High-field imaging at low SAR: Tx/Rx prostate coil array using radiative elements for efficient antenna-patient power transfer

Simulation results are presented in figure 2 and 3. Results show that the B1 + level in the prostate with the radiative array is comparable to the level with the stripline array (0.11 vs 0.13 uT @ 1W delivered power). For both coil arrays, the SAR level at the dorsal elements is higher than at the ventral elements, due to the higher abundance of muscle tissue. For the radiative elements, the SAR level is lower than for the stripline elements (0.8 vs 0.5 W/kg, 10g average, 1W delivered power). Measurement results are shown in figure 4. These results show that the radiative antenna array is capable of acquiring good and homogeneous T1w images of the pelvic region (figure 5a). In comparison to images obtained with a 8-element stripline array (figure 5c) [3], the images are much more homogeneous. Note the absence of inversion bands near the elements, indicating lower B1 + (and SAR) at the surface. T2w images of the prostate have been measured as well (figure 5b). The measured B1 + level was 4 μT which is roughly in agreement with the simulations. The strongest coupling between two elements was measured to be -22 dB. Conclusion The radiative antenna array is a promising alternative for pelvic imaging at 7 Tesla. Performance is improved in terms of lower local SAR and more homogeneous image intensity. In future, the number of elements will be increased to achieve even higher levels of B1 + while maintaining the low SAR