Tng quan v my MRI1./ L ch s pht trinFelix Block v Edward Purcell pht hin ra hin tng cng hng t ht nhn vo nm 1946 v t nhng nm 1950 n nm 1970 cng hng t c ng dng v pht trin rng ri. Thnh qu c chng nhn bng gii Nobel Vt l vo nm 1952 cho 2 nh vt l Felix Block v Edward Purcell. V l c s vt l quan trng cho s pht trin MRI.n nm 1970, nn to nh y hc th gii c mt s thay i ng k vi s cng b kt qu nghin cu ca tin s Raymond Damidian. ng pht hin ra cu trc c th ngi bao gm phn ln nc v l cha kha cho to nh cng hng t, v rng nc pht ra mt tn hiu m c th d v ghi li c. Sau tin s Damidian v cc cng s tip tc nghin cu mit mi trong 7 nm v thit k, ch to ra chic my qut cng hng t u tin dng trong vic to nh y t ca c th ngi.n nm 1980 chic my cng hng t u tin c a vo p dng. n nm 1987 k thut Cardiac MRI c a vo s dng cho vic chn on cc bnh v tim mch. n nm 1993 th FMRI dng chn on cc chc nng v hot ng ca no b

K thut to nh cng hng t (MRI) hin tr thnh mt phng php ph thng trong y hc chn on hnh nh. Cc thit b MRI u tin ng dng y hc xut hin vo u nhng nm 1980. Vo nm 2002, c gn 22.000 camera MRI c s dng trn ton th gii. Trn ton th gii mi nm c hn 60 triu ca chn on bng MRI v phng php ny vn ang pht trin nhanh. MRI thng tt hn cc k thut hnh nh khc v c ci thin ng k v chnh xc trong vic chn on nhiu cn bnh. N thay th mt s phng php kim tra theo kiu a thit b vo c th, do gim au n, ri ro cng nh s bt tin cho nhiu bnh nhn. Chng hn nh s dng phng php ni soi kim tra tuyn ty hoc tuyn mt c th gy mt s bin chng nghim trng.Li th ca MRI l tnh v hi ca n. MRI khng s dng bc x ion ho ging nh phng php chp X quang thng quy (Nobel Vt l -1901) hoc chp CT (Nobel Y hc -1979). Tuy nhin, n c mt nhc im l bnh nhn no phi tim kim loi t hoc mang my iu ho nhp tim khng th c kim tra bng MRI bi MRI c trng t tnh mnh. Ngy nay, MRI c s dng kim tra gn nh mi c quan trong c th. K thut ny c bit c gi tr trong vic chp nh chi tit no hoc dy ct sng. K t khi MRI mang li nhng hnh nh 3 chiu, bc s c th nm c thng tin v a im thng tn. Nhng thng tin nh vy rt c gi tr trc khi phu thut chng hn nh tiu phu no.2./ Nguyn l to nh phng php chp nh cng hng t ht nhn MRI (Magnetic Resonnance Imaging), ngi ta a c th bnh nhn vo vng c t trng mt chiu rt mnh, hin nay ph bin l dng t trng sinh ra do cun dy siu dn c dng in rt ln chy qua. Trong c th c nhng nguyn t m ht nhn c momen t tng t nh c gn mt thanh nam chm cc nh. Di tc dng ca t trng ngoi, momen t ca ht nhn nguyn t quay o tng t nh con quay di tc dng ca trng trng trn mt t. Nu ht nhn ang quay o vi tn s w m c thm sng v tuyn cng tn s w tc dng, ht nhn s quay o cc mnh v c hin tng cng hng. l cng hng t ht nhn. Khi ngng tc dng sng v tuyn, ht nhn s t trng thi quay o cc mnh tr v trng thi quay o bnh thng. Ht nhn c momen t quay nh vy s sinh ra sng in t pht ra khng gian xung quanh, c th o c sng in t nu t vo y mt cun dy in.

