Room: Room 207
Purpose: MRI of the prostate has become a crucial component of prostate cancer diagnosis. Most clinical sites use 2D fast spin echo (FSE) pulse sequences for T2-weighted imaging. However, drawbacks exist and some institutions have moved to 3D using variable flip angle (VFL) FSE sequences. While a variety of groups have presented clinical results using 3D T2-weighted FSE-VFL, none have published detailed investigations of different flip angle trajectories and parameter choices for maximizing lesion contrast in prostate cancer imaging. We propose to simulate several flip angle trajectories for 3D FSE-VFL and compare to standard 2D FSE using T1 and T2 values appropriate for prostate.
Methods: Standard 2D FSE and 3D FSE-VFL sequences were simulated across Peripheral Zone, Transition Zone, and tumor T1 & T2 times. Standard 2D FSE was simulated at constant flip angles of 180Â° and 123Â° at a TR of 5 s, echo-spacing of 11.6 ms, and echo train length of 25. 3D FSE-VFL was simulated at a ramped constant flip angle (CFL) of 75Â° and at three optimized VFL trains based on T2's of Peripheral Zone, Transition Zone, and tumor, respectively. For all 3D FSE-VFL, TR was 1400 ms, echo-spacing was 14.4 ms for the first echo and 4.44 ms for all subsequent echoes, and echo train length was 106.
Results: As expected, 2D-FSE-180Â° gave the largest contrast difference across tissues, followed by 2D-FSE-123Â°, VFL-T2-PZ, VFL-T2-TZ, VFL-T2-Tumor, and CFL-75Â°. VFL-T2-PZ and VFL-T2-TZ clearly showed the best results for the FSE-VFL techniques. Echo-times at max contrast were longer than cited by literature, ranging from 113-147 for 2D-FSE, from 143-178 for CFL-75Â°, and from 263-285 for VFL-T2.
Conclusion: Signal simulations have proven useful for analyzing different parameters and flip angle trajectories for T2-weighted sequences and can help design new flip angle trajectories and guide parameter choices.