Assessing the Impact of Imaging Parameters on MRI Measurement of Kidney T2

Background: T2-mapping has promise to evaluate kidney pathophysiology. Prior studies show a large variance in kidney T2, likely due to the differing acquisition sequences. Purpose: To compare four T2-mapping sequences to investigate kidney T2.Study Type: Phantom and prospective in-vivo assessments.Participants: ISMRM/NIST and QASPER phantoms;8 healthy volunteers (4 female,30±8 years).Field Strength/Sequence: 3T. Spin echo-echo planar imaging (SE-EPI), multi-echo-spin echo (ME-SE), Gradient and Spin Echo (GraSE) vendor-provided sequences, and custom T2-prepared EPI, Dual-echo B0-mapping and DREAM B1-mapping.Assessment: T2-mapping accuracy in the ISMRM/NIST phantom in the presence of B0 frequency offset and B1+ by scaling of flip angles, and in the QASPER phantom in presence of diffusion by altering pump rate compared to being turned off. Participants underwent a single 45-min exam to collect four T2-mapping sequences, B0 and B1 maps. In-vivo T2 values compared across sequences and influence of B0 and B1+ was evaluated.Statistical Tests: Shapiro-Wilk, Wilcoxon signed-rank, Student’s t-test, Coefficient of Variation, Pearson’s correlation coefficient, linear mixed effect model. p<0.05 considered statistically significant.Results: SE-EPI, ME-SE, GraSE, and T2-prepared EPI had a mean absolute scaled error of 0.52, 0.52, 0.36, and 0.27 over kidney T2 range of the ISMRM/NIST phantom. GraSE was most robust to perturbations in B0/B1+. In the QASPER phantom, SE-EPI was highly sensitive to diffusion leading to T2 shortening (66%), whilst multi-echo sequences had lower diffusion sensitivity ordered by shortest echo spacing (ME-SE 81%, T2-prepared EPI 90%, GraSE 95% reduction in T2). In-vivo, SE-EPI measured T2 was significantly lower than multi-echo sequences, and SE-EPI and T2-preparation had a -0.52±0.08ms/% and -0.57±0.06ms/% dependence on B1+. Data Conclusion: To reduce B0, B1+ and diffusion sensitivity for kidney T2-mapping, a multi-echo sequence spanning echo times up to the kidney T2 (~140ms at 3T) is recommended. Collecting data with different echo-spacings can isolate the diffusion- related T2 component.