Vic ht nhn t trng thi quay o mnh do cng hng tr v trng thi quay o bnh thng nhanh hay chm cn ty thuc vo cc nguyn t quanh ht nhn cn tr chuyn ng quay t hay nhiu. V d, ht nhn ca nguyn t H trong phn t nc (H2O) ca mu, t trng thi cng hng quay v trng thi thng rt nhanh nu mu ang lu thng trong mch mu, tri li quay v rt chm nu mu chy thm ra ngoi tht, m. my MRI, ngi ta c th to ra cng hng ng vi mt loi ht nhn no (v d ht nhn hyr) trong tng th tch c milimet khi ca no v theo di trng thi cng hng. Ln lt qut th tch c cng hng ny, s c c hnh nh cng hng t ht nhn tng lp. C th theo di nh bit c cu to bn trong ca no lc c th ang sng (bit c c chy mu trong no hay khng, chy ch no). C th dng MRI theo di hot ng ca no, v d nh khu vc no ca no hot ng, mu a oxy v vng mnh hay yu...c im MRI phn gii khng gian rt cao, cn phn gii thi gian va phi: Phn gii khng gian: 3 mm v phn gii thi gian: 3 giyy l phng php hiu nghim v d s dng nht hin nay nghin cu v no. Ngi ta pht trin phng php chp nh cng hng t chc nng (FMRI Function MRI) nghin cu khng ch v cu to m cn v chc nng hot ng ca no.Tuy nhin, phng php ny kh tn km do phi dng hli lng lm lnh cun dy siu dn.u imnh cu trc cc m mm trong c th nh tim, phi, gan v cc c quan khc r hn v chi tit hn so vi nh c to bng cc phng php khc.MRI gip cho cc bc s nh gi c cc chc nng hot ng cng nh l cu trc ca nhiu c quan ni tng trong c thS chi tit lm cho MRI tr thnh cng c v gi trong chn on thi k u v trong vic nh gi cc khi u trong c th.To nh bng MRI khng gy tc dng ph nh trong to nh bng chp X quang thng quy v chp CTMRI cho php d ra cc im bt thng n sau cc lp xng m cc phng php to nh khc kh c th nhn ra.MRI c th cung cp nhanh v chun xc so vi tia X trong vic chn on cc bnh v tim mch.Khng pht ra cc bc x gy nguy him cho con ngi.Nhc imCc vt bng kim loi cy trong c th khng c pht hin c th b nh hng bi t trng mnhKhng s dng vi cc bnh nhn mang thai 12 tun u tin. Cc bc s thng s dng cc phng php to nh khc, v d nh siu m, vi cc ph n mang thai tr phi tht cn thit bt buc phi s dng MRI.3./ p dngCc bnh l thn kinh : ng kinh , bnh mt Myelin, bnh no bm sinh, u bu , vim nhim, .. . ca no v ty sng .Mch Mu : D dng , x va , teo hp mch mu no b v tn thng.C xng khp : bnh l vim c xng khp, dy chng, c bp.Mt, tai mi hng : U hc mt, u ni nh, u hu hng, vim nhim, p xe ...Tim mch : bnh l c tim, ng mch c, ng mch ch, ng mch ngoi viC quan ni tng : cc bnh l gan, thn ty, lch ...U buu : pht hin, nh gi mc xm ln theo iu tr.4./ So snh MRI vi CTChp ct lp in ton (CT Scan) s dng tia X v h thng detector thu thp tn hiu khc nhau ca tng im trn c th sau ti to li hnh nh theo tng lt ct.Chp cng hng t (MRI) s dng t trng