch nh ca thy thuc, chng song song tn ti v h tr nhau.

1.2.2. Cng dng v hn ch a. Cng dng Trong ngnh y t, my X quang c ng dng ph bin ti cc bnh vin

t tuyn huyn n trung ng. N l thit b ch yu dng trong vic chn on thng qua vic c, nh gi hnh nh trn phim. My c th c dng chn on nhng bnh thuc cc b phn sau:

- Xng: rn, gy, vim khp, cc khi u - S no: chn thng, nhim trng, khi u ... - Lng ngc: lao, nhim trng h hp, cc bnh v tim... - bng: chn thng, tc rut, si thn, tit niu... - M mm: k sinh trng, s vi ho...

b. Hn ch My X quang truyn thng c nhng hn ch nht nh. nh X quang l

nh xp chng, mt khc phn gii v i quang ca nh cha tht cao nn kh thm khm nhng b phn nm su trong c th nh pht hin khi u trong s no, nhng khuyt tt trong mao mch c bit trong giai on u

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khi nhng triu chng cn cha r rt. Hn na tia X l tia c hi cho c th, v vy vic thm khm bng my X quang khng th p dng cho mi i t-ng.

b khuyt cho nhng hn ch ca my X quang truyn thng, trong vi thp k gn y, cc nh nghin cu pht minh ra hng lot thit b chn on hnh nh mi nh siu m, chp ct lp my tnh, chp cng hng t. Nhng thit b ny ang ngy cng c s dng rng ri, tuy nhin chng cng c nhng hn ch, v d nh chi ph u t thit b v chi ph cho mt xt nghim bng my chp ct lp in ton cao hn nhiu ln so vi my X quang truyn thng, v vy chng ch b sung m khng loi tr nhau. My X quang v vn l mt thit b chn on hnh nh quan trng trong y t.

1.3 MY X- QUANG TNG SNG TRUYN HNH 1.3.1. My X quang tng sng

T 60 nm v trc, ngi ta khm X quang bng phng php chiu X quang v chp X quang. Trong thi gian , cc tin b v k thut cho php ch to nhng my pht in v bng X quang ngy cng mnh v tinh xo. Nhng s ci tin cn tng i chm trong phm vi cc b phn tip nhn nh mn hunh quang chiu X quang, phim v mn tng quang.

Chiu X quang vn l phng php n gin nht lm cho thy c hnh nh ca c th. Nhng hnh khng r do trong iu kin t nh sng, mt tip nhn hnh nh thng qua cc t bo que trong vng mc. Nhng t bo ny khng phn bit c cc chi tit v m nht bng cc t bo hnh nn. sng ca mt mn chiu X quang l chng 0,1 - 0,001cd/cm2. nh sng bnh thng ca mt vt m ta nhn r c l 100cd/cm2.

S thay i ca cc photon nh sng ln hn nhiu s thay i lng ca

cc photon chm tia X. R. E. Sturm v R. H. Morgan chng minh rng vng mc tip nhn t photon nh sng hn l mn hunh quang. Ngi ta c

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th lm cho hnh r hn bng cch tng cng tia X nhng liu hp th tia X ca bnh nhn bt buc vn phi tng i thp.

S cn thit tng sng r rt. nh trn y khng phi l mi. T nm 1934, Philips tm ra nguyn l truyn hnh, nhng lc k thut cha cho php to ra my ni trn.

S ra i ca my tng sng cn ph thuc vo cc tin b trong cc lnh vc khc nh:

- Vic nghin cu s thay i cc bc sng ca cc tia khng nhn thy c thnh nh sng (bng hunh quang).

- S nghin cu cc hin tng quang in (bng, my quay phim truyn hnh). - S nghin cu v quang in t (ng tia m cc). Ngi ta c th ni, b phn tng sng l tng hp ca cc my trn,

c pht minh nh cc cng trnh nghin cu mi. C hai gii php dng thc hin bng tng sng X quang: - Gii php trc tip ngn mn soi X quang v b phn tng sng. Gii

php ny ph bin nht. - Gii php gin tip ngn mn soi X quang v b phn tng sng. Mi lin

lc gia hai phn trn c bo m bng cc thu knh hoc cc b phn quang hc c gng phn chiu.

a. Nguyn l my tng sng trc tip Bng tng sng l mt bng chn khng c hai mn chn: mt mn s cp (mn

vo) c kch thc ln v mt mn th cp (mn ra) bng 1/10 mn th nht. Hnh chiu sng c chm tia X a ti mn hunh quang sau khi xuyn

qua bnh nhn. Mn chuyn cc photon tia X thnh photon nh sng. Cu to ca mn ny cng nh mn soi X quang (c km sulfat v caimi) nhng mng hn (vi phn mi ca 1mm). Vi mt cng 1mAs, t 60 - 100kV, mt tia X l 2.105 photon/1mm2 trong 1s. Mi photon tia X bin thnh 5.000 - 6.000 photon nh sng. Trong cc iu kin trn, mn c

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sng khong 10-2cd/mm2. Mt lp nhy cm nh sng ca mn hp th hu ht cc photon nh sng v pht ra cc photon in t. Lc cc in t c gia tc bi mt in th chng 25kV v c t trng tp trung p vo mn th cp kch thc nh hn.

Mn th cp thuc loi P.20, c mt hunh quang vng l m v cho mt hnh nh sng hn hnh ca mn chiu X quang t ch mn s cp ca bng hng nghn ln. S tng sng mt phn nh c s gia tc cc photon in t v mt phn nh vic gim ng knh ca mn th cp so vi mn

s cp.

Hnh nh trn mn th hai li c truyn i: - Hoc qua b phn quang hc quan st trc tip. Gii php ny khng

c ph bin v nguy him cho thy thuc ng gn bng X quang. - Hoc qua mt my quay phim truyn hnh. - Hoc c kt hp vi mt my quay phim X quang. Hai cch dng di

l ph bin v thng c phi hp vi nhau.

b. c im ca bng tng sng - ng knh ca mn s cp Cc bng tng sng u tin c mt ca vo ng knh 12,5cm, khng

cho my c p dng rng ri trong lm sng. Ngi ta c hng ch

Hnh 1-48. S nguyn l bng tng sng 1: mn s cp; 2: lp nhy i vi tia X; 3: in cc hi t;

4: mn th cp; 5: ng knh; 6: ant

1 2 3

5

6

4

in t Photon tia X

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to th cc bng tng sng ln nhng vn m bo khng kch thc v cn nng qu mc.

Hin nay kch thc bng nhiu nc t 16 - 30cm (Thomson). Loi 16cm nh dnh cho cc my lu ng. Loi 22cm, kch thc va phi c dng vo nhiu hot ng. Loi 30cm trong mt s trng hp cho php tin hnh tt c cc xt nghim thng thng.

- Kch thc ca mn th cp Kch thc ca mn th cp lin quan n kch thc ca mn s cp.

Vic gim hnh l mt yu t lm tng sng nn rt c li khi ngi ta ch to mn th cp nh ti thiu.

- c im ca hnh thu c

Hnh thu c c nh gi qua tng sng v yu t chuyn hnh.

tng sng l t l gia sng ca mn th cp v mn chiu X quang, vi cng tia X nh nhau. Lc u, tng sng ca cc my c chng 1.000 ln. Hin nay, cc my c tng sng t 3.000 - 6.000 v mt s t n 9.000 ln.

Ngi ta nh gi mt bng tng sng c v yu t chuyn hnh: l t l gia sng ca mn s cp vi cng chm tia X. Yu t chuyn hnh chng 50 - 100 cd/m2 vi cng 1mR/s. N ph thuc vo bn cht ca mn v thay i vi cht lng ca tia X.

1.3.2. V tuyn truyn hnh X quang Cc hnh nh hot ng trn mn X quang c th truyn i c xa. S

pht trin ca v tuyn truyn hnh trong ngnh X quang i i vi vic hon thnh bng tng sng.

V tuyn truyn hnh X quang l mt phng php ging dy tt: vic

truyn hnh X quang i mt khong ngn, ngay trong phng khm bnh c

p dng rng ri, c nhiu u im v thay th cho cng tc chiu X quang

trong bung ti. mt s nc, thy thuc ch c chiu X quang qua v

16

tuyn truyn hnh v liu lng tia X pht ra rt t. Nhiu thy thuc c th

cng quan st hnh X quang trn mn v tuyn m khng gy tr ngi, lm

vng ngi ang phu thut. Ngoi ra hnh nh trn mn v tuyn rt sng

v chng ta c th quay thnh phim chiu bng c.

a. Nguyn l Nu ch cn truyn i s thay i theo thi gian ca cng nh sng

mt im c nh th cng ging nh vic truyn i cng ca m thanh.

im pht sng, nng lng nh sng bin thnh in nng nh mt t bo

quang in v tn in ny s c truyn n my thu cng vi s thay i

bin ca nh sng.

Nhng i vi mt hnh nh cu to bi hng nghn, vn im sng, th

vic truyn nhiu tn in li cng phc tp, v ngoi cng nh sng cn

phi em n my thu v tr ca cc im sng mt cch chnh xc.

Mt sng in khng th truyn i cng mt lc cc tn hiu ca mt hnh

nh. Vic phn tch quy m mt hnh nh bng mt im sng (spot) trong ng knh truyn hnh gi l mch qut.

S mch qut trong v tuyn truyn hnh (625 dng): im sng (spot) i theo cc dng s l ri qua cc dng s chn. Trong 1s im sng (spot) qut 50 mch chn v 50 mch l.

Hnh nh hin ln mn thu cng c to nn nh mt im sng (spot) qut ln mn do mt s mch ging ht cc mch trong ng knh truyn hnh.

S tn ti nh sng trn mn mt thi gian ngn v s lu li cm gic ca

vng mc cho ta thy ton b hnh nh pht i t bng tng sng.

ng knh truyn hnh dng trong X quang c hai loi: ng Vidicon v ng

Orthicon.

B phn quang hc dng t hnh X quang ln m cc trong my truyn hnh

phi c cht lng tt, tht sng gim bt liu hp th tia X cho bnh nhn.

17

b. ng Vidicon Nguyn l ca ng ny da trn hiu ng quang dn. Pha trc ng c mt tm bia rt mng c tnh cht quang dn. Cht selen

dng lm cht quang dn lc u c thay th bng cht trisulfua antimoan rt nhy cm v thch hp vi mn th cp P. 20 ca bng tng sng. C ni sn xut bia bng plumbicon. nh sng chiu vo bia s lm gim in tr v mt dng in s pht sinh. Cng dng in mi t l thun vi sng ca im chiu ln mn. Ngoi tm bia cn c hai cun dy hi t v qut a dng in qua dy cp ng trc vi mn thu hnh.

c. ng Orthicon Nguyn l ca ng ny dng hiu ng quang in. Mn knh mng qut bt cesi pht sinh ra quang in t khi b photon nh

sng p vo. Cc in t c gia tc v p vo tm bia thy tinh mng to nn mt lung in ti dng t l thun vi cng ca tia sng i ti. Mt chm tia in t c sng in t bn i ti tm bia v tr li b phn bi nhn in t.

Hnh 1-49. Cu to ng Vidicon 1: bia; 2: h thng hi t; 3: ant;

4: catt; 5: h thng qut; 6: quang knh

Tn hiu

Chm in t

18

1.4. S lc v vic ng dng vi x l trong thit b X- quang Vic ng dng k thut s v mch vi x l (microprocessor) trong h

thng iu khin l mt tin b mi trong cng ngh ch to my X quang trong nhng nm gn y. Microprocessor thng c ng dng trong cc my X quang cao tn.

Nh ng dng Microprocessor, my X quang tr nn a nng, qu trnh chp nhanh chng, chnh xc v tin cy hn. Hn na, my ngy cng tr nn gn nh hn, chim t din tch hn v c ng. Ngi s dng c th xy dng v lu tr cc chng trnh thm khm ph hp vi cng vic ca mnh trong b nh ca my v c th bt my thc hin cc chng trnh ny ch cn vi vi thao tc n gin.

Ngi sa cha, bo dng cng s c h tr bi thng tin do my cung cp v tnh trng ca n thng qua cc chng trnh kim tra v cc thng bo li (nu xy ra). Ngoi ra, mt iu khng km quan trng l gi my khng nhng khng tng m cng ngy cng gim nh vic ng dng ph cp nhng cng ngh in t cao cp ny.

