Dixon or DWI - Comparing the utility of fat fraction and apparent diffusion coefficient to distinguish between malignant and acute osteoporotic vertebral fractures.

ABSTRACT

PURPOSE: To compare fat fraction (FF) and apparent diffusion coefficient (ADC) as discriminators distinguishing malignant from acute/subacute osteoporotic vertebral fractures. METHOD: 1.5 T MRIs of 42 malignant and 27 acute/subacute osteoporotic vertebral fractures (38 patients) were retrospectively reviewed. Two readers independently classified fractures as malignant or osteoporotic based on conventional imaging morphology. Diagnostic reader confidence was rated as confident or not confident. FF was derived from axial T1 gradient-echo 2-point Dixon MRI. ADC maps were calculated from axial b50 and b900 images. Both readers independently performed ROI measurements of mean FF and ADC of the same fractured vertebrae. FF and ADC values, corresponding ROC curves and optimized cut-off value performance were compared. Inter-reader agreement was analysed by calculation of intraclass correlation coefficients (ICCs). A p-value < 0.05 was deemed significant. RESULTS: Mean FF and ADC were significantly lower in malignant (9.5 % and 1.05 × 10-3 mm²/s) compared to osteoporotic fractures (32 % and 1.34 × 10-3 mm²/s, all p < 0.001). The optimal cut-off FF was 11.5 %, detecting malignant fractures with 86 %/89 % sensitivity/specificity. The optimal ADC cut-off of 1.04 × 10-3 mm/s² yielded 62 %/96 % sensitivity/specificity. FF AUC (0.93) was significantly larger than ADC AUC (0.82, p = 0.03). In the subgroup of nine cases reported with low expert reader confidence, the optimized cut-off specificities of FF (83 %) and ADC (83 %) exceeded reader specificity (50 %). There was excellent inter-reader agreement for mean FF (ICC = 0.99) and good agreement for mean ADC (ICC = 0.86) measurements. CONCLUSION: FF and ADC can improve reader specificity to distinguish between malignant and acute or subacute osteoporotic vertebral fractures. As single discriminator, FF was superior to ADC.