new technology: 核磁共振相容節律器 - ”mri standard of care for...
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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
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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.
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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
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設備圖
Magnet Gradient Coil RF Coil
RF Coil
4T magnet
gradient coil
(inside)
B0
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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
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Transmit Receive
RF
coil
RF
coil
Main
magnet Main
magnet
Gradient Shimming
Control
Computer
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質子 (Proton)
•帶正電
•會自旋
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The Effect of Irradiation to the Spin System
Lower
Higher
Spin System After Irradiation
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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
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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
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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
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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
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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.
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MRI: Three Powerful Fields
Static Field
Gradient Field
RF Field
MP – 14
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背景磁力永遠存在
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Static Gradient RF
Device Interactions
Stimulation (UCS)
Lead Heating
UCS = unintended cardiac stimulation - Inhibitor pacemaker function
- Trigger rapid pacing
- Deliver inappropriate shocks
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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
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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
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Device Interactions Clinical
Impact
Failures can be temporary or permanent
MP – 53
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Pacemaker System Design
Solutions
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Device Design Solutions
• Minimize ferromagnetic content
Unintended cardiac stimulation Device interactions Force and Torque
• Hybrid-case connection
• Hall sensor
• Optimize input circuitry
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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
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Clinical Confirmation of
Safety
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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
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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
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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)
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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
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• 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
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• 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
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Patient Care Pathway
1. Pre-Screening and Scheduling
2. Pre-scan
3. Scan
4. Post-Scan
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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
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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
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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
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SureScan Programming Steps
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
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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
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Post-Scan
1 PRE-
SCREENING
2 PRE-SCAN
3 SCAN
4 POST SCAN
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Thank you!!