Hnh 1-50. Cu to ng Orthicon 1: mn nhy sng; 2: biathu tinh; 3: h thng hi t; 4: h thng qut; 5: sng in t; 6: b nhn in t;

7: quang in t; 8: quang knh

Tn hiu

5

4 3

2 1

8 7

6

19

B no ca h thng iu khin l mt b x l trung tm (Central Processing Unit - CPU). N chnh l mt b vi x l chu trch nhim iu hnh, kim sot v ghp ni mi hot ng ca mi thit b nm trong h thng sao cho c h thng thc hin lnh ca ngi vn hnh mt cch trt t

v hon ho. Vic ghp ni gia CPU vi cc thnh phn khc trong h thng iu khin nh cc b nh (memory), cc cng giao din (port)... v cc thit b khc nh bn phm, khi cao th... c thc hin thng qua cc tuyn tn hiu bao gm tuyn iu khin (control bus), tuyn a ch (address bus) v tuyn d liu (data bus). Cc chng trnh v d liu trong h thng iu khin c lu tr trong hai loi b nh l b nh tnh v b nh ng. B nh tnh hay cn gi l b nh ch c ROM/PROM (Read Only Memory) l b nh lu tr chng trnh chnh ca h thng iu khin nh chng trnh kim tra khi bt my, cc th tc ca mt thao tc nh chiu hoc chp, chng trnh kim tra tnh trng thit b v thng bo li... B nh ng l b nh c th ghi v c RAM (Random Access Memory), n lu tr nhng thng tin tm thi trong qu trnh hot ng v vy khi tt my th nhng thng tin ny s b xo. Ti mt s my RAM cn lu tr nhng chng trnh v s liu do ngi vn hnh thit lp trong trng hp ny RAM s c nui bng ngun cquy bo tn thng tin khi tt my.

H thng iu khin giao tip vi cc thit b ngoi vi thng qua cc cng (port), mi cng s c gn mt a ch v mt th t u tin nht nh sao cho chng hot ng ng b v khng gy nhiu cho nhau.

Trn y l mt vi nt chung rt s lc v h thng iu khin ng dng CPU, do c nhiu loi CPU nn trong thc t cc my s khc nhau. V nhng loi my X quang ny kh phc tp nn cc cn b k thut cn hiu thu o nguyn l hot ng ca tng khi thit b v bit cch khai thc cc chng trnh kim tra, hiu r ngha cc thng bo li khu tr c khu vc hoc

20

bng mch in b trc trc. Vic pht hin v thay th cc linh kin b hng thng t c c hi ngoi tr phn ngun cp in.

1.5. Kt lun Vi vic pht hin v ng dng tia X vo trong lnh vc y t em li

hiu qu trong chn on v c tc dng to ln i vi s pht trin ca y hc hin i. Ngy nay cng vi vic pht trin ca khoa hc k thut, vic ng dng tia X c nng ln mt tm mi. T ch ch l X- quang thng thng, n nay cc k thut tng sng, truyn hnh cho php bc s c th thc hin cc k thut X- quang can thip vo bnh nhn bng quan st trn mn hnh kt hp thao tc trn bnh nhn. K thut vi x l c ng dng lm cho cc qu trnh x l ca my c t ng ho, chnh xc, an ton, tin cy c ci thin ng k.

21

Chng 2 S KHI V CHC NNG CA MY XM-1550

2.1. Thnh phn chc nng a. Chc nng Thit b l loi my ng dng tia Rnghen trong vic chn on. Cng

nh nhng thit b ng dng tia X khc nhng n thit b ny c s ci tin v pht trin mnh m hn cc thit b X-quang thng thng nh k thut tng sng v truyn hnh. Vi my X- quang tng sng truyn hnh, ngi bc s c th thc hin k thut X-quang can thip, bnh nhn c th phi ung thuc cn quang trc khi chiu. Khi chiu nh tc dng thuc cn quang m ngi bc s d dng quan st trn mn hnh v thc hin mt s can thip chuyn mn trc tip vo bnh nhn. Khi cn thit lu li hnh nh phc v chn on, hi chn, qu trnh iu tr tip theo k thut vin c th iu chnh t bn iu khin sao cho hnh nh t c trn mn hnh nh mong mun v chp. nh s c lu li trn phim ng trong catxet.

b. Thnh phn My X-quang tng sng truyn hnh XM-1550 c s khi nh sau:

Thit b x l tn hiu

Thit b quan st

Lng knh

Bng X-Quang

Bnh nhnThit b tng

sngThit b thu

nh

ng nhn quang

Thit b t ng iu khin nh

sng

Thit b cao th

Hnh 2-1. S khi ca my X-quang tng sng truyn hnh

22

+ Khi cao th: To ra in p cao t 40 150 KV t vo hai cc ca bng X- quang. Nh in th cao m c s chnh lch in p gia hai cc ca bng X-quang. S chnh lch ny s ht m my in t ti catt n p vo ant to sinh ra tia X.

+ Bng X-quang: Nhim v to tia X, y l b phn thit yu ca thit b. m my in t sinh ra do ta cung cp dng cho si t ca catt. m my ny nh s chnh lch in p gia hai cc n va p vi ant. Mt phn trong s sinh ra tia X. Tia X ny c nh hng pht ra theo hng

xc nh phc v chiu v chp tip theo. + Thit b tng sng: Nu nh thc hin thu v bin i trc tip tn hiu

sau bnh nhn ri a ln truyn hnh th khi ta quan st trn mn hnh bng cch thng thng s khng th phn bit c cc chi tit m bo cho vic chn on do khng sng. Do vy ta phi c thit b tng sng, thit b tng sng ny c tc dng bin c mt photon tia X thnh 5000 6000 photon nh sng.

+ Thit b thu nh: y l b phn bin i tn hiu quang thnh tn hiu in. phc v cho vic x l tn hiu v a ln h thng truyn hnh quan st. Trong thit b ngi ta thng s dng b cm bin quang in CCD. Tuy nhin trong mt s trng hp ngi ta cng dng ng Vidicon thc hin chc nng bin i ny.

Bng cch dng mt camera CCD 2/3, hnh nh ng nht ca phn c nhy cao v t trng cao n phn chia nh ca camera, chng hn dng khuych i hnh nh c nhiu thp, dng b gama, dng gim mc nhiu v dng white-compressing, thit b c th em li hnh nh sinh ng v gim mc nhiu xung thp hn.

Bng cch dng camera CCD trong vic chia nh ca camera, n khng yu cu nhiu hn trong vic s dng thit b iu khin camera v cp ca camera. Chnh v vy lm cho n rt nh v mt kch thc v nh v mt

23

trng lng, i chiu vi tiu chun dng camera ta c th s dng ng Vidicon. Hn na n l mt dng tng thch vi ng tng sng, cho php d dng kt hp, v chnh v vy n cng c ci tin tin cy cho thit b.

Bng cch dng mt camera CCD 2/3 cho phn nhy cao v t trng cao, s thu c hnh nh cht lng cao. Dng khung u ra c phn gii ngang 560 dng, 450 dng cho phn gii dc(350 dng trong trng hp dng ng l Vidicon).

Vic chn CCD c ci tin cc c tnh bin iu vng gia v hnh nh tng phn tt hn (2.5 MHz, ln hn xp x 10% so vi cch dng Vidicon).

+ Thit b x l tn hiu: Tn hiu video trc khi c hin th trn mn quan st s c x l ng b vi bng hnh.

+ Thit b quan st: Qu trnh chp, nh c hin th trn mn hnh gim st thc hin cc

k thut X- quang can thip. Hoc sau khi iu chnh trn mn quan st v thy rng iu kin chn on th ngi k thut vin thc hin thao tc chp lu nh trn phim s dng lu di trong qu trnh theo di ngi bnh. Thm ch khi bn ang chy ch chp Radiography, bn c th quan st hnh nh ging nh Fluoscopy vi mu trng c nn t hn trong mt nh.

+ ng nhn quang: Nh trong s khi ch ra th c th thy rng cc photon nh sng c ly t phn gia ca ng tng sng v phn thu

nhn tn hiu. Cc photon nh sng ny c a quan ng nhn quang a n thit b t ng iu chnh nh sng. y ng nhn quang c tc dng bin i tn hiu quang thnh tn hiu in.

+ Thit b t ng iu khin nh sng (ABR Automatic Brightes Regulation): C chc nng t ng iu chnh nh sng lm cho ta c hnh nh ph hp trn mn hnh gim st thng qua vic iu khin in p chiu

24

ca ng tia X( F - KV). Khi ny c to thnh t mt s mch iu chnh mA, kV v tch dng x thi gian.

c. Hot ng theo s khi Hnh chiu sng c chm tia X a ti mn hunh quang sau khi

xuyn qua bnh nhn. Mn chuyn cc photon tia X thnh photon nh sng. Cu to ca mn ny cng nh mn soi X quang (c km sulfat v caimi) nhng mng hn (vi phn mi ca 1mm). Vi mt cng 1mAs, t 60 - 100kV, mt tia X l 2.105 photon/1mm2 trong 1s. Mi photon tia X bin thnh 5.000 - 6.000 photon nh sng. Trong cc iu kin trn, mn c sng khong 10-2cd/mm2. Mt lp nhy cm nh sng ca mn hp th hu ht cc photon nh sng v pht ra cc photon in t. Lc cc in t c gia tc bi mt in th chng 25kV v c t trng tp trung p vo mn th cp kch thc nh hn.

Mn th cp c mt lp hunh quang vng l m v cho mt hnh nh sng hn hnh ca mn chiu X quang t ch mn s cp ca bng hng nghn ln. S tng sng mt phn nh c s gia tc cc photon in t v mt phn nh vic gim ng knh ca mn th cp so vi mn s cp. Vic

tng sng ny cng chnh l u im ca my X-quang tng sng so vi my X-quang thng bi v nh chng ta bit th mt thng ca chng ta ch nhn r vt c sng 100cd/mm 2 . Trong khi sng ca mt mn X-quang chng 0.1 0.001 cd/mm 2 .

Nh trong s ch ra th hnh nh tng sng s chiu n lng knh quang hc (thc cht lng knh ny gn ngay sau ng tng sng). nh sng c khc x vo ng thit b thu nh. Thit b thu nh c nhim v bin i dng tn hiu quang thnh tn hiu in. Tn hiu in tip tc c x l hin th trn mn hnh. Qu trnh chiu v hin th lin tc nh vy l mt u im rt ln ca my tng sng truyn hnh, n cho php ngi bc s c th can thip trc tip vo cc b phn trn c th v gim st qua h thng

25

hin th. Ngoi ra ngi bc s cn c th dng thm thuc cn quang cho bnh nhn ung lm r mt s ni tng trong qu trnh chiu.

2.1.1. Tnh nng k thut a. H thng ngun cp Dng tn hiu ------------------------------------------------------n pha.

Tn s ngun-------------------------------------------------------50Hz/60Hz Cng sut-----------------------------------------------------------30kVA Phm vi iu chnh------------------------------------------------+/-10%

Ngun in p------------------------------------------------200V,220V, 240V Phm vi iu chnh in p---------------------------------------+/-10% in tr ni t-----------------------------------------------------

26

Cc k thut vn hnh

Php nghim hunh quang t ng: Chp X- quang tng qut: Chp X- quang nhanh: Php nghim hunh quang bng tay: K thut b tr:

Cc h s k thut chp X-

quang

in th bng: 40-125/ 150kV (1kV/ bc). Tch s dng- thi gian: 2- 250mAs (27 bc).

