3D MR Fingerprinting for Quantitative Bladder Wall T ₁ , T ₂ , and M ₀ Mapping in Healthy Subjects at 1.5 T and 3 T

ABSTRACT Current diagnostic tests for lower urinary tract symptoms (LUTS) do not assess tissue‐level alterations in the bladder wall. This study assesses the feasibility of 3D magnetic resonance fingerprinting (MRF) for simultaneous T 1 , T 2 , and proton density (M 0 ) mapping of the bladder wall in healthy subjects at 1.5 T and 3 T. A 3D MRF acquisition was combined with a deep image prior reconstruction to achieve whole‐bladder T 1 , T 2 , and M 0 mapping in 11.8 min at an acquired voxel size of 1 × 1 × 3 mm 3 (interpolated to 0.5 × 0.5 × 1.5 mm 3 ). Twenty‐nine healthy subjects (14 female, 18–78 years) were enrolled, with 16 scanned at both 1.5 T and 3 T. Conventional maps were acquired using MOLLI and T 2 ‐prepared GRE sequences. Maps were analyzed by measuring mean global and regional T 1 and T 2 values, with spatial heterogeneity assessed using the coefficient of variation (CV). Bladder wall thickness (BWT) was measured from synthetic weighted images derived from MRF maps, compared to reference values from conventional T 2 ‐weighted MRI. Mean global MRF bladder wall measurements were 984 53 ms (T 1 ), 51.4 5.6 ms (T 2 ), and 4.5 1.6 mm (BWT) at 1.5 T and 1468 118 ms (T 1 ), 43.5 4.0 ms (T 2 ), and 4.3 1.6 mm (BWT) at 3 T. MRF T 1 values were significantly lower than MOLLI at 1.5 T (bias −151 ms) but not significantly different at 3 T. MRF T 2 values were significantly lower (by 7–8 ms) than T 2 ‐prepared GRE at both field strengths. MRF exhibited lower CV than MOLLI T 1 mapping at 1.5 T. BWT from synthetic images exhibited excellent agreement (bias .1 mm) with conventional T 2 ‐weighted images. Regionally, T 1 and T 2 tended to be higher in the dome and posterior wall. In an exploratory analysis, a positive association between age and T 2 was observed. In conclusion, 3D MRF of the bladder wall is feasible in healthy subjects, providing a baseline for translational studies to characterize pathological remodeling in LUTS.