lm phn cc cc nguyn t Hydro c trong phn t nc ca c th. Khi cc nguyn t H o cc s cho cc tn hiu in t c ghi nhn. V hm lng nc khc nhau trn mi loi m nn tn hiu nhn c s khc nhau, to ra hnh nh khc nhau ca cc vng m trong c th.CT v MRI u l phng tin chn on hnh nh cao cp, thu nhn cc hnh nh bnh l nm su trong c th chn on bnh. Hnh nh thu c c th ti to thnh hnh 3 chiu, lt ct rt mng v chi tit rt nh gip ch rt nhiu trong chn on.CT s dng tia X nn c tc hi do c th b nhim tia, gi r hn MRI.MRI s dng t trng, hon ton khng tn hi c th nh gi mc hn.5./ ng dng Vit NamNgy 14/7/1996, ti Medic khnh thnh my MRI u tin ti Vit Nam vi s hin din ca GS. Trn Vn Giu, my MRI hiu Toshiba Access loi m (open).ngy 14-07-1996 khai trng MRI..u tin ca MEDIC. My MRI u tin ny hot ng khi m ngi bnh cn cha sn lng xt nghim bng k thut ny v qu mi, gi cao,, bc s cha bit r ch nh khi no cn chp MRI.i ng bc s chn on s dng cng hng t (MRI) c o to ti Singapore v M Lai, ri M dn uy tn v nhu cu chn on vi MRI trong lnh vc no v ct sng, lm nn cho 2 chuyn khoa ny pht trin. Nhu cu chp MRI tng ln cao, MRI th 2 ra i bnh vin Vit X v sau l bnh vin ch Ry ri ph bin rng ra ton quc.Ti Medic, TPHCM, nhu cu chp MRI tng nhanh, my MRI th 2 ca Medic ra i, loi siu dn 1,5T GE LX. Ri tip tc li cn thm my th 3 MRI siu dn 1,5T CVI GE Hin ti, mi ngy Medic chp 50 bnh nhn vi nhiu k thut, nht l ct sng v no.Hin ti trn ton quc c 23 my MRI phn b nh sau :H Ni : 9 myBV Bch MaiBV Vit cBV Saint-PaulBV Qun Y 103TT AmticTT chn on (178 Thi H)TT chn on (107 Tn c Thng)BV Vit X (1T)BV 108 (1,5T)Hu Nng : 3 myBV Trung ng Hu (1,5T China)BV a khoa Nng (open Hitachi)BV Hon M Nng (open Toshiba)

TPHCM : 11 myMedic (3 my : 2 GE 1,5T v 1 open)BV Ch Ry (2 my : 1T v 1,5T Siemens)BV i hc Y (1,5T Siemens)BV Thng nht (1,5T Philip)BV 115 (1,5T Siemens)BV Vn Hnh (open - Siemens)BV Chn thng Chnh hnh (open Hitachi)BV 175 (open Philip)

ng bng Sng Cu Long : 1 myBV a khoa Kin Giang (open Hitachi)TNG CNG : 23 MY (C 11 MY LOI SIU DN)Tng lai s cn nhiu my MRI ra i na, ko theo cc chuyn khoa su pht trin nh thn kinh, ct sng, khp, v mt tin vui cho ngnh ung th l c th pht hin ra ung th sm vi cht cn t nano c bit, mt ng r ca cng hng t tng lai cnh tranh vi k thut PET trong truy tm ung th sm.Sau 10 nm pht trin (1996 2006), t 1 my nay c 23 my, ngi bnh Vit Nam gi y khng cn phi ngh l phi i Singapore chp MRI na, c ai bit chi ph chp ti Vit Nam ch l 20% so vi gi chp nc ngoi, khng cn chi ph v my bay v khch sn, khng cn i ch xp hng lu na. Tt c s thun li cho bnh nhn c cht lng iu tr cao v chi ph r phi cn 10 nm qua pht trin.(Trch bo co ca K47 TYS H BK Hhn 4: Chp cng hng t l g?

