Impact of MRI slice thickness and fiducial marker orientation on geometric accuracy in multi-echo GRE imaging for prostate radiotherapy planning.

Abstract

BackgroundPrecise target definition in prostate radiotherapy requires accurate computed tomography (CT)-magnetic resonance imaging (MRI) image registration using gold fiducial markers (GFMs). While multi-echo gradient recalled echo (ME GRE) sequences facilitate GFM identification, the quantitative impact of acquisition parameters on physical measurement accuracy remains insufficiently understood.PurposeThis study evaluates how MRI slice thickness and marker orientation angle jointly affect GFM visualization and geometric accuracy to characterize the resulting localization uncertainties.MethodsA kiwifruit-based phantom (T1: 1603.3 ms; T2: 72.3 ms) that mimics the relaxation times of the human prostate was imaged with 3.0T MRI. Imaging was performed using a 3D ME GRE sequence with three slice thicknesses (1.0, 2.0, and 3.0 mm) and 12 orientation angles ranging from horizontal to 90°. Five multidisciplinary observers independently identified marker coordinates while blinded to the acquisition parameters. Subjective confidence scores were also recorded.ResultsTwo-way analysis of variance (ANOVA) revealed significant main effects for slice thickness (F(2, 144) = 32.03, p ConclusionsMRI slice thickness and marker orientation significantly impact GFM visualization accuracy. The results suggest that a 1.0 mm slice thickness offers a technical advantage for maintaining sub-millimeter localization accuracy across various marker orientations and highly desirable for high-precision radiotherapy planning.