Pulse sequence considerations for simulation and postimplant dosimetry of prostate brachytherapy.

PURPOSE: The purpose of this work is to present a brief review of MRI physics principles pertinent to prostate brachytherapy, and a summary of our experience in optimizing protocols for prostate brachytherapy applications.

METHODS AND MATERIALS: We summarized essential MR imaging characteristics and their interplays that need to be considered for prostate brachytherapy applications. These include spatial resolution, signal-to-noise ratio, image contrast, artifacts, geometric distortion, specific absorption rate, and total scan time. We further described the optimization of the protocols for three pulse sequences: three-dimensional (3D) fast-spoiled gradient echo sequence for T1-weighted imaging, 3D fast-spin echo sequence for T2-weighted imaging, and 3D fast imaging in steady-state precession sequence for combined T1 and T2-weighed imaging. The utilization of an endorectal coil was also described.

RESULTS: Using the optimized protocols, we acquired high-quality images of the entire prostate within 3-5 minutes for each sequence. These images display the desired image contrasts and a spatial resolution that is equal to or better than 0.59 mm × 0.73 mm × 1.2 mm. While 3D fast-spoiled gradient echo sequence and 3D fast-spin echo sequence depict radioactive seed markers and anatomic structures separately, 3D fast imaging in steady-state precession sequence demonstrates great promise for imaging both seed markers and prostate anatomy simultaneously in a single acquisition.

CONCLUSIONS: We have optimized current MRI protocols and demonstrated that the anatomic structures and positive contrast radioactive seed markers for prostate post-implant dosimetry can be adequately imaged either separately or simultaneously using different pulse sequences within a total scan time of 3-5 minutes each.