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MRI Conditional Pacemaker
核磁共振相容節律器
Sep 07, 2013
振興醫院 張鴻猷醫師
2013 Taiwan Heart Rhythm Society –
Allied Professional Education Program
MR Conditional Labeling*
MR Safe
MR Conditional
MR Unsafe
*ASTM standard F2503: Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment
An item that has been demonstrated to pose no known hazards in a specified MRI environment with specified conditions of use.
MRI 基本步驟
•1. 把人放進去MRI裡
•2. 給能量去激發人體內的氫原子
•3. 把能量關掉
•4. 接收氫原子激發後回傳的能量波
•5. 轉換此能量波訊號成為影像
設備圖
Magnet Gradient Coil RF Coil
RF Coil
4T magnet
gradient coil
(inside)
B0
Main Components of a MRI
Scanner
• Static Magnetic Field Coils
• Gradient Magnetic Field Coils
• Magnetic shim coils
• Radiofrequency Coil
• Control computer
1.5 or 3.0 telsa
1 telsa (T) = 10000 gauss
地球磁場 = 0.5 gauss
Transmit Receive
RF
coil
RF
coil
Main
magnet Main
magnet
Gradient Shimming
Control
Computer
質子 (Proton)
•帶正電
•會自旋
The Effect of Irradiation to the Spin System
Lower
Higher
Spin System After Irradiation
MRI 原理
•利用磁場原理，把人體置於強大且均勻的靜磁場 (static magnet) 中，再利用特定的射頻無線電波脈衝，激發人體組織內的氫原子核
•由於人體內的水分子和脂肪都含有氫原子核，這些氫原子核本身又具有磁場特性，如同一個小小的磁鐵
•若使儀器改變體內氫原子核的旋轉排列方向，原子核就會釋放吸收的能量，能量激發後放出電磁波信號，再經由電腦分析組合成影像，這就是一般所看到的 MRI 影像
•由於不同的組織受到刺激後，釋出不同的回波，因此在影像上便會產生非常良好的對比
MRI 優點
•非侵入性、無傷害的診斷系統，沒有使用 X 光及放射線物質
•安全、無痛苦，能呈現具體的多方向切面影像
•可以很精細的提供腦部、脊椎、軟組織的狀況
•所測量的不僅是組織的解剖影像，更重要的是組織的各種功能性影像，具備對各種組織器官功能性與新陳代謝性障礙的診斷能力
•檢查前病患不需要特別做什麼準備，例如在檢查前不需要空腹、可以進食
MRI 缺點
•設備費用昂貴，檢查費用較高
•掃描時間需時較長
•對肺部的檢查不優於X射線或CT檢查
•對身體移動非常敏感，若移動易產生偽影，故不適合急診病患及危急病人，也容易引發禁閉恐懼症
•心律調節器、金屬性人工心臟瓣膜、各類電子傳導器、腦動脈瘤手術夾等裝置會受到磁場干擾，患者不適合 MRI 檢查
•無法鑑別鈣化點
裝置節律器的病人常需要MRI檢查
It is estimated that 50 to 75% of pacemaker patients will have a medical need for an MRI over the lifetime of their device