MRINguyenTriPhuong- Chp cng hng t ( MRI scan ) ph bin trn th gii cng nh Vit Nam bi tnh u vit ca n so vi cc phng php to nh y hc khc, nhng phn lnchng tavn cha c hiu bit c bn v phng php chp cng hng t, tuy nhin hiu chi tit v phng php ny th l cng vic ca cc nh vt l vchng tach cn hiu c bn v n tn hng nhng thnh tu ca khoa hcm nmang li nhng lich cho cuc sng. Vy cng hng t l g? Chp cng hng t hay cn gi l chp MRI (Magnetic Resonnace Imaging) l phng php a c th vo vng t trng mnh ng ha chiu chuyn ng ca cc nguyn t Hydro trong cc phn t nc ca c th v mt ng ten thu pht sng radio tn s thp (tn s radio ny c thay i trong vng t trng n nh ca nam chm chnh ty theo mc ch kho st ca s phn bit m, nc, v v) c s dng gi tn hiu n c th gp cc nguyn t Hydro ca c th sau nhn li tn hiu v chiu chuyn ng ca cc nguyn t ny, tn hiu ca ng ten c truyn v trung tm my tnh x l tn hiu s sau cc tn hiu c truyn v my tnh iu khin v cc hnh nh cu trc c th c m phng ti y.N) Nguyn l ca chp cng hng tng lc: Th ba - 15/04/2014 13:50 - Ngi ng bi vit:admin

Nguyn l ca chp cng hng tBnh vin a khoa tnh k Lk va a vo s dng h thng chp cng hng t (Magnetic Resonance Imaging: MRI). c phim ng, thy thuc phi tip cn vi mt s khi nim i khi kh tru tng. V th, chng ti xin trnh by khi qut mt s khi nim thng dng ca phng tin ni trn. Cc vn c th v vai tr ca phng tin ny trong chn on cc bnh l ca nhng c quan khc nhau s c trnh by trong lot bi khc.Nguyn l hot ng ca MRI (Magnetic Resonance Imaging)Chng ta u bit mi vt th u c cu to t nguyn t. Ht nhn nguyn t c cu to t cc proton (mi proton mang in tch +1) v cc neutron (khng mang in tch). Quay quanh ht nhn l cc electron (mang in tch m). Trong nguyn t trung ha in tch, s proton ca ht nhn bng ng s electron ca nguyn t . Tt c cc tiu th ny u chuyn ng. Neutron v proton quay quanh trc ca chng, electron quay quanh ht nhn v quay quanh trc ca chng. S quay ca cc tiu th ni trn quanh trc ca chng to ra mt mmen gc quay gi lspin. Ngoi ra, cc ht mang in tch khi chuyn ng s sinh ra t trng. V proton c in tch dng v quay nn n to ra mt t trng, ging nh mt thanh nam chm nh, gi lmmen t(magnetic moment) (Hnh 1). Nh cc c tnh vt l nh vy, khi t mt vt th vo trong mt t trng mnh, vt th c kh nnghp thvbc xli cc xung in t mt tn s c th. Khi hp th, trong vt th din ra hin tngcng hng t ht nhn(Nuclear Magnectic Resonance: NMR). Tn s cng hng ca cc vt th m thng thng nm trong di tn ca sng v tuyn (radiofrequency: RF). Cn khi bc x, vt th cng pht ra cc tn hiu v tuyn (Hnh 2).C th chng ta cu to ch yu t nc (60-70%). Trong thnh phn ca phn t nc lun c nguyn t hydro. V mt t tnh, nguyn t hydro l mt nguyn t c bit v ht nhn ca chng ch cha 1 proton. Do , n c mt mmen t ln. T iu ny dn ti mt h qu l: nu ta da vo hot ng t ca cc nguyn t hydro ghi nhn s phn b nc khc nhau ca cc m trong c th th chng ta c th ghi hnh v phn bit c cc m . Mt khc, trong cng mt c quan, cc tn thng bnh l u dn n s thay i phn b nc ti v tr tn thng, dn n hot ng t ti s thay i so vi m lnh, nn ta cng s ghi hnh c cc thng tn.ng dng nguyn l ny, MRI s dng mt t trng mnh v mt h thng pht cc xung c tn s v tuyn iu khin hot ng in t ca nhn nguyn t, m c th l nhn nguyn t hydro c trong phn t nc ca c th, nhm bc x nng lng di dng cc tn hiu c tn s v tuyn. Cc tn hiu ny s c mt h thng thu nhn v x l