Cc h s k thut chp nh hunh quang

in th bng: 40-120(c gii hn n 110 kV v chn trong gii hn bc x cho php ti bnh nhn.) Dng bng: c ba mc 0.9mA, 1.2mA, 1.5mA. i vi ch chiu, b nh thi gian s t trc thi gian n ti a l 9min. nu n c t nh hn 5min, ci bo s ku trong 30s trc khi nhn gi tr thi gian t. Thi gian c th c t li khi cn thit. Cn nu thi gian c t t 5-9 pht, th ci s ku lin tc khi qua 5s u. Nu thi gian khng c t li, vic chiu tia s b dng li (ngt) t ng.

chnh xc

kVp Khi ln hn hay bng 40ms: 10% Nh hn 40ms: 5% +3kV.

mA Khi ln hn hay bng 40ms: 15% hay 5mA vi bt c gi tr no ln hn. Nh hn 40ms: 12% hay 5mA vi bt c gi tr no ln hn.

mAs 20% vi thi gian ln hn hoc bng100ms v dng ln hn hoc bng 50mA. Nu khng th chnh xc l tch ca thi gian v chnh xc ca dng.

T gi tr u ra nh mc ca khi in p cao X- quang, in p bng v tch s dng- thi gian c khng ch theo kh nng chu ng ca b phn v bc bng. Vic nh mc c m t bng cc gi tr thc. i vi my pht cao th dng dng 500mA.

27

c. iu kin mi trng Gii hn iu kin mi trng cho h thng nh sau: + Gii hn nhit hot ng t +5 C n +35 C . Tt nht t :+20 n 30 C.

Gii hn m cho hot ng: 45% n 85% Tt nht t : 50 n 60% + Phng iu khin Gii hn nhit + 5 C n +35 C Gii hn m 45% n 85% H thng my tt nht l c t trong phng c h thng iu ho v

nh vy va m bo nhit v m. 2.2. S NGUYN L V HOT NG CA MY 2.2.1. Bng X quang

Bng X quang c th xem nh dng c bit ca it chnh lu chn khng. Trn hnh 2-2 minh ho cu trc n gin ca mt bng X quang.

Bng X quang gm cc b phn ch yu sau: - Ngun bc x in t (catt). - Ngun pht x tia X (ant) l vt cn trn ng i ca chm tia in

t. Din tch ni chm tia in t bn vo gi l im hi t - chnh l ngun pht x tia X.

Hnh 2-2. Ngun bc x tia Rnghen (tia X)

Tia X

Catt Ant e

28

- V thu tinh (v trong) bao quanh ant v catt, c ht khng kh to p lc m loi tr cc phn t kh cn tr trn ng i ca chm tia in t.

- V bng (v ngoi) thng lm bng hp kim nhm ph ch ngn nga tia X bc x theo nhng hng khng mong mun c hi cho mi tr-ng xung quanh v cn c tc dng tn nhit. Ngoi ra trn v cn b tr ca thot tia X, ni ghp vi hp chun trc v v tr cc u ni.

a. Trng thi bo ho v hiu ng in tch khng gian Khi catt c nung nng, ti b mt ca n s bc x ra chm tia in

t (electron). Kh nng bc x ph thuc vo nhit (dng si t) v din tch b mt pht x (cu trc ca catt). m my in tch m bao quanh catt do cc in t to nn gi l vng in tch khng gian.

Khi t mt hiu in th mt chiu vo gia ant v catt trong ant mang in th dng so vi catt th in t s chuyn ng v pha ant v to nn dng in chy trong bng X quang.

Nu ta duy tr nhit catt mt gi tr no (do dng si t quyt nh) th s lng in t bc x ra s khng i. Khi tng in th ant, s lng in t dch chuyn v ant s tng theo khin cho dng bng tng. y l trng thi lm vic c gi l trng thi di mc bo ho, trong in p v dng in ca bng X quang ph thuc nhau.

Khi in p ant tng ti mt gi tr, ti ton b s lng in t bc x c ht ht v pha ant, lc ny bng X quang lm vic trng thi c gi l trng thi bo ho. K t mc tr ln, vic thay i in p ant khng lm thay i dng in, ngha l dng in v in p bin i c lp vi nhau, bng X quang lc ny lm vic trng thi trn mc bo ho. y chnh l trng thi mong mun i vi ngi s dng thit b X quang.

29

Tuy nhin, trong thc t, khng phi lc no cng t c trng thi ny. Thc t chng t rng, ch phm vi dng ca bng X quang tng i thp (di 100mA) th d dng t c trng thi lm vic trn bo ho ngay c khi in p ant cn tng i thp (khong 40kV). Cn khi bng hot ng vi dng ln hn th d vi in p ant kh cao, mt s lng in t bc x khng c ht v ant m to thnh mt m my in t bao quanh b mt catt. Chng lm cho dng in qua bng X quang thay i theo in p ant, to nn mt hiu ng gi l hiu ng in tch khng gian.

V d di y biu din mi quan h gia in p v dng in ca mt bng X quang (ng vi dng si t c nh) khi bng lm vic trong trng thi di mc bo ho ngha l di tc ng ca hiu ng in tch khng gian.

Quan h gia in p v dng in in p (kV) Dng in (mA)

50 350 70 400

90 460

Hiu ng ny nh hng xu n nh chp X quang. V vy, trong cc thit b X quang hin i ngi ta s dng nhng mch in loi tr nh hng ca in tch khng gian (gi l mch b in tch khng gian) sao cho trong sut di in p lm vic vn c th iu chnh c lp gia in p kV v dng in mA.

b.Cc b phn bng X-quang Bng X quang c minh ho trn hnh 2-3. N c nhng b phn :

catt( hi t n v kp); ant; v thu tinh (v trong), v ngoi v vic lc s b chm tia.

30

- Catt bao gm si t v gi bng kim loi si t ng thi cn to khe hi t. Si t c ch to bi dy vonfram c nhit nng chy rt cao (3.3600C). Si t c dng hnh xon c to din tch bc x in t rng. hi t chm tia in t ngi ta t si t trong mt khe ca

gi v chm tia in t bc x t si t qua khe ny. Kch thc, hnh dng ca si t v khe c thit k v ch to theo nhng yu cu k thut rt kht khe v si t c t cn thn trong khe sao cho chm tia in t tp trung (hi t) ti mt im vi din tch rt nh trn b mt ant. Din tch m tia in t hi t ti gi l im hi t, chnh l ngun pht x tia X. im hi t thng c dng ch nht, chiu di bng 3 - 4 ln chiu rng v din tch ca im hi t khong 1 - 2mm2 (tiu im nh) ti 10 - 15mm2 (tiu im ln).

Catt c hai loi: hi t n v hi t kp. + Loi catt hi t n ch gm mt si t v mt khe bc x. + Loi hi t kp gm c hai si t t trong hai khe bc x tng

ng vi hai din tch to v nh. Hai khe ny li c b tr k nhau trong mt phng ng hoc ngang. Khe hi t nh ng vi cng sut bc x thp (mA thp), c s dng chp nhng i tng c hp th tia thp chng hn ngi gy, tr em hoc nhng b phn phn nng ca c th, trong tr-ng hp ny ngi ta dng dng in nh nhng vi thi gian ko di hn. Tri li, khe hi t ln ng vi cng sut bc x cao (mA cao) c dng cho nhng i tng c hp th tia cao nh ngi bnh bo hoc cc b phn dy ca c th. Khi ngi ta dng dng in ln nhng vi thi gian chp ngn.

31

Ngun in cp cho si t l ngun in p thp c vi chc V vi dng t vi A n 10A. m bo cch in cao v lm ngui, bin th cp in cho si t thng c t trong thng cao th cng vi bin th cao th.

- Ant: C nhim v hng chm tia in t bn vo, ri pht x chm tia X. Chm tia ny phi cng tp trung cng tt to c hnh nh r. Ant quay vi tc ln tc ln t 3000 - 9000 vng/pht (50 - 150 vng/s) ngha l nu thi gian chp din ra trong vng 0,ls th ant quay t nht 5 vng.

Ant gm mt a c ch to bi vonfram hoc bng mlipen ph vonfram hoc ph hp kim vonfram - gecmani. a ny c gn vo mt mlipen cch nhit vi rto. Mt kia ca mlipen c gn vi rto

V ngoi (trng ch)

Stato Mng chn co dn

Cch in catt

Cch in ant

Ca s

ng tia bn trong

Rto u dy stato

Ant

Chm tia X pht x

Catt

Hnh 2-3. Cu trc bng X quang ant quay

32

ca ng c. Mt a ant khng phng m vt cho ra - ni chm in t bn vo, gc vt t 15 - 200 tu theo loi bng. Trc ca rto c gn mt vng bi, bi trn vng bi ny c m bc hoc ch ch khng tra du v s lm hng chn khng ca bng. Tc quay ca ant thng t 3000 - 9000 vng/pht. Vi tc thp, ngun in cp cho ng c l ngun AC 50Hz, t c tc cao, ngi ta phi s dng b bin tn to ngun AC c tn s ti 150Hz. Ant, rto, vng bi c t trong v thy tinh. Bn ngoi, st vi rto l cc cun dy v li st ca stato. Mun bng lm vic bnh thng, ant phi quay v nhanh chng t c tc yu cu (v d sau khong 1s) do vy trong thit b X quang ngi ta thit k cc mch bo v v tng tc ant. Chm tia in t bn vo ant khng phi ti mt im c nh m trn c hnh vnh khn, hn na hnh vnh khn ny li quay nhiu

vng trong sut thi gian pht tia. V vy din tch im hi t hay ni cch khc din tch pht x tia X nh hn din tch tn nhit rt nhiu. Nh c din tch tn nhit ln, bng X quang ant quay c th hot ng vi dng ln do vy tng c cng sut pht x tia X (tng ng vi tng mA).

- V thu tinh (v bn trong): c dng hnh tr bao quanh v ng thi lm gi catt v ant. V ny c ch to t loi thu tinh c bit c kh nng chu nhit cao, c cch in cao, c h s dn n ng nht vi s dn n ca cc in cc v chu c p lc chn khng ln.

- V bn ngoi: bao quanh bng X quang, c ba nhim v: + Ch cho tia X bc x qua ca s. + Hp th tia X theo cc hng c hi cho ngi bnh v mi trng

xung quanh.

+ Chng in git.

V ngoi c ch to t nhm, hp kim nhm hoc thp, b mt trong ca v c trng mt lp ch dy hp th tia X, hn ch s pht x tia X ra xung quanh (tr ca s) ti mc cho php khng gy nguy him cho

33

bnh nhn v cho mi trng xung quanh. m bo cch in, ngi ta y du cao th vo khong gia hai lp v. Ngoi tc dng cch in, du cn c tc dng tn nhit v lm mt bng. Khi bng hot ng, n s nng ln khin cho du dn n nn mi pha u v phi c mt khoang dn n ch to bi mng cao su hnh lng xp. bo ng tnh trng bng qu nng do hot ng lin tc, ngi ta gn mt cng tc hnh trnh vo mt b mt khoang dn n, khi khoang dn ra ti mc nht nh, v d vi mt loi bng khi th tch du tng t 1l n 1,3l (tng ng vi nhit du l 700C) th cng tc tc ng ng mch pht tn hiu cnh bo (ci hoc n nhp nhy). Lc tia mm

Khi pht x t im hi t trn ant, chm tia X bao gm nhiu bc sng khc nhau. Trong s ny, nhng bc sng di nht s b hp th bi da v cc m mm phn nng ca c th nn chng ch lm tng liu lng tia X trong c th m khng ci thin c cht lng hnh nh v chng khng xm nhp ti phim . Do vy, cn phi lc b nhng bc sng c hi ny i trc khi chm tia X ti bnh nhn. Thc cht, chm tia X sau khi i qua v thu tinh, lp du bao quanh v v ca s c ch to bng cht do, cc bc sng di b lc bt. Vic lc ny c gi l lc ni b (tng ng vi dy 1mm nhm). Khi cn thit ngi ta b sung thm mt lp nhm na ti ca s bng sao cho b dy lp lc tng cng tng ng vi l nhm c b dy khong 1 - 2mm.

2.2.2. Khi cao th a. Bin p cao th

Chc nng Bin p cao th c nhim v tng in p ngun (220V hoc 380V) ln

ti hng trm kV (t 20kV - 120kV), nn y l loi bin th tng p. N c th l bin th mt hoc ba pha tu theo yu cu ca chnh lu cao th.

34

Cu to Gm c hai cun dy nu l bin th mt pha hoc 6 cun dy nu l

bin th ba pha. Chng c cun quanh li st silic. Bao quanh cun s cp (ni vi ngun AC) thng c mt lp v bc kim bng ng mng khng khp kn. Lp v ny dng vi mc ch an ton phng khi cc lp cch in b hng, in th cao s phng qua lp ng ny xung t.

