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

ABSTRACT 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.