in ton to ra hnh nh ca i tng va c a vo t trng .Qu trnh chp MRI gm c 4 giai on. Nguyn l ca 4 giai on nh sau:Giaion 1: Sp hng ht nhnMi proton trong mi trng vt cht u c mt mmen t to ra bi spin (xoay) ni ti ca n. Trong iu kin bnh thng, cc proton sp xp mt cch ngu nhin nn mmen t ca chng trit tiu ln nhau do khng c t trng d ra ghi nhn c. Khi t c th vo my chp MRI, di tc ng t trng mnh ca my, cc mmen t ca proton s sp hng song song cng hng hoc ngc hng ca t trng. Tng tt c mmen t ca proton lc ny c gi lvect t ha thc(net magnetization vector). Cc vect t sp hng song song cng chiu vi hng t trng my c s lng ln hn cc vect t sp hng ngc chiu v chng khng th trit tiu cho nhau ht. Do vect t ho thc c hng ca vect t trng my. ltrng thi cn bng. Trong trng thi cn bng khng c mt tn hiu no c th c ghi nhn. Khi trng thi cn bng b xo trn s c tn hiu c hnh thnh.Ngoi s sp hng theo hng ca t trng my, cc proton cn c chuyn ng o (Precession), tc quay quanh trc ca t trng my. Chuyn ng o l mt hin tng vt l sinh ra do s tng tc gia t trng v ng lng quay ca proton. Chuyn ng o ging nh hin tng con quay, n lm cho proton khng ng yn m o quanh trc ca t trng bn ngoi (Hnh 1). Tn s ca chuyn ng o nm trong di tn s ca tn hiu RF v c xc nh bng phng trnh Lamor. Khi pht xung RF cng tn s vi proton ang chuyn ng o th proton hp th nng lng xung to nn hin tng cng hng t ht nhn.

Hnh 1: M t mt proton c mmen t c t trong t trng ngoi B0v c chuyn ng o Giaion 2: Kch thch ht nhnSau giai on sp hng ht nhn, cun pht tn hiu (transmitter coil) ca my pht ra cc xung in t ngn (o bng mili giy) gi l xung tn s v tuyn (radiofrequency pulse: xung RF). V cc xung pht ra c tn s RF tng ng vi tn s cng hng ca proton nn mt s nng lng s c proton hp th. S hp th nng lng ny s y vect t ho lm chng lch khi hng ca vect t trng my. Hin tng ny gi l kch thch ht nhn (Hnh 2).

Hnh 2: M t qu trnh kch thch ht nhn (cng hng) v qu trnh dn (bc x nng lng di dng tnh hiu RF)C hai khi nim quan trng trong x l tn hiu lt ha dc(longitudinal magnetization), song song vi t trng ca my vt ha ngang(transverse magnetization), vung gc vi t trng my.T ha dcl hin tng t ha do nh hng ca t trng my. chnh l trng thi cn bng nh trnh by trn. Trng thi ny c duy tr cho n khi c mt xung RF tc ng lm vect t ho lch khi hng ca vect t trng my. Khi pht xung RF, sau mt thi gian no , vect t ho li khi phc tr v v tr dc ban u. Qu trnh khi phc (recovery) theo hng dc ca t trng my gi l qu trnhdn theo trc dc(longitudinal relaxation) (Hnh 3).Thi gian dn theo trc dc(longitudinal relaxation time) l thi gian cn thit hin tng t ha dc t 63% gi tr ban u ca n. Thi gian ny cn gi lthi gian T1.T ha ngangxy ra khi pht xung RF ln m. Xung ny thng l xung 900. Do hin tng cng hng nn vect t ho lch khi hng ca vect t trng my v b y theo hng ngang to nnvect t ha ngang(transverse magnetization vector). T ha ngang l trng thi khng n nh, kch thch v nhanh chng phn r khi kt thc xung RF. T ho ngang cng l mt qu trnh dn gi ldn theo trc ngang(transverse relaxation). Khi ngt xung RF, vect t ha ngang mt pha, suy gim nhanh chng v dn dn tr v 0. Thi gian cn thit 63% gi tr t ho ban u b phn r gi lthi giandn theo trc ngang(transverse relaxation time) (Hnh 3). Thi gian ny cn gi lthi gian T2. Thi gian T2 ngn hn nhiu so vi thi gian T1.

