Changes in the specific absorption rate (SAR) of radiofrequency energy in patients with retained cardiac leads during MRI at 1.5T and 3T.

PURPOSE

To evaluate the local specific absorption rate (SAR) and heating around retained cardiac leads during MRI at 64 MHz (1.5T) and 127 MHz (3T) as a function of RF coil type and imaging landmark.

METHODS

Numerical models of retained cardiac leads were built from CT and X-ray images of 6 patients with retained cardiac leads. Electromagnetic simulations and bio-heat modeling were performed with MRI RF body and head coils tuned to 64 MHz and 127 MHz and positioned at 9 different imaging landmarks covering an area from the head to the lower limbs.

RESULTS

For all patients and at both 1.5T and 3T, local transmit head coils produced negligible temperature rise ( ) for . For body imaging with quadrature-driven coils at 1.5T, during a 10-min scan remained < 3°C at all imaging landmarks for and <6°C for . For body imaging at 3T, during a 10-min scan remained < 6°C at all imaging landmarks for . For shorter pulse sequences up to 2 min, remained < 6°C for .

CONCLUSION

For the models based on 6 patients studied, simulations suggest that MRI could be performed safely using a local head coil at both 1.5T and 3T, and with a body coil at 1.5T with pulses that produced . MRI at 3T could be performed safely in these patients using pulses with .