The overall goal of this research is to predict and minimize the radio frequency (RF) losses affecting the success and safety of human head imaging over the 64MHz - 300MHz band. This goal will be pursued by proving the hypothesis: "RF losses in high field MR head imaging can be minimized by appropriate coil design." The rationale for this study lies in the need to know and control RF dependent transmit power, tissue heating, field penetration, and signal-to-noise for high field human head studies. As part of this collaboration, we have previously reported building a 400-MHz, circularly polarized, 16 element, 15 cm inner diameter x 15 cm length (3/5 scale human coil dimensions) coil was built. We also reported last year obtaining images at 9.4 Tesla with this coil. The homogeneity across the 6-cm head appeared uniform and signal variation averaged 112%. The B1 power required for an optimized 900 flip angle in the monkey's head was a third that required for a human at 4T. Even though the 9.4 T images were not optimized and suffered CNR and SNR due to TE values comparable to T2 we had to use due to current instrumentational limitations, the signal-to-noise ratio in the monkey at 9.4T was approximately twice that of comparable but optimized 4T human images. In the past year, the coil as optimized further and additional imaging studies performed, yielding even better results and gains in SNR, Thus, (1) An efficient homogeneous monkey head coil (3/5 scale human) was built for 400 MHz imaging. (2) Homogeneous monkey head images were acquired at 9.4T without using excessive RF power. (3) Significant signal-to-noise ratio increases were measured at 9.4T in vivo. These results have so far been presented in an abstract form.
NIH ExPorter
NIH ExPorter