1. MR Scanner Transmit Gain as a Potential Indicator For Lead Heating
November, 2006

2. The Question Repeated MRI lead heating experiments using the same:
Imaging parameters
Lead samples
Phantom
Setup & position
SAR level
MRI scanner
yielded different
results. Why?
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3. Materials Test Samples Used: An industry available standard active
fixation bipolar pacing.
Prototype bipolar active fixation pacing lead with resonant circuit in distal tip.
Prototype bipolar active fixation pacing lead without resonant circuit in distal tip.
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4. Methods
Luxtron® model 3100 fluoroptic thermometry system with SSM model optical probes
Gelled-saline solution: 5.8 g PAA, 0.8g NaCl per liter of de-ionized water in head/torso phantom
GE 1.5-T MR system, FSE-XL, whole body average SAR = W/kg
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5. Materials and Methods
Three (3) samples positioned in identical configurations:
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6. Transmit Gain Variable Observed
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7. Further Study
Three different leads tested at the same SAR level, different TG values.
Linear scale
Logarithmic scale
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8. Clinical Scanner Transmit Gain History
For a single clinical MR scanner using the same phantom and imaging sequence the reported transmit gain (TG) can vary.
Date:
7/03/06
7/10/06
7/17/06
7/24/06
TG:
113 96 94
7/31/06
8/14/06
8/21/06
8/28/06 97
117
119
Min: Max: Ave: 104
* Data from University Medical Imaging, Rochester, NY
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9. Discussion & Conclusions
It is known that the scanner calculated and reported SAR level
can be different between different MRI scanner types.*
For the same experimental setup on the same MRI scanner using
the same imaging sequence and reported SAR level, lead heating
can significantly vary due to transmit gain.
The MRI scanner’s transmit gain varies for the same reported
SAR level using identical imaging parameters.
*See: Baker et al., “Evaluation of Specific Absorption Rate as a Dosimeter of MRI-Related Implant Heating”, Journal of Magnetic Resonance Imaging, 20: , 2004
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