Cun th cp c cun lm hai na. im gia ca chng c ni t. Cch b tr ny lm gim nhu cu v cch in i mt na, do vy lm gim c chi ph bin th v cp cao th. Thc vy, gi s hiu in th gia hai pha cun dy th cp l 100kV th gia mt pha vi t ch cn 50kV, do vy ch phi m bo cch in gia hai u bin th so vi t l 50kV m thi.

Cc cun dy s v th c cch in tht tt vi nhau. T s vng gia chng bng t s in p:

1

2

1

2

UU

NN

=

N1, N2, U1, U2: s vng v in p cc cun s cp v th cp tng ng. Ch rng khi ni v tr s in p cun s cp (in p ngun), v d : 110V, 220V hoc 380V l ni v tr s hiu dng U hd . Trong khi , tr s

in p cao th pha th cp thng cp ti, l gi tr nh (U max ).

2UU maxhd =

Vn cch in trong khi cao th

m bo cch in gia cc linh kin trong khi cao th, gia cun dy s v th cp, gia bin th vi chnh lu cao th v gia chng vi t, ngi ta nhng ton b cu kin ca khi cao th vo trong thng cha du cao th. Ngoi tc dng cch in, du cn lm mt nhng cu kin ny. Khi np du phi ht ht kh trong thng, du c th thm nhp vo ton b cc

35

khe h trong cc linh kin v cu kin sao cho khng cn bt kh. Sau phi ng kn thng cao th li.

b. Chnh lu cao th S mch in thu gn v cc dng sng c trng cho in p chnh

lu, dng in v nng lng tia X c minh ho trn hnh 2-5. Trong loi chnh lu ny, c hai na chu k ca dng in xoay chiu (c chu k) u c s dng. Nh tng ng k cng sut pht x tia X, hiu sut ca khi cao th v m rng phm vi ng dng ca thit b.

U

I

D

Hnh 2-5. Mch chnh lu 1 pha c chu k

Hnh 2-4. Bn trong mt thng cao th 1: v; 2: ca s ra; 3: stato ng c quay ant; 4: bng X quang;

5: khoang dn du ; 6:cch in cao th; 7: bin p cao th ; 8: bin p si t catt.

a)

b)

36

- Nguyn l hot ng Mch chnh lu thuc loi chnh lu cu gm 4 it D1, D2, D3, D4.

Trong mt na chu k, D1 v D3 thng, trong na chu k cn li D2 v D4 thng do vy lun c dng chy trong bng X quang trong c hai na chu k ca ngun AC. Dng in i qua ng h ch th l dng xoay chiu nn mun o gi tr ca n bng nhng ng h in t ch kim hoc ng h hin s cn phi chnh lu dng in ny thnh dng mt chiu nh s dng cc cu chnh lu. Nhng it chnh lu trong mch in chnh lu mt pha

c chu k cng nh trong mch in chnh lu 3 pha l loi it cao th, chng phi t c cc ch tiu c bn sau:

+ Chu c dng ti ln - I thun t hng trm ti 1.000mA. + St p trn it phi nm trong gii hn cho php c di mi kV. + Chu c in p ngc t vi chc ti hng trm kV tu theo loi

mch ng dng. Trc y, trong nhng thit b X quang c in, ngi ta s dng

nhng bng it in t chn khng rt cng knh, nng n, mch nung si t rt phc tp, tui th thp.

Ngy nay, nh s pht trin ca cng ngh vt liu bn dn, trong cc my X quang hin i, it bn dn c dng ph bin, chng c nhng u im c bn sau:

+ St p trn it kh nh.

+ Chu dng ti ln c 1000mA. + Chu c in p ngc rt ln. + Hot ng tin cy, tui th cao.

+ Kch thc v trng lng nh.

+ Khng i hi ngun nung si t. Cc it v trn hnh 2-5 ch l nhng k hiu quy c. Thc cht,

l nhng ct it ni tip nhau, mi ct gm vi chc tm it ring l ghp

37

li, hai u ct c l xo nn chng li vi nhau. Mi tm hnh ch nht hoc trn c tit din khong 0,8 - 1cm2 dy khong 0,4mm. Mi ct chu c dng ti t vi trm n khong 1.000mA v in p ngc ti vi chc kV.

- c trng ca chnh lu mt pha c chu k

Bng X quang dn dng trong c hai na chu k nn kV trong c hai na chu k bin thin nh nhau. Cng do bng X quang thng trong c hai

na chu k nn tr s dng nh I P khc bit dng trung bnh Itb t hn so vi

s khc bit trong kiu chnh lu na chu k: I p = 1,5I tb . Do vy c th dng

dng I tb cao hn v tng cng sut pht x tia X.

in th ant lun lun dng so vi catt nn khng cn nguy c ca vng hi tip dng v nhit do s bc x in t th cp gy ra. in th kV gia rut v v cp cao th lun ch thp hn hoc bng mt na kVp nn yu cu v cch in i vi cp cao th thp hn, cho php c th dng cp ni gia bin th v bng. - Nhng u, nhc im ca chnh lu cao th mt pha c chu k

Nh phn tch trn, ta thy loi chnh lu mt pha c chu k so vi

loi chnh lu na chu k c nhng u im sau: + Cng sut pht x tia X cao hn. + Hiu sut s dng bng X quang ln hn. Tuy nhin, n cng tn ti nhng nhc im nh:

+ Cu to phc tp hn. + Kch thc ln hn.

+ Trng lng nng v gi thnh cao hn. - Phm vi ng dng

Nh c nhng u im ni trn, kiu chnh lu mt pha c chu k c ng dng ch yu trong cc thit b X quang loi ln, lp t c nh, p ng

38

c nhng yu cu chp chiu thng thng v mt s k thut chp chiu c bit. Dng in v in p cc i ca bng X quang trong kiu chnh lu loi ny t ti khong 500mA v 120 - 130kV tng ng. 2.2.3. B t ng iu chnh nh sng

Vic thc hin php chiu v chp i vi my tng sng truyn hnh XM- 1550 cho tng i tng c th l khc nhau. V d khi chp cho ngi bo th yu cu v tia X khc so vi ngi gy, tr em th khc vi ngi ln, ngay c cc b phn khc nhau trn cng mt c th cng khc nhau v liu lng tia X. My XM- 1550 cho php ta iu chnh s khc nhau ny thng qua vic iu chnh cc thng s mA, kV v tch s dng x thi gian. C th trong khi ny c cc mch sau: mA CONT- 70 PCB thc hin iu chnh mA, kV CONT- 70 PCB thc hin iu chnh kV. Sau y ta i su tm hiu

vic thc hin iu khin mA.

a. Gii thiu vic iu khin dng ca bng X-quang c chnh xc v n nh,

h thng c nhng mch di y: 1) iu khin c nh dng si t bn s cp. 2) Dng dng nung si t a qua b o( 125 Hz) 3) nh trc t l, dng si t s dng. 4) Mch b s suy hao ca dng bng trong qu trnh chiu. 5) Mch nung tng ng cho hot ng ca dng si t.( p dng cho

cc bng s dng dng 5A hoc nh hn.) Phng php Hi t T l nung

Phng php ngt chiu Tc nh khong 17% Tc ln Khong 34%

Phng php dng mt h thng chiu

Tc nh 0 n 48% Tc ln 0 n 71%

Phng php dng 2 h thng chiu

Tc nh 0 n 48% Tc ln 0 n 71 %

39

b. Nguyn tc chung 1. Xy dng

Vic iu khin dng si t bng X-quang c thc hin bng hai bng mch mA CONT(A)-70 v mA CONT(B)-70. 2. c im k thut

1) Ngun cung cp AC 160V AC 60V (Cho tc ln) AC 12V 3 mch

DC 15V (DC c bin i t ngun cung cp) 2) Cng sut Cng sut ti a cho vic s dng

Dng in in p

Th cp 7.5 A 20 V (MAX) S cp 1.36 A 150 V( MAX)

3) Bin p cch in Bin p cch in, in p thp v in p cao ca mch in si t

phi m bo yu cu sau: T s dng : Khong 5,5 : 1 T s in p: Khong 7 : 1

3. M t chung ca cc mch + mA CONT(A)-70 PCB:

Hnh 2-6 ch ra s nguyn l ca bng mch ny:

40

D2

Mch iu khin cng SCR

Mch khuych i vi sai

Mch iu khin cc B

Mch to dng tn hiu

(1)

(2)

(3) (4)-

+

(c)

mA CONT(B)- 70

Fil-

Fil+Q1 Q2 (b)

R10,R11

(a)

C4 R3

R4

AC 160V

C1 R5

R6

OP amp

FV SET

Thit lp dng bng

+2V(d)

Hnh 2-6. S nguyn l bng mch mA CONT(A)- PCB Mch ny dng to in p mt chiu (Fil+, Fil-) ging nh m t

phn trn ca hnh 2-6. Tn hiu ny c a n mA CONT(B) 70 PCB bin i thnh dng tn hiu dng xung.

Kt qu ca mch ny nhm t ti mc gi tr in p mt chiu ph hp vi mc gi tr dng thit lp cho bng. Sau y l m t ngn gn chc nng ca bng mch ny:

in p t ngun AC 160V c chnh lu c sng bng b chnh lu D2. Chc nng ca SCR Q3 l iu chnh s khc nhau v in th gia im (a) v (b) trong hnh, n lun t trn di 30V( Tng ng hai bn cc C-E ca transitor Q1, Q2), bng hot ng ng m(ON/OFF) tun hon. Trong khi t C4 v C1 c tc dng l phng in p.

in p (a) v (b) tng ng c tch bi R3, R4 v R5, R6, ri chng c a ti mch khuych i vi sai (2). Ti y, in p t (b) s c cng thm 2V t ngun in p (d). Sau khi cng thm 2V, b khuych i vi sai (2) v mch iu khin cng SCR (1) lm vic cng nhau trn cng

41

SCR Q3 iu khin in p (a) duy tr c mc cao hn in p (b) l 30V. Bng cch iu khin ny transitor c ngn nga khi s tiu tn nng lng khng cn thit.

Mi bng mch cho ra gi tr tn hiu thit lp dng bng tng ng cho mi phng php chp khc nhau. Mch to dng tn hiu (FV SET), tn hiu sau khi c to dng FV SET c o ri a vo b khuych i OP (4). m bo hot ng ca b khuych i (4), mt gi tr in p c bin i t dng si t s cp (trong hnh) qua in tr R3, gi tr in p (c) bt u c a vo. B OP apm hot ng nh mt b so snh, nh vic pht hin khi no in p ca FV SET( tn hiu to dng) cao hn in p (c) mt mc no , th u ra mc H v qua mch iu khin Baz ca transitor (3), cc trig v transitor Q1, Q2 c bt (ON). Bng cch ny in p ti (c) dng si t c iu chnh tng ng n gi tr ca FV SET. y l nguyn tc c bn ca vic iu chnh c nh dng si t. + Bng mch mA CONT(B)- 70 PCB

Hnh 2-7 cho ta s cc thnh phn c bn trong mch.

Mch iu khin t

Mch iu khin cc B

Mch gi chm chuyn mch

t

Fil+

Fil-

T mA CONT[A]-70

Q4

Q3

(b)

(a)

(1) (2)

(3)

(4)

VR1

AC160VMch t t ln(trong php chiu)

C1

Q1

Q2

CLCS

Hnh 2-7. S nguyn l bng mch mA CONT(B)- PCB

42

F i l+ F i l -

8 m s

( a )

( b )

C 1 - C L( C 1 - C S )

1 2 5 H z

Hnh 2-8. Qu trnh hnh thnh dng sng trong mch

Nh ni trn, c th sau y l hot ng thit lp dng cho bng. in p mt chiu DC (Fil +, Fil -) c a n CONT(B) 70 PCB. Transitor Q1 qua Q4 c s dng bin i in p ny thnh dng in p xoay chiu hnh ch nht tn s 125 Hz.

