Diffusion-Weighted Imaging Distinguishes Between Osteomyelitis, Bone Marrow Edema, and Healthy Bone on Forefoot Magnetic Resonance Imaging.

BACKGROUND

Diagnosis of osteomyelitis by imaging can be challenging. The feasibility of diffusion-weighted imaging (DWI) as ancillary sequence was evaluated in this study.

PURPOSE: To evaluate DWI for differentiation between osteomyelitis, bone marrow edema, and healthy bone on forefoot magnetic resonance imaging (MRI).

STUDY TYPE: Prospective.

SUBJECTS: A total of 60 consecutive patients undergoing forefoot MRI divided into three study groups (20 subjects each): osteomyelitis, bone marrow edema, and healthy bone.

FIELD STRENGTH/SEQUENCE: A 1.5T and 3T MRI scanners; readout-segmented multishot echo planar DWI.

ASSESSMENT: Two independent radiologists measured apparent diffusion coefficient (ADC) values within abnormal or healthy bone.

STATISTICAL TESTS: ADC values were compared between groups (pairwise t-test with Bonferroni-Holm correction for multiple testing). Intraclass correlation coefficient (ICC) was calculated to assess inter-reader agreement. Threshold ADC values were determined as the cutoffs that maximized the sum of sensitivity and specificity. Receiver operating characteristic (ROC) analysis was performed with statistical threshold of P < 0.05.

RESULTS

Inter-reader agreement was 0.92 in the healthy bone group and 0.78 in both the edema and osteomyelitis groups. Average ADC values were significantly different between groups: 1432 ± 222 × 10-6  mm2 /sec (osteomyelitis), 1071 ± 196 × 10-6  mm2 /sec (bone marrow edema), and 277 ± 89 × 10-6  mm2 /sec (healthy bone). A threshold ADC value of 534 × 10-6  mm2 /sec distinguishes between healthy and abnormal bone with specificity and sensitivity of 100% each. For distinction between osteomyelitis and bone marrow edema, two cutoff values were determined: a 95%-specificity cutoff indicating osteomyelitis (>1320 × 10-6  mm2 /sec) and a 95%-sensitivity cutoff indicating bone marrow edema (<1155 × 10-6  mm2 /sec). Diagnostic accuracy of 95% was achieved for 73% (29/40) of the subjects.

DATA

CONCLUSION

DWI with ADC maps distinguishes between healthy and abnormal bone on forefoot MRI. Calculated cutoff values allow confirmation or exclusion of osteomyelitis in a high proportion of subjects.

EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.