Average Age of Pacemaker Patient
13% Ages 25-64
86% Age 65+
The Prevalence of Common
Comorbidities Increases Rapidly
Over Age 65
慢性病多、需要多專科同時照護
Number of Comorbidities in
Pacemaker Patients
85% of all pacemaker patients have one or more comorbidities
15% 0 comorbidities
30% 1 comorbidity
28% 2 comorbidities
27% 3 or more
comorbidities
Opthalmology
Otolaryngology
Neurosurgery
Neurology
Cardiothoracic Surgery
Surgical Oncology
Nephrology
Gynecologic Oncology
Urology
Rheumatology
Oncology
Radiation Oncology
Interventional Radiology
Gastrointestinal Surgery
Orthopedic Surgery
Vascular Surgery
85%1 1 or more
comorbidities
1 Kalin R, Stanton MS. PACE. 2005;28:326-328.
MRI: Three Powerful Fields
Static Field
Gradient Field
RF Field
MP – 14
背景磁力永遠存在
Static Gradient RF
Device Interactions
Stimulation (UCS)
Lead Heating
UCS = unintended cardiac stimulation - Inhibitor pacemaker function
- Trigger rapid pacing
- Deliver inappropriate shocks
Lead Heating Clinical Impact
• PCT = Pacing Capture
Threshold
• PCT is lowest at implant
• Healing produces scar
• Increased distance
increases PCT
• Significant heating causes tissue damage
• Increased scar volume increases PCT
Stimulation hazard gradient-induced high
rate pacing
Start of Scan
EKG
Pulse Ox
Canine Test
Unintended Stimulation Clinical
Impact
The MRI scanner is pacing the heart
Device Interactions Clinical
Impact
Failures can be temporary or permanent
MP – 53
Pacemaker System Design
Solutions
Device Design Solutions
• Minimize ferromagnetic content
Unintended cardiac stimulation Device interactions Force and Torque
• Hybrid-case connection
• Hall sensor
• Optimize input circuitry
Lead Heating Design Solution • Lead inner conductor coil design mitigates lead heating
• 4 filar to 2 filar increases inductance and reduces
heating
• 5086 provides 3:1 reduction in lead tip heating
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45 50
Perc
en
t o
f M
axim
um
Lead Path
5076 vs. 5086MRI Comparison
5076 - 52
5086 - 52
Clinical Confirmation of
Safety
Clinical Study Experience (EnRhythm MRI)
• Prospective, randomized, multi-center – Implantation: 464 subjects
– 41 international centers • 21 Europe, 13 U.S., 6 Canada, 1 Middle East
• Enrollment: – February 2007 through July 2008
• Primary End Points: – Consistent Capture Thresholds
– Consistent Sensed Amplitudes
MRI Group
MRI Scans
9-12 Week Visit
Post-MRI
Pre-MRI
Control Group
No MRI
1-Week Post-MRI
Visit
1-Month Post-MRI
Visit
Enrollment
2 Month
Visit
Implant
and Randomization
Clinical Visit Schedule
6-Month
Post-Implant Visit
and Every Six
Months Thereafter
Primary Effectiveness Endpoint
No measurable difference between MRI and control groups
Atrial & Ventricular Capture Threshold: Pre-visit to 1-month post-visit
0
20
40
60
80
-1 -0.5 0 0.5 1
Change in Atrial
Threshold (V)
% o
f P
ati
en
ts
MRI
(n=165)
Control
(n=164)
0
20
40
60
80
-1 -0.5 0 0.5 1
Change in Ventricular
Threshold (V)%
of
Pati
en
ts
MRI
(n=190)
Control
(n=184)
Clinical Confirmed Safety and
Effectiveness
• Safety demonstrated – No MRI-related complications
– No sustained ventricular arrhythmias or
asystole
• Effectiveness demonstrated – Consistent capture thresholds
– Consistent sensed amplitudes
• Complete system: MRI compatible
pacemaker with two MRI compatible leads
• Implanted for at least 6 weeks
• No abandoned leads
• Pacing capture threshold ≤ 2.0 V at 0.4 ms
• Lead impedance of 200 Ω to 1500 Ω
• SureScan programming
US Conditions of Use – Cardiology
• 1.5 Tesla Scanner
• Gradient field:
– Maximum Gradient Slew Rate ≤ 200 T/m/s (per axis)
• RF field: Normal Operating Mode
– Whole body SAR ≤ 2.0 W/kg
– Head SAR < 3.2 W/kg
• Patient monitoring
US Conditions of Use – Radiology
Patient Care Pathway
1. Pre-Screening and Scheduling
2. Pre-scan
3. Scan
4. Post-Scan
Pre-screening
• Ways to ID
pacemaker system:
1. Patient ID Card
2. X-Ray
3. Call cardiology
1
PRESCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
X-Ray
Radiopaque identifies the system via unique radiopaque visible under x-ray
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
1 Location of the device radiopaque symbol 2 Device radiopaque MRI symbol 3 Lead radiopaque MRI symbol
Programmer print out
Programmer
Printout
Provides
confirmation that
the system is MR-
Conditional, model
number and
checklist for
relevant conditions
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
SureScan Programming Steps
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
During the Scan – Monitoring
• Patient must be monitored during the MRI
scan:
– Visual and verbal contact
– Pulse oximetry
– Blood pressure
– Electrocardiography (rate only)
• There is no requirement for the monitoring
person to be from cardiology.
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
Post-Scan
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
Thank you!!
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