Dng dng c bn ca transitor Q3 v Q4 ln lt c ch ra trong hnh (a) v (b) ca hnh 2-8 vi tn s 125Hz. Gi s Q3 v Q2 thng v dng c biu din bng ng lin nt nh hnh v. Trong chu k k tip Q4 v Q1 thng dng in c biu din bng ng t nt. Kt qu l ta c dng sng hnh ch nht c biu din trong hnh 2-8(125Hz). Mch iu chnh t (2) v mch gi chm t (3) c s dng la chn s thay i t ln v nh. Mch thit lp t ln(4) c s dng thit lp gi tr t ln trong sut qu trnh chp, phng php ny c dng cho c k thut chiu v k thut chp im nh. Lu l cc mch ny s dng ngun cung cp c tn s 50 hoc 60Hz.

43

c. Mch mA CONT(A)- 70 PCB 1. Mch to dng tn hiu thit lp dng cho bng - FV SET

Trong tt c cc phng php chiu, chp, kt qu cn t l cc dng cung cp cho si t phi t n gi tr dng thit lp.(gi l dng FV SET ).

Trong phng php chiu v chp t ng, mt in p mt chiu DC gi l FVR c to ra t bn iu khin, trong qu trnh chp c mt in p mt chiu DC l FVF v qu trnh chp t ng c mt in p mt chiu DC l FVC c to ra ln lt t mch MEASURE- 70 PCB v t mch CINE

CONT -70 PCB. Chng c a n mA CONT(A) 70 PCB v qua cc mch nh ch ra trong hnh 2-9, dng cui cng ca chng l tn hiu nh dng FV SET c s dng lm dng si t. Sau y ta tm hiu vic nh dng tn hiu trong mi phng php. (a) Trong phng php chiu v chp t ng.

44

Hnh 2-9. S nguyn l mch to dng tn hiu mA CONT(A)- PCB

T bn iu khin, mt in p mt chiu DC FVR c a vo A16. Mi quan h gia FVR v dng si t th cp c gi t l 5V/5A. Tn hiu FVR l tn hiu u vo cho chn 3 ca A6. Sau c a n chn 11 ca S5. By gi chn 10 v 11 ca S5 c ni. Trc khi hot ng

45

Ready din ra th B20 (KC) bt OFF, chn 16 ca S3 bt H, tc l khng cho php chn 14 v 15 ca S3 v chn 14, 15 ca S4 dn. Kt qu l in p FVR c chia i bi: RM13 (5)- (6) (10K) v RM13 (7)- (8) (10K), dn n gi tr chn 14 ca S4 gim xung cn FRV/2 . Gi tr ny l u vo cho chn 11 ca S4 sau khi gim xp x nh RM14 (5)- (6) (100K) v RM14 (8)- (7) (100K). Vi phng php m khng lin quan cho vic chiu, th A17(KSF) l OFF v READY khng thc hin, chn 11 v chn 10 ca S4 ngn mch. A10 l mt b khuych i c h s khuych i 10/14.53. Ta t c tn hiu FV SET ti CP15. V d, gi tr in p ti CP15 khi FVR l 5.0 v t khong 0,9V.

Tip theo l hot ng Ready c thc hin. Ti B20(KC) bt ON, chn 1 ca S2 v chn 16 ca S3 l bt mc L, chn 2 v 3 ca S2, chn 14 v 15 ca S3 dn, chn 8 ca S2 c bt mc H, v chn 6, chn 7 ca S2 khng dn, dn n dng chnh lch in th vi FVR nh trong hnh 2-9(b) c thit lp trong (FLR)(CP17) v c cng vi gi tr ln nht ca FVR ch l 0.8 s. iu chnh t nh, chn 9 ca S2 c bt n L v chn 10, chn 11 ca S2 dn, nu iu chnh t ln ta thm mt na dng sng.

Khi chn 16 ca S4 c bt v L, chn 14 v 15 ca S4 dn, v (5), (6) ca in tr RM13 b ngn mch. Cui cng c dng in p FVR ng nht ti chn 14 ca S4. T c ta thy hot ng ca cc mch khc cng

tng t nh trn, Gi tr FV SET c nhn i so vi ban u v dng si t cng c tng gp i. Ti B17(MAFC) tn hiu gi n mch MEASURE-70 PCB b dng bng hao ht trong thi gian chiu. Khi ta o dng bng trong sut qu trnh chiu thy n b gim gn 1V, tn hiu ny s c cng nh FVR tng dng si t. (b) Phng php chiu tng qut

46

Vi phng php chiu ny, ti A17 c bt ON, v khi php chiu

Fluoroscopy c la chn, in p mt chiu DC FVF t bng mch

MEASURE- 70 PCB c cp cho u A21. Mi quan h gia FVF v dng

si t th cp cng xp x 5V/5A nh trong trng hp (a) trn. Ban u FVF s b gim xung 0.54 bi in tr R42 (10K) v in tr R41 (12K). Ti A17(KSF) ON v B20(KC) OFF, chn 6 v chn 7 ca S4 ngn mch. Ti A10, kt qu to thnh tn hiu FV SET vi vic khuych i tng t

nh trong trng hp (a). Tip theo, khi ta thay i t php chiu fluoroscopy sang php chp

Radiography. Trong trnh t tin hnh php chp, Ready c thc hin, B20

c bt v ON, pin 6 v 7 ca S4 khng b ngn mch. Ti thi gian chp

Radiography, ging nh trong trng hp (a) tn hiu FVR t bn iu khin s to dng tn hiu FV SET. Tip theo Ready hot ng, chn 8 ca S4 c

bt v H, chn 9 ca S4 c bt n L,chn 6 v 7 ca S4 khng dn,

chn 10 v 11 ca S4 dn.

iu chnh t ln vi phng php s dng mt h thng chiu,

chn 16 ca S1 c bt v L, cho php chn 14 v 15 ca S1 dn. Tip

theo Ready hot ng, chn 1 ca S2 v chn 16 ca S3 c bt n L,

chn 2 v 3 ca S2 v chn 14, 15 ca S3 dn. Chn 8 ca S2 c bt v v

tr H, v chn 6, 7 ca S2 khng dn. Mt s chnh lch in th gia FVR

v VR2 ti CP17 c hnh thnh nh trong hnh 2- 9(b) v chng c cng vi FVR t c gi tr ln nht cho mt chu k l 0,8 s.

Tip theo chn 14 v chn 15 ca S4 dn v (5) (6) ca in tr RM13 ngn mch, lm cho tn hiu sau to dng FV SET tng t nh trong trng

hp (a).

47

2. Mch to tn hiu mt chiu DC(Fil+, Fil-) S nguyn l nh trong hnh v 2- 10 ch ra. u tin, ngun cung cp AC 160V s c chnh lu c sng qua cu

diot D2. B ghp quang Photo-coupler M2 s ng OFF khi gi tr sau chnh lu c sng gim n mt mc no . Khi C5 s c np n +15V qua R26 v D4. Khi M2 bt ON anot ca D4 v trng thi L v in tch trong C5 c gii phng qua R20. Gi tr ny c th b gim xung 1/3 do R37 v R36. Trong hnh 2- 11 cho ta bit dng sng ti cc im nt. Cc tn hiu ny c s dng cho pha iu khin ca SCR Q3.

By gi ta xem xt trng thi ca mch khi SCR Q3 c bt ON. in p khng xut hin trn CP4 CH VOL v CP5 FV PRI. Do in p chn 6 ca A2 l 0V, chn 5 b chia gi tr 15V bi in tr R21 v R22. A2 l b khuych i vi sai cho ra in p vo khong 2V t pin 7 (CP7 CH DIFF). Gi tr ny c s dng lm u vo cho chn 3 ca A1. Mt ngun khc s cp cho chn 2 ca A1 dng tn hiu ging nh dng sng ti CP6 ca hnh 2- 11. T ta thy b OP amp c chc nng nh mt b so snh, khi gi tr ti chn 3 vt qu gi tr ca chn 2 ( tc l khi gi tr ca CP7 vt qu gi tr ca CP6), chn 1 ca A1 c u ra H v Q5 c bt ON. Kt qu, dng sng ti CP9 ging nh trong hnh 2- 11 m t.

48

Hnh 2-10. Mch to tn hiu mt chiu DC (Fil+, Fil-)

49

230V

D2+

AGND

AGND

AGND

Q3 ON

CP9

CP7

CP6

+15V

Hnh 2- 11. Dng sng ti cc im nt

Khi CP9 trng thi L , SCR Q3 c bt v t C4 bt u c np. Khi ti qu ln, thi gian bt ln n L ca CP9 gn t n gi tr nh ca in p ngun.

By gi gi s Q1, Q2 khng thng ON. Dng s cp khng c cp qua CP2 Fil- v AGND khng c in p . Nn gi tr chn 2 ca A2 l 0V. Cn chn 3 ca A2 c u vo l tn hiu c to dng FV SET nh trnh by trn. Do trng thi ca chn 1 ca A2 (b so snh) l H, Q4 c thng, M1, Q1 v Q2 cng thng. Kt qu l ta c in p t l vi gi tr dng si t qua CP2, ta c t l nh sau: gi tr dng si t th cp t 5A th in p vo khong 1,82V. Tht vy ta c th tnh c gi tr in p ny: vi t s 5,5:1, vi vic kt hp ca in tr R10, R11 c gi tr n 2,

ta c: 25,5

5x

A =1,82 V.

50

Chnh v vy cc chn 3, 2 v 1 ca A2 c chc nng iu khin ng m Q1 v Q2 duy tr in p to dng FV SET tng ng mc Fil- trong qu trnh hot ng. in p ti CP1 Fil+ bt u c cp n CP5 FV PRI, ta thy trn hnh v in p ti CP1 c chia bi R5 v R6, v ti CP5 th in p t c 10V khi in p (Fil+, A GND) t 130V. Gi tr in p ny c a n u vo 5 ca A2 v a ra gi tr 2V nh ni trn. Ti u vo 6 ca A2 l gi tr in p np cho t C4 sau khi c chia bi cc in tr R3 v R4 nh trn hnh v. Chnh v vy nn chc nng ca A2 l

lm tng in p ca CP4 CH VOL n gi tr 2V nh CP5 FV PRI. Kt qu cui cng, in p np cho t C4 ln hn in p np cho t C1 l khong 30V. Tm li iu ny tng ng vi vic ta cp mt in p c gi tr khng i xp x 30V t C- E ca Q1 v Q2 bt chp ti mc no. Qua y ta thy khng cn nng lng tiu tn cn tr transitor, chnh v vy lm tng tui th ca chng. 3. Mch gii hn qu dng, mch gii hn thit lp dng v mch kim tra nhit

Hnh 2- 12 m t cc mch ny

(a) Mch gii hn qu dng. Mch ny ngn chn dng si t th cp khng cn thit. Nh ni

trong phn 2 th dng si t th cp sinh ra t CP2 Fil- sau chng c bin i v tch in p t dng si t s cp. Dng tn hiu ny c l phng nh t in C3 v C11, sau i vo chn 5 ca A8 vi in p khong 1,8 V v dng in t 5A.

Chn 2 v 3 ca S5 thng dn, Ready hot ng, chn 6 ca A8 c in p u vo l LMT sau khi c chia bi R45 v R46. Tn hiu LMT c a ti t bng mch XSYS -86 trn mch iu chnh t ca ng tia X vi dng si t ti a t t l dng 5A v in p l 5V. Chnh v vy, nu dng

51

si t s cp l 5,4A, LMT s l 5,4V: ta tnh c in p a ti chn 6 ca A8 nh sau:

5,4 x2510

= 2,16V

Tng ng ta c gi tr ca dng th cp vo khong 6A (82,116,2

x 5 = 6A)

Tm li, khi dng th cp vt qu 1,1 ln dng si t s cp a n bi LMT, chn 7 ca A8 c bt v trng thi H v chn 13 ca M15 cng c bt v trng thi H. Kt qu l LED mA OVR c bt sng, MABR c bt ON, v MAB cng c bt ON. Tn hiu MABR ny c gi n bng mch EMC-70 PCB s dng lm ngng vic pht tia. Tn hiu MAB c gi n bng mch mA CONT[B]-70PCB ng cc transitor.

Khi ng chn 12 ca M12 v v tr H, chn 10 ca M9 v v tr L v ng cc transitor Q1 v Q2.