Hnh 3: M t qu trnh t ho dc v t ho ngang. M0l vect t ho thc trng thi cn bng. Y l hng ca vect t ho ngang. MZl vect t ho khi dn theo trc dc.Giaion 3: Ghi nhn tn hiuKhi ngt xung RF, cc proton ht b kch thch, tr li sp hng nh c di nh hng ca t trng my (gi l qu trnh dn theo trc dc nh trnh by trn). Trong qu trnh ny, khi mmen t ca cc proton khi phc tr li v tr dc ban u, chng s bc x nng lng di dng cc tn hiu tn s v tuyn. Cc tn hiu ny s c cun thu nhn tn hiu (receiver coil) ca my ghi li.Giaion 4: To hnhnhCc tn hiu v tuyn bc x t vt th m sau khi c cun thu nhn tn hiu ca my ghi li s c x l in ton to ra hnh nh. Cng bc x t mt n v khi lng m c th hin trn phim chp theo mt thang mu t trng n en. Trong mu trng l cng tn hiu cao, mu en l khng c tn hiu (Hnh 4).

Hnh 4: M t mi lin h gia thi gian T1, T2 vi mc t ho v cng tn hiu trn phim chp.Trong qu trnh dn (tng li) ca t ho dc, cc m khc nhau s c mc t ho khc nhau. V th tc tng s khc nhau, hay ni cch khc gi tr T1 khc nhau. M vi gi tr T1 ngn hn c tc tng li s t ho dc nhanh hn. Do vy, trong sut thi gian ny n c mc t ho cao hn, to tn hiu mnh hn v xut hin trn nh sng hn.Trong qu trnh phn r s t ho ngang, cc m khc nhau c mc t ho khc nhau do tc phn r khc nhau, hay T2 khc nhau. Gi tr T2 di tc m c mc nhim t cao, to ra tn hiu mnh hn v sng hn trong nh so vi m c gi tr T2 ngn. Ti thi im bt u chu k, khng c tng phn T2, nhng tng phn T2 tng dn trong qu trnh dn.C th thy rng, phng thc to nh MRI c hai pha khc nhau. Mt pha i cng vi s t ho dc v pha kia i cng vi s t ho ngang. Mt khc, nh trn trnh by, trong thi gian T1 khi mmen t ca cc proton khi phc theo chiu dc di nh hng ca t trng my th tng tt c mmen t ca proton lc ny c gi lvect t hathc. ln ca vect t ho thc ph thuc vo mt proton ca m . Gia hai m ln cn, d thi gian T1 c th bng nhau nhng nu mt proton khc nhau th mc t ho s khc nhau. V th cng tn hiu bc x ra cng khc nhau nn s to ra tng phn nh khc nhau. Nh ta c th nhn bit ring bit c chng qua s tng phn trn nh. Nu hai m c gi tr T1 khc nhau, th s tng phn s cng tng ln. Nhng khi cc m tin dn ntrng thi cn bngth mt proton li tr thnh mt yu t chnh nh hng n tng phn gia hai m.Nh vy, u im vt tri ca phng php to nh MRI so vi cc phng php khc l ch ta c th chn cc c tnh khc nhau ca m to ra tng phn hin th trn phim chp. C 3 c tnh c bn ca m l ngun tng phn nh : (1) mt proton kt hp vi thi gian dn dc T1, (2) thi gian dn dc T1, (3) thi gian dn ngang T2.Khi nim TR, TE, T1W, T2W, PD v PDWNh bit trn, cng tn hiu tng dn t 0 n cc i trong thi gian T1 v gim dn t cc i tr v 0 trong