Evaluation of specific absorption rate as a dosimeter of MRI-related implant heating.
OBJECTIVE
To compare the magnetic resonance imaging (MRI)-related heating per unit of whole body averaged specific absorption rate (SAR) of a conductive implant exposed to two different 1.5-Tesla/64 MHz MR systems.


METHODS
Temperature changes at the electrode contacts of a deep brain stimulation lead were measured using fluoroptic thermometry. The leads were placed in a typical surgical implant configuration within a gel-filled phantom of the human head and torso. MRI was performed using two different transmit/receive body coils on two different generation 1.5-Tesla MR systems from the same manufacturer. Temperature changes were normalized to whole body averaged SAR values and compared between the two scanners.


RESULTS
Depending on the landmark location, the normalized temperature change for the implant was significantly higher on one MR system compared to the other (P < 0.001).


CONCLUSIONS
The findings revealed marked differences across two MR systems in the level of radiofrequency (RF)-induced temperature changes per unit of whole body SAR for a conductive implant. Thus, these data suggest that using SAR to guide MR safety recommendations for neurostimulation systems or other similar implants across different MR systems is unreliable and, therefore, potentially dangerous. Better, more universal, measures are required in order to ensure patient safety.
Department of Neurology, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Desk S-90, Cleveland, OH 44195, USA. bakerk@ccf.org
Kenneth B
KB
Baker
Jean A
JA
Tkach
John A
JA
Nyenhuis
Michael
M
Phillips
Frank G
FG
Shellock
Jorge
J
Gonzalez-Martinez
Ali R
AR
Rezai
D001831:Body Temperature / Q000502:physiology; D004567:Electrodes, Implanted; D004869:Equipment Safety; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000592:standards*; D019047:Phantoms, Imaging; D011874:Radiometry; D013696:Temperature