Khi Ready hot ng tc l si t c nung, th ngay lp tc dng si t vt qu gi tr dng si t ti a. Chnh v vy ta dnh cho hot ng Ready 0,8 s, v so snh in p cp vi gi tr in p thit lp cho vic nung ( gi tr in p ny gp 1,2 ln in p ti chn 1 ca A11). (b) Mch gii hn qu dng thit lp

y l mch bo v, ngn chn vic in p to dng FV SET ln trn mc cn thit. Ti u vo ca A8: chn 3 c cung cp tn hiu FV SET, chn 2 c cp bi in p 3,26V. Khi in p ti chn 3 vt qu 3,26V th chn 1 c thit lp mc H. y l mch pht hin hng hc ca cc mch FV SET dn n khng m bo chc nng. MABR v MAB c bt n ON ging nh dng trong phn (a). (c) Mch kim tra nung si t.

52

Dng si t c bin i. Tn hiu ny di dng in p s c a qua CP2 Fil-, lm u vo cho chn 5 ca A7 sau c l phng bi t C11. Chc nng ca A7 nh mt b khuych i, n iu khin VR1 IFD ADJ t in p 5V ti CP13 IFD khi dng si t th cp l 5A. Tn hiu IFD c a n bn iu khin lm hin th trn ng h o tn s trung gian IF meter. Gi tr ti CP10 P.CUR l u vo cho chn 3 ca A7. Chn 2 ca A7 c u vo l 0,35V. Gi tr ny tng ng vi 1A cho dng si t th cp. Khi dng si t th cp vt qu gi tr ny, th chn 1 ca A7 c mc u ra H. V chn 14 ca M9 bt ON, n LED HEAT READY bt sng v tn hiu OKF c bt ON. Tr khi OKF c bt ON cn li trong cc trng hp khc trng thi ca c cu ny u khng hot ng.

Vi vic m bo 0,8 s cho hot ng Ready, chn 7 ca M10 c bt v L khng cho php OKF bt v ON.

Vic ngn nga trng thi pht tai ca ng tia X c tc dng lm cho lng nhit nung l va .

53

Hnh 2-12. Mch gii hn qu dng, mch gii hn thit lp dng v mch kim tra nhit

54

2.2.4. B to nh a. To nh bng truyn hnh

1. Mng cm quang CCD

a. Chc nng Chc nng cm nhn ca CCD c thc hin bi mt mng cc diot

pht quang c kch thc im nh. Mi diot to ra in tch tng ng vi chiu sng ca nh ti mi im. Chc nng ny ca diot pht quang c kt hp vi chc nng chuyn dch in tch ca CCD.

phn gii ca camera s dng CCD c xc nh bi s lng cc phn t cm quang. Bi v mi hng ca cc phn t ny cung cp mt tn hiu cho mt dng qut, th s lng cc hng phi t nht l bng s lng cc dng qut. S lng cc phn t ca mi ct s xc nh theo s xc nh ca hng ngang tng ng vi l thuyt ly mu v theo s xc nh rt nghim ngt ca hin tng chng ph trong tn hiu s.

Trong truyn hnh qung b mt thit b CCD in hnh c 492 dng, bng s dng qut tch cc h thng truyn hnh NTSC, v 512 ct. Vi s lng cc phn t nh vy rt thch hp trong cc tiu chun truyn hnh

qung b, nhng li khng ph hp cho h thng tn hiu phn gii cao HDTV, n yu cu khong gp i s hng v s ct trn, hay gp bn ln s phn t nh. R rng gii quyt cho cc chip CCD xy dng t cc phn t nh hn c hai vn cn gii quyt: Th nht l vn gia cng, khi phi

sn xut vi s lng phn t gp bn ln chc chn s dn ti nhiu thiu st. Th hai l nhy thp, kt qu ny l do vic to ra cc in tch bi mi phn t t l vi din tch ca chnh n. Nhng vn ny ang c gii quyt v chc chn rng CCD s c s dng cho tn hiu HDTV khi n p ng c nhu cu thng mi.

CCD ng dng trong my truyn hnh XM-1550 c phn gii ti khung u ra l : 560 dng v 450 ct.

55

b. Kin trc chuyn giao v c ra ca CCD. Vn thit yu ca CCD l phng php, thng c gi l kin trc

ca vic chuyn i cc mu in tch ca bn thn chng trong mt mng gm cc b phn cm quang a vo trong tn hiu video bin i theo thi gian. C ba kin trc thng c s dng l: Chuyn khung hnh(FT-Frame Transfer), chuyn dng (IT- Interline Transfer), v chuyn dng hnh(FIT-Frame Interline Transfer). * Cu trc chuyn khung(FT)

S S S S S S S

S S S S S S S

S S S S S S S

S S S S S S S

S S S dfe S S S

S S S S S S S

Hng chu

yn in tch

S S S S S S

S S S S S S S

S S S S S S S

S S S S S S S

S S S S S S S

S S S S S S SC1

C2

B 1

B2

A1

A2

Ra video

Thanh ghi ra

Xung ng h

Din tch nh mnh

D in tch cm bin

Hnh 2-13. Cu trc chuyn khung Cu trc chuyn khung c miu t trong hnh hnh 2-13, cu trc CCD

c phn ra lm ba vng, mt mng cc sensor, mt mng thanh ghi lu tr, v mt thanh ghi u ra theo hng ngang.

Quang in tch c to ra bi nh sng to ti thanh ghi, cc in tch c tch tr trong mi b cm quang hon chnh mt hnh. Khi c tn hiu bt u qut mnh, ton b mu in tch c chuyn song song qua cc ct

56

CCD thng ng vo thanh ghi ca b nh. Thanh ghi nh do vy c t do bt u t hp mnh tip theo. Trong thi gian mnh th hai ny, cc b in tch thanh ghi b nh c chuyn mi ln mt hng vo thanh ghi ra t chung c gi lin tip ti tng ra. Khi tt c cc hng ca thanh ghi

b nh c c ra, thanh ghi cho php tip tc chuyn song song tip theo t thanh ghi nh v chu trnh lm vic lp li to ra cc tn hiu video.

c im ca cu trc ny l kh nng qu ti cc n v lu tr im nh ti cc khu vc qu sng ca hnh nh. Mt cch gii quyt hiu qu cho

vn ny l s dng mt ca sp che i vng cm quang khi s chiu sng trong sut qu trnh chuyn giao, nhng iu ny c s bt li khi a cc thit b c kh vo trong cc sn phm in t. + Cu trc chuyn gia cc dng.

S S S SS

S S S SS

S S S SS

S S S SS

S S S SS

S S S SS

Xung ng h

Ra video

S=cht cm quang Phn t nh

B1 B2

C1C2

Hnh 2-14. Cu trc chuyn gia cc dng

57

Hot ng ca cu trc chuyn gia cc dng c m t nh hnh trn. Cc ct dc ca b cm bin quang c ni vi cc ct xen k ca cc thanh ghi chuyn giao CCD.

Trong mi ln l sng qut mnh, in tch tch t li cc l chiu sng.

Khi c tn hiu ng b th v tr to nh ti mi im nh trn mi ct c chuyn dc theo c hng ca chng ti ct ca thanh ghi chuyn giao CCD bn cnh. Nhng ct l tng ng vi thanh ghi b nh cu trc chuyn khung hnh trn. Sau khi tt c cc hng in tch tn hiu dch chuyn vo thanh ghi ra v c chuyn vo tng ra, th chu trnh lp li vi ln qut mnh tip theo.

Trong c bn ca cu trc ny, cc ct chuyn in tch(ct thanh ghi hng dc) phi b bao ph bi cc thanh ghi mt n(mng) khng trong sut(m),lm gim vic s dng nh sng ti (39-50%) hay ni cch khc ch c 30% n 50% ca vng cc b cm quang l c tnh cm quang. +Cu trc chuyn dng hnh

Vng hnh nh

Cng la chn

Vng lu tr

Rt in tch

Thanh ghi c ra

Hnh 2-15. Cu trc chuyn dng hnh

58

c im ca k thut chuyn dng hnh l mt hng cc cng chon la gia hnh nh v vng lu tr nh hnh di y. Cc cng ny c chuyn cho ti khi cc in tch ti cc vng tri ti mc xc nh ban u c rt ht t h thng trc khi c chuyn ti vng lu tr.

c. Tiu chun thit b CCD + phn gii

phn gii ca CCD c th xp x bng cch nhn mt s lng cc phn t trn mt n v chiu cao ca nh vi h s Kell. Khong 560 n 450 cc b cm ng trn vi h s Kell l 0.7, phn gii theo chiu ng l s l 392 dng(560 x 0.7) v hng ngang l 236 dng (450 x 0.7 x 0.75). + c tnh s dng ca CCD

CCD c u im v kh nng d dng vn hnh thit b. Cu trc nh gn, gim bt khi lng thit b. ngoi ra, thit b CCD cn c u im v tit kim nng lng, khng chu nh hng rung c hc vn c thit b s dng hiu ng quang in.

Hn na, phn gii v kh nng x l ca CCD cho php to c hnh nh vi phn gii cao hn ng Vidicon. Trong tng lai, cc camera truyn hnh s c s dng loi thit b ghp ni in tch ny, thay th cho cc thit b s dng hiu ng quang in vn c. 2. ng Vidicon

a.Cu to Kt cu ng vidicon ch ra trong hnh v di y. Trong ng thu tinh

hnh tr ng knh khong 13-38mm, c cc linh kin sau: -Bia (1): Gm mt mng kim loi rt mng, nh sng c th xuyn qua

c v ph ln mt trong ca thnh trc ng. Trn lp kim loi ny ph

mt lp quang dn in mng(2-3) m. T lp kim loi ny c li ra ly tn hiu U th trn R t .

59

-Sng in t: Gm catt (2), cc khng ch (3), ant th (4), cc ant th hai(5). Cc hnh tr(6), bn tri cc ny c mt li c mt rt nh,dng to in trng u gn bia. trong mt vi loi ng, cc (5) v (6) lin lm mt.

-Cun cm di (7) dng tiu t v cun lch (8) lm lch tia in t qut. Nu do lp rp sng in t khng chnh xc, tia c b hi lch khi trc ng th c th chnh li bng cun sa (9).

`

a

bCnh vt

Thu knh

+(300-500V)

17 8

9

2345

6

R

Eb (10-100V`)

Hnh 2-16. Kt cu ng Vidicon -in th mng kim loi vo khong +(10-100)V. in th ca li kh

cao, khong +100. in th ant th hai +(300-500) V so vi catt. Ant th hai to trng ng th, v khu vc cun lch s lm lch tia in t ant ny v thu cc in t th cp t bia bt ra. in th ant th nht thng xp x in th ant th hai. Trn ant th hai c l nh gia vi ng knh

(50-60) m hn ch dng knh tia qut. b. Nguyn l lm vic

Nguyn l lm vic ca ng Vidicon da trn hiu ng quang in trong ca bia, ngha l dn in theo chiu ngang ca bia thay i theo cng tia sng ri ln n. Tia ny c th l nh sng nhn thy c nh l tia hng ngoi hoc tia t ngoi.

60

+To nh ni in th. Qu trnh hnh thnh in th trn bia trong ng Vidicon ch ra trn hnh

2-17. Mi phn t bia c th tng ng vi mt t in C v in tr R mc song song vi n, R l in tr theo chiu ngang ca mi phn t. M

tri t C l mng kim loi ca cc tn hiu, m phi t l mt bn phi ca mi phn t kia.

in tr R cng nh khi ri trn phn t cng ln, ngha l khi ri mt nh ln bia th ni chung in tr R ca cc phn t bia s khc nhau.

+Khi bia khng ri sng, tc E q = 0, v cha c tia qut. V c R nn m

phi ca t C cng c in th U b = +E b nh m tri t C, ngha l t C

khng c np, in p trn t C bng khng(U r = 0). +Khi khng chiu sng bia(E q =0) v c tia qut lm vic ch in

t chm. in t ca tia qut c tng tc khi qua khu vc ca ant. Sau trong qu trnh tin ti bia, vn tc tia in t gim dn v cc tn hiu(mng kim loi) c in th E b thp hn in th ant rt nhiu (E b

61

in th. ng vi im sng ca nh, in th cng dng; cn ng vi im ti in th gn bng khng.

