On‐Scanner Correction of Gradient Nonlinearity Bias for Accurate Assessment of Diffusion Heterogeneity Across Bone Sites in Myelofibrosis Patients

PURPOSE: To improve accuracy of apparent diffusion coefficient (ADC) measurement across different bone-marrow (BM) sites for myelofibrosis (MF) patients. METHODS: Vendor-provided ADC gradient nonlinearity correction (GNC) was implemented for 41 MF study subjects on a 3T clinical scanner. The degree of bias correction was assessed on b-maps across the BM regions-of-interest defined for femoral trochanter, posterior ilium and spine vertebrae of all subjects. Bias variability from subject repositioning was evaluated for five subjects with longitudinal scans using Bland-Altman analysis. BM ADC with and without GNC were compared in 22 subjects with MF grade > 0 (iliac fat fraction < 40%). The GNC effect on ADC heterogeneity trends across bone sites was assessed using paired t-test and correlation to MF-grade. RESULTS: The observed bias was substantial across BM sites ranging from -10% for edge vertebrae to +8.4% for trochanter across all subjects with a 13.7% intra-subject median range. The effect of irreproducible positioning in longitudinal scans was ±4.2% bias (95% limits-of-agreement) with range of ±8.5% (highest for L1 and L5). By removing bias, GNC improved ADC accuracy and longitudinal reproducibility and emphasized biological heterogeneity for femoral trochanter versus ilium and edge vertebrae (T11-L1, L5, and S1). GNC revealed significant ADC differences between trochanters and edge vertebrae (p = 0.007), while edge vertebrae and ilium ADC became more uniform (p = 0.07), with heterogeneity and values correlated to MF-grade. CONCLUSION: On-scanner correction of gradient nonlinearity bias in bone marrow ADC reduces technical nonuniformity and variability and allows accurate and reproducible characterization of heterogeneous disease for myelofibrosis patients.