thi gian T2. Nhm to ra s tng phn tt nht v hnh nh ca cc m, ngi ta phi chn thi im T1 v T2 thch hp thu nhn cc tn hiu bc x cung cp cho qu trnh to nh. TR v TE chnh l cc thng s v thi gian o tn hiu c ngi vn hnh my thit lp trc khi chp MRI.TR(Time of Repetition) l khong thi gian t khi bt u dn dc n khi mc t ho ca m c o to ra tng phn nh. Xc nh gi tr TR l xc nh thi im chp nh.TE(Time of Echo event) l khong thi gian t khi bt u dn ngang n khi mc t ho ca m c o to ra tng phn nh. Cc gi tr kt hp gia TE v TR c chn qua cc bng tu thuc vo tng loi m.Bng cch iu chnh cc gi tr TR v TE ca T1 v T2, ta thu c cc tng phn nh tng ng vi mt c tnh m ring bit. nh ca T1 v T2 trong trng hp ny gi lT1 iu chnh(T1-weighted: T1W) vT2 iu chnh(T2-weighted: T2W).Nhm to nh T1 iu chnh, ngi ta cn chn mt gi tr TR tng ng vi thi gian m ti tng phn T1 ln nht gia hai loi m. Nu la chn TR di hn s to ra cng tn hiu ln hn nhng tng phn T1 t hn. Vic la chn TR thch hp vi cc gi tr T1 ca m rt c ngha trong chn on lm sng, c bit khi phn bit gia m lnh v m bnh l. Nu gi tr TR c chn bng gi tr T1 ca m, l nh c chp khi m tr li 63% s nhim t m ca n.Nhm to nh T2 iu chnh, ngi ta cn chn mt gi tr TE tng ng vi thi gian m ti tng phn T2 ln nht gia hai loi m. Tng phn T2 cc i thu c bng cch dng TE tng i di. Tuy nhin, nu dng TE qu di th s nhim t v tn hiu RF li qu thp hnh thnh mt nh.Mt k thut to nh hay gp na l PD.PD(Proton Density) l nh kho st mt proton. Nh ni trn, khi s nhim t dc t gi tr cc i th tng phn theo thi gian T1 s km i. Lc ny tng phn nh do mt proton ca m quyt nh. Do vy, nu ta chn gi tr TR tng i di to nh tng phn mt proton th gi l nh mt proton iu chnh (Proton Density-weighted:PDW).Kt lun: Vic hiu bit nguyn l hot ng v cc khi nim c bn ca chp cng hng t s gip thy thuc nhn nh ng cc cu trc bnh thng hoc bnh l ca cc m. Khi c bt k phim MRI no, trc tin phi nhn bit l phim T1 hay T2. C th thy rng nc (hay cht lng ni chung) v c mt proton cao nn thi gian n khi phc li 63% gi tr t ho ban u s ko di hn so vi m c t nc. V th nc (hay cht lng ni chung) c cng tn hiu yu trong thi gian T1 v th hin bng mu ti (en) trn phim T1W. Ngc li, v c mt proton cao nn u thi gian T2, nc (hay cht lng ni chung) c cng tn hiu cao v suy gim ko di hn nn th hin bng mu sng (trng) trn phim T2W. Cc m b ph n, vim, nhim trng v cc nang cng c tnh cht tng t. V vy khi c bt k phim MRI no, trc tin phi tm nhng cu trc no m ta bit chc chn l nc nh dch no tu trong cc no tht v ng sng, nc tiu trong bng quangNu cu trc nc y c mu ti th l nh T1W, nu mu sng th chnh l nh T2W.