Abstract
PurposeTo compare fat fraction (FF) and apparent diffusion coefficient (ADC) as discriminators distinguishing malignant from acute/subacute osteoporotic vertebral fractures. Method1.5 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. ResultsMean 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. ConclusionFF 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.
Highlights
The spine is a common site of metastases, which can lead to malig nant vertebral fractures [1,2]
Distinguishing between malignant and acute or subacute osteoporotic vertebral fractures can be challenging for the radiologist, as fracture related bone marrow signal changes can mimic malignancy
The Dixon magnetic resonance imaging (MRI) parameters fat fraction (FF) and diffusion-weighted MRI (DWI) derived apparent diffusion coefficient (ADC) have both been identified as potential dis criminators, which are able to distinguish between malignant and benign vertebral fractures [4,5,6,7]
Summary
The spine is a common site of metastases, which can lead to malig nant vertebral fractures [1,2]. Distinguishing between malignant and acute or subacute osteoporotic vertebral fractures can be challenging for the radiologist, as fracture related bone marrow signal changes can mimic malignancy. The radiologist most commonly arrives at a diag nostic conclusion by appraisal of morphologic features of fractured vertebrae [3]. This subjective approach has proven to be effective in clinical routine, but it leaves a reader-dependent level of uncertainty. Soft tissues including most vertebral malignancies are largely comprised of water-vector voxels whereas adult patients’ bone marrow is mostly comprised of fat voxels.
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