Ub

Bia khng c chiu sng Eq = 0 Bia khng chiu sng Eq = 0

EbT in tch in = Eb Sng

TiPhng

Np

Khng c tia qut C tia qut

Tv Tv

t v Tv

Tv

t v

+Eb- Eb

+-

Eb

Uc = 0Phn t bia

i qi tb

U tbR

C

Eb

RtCatt

Catt

R

+ -Uc = Eb

0UbRt

Utb

Uc Eb

Hnh 2-17. Qu trnh hnh thnh in th trn bia trong Vidicon

Tm li qu trnh to nh ni in th xy ra trong cc khong thi gian

di bng T 1 , khi cc t phng in qua cc in tr ngang ca mi phn t

ca bia.

62

+Ly tn hiu ra. Khi qut qua m phi cc t, tia qut h in th ca chng ti mt

in th catt; tc np cho cc t ti mc nh nhau v in p U c ca

chng u tin ti bng E b .

Mc en

Mc trng

Uth

t

T = 64 sH

0

Hnh 2-18. Dng in p tn hiu trn ti Vidicon Sau khi b tia in t qut qua in tch trn mi t C t mc d c

np nh nhau(in p trn u bng E b) s phng i trong khong thi gian t p = TV mt lng in khc nhau(ng vi im cng sng lng in phng cng nhiu). n khi b qut ln lt tip theo mi t li c np b vi lng in tch np li bng lng in tch phng i. Bi v mi khi

b qut cc t li c np n mc nh c, tc l U c = E b . Thi gian np

tV ca cc t nh nhau, nn dng np ca chng khc nhau(ng vi im cng sng, dng np cng ln). Cc dng np b ny chy qua ti R t to nn in p tn hiu cn ly ra. Dng in t np cho cc t C s i theo cc mch sau:

tia qut m phi t - m tri t - ti R t - ngun E b - im chung(catt). Nh vy dng in np, tc dng tn hiu s i t di ln(nh hnh 2-17) v s cho tn hiu cc tnh m nh hnh 2-18.

63

Tm li, qu trnh to tn hiu xy ra khi tia qut lt qua cc phn t ca bia v tch in vo cc t.

Nh nhn xt phn trn, to nh ni in th xy ra trong thi gian di t p = TV - t n TV Khi m cc t in phng qua in tr R ca cc phn t.

TV l chu k qut mnh, t n l thi gian rt ngn tia qut xong mt phn t.

Trong thi gian ngn t n , t np rt nhanh. Nh vy c th coi dng np(dng tn hiu) ln hn dng phng k a z 2 ln (k a z 2 l s phn t ca mt qut). ngha tch lu in tch Vidicon l nh vy.

Nguyn l tiu t v lm lch tia qut nh cun cm di (7), cun lch (8) (hnh 2-16). Ngoi khu vc tc ng ca cun lch, tia qut ch chu tc ng ca t trng song song vi trc ng do cun tiu t to ra, nn tia qut ti thng gc vi mt bia, cht lng tn hiu ly ra ph thuc vo gc ti ca tia qut. c. Qun tnh ca Vidicon

Khc vi cc dng c bin i quang - in khc l Vidicon c qun tnh. C hai nguyn nhn gy ln qun tnh l: hiu ng quang dn in v qun tnh khi ly tn hiu.

Khi chiu sng bia, dn in tng v ngc li, khi che ti dn in gim. S thay i dn khng theo kp s thay i chiu sng, Mc qun tnh ny ph thuc vo vt liu ch to bia, t l gia cc thnh phn trong vt liu, cng ngh ch to v mc chiu sng. Chiu bia cng sng, qun tnh cng nh.

Qun tnh gy ra tn hiu l do dng in t qut nh, khng ln. Nh bit mc ly tn hiu ra ca Vidicon, khi qut a in th cc phn t ca bia xung bng in th catt, tia qut ddax li phn sng ca bia nhiu in t hn l li phn t ti. Ni cch khc ng vi im sng nht, tc c in th dng cao, th phn ln in t ca tia qut khi gn n bia s quay ngc tr li. Trong khi np in cho t C nh vy ta c

64

dng tn hiu cn thit. V vy i hi dng in tia qut phi ln np y in tch cho cc t ti mc in p U r -> E b . Nu khng ln, th sau

mi ln qut ly tn hiu s ly khng ht, c th cn st li 25-30%. Tn hiu cn st li ca mt s nh trc khi qut, lm cho cc chi tit chuyn ng ca nh b nho i, sc nt v r ca nh truyn hnh km i.

Mun ci thin loi qun tnh ny, c th tng dng qut hoc gim in p cc tn hiu E b , m vn gi dng qut nh c. Gim E b tc l i hi dng

np cho cc t C khng ln, nn dng dng tia qut khng ln lm vn m bo yu cu trn. Nu tng dng qut thc t c kh khn, v ng knh tia qut trn mt bia tng ln, lm gim r ca nh truyn hnh. nng cao kh nng phn bit ca vidicon, phi tiu t rt cn thn m bo cho ng knh tia qut ch cn khong vi chc micron(v in tch bia ca vidicon thng kh nh, c 1 cm 2 ).

Tuy c hai loi qun tnh k trn, nhng qun tnh ca vidicon phn ln ph thuc vo ri trn bia. ri cng ln, qun tnh ca vidicon cng nh. Do vidicon c qun tnh nn khi pht nh ca vt chuyn ng, nh truyn hnh s khng sc nt, thm ch nho hn i v c ui di khi vt chuyn ng qu nhanh. d. Cc c tuyn ca vidicon +c tuyn nh sng

0.200.100.05

0.011 10 100

EE

E1b

2b

3b

1bE > >E 2b 3bE

Eq

ith( m )

Hnh 2-19. c tuyn nh sng ca vidicon

65

c tuyn nh sng khng ch ph thuc thng s ca bia, m cn ph thuc c vo ch cung cp in. hnh 2-19, v cc c tuyn nh sng cng vi cc in p cc tn hiu E b khc nhau. Cc trc khc theo logarit.

Trong phm vi ri thng dng, gi tr khng i v c tr s =0.7. +c tuyn ph

Tu thuc vo vt liu ch to bia, vidicon c th nhy cm vi cc nh sng trng thy c nh tia X, tia t ngoi hoc tia hng ngoi v.vHnh 2-20 l c tuyn ph ca hai loi vidicon.

Trn hnh ny cng v c tuyn ph ca tng i ca mt so snh(ng t nt). Nu dng cc ng loi ny th hnh nh truyn hnh s mt trung thc v c tuyn lch sang pha mu xanh v tm. Trong truyn hnh en trng, i vi cc chi tit mu xanh v tm ca vt th trn mn hnh, chi ca cc chi tit khng trung thc na.

Hnh 2-20. c tuyn ph ca vidicon +c tuyn aperture

Ta c th xt kh nng phn bit ca mt dng c bin i quang - in bng c tuyn aperture ca n. Kh nng phn bit ca ng ch yu ph thuc vo cht lng tiu t tia qut v tia quang in t dch chuyn nh t catt quang in sang bia. e. c tnh v s dng

ng vidicon c u im s dng d dng, kt cu gn nh n gin. ng knh cc loi vidicon trong khong 13- 18mm, ngha l kh gn. Tuy n gin nh vy, nhng mt vi b phn i hi gia cng phc tp, trng

66

cng ngh vic ch to cun lch v sng in t phi kh chnh xc. i vi sng in t, nu cn iu chnh sai lch do lp rp, dng hai cp cun iu chnh 9 (hnh 2-16).

b. To nh bng phim Khi chp nh s c ghi trn phim X quang. tng hiu sut tia X

ngi ta thng s dng mt cp ba tng quang, chng c t trong catxet. 1. Phim X quang

Phim X quang c ch to t mt tm cht do trong sut gi l ct phim, hai mt ph mt lp nh tng c bit. Ct phim thng bng polyeste hoc cellulotriaxetat. Lp nh tng l lp sa keo gelatin vi halogenua bc m hay dng nht l bromua bc c thm mt t iodua bc tng thm nhy i vi tia X.

Nhng ht bromua bc ny s b kch hot bi nh sng hoc tia X v vy lp nh tng ny c c tnh l nhy cm vi nh sng trng v tia X v s bin thnh mu en khi c nh sng hoc tia X chiu vo (sau khi c ra bng cc thuc hin, hm phim).

Bromua bc trn u vi gelatin di dng tinh th rt nh 0,1 - 2,5m. Nh tng gelatin - bromua bc thng gm 40% trng lng bromua bc v 60% gelatin, ph dy khong 0,25mm trn ct phim. Mi cm2 phim c t 10 - 15g bc tng ng vi 500 triu tinh th bromua bc. Cc loi phim rt d bt la cho nn phi ch phng chy.

Hnh 2-21. Cu trc phim X quang

(1): Lp gelatin v bc bromua AgBr. (2): Lp gelatin kt dnh. (3): Ct phim (polyeste)

1 2

3

67

Hin nay ngi ta sn sut ra loi phim kh chy axetat, mt khc khi chy to ra loi kh axetic khng c.

Hiu sut chuyn i tia X thnh hnh nh ca phim thp hn nhiu so vi hiu sut chuyn i nh sng nn trong thc t thng phi dng thm mt cp ba tng quang tng cng hiu sut ny (xem phn catxet v ba tng quang). Lp nh tng ph trn b mt phim c c tnh mm v d b h hng nu phim khng c bo qun tt. 2. Ba tng quang

Ba tng quang (cn gi l tm tng quang, mn tng quang) c tc dng lm tng hiu sut chuyn i tia X thnh hnh nh. Nguyn l chp X quang da trn tc dng ca tia X ln nh tng ca phim. Cc cht nh tng trn phim rt nhy cm vi nh sng v tia t ngoi nhng i vi nh

sng c bc sng ngn th tc dng khng cao. tng nhy cm ca phim i vi tia X, ngi ta li dng tnh pht quang ca mt s cht i vi tia X nh canxi tungstat, km sunfua bng cch t phim vo gia 2 tm ba c ph cc cht ny.

Ba tng quang l tm ba c ph cc ht mui canxi tungstat, canxi volframat, gn y cn dng km sunfua + bismut manganat, cc ht mui ny s pht sng mu xanh l mu nhy cm nht i vi phim X quang. Khi tia X i qua cc tm ba tng quang s pht sng (chuyn i bc x tia X thnh nh sng), cng sng ph thuc vo cng chm tia do vy to c nh ca i tng cn thm khm ln trn phim. Nh c cc tm ba tng quang m hiu sut s dng tia X tng ln rt nhiu v nhng l do sau:

- Kh nng hp th tia X ca ba tng quang cao hn phim khong t 20 - 130 ln tu thuc vo cng bc x.

- Mi photon tia X khi tc ng vo ba tng quang s to ra nhiu photon nh sng v mi photon nh sng ny s tc ng vo cc ht mui

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bromua bc khin cho chng chuyn mu thnh en khi phim c ra, kh nng tng trng ny vo khong 60 ln.

Tng hp hai u im trn, ba tng quang lm tng hiu sut chuyn i chm tia thnh hnh nh khong t 100 n 1000 ln tu thuc vo cn

trc ca n.

Tuy nhin, ba tng quang cng c nhc im l khi pht quang cc ht mui tungstat canxi cng to ra s pht quang th cp t nhng ht mui

tungstat canxi ln cn (hnh 2-22), iu ny lm gim sc nt ca nh. V vy, cc nh sn xut ch to nhiu loi ba tng quang c cc c trng thch hp cho nhng mc ch s dng khc nhau. Nhng ba tng quang c lp ph mng v ht mui tungstat canxi mn th c tng trng thp tuy

nhin phn gii li cao, ngc li ba tng quang c lp ph dy v ht mui tungstat canxi th t tng trng cao nhng nh c phn gii thp. Vi nhng ng dng ph cp th nn chn loi ba tng quang loi trung bnh. Mt s nh ch to gi loi ba tng quang ht mn l loi F (Fine), loi trung bnh l loi U (Universal) v loi c nhy cao l loi E.

