Fig. 9.

Phantom data with FUS heating were acquired using three different 2D pulse sequences: the dual-pathway unbalanced SSFP sequence from Fig. 2c, a regular gradient-echo sequence (i.e., FISP only), and the dual pathway interleaved-EPI sequence from Fig. 4. Temporal resolution was more than two-fold better for EPI than for the ub-SSFP sequence (272 compared to 614 ms). a) Temperature maps are shown for the time frame with maximum heating (about 8 °C at focus). To evaluate temperature noise, the standard deviation was calculated along the time axis for each pixel in the non-heated ROI (shown in blue). Results for all the pixels in this ROI were then averaged and the resulting value is displayed in the upper-left corner of each image in (a). Notice that the dual-pathway ub-SSFP implementation (top row) provides about a 35% improvement in TNR compared to its single-pathway counterpart (middle row), as 0.27 °C / 0.20 °C = 1.35. b) The magnitude component of data employed to generate the images in (a) is also displayed here. Notice that although the EPI implementation (bottom row) provides superior TNR and higher frame rates, the ub-SSFP short-TR implementation (top row) also has value, as it provides better anatomical images with less geometric distortion for potentially superior motion tracking. c) The temperature information from (a) is displayed as an overlay onto the magnitude information from (b). Throughout this figure, the same windowing settings were used whenever comparing results from different sequences or pathways.