Photon tia X

Catxet Ba tng quang

Lp d

Ct phim Lp nh tng

Hnh 2-22. Ba tng quang v s pht quang th cp

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2.3. Kt lun vic khai thc c hiu qu th chng ta phi nm c tnh nng k

thut, s khi, cch thc hot ng ca my. Trong chng ny trnh by c cc tnh nng k thut c bn, cng nh cc iu kin bo m cho hot ng ca my. ng thi vic khai thc t cht lng phc v cho cc hot ng sa cha tt bn thn ti c gng i tm hiu, phn tch cc khi v i su phn tch khi bng X- quang, b t ng iu chnh nh sng. y l nhng thnh phn c bn v quan trng nht, ngoi ra trong phn ny cn cp n mt s vn lin quan n vic to nh ca my.

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Chng 3 VN HNH BO DNG V CCH KHC PHC

MT S HNG HC THNG THNG

3.1. CC THAO TC VN HNH MY 3.1.1. Nhng ch v an ton Mc d thit b ny c xy dng theo nhng tiu chun an ton cao nht c v in v c kh, nhng chm tia X- quang c ch vn l ngun gy nguy him i vi nhng ngi vn hnh khng ng nguyn tc v thiu hiu bit. Vic chiu chm tia X- quang qu lu s gy ra tn thng cho m ca c th. V vy vic phng y s gip ngi vn hnh khng ng

nguyn tc v thiu hiu bit hay nhng ngi khc trnh c bc x. * Nhng yu cu i vi ngi vn hnh v ngi bo dng.

- Cn phi c k ti liu hng dn vn hnh trc khi s dng thit b. - Khng ai c s dng thit b ny tr chuyn gia X- quang hay bc s X- quang.

- Khng c dng cc thit b sau gn my X- quang, n s lm cho my X- quang hot ng khng ng: in thoi di ng, my thu thanh, chi iu khin bng v tuyn. Nhn vin y t qun l thit b ny phi ch dn cho k thut vin tun th hon ton cc quy tc trn.

3.1.2. Cch thc t ng phim - Quan st kim tra thy n PAD phi khng sng trong khi chuyn mch chnh ca khi t v tr I.

- Nu n PAD sng th c ngha l phim ang c truyn ti.

Trong trng hp ny khng c thao tc ng phim cho n khi no n ny tt. Ngay c khi n ny khng sng, phim vn ang c cun vo t ng bng ch th . Khi n Film Ready sng ln, c ngha l phim

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vn ang trong gi. V vy ta phi n nt Clear panel iu khin ly phim ra.

- Khi np hoc ly ng phim ra cn h thp chiu cao ca bng X- quang v phn bng tng sng I.I v v tr thch hp thun tin thao tc. - Trong phng ti, vic np 50 tm phim phi theo v tr t u n cui. Nng ci mc kim loi ln v sau ko np ra. Trong phng ti cn xc nh r Receive Magazine R l rng. Sau khi c S v R t xong thuc tnh, n Magazine Set mu xanh s

sng. trng thi ny n SM v RM trn panel iu khin s tt. - Vic thao tc ng phim thc hin nh sau: tay phi xoay v bn tri v dng ngn ci n ci ny v ko ca ra, ng thi tay tri gi pha di ng phim.

Ch : nu m np bng R/F sau khi ch t mt mt ng phim, phim c th b m.

3.1.3. Cch thc vn hnh bng iu khin thao tc bng tay

Bng iu khin thao tc bng tay c s dng vn hnh bng R/F v thc hin trong chn on X- quang vt v php nghim hunh quang.

chuyn sang bng iu khin thao tc bng tay, ta tin hnh tt b chn bng R/F ca panel iu khin v m b chn bng R/F ca bng iu khin thao tc bng tay. Th tc vn hnh cc b chn ny tng t nh ca php nghim hunh quang v X- quang vt v ca cch vn hnh bng R/F.

3.1.4. Vic vn hnh gi chn, tay g v gi vai - Gi chn hot ng bng cch nng v ko ng thi cc nm ca b gi v pha ngi thao tc. V mc ch an ton, ta phi chc chn t cc nt tt c cc mt xung trc khi t bnh nhn ln bn. Chiu cao ca gi chn c hiu chun theo ba bc (10 cm).

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- Cc tay g c th c t li v tr ln hay xung bng cch tho cht (Stopper) ra. Cn phi c nh chc chn cc tay g trc khi thao tc. - Cc tay g pha trn c th s dng khi cn gi cc tay ca bnh nhn. - Gi vai dng ngn nga s trt vai ra khi v tr, nu cn ta hiu chnh rng u v v tr vai bnh nhn.

3.1.5. M bng X- quang

- Trong chp X- quang ngc vi h thng bng X- quang n, ta tho cht gi ca bng X- quang ra v t kiu lm vic ca bng theo Direction of Learders Radiographic stand and Bucky stand. ng thi hiu chun chm tia gc ph hp vi phim. Sau khi hon thnh cng vic trn, ta quay li hiu chnh cht gi v gc thch hp. Nu tr, n c th gy ln cc vt xc trn nh trong qu trnh chp X- quang .

- Chp X- quang vi bng t trn xung bng cch s dng simple radiographic table. Ta thc hin tho cht bng X- quang v vn kho, ri t ch Chp X- quang vi bng t trn xung. Sau khi hon thnh, ta t li thuc tnh cho n khi thch hp.

3.1.6. Cc thit b v dng c bung ti 1. Bung ti Phim X quang c x l (ra v trng) trong bung ti. y cng l

mt khu quan trng trong vic bo m cht lng nh X quang. Bung ti phi t cc ch tiu sau:

- Tuyt i ti c ngha l hon ton khng lt sng. Li vo bung ti phi c hai ca khi m mt ca nh sng vn khng th lt vo bung.

- Phi c thng gi tt thi loi hi ho cht bc ra t thuc hin, hm v lm gim m trong bung.

- Vt liu xy dng v ni tht phi chu c m v s n mn ho hc. - Phi c ng cp thot nc.

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Hnh nh mt bung ti v cc thit b cng nh s b tr cc bung c minh ho trn hnh 3-1. Trong bung ti thng thng phi c cc trang thit b sau:

- Thng ra, trng phim.

- Bn lp, tho phim (bn thao tc phim). - My sy phim. - Khoang chuyn giao catxet (ca a phim). - Gi treo phim.

- Khung phi phim.

- n soi trong bung ti. - ng h bo gi - Qut thng gi. Ngoi ra ti nhng phng X quang c lu lng bnh nhn cao c th phi

dng mt my ra phim t ng thay cho thng ra phim v my sy phim.

Bung ti x l phim phi m bo ti, khng c c bt k nh sng no lt vo khi ng ca bung. Kim tra ti ca bung bng cch vo bung, ng ca li khong 10 pht, sau nhn quanh kim tra m bo

Ca a phim

Bn thao tc phim

Gi treo phim

Thng ra

phim

Gi phi phim

Ca i

Bung ti

Hnh 3-1. Kin trc bung ti

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khng c nh sng lt vo t bt k im no; kim tra nhiu ln trong ngy m bo ti vi tt c cc gc chiu ca mt tri.

Bung ti phi lun sch s, thong, kh, khng c bi bn, hi m nht l cc bn thao tc vi phim v catxet. Sn nh nn lau chi hng tun. B cha ho cht x l phim cn phi gi sch v bc kn khi khng s dng, k c trong thi gian ngn nht cng phi y np. B nc dng ra v ngm phim phi lm bng ximng hoc tt hn l bng thp khng g nh hp kim thp - mlipen.

2. nh sng an ton trong bung ti nh sng trong bung trng phim rt quan trng. Tng nn qut vi

mu xm nht tt hn l mu en. nh sng c dng trong bung ti c th l xanh l cy, da cam,

vng hoc nu. Trong hp ng phim nh sn xut thng thng bo chi tit loi nh sng thch hp vi phim. Tt c cc loi n chiu sng an ton nn

b tr pha trn bn thao tc phim, cch mt bn t nht l 1,3m. Cng sut bng n pht ra nh sng an ton khng vt qu 25W.

Phim cha lp Phim lp

Hp phim Hp phim

n

Hnh 3-2: Bn thao tc phim

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Sau khi x l phim, nu phim c x l b m th kim tra li xem nh sng c lt vo bung ti khng, n pht nh sng an ton c m bo khng (c th hng b phn lc sng, cng sut bng qu 25W)

3. Thng ra, trng phim

Thng lm bng tn trng men, bakelit hoc thp khng g (ciment gi m), cha ng c nhiu loi phim khc nhau. Thng c np y ngi ra phim c th lm vic khc di nh sng.

Nhng c s chp t, c th trng phim trong khay, chu tit kim thuc ra phim, tuy nhin ch ra c tng ci mt v phi lng phim cho u.

4. Khung phi phim Khung phi phim thng lm bng nha hoc thp khng g. C kch

thc tng ng vi phim, thun tin cho qu trnh trng phim v phi phim.

5. Ca a phim

Ca a phim (khoang chuyn giao catxet) phi c cu trc m bo khng lt nh sng vo bung ti khi chuyn phim cha chp t bung ti

H

N N

2

s

1

Hnh 3- 3: Cu trc thng ra phim N: nc; H: thuc hin hnh; : thuc nh hnh; : n an ton; s: n chiu

sng thng; 1: nc chy lin tc; 2: nc trn thot ra

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ra phng chp v chuyn phim chp vo bung ti. Mt s kiu cu trc ca a phim thng dng biu din trn hnh 3- 4.

3.2. BO DNG 3.2.1. Lm sch mn tng sng

t bng chp hunh quang nm ngang, sau m ca s mt bn bng bo v. Khi ta s trng thy thit b Spot Film.

M hai nt du v v tr thch hp v sau m np y. Ly mm cp phim ra theo ch dn mt bn ca bng bo v v lm sch mn tng sng bng dng c lm sch. Thay th mm cp phim v v tr ban u theo th t ngc li. - Nu ca s bn tri m, b ch th trng thi vt Spot- status (10) s sng v vic chp X- quang vt hay chp hunh quang b ngt.

3.2.2. Qu trnh bo dng nh k Thit b ny yu cu c bo dng nh k m bo an ton v

chnh xc. Cng tc bo dng c thc hin bi nhng ngi c nng lc. Cc ni dung cn bo dng cho trong danh sch di y.

a)

Hnh 3- 4: Cu trc ca a phim a): ca quay; b): bung ngn na ti; c): ca che

Vi che

c) b)

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S th t Ni dung bo dng

1 Kim tra bn ngoi thit b.

2 Kim tra sng ca s phng.

3 Kim tra cng tc- chuyn mch.

4 Kim tra n ch th.

5 Vn hnh cc ny. 6 Kim tra b ch th hin th s.

7 Kim tra cch ly.

8 Kim tra mch khi ng.

9 Kim tra mch tch tia X.

10 Hiu chnh R-kV.

11 Hiu chnh F-kV.

12 Hiu chnh R-mA.

13 Hiu chnh F-mA.

14 Kim tra thi gian chiu x.

15 Thay th cu ch. (Bn iu khin) 16 Kim tra vic np chi qut bin th t ng.

17 Kim tra du thng cao th.

18 Kim tra cp cao th.

19 Kim tra Rotor.

20 Tra du m cp cao th.

21 Kim tra qut.

22 Kim tra cp ng chun trc v Rotor.

23 Hiu chnh chm tia ng chun trc.

24 Hiu chnh di sng ca n.

25 Hiu chnh di n v b thi gian. 26 Collimator Blade Movement.

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27 Kim tra vic np phim.

28 Kim tra hot ng n phim.

29 Kim tra bng ch dn phim.

30 Kim tra tc b cun phim.

31 Kim tra hot ng nhn phim.

32 Kim tra ng phim.

33 Kim tra tip xc mm cp phim.

34 Kim tra s di chuyn mt n.

35 Kim tra vic in tn ID.

36 Kim tra s iu khin SFD.

37 Kim tra vic che mm cp phim.

38 Kim tra phn gii ca I.I.

39 Kim tra u ra cao th I.I.

40 Kim tra chi tng i ca I.I. Kim tra chi nh

41 Kim tra hi t CCD.

42 Kim tra cp truyn nh.

43 Kim tra cht lng nh.

44 Hiu chnh F-kV i vi