Characterization of small (≤10 mm) focal liver lesions: Value of respiratory-triggered echo-planar diffusion-weighted MR imaging

Purpose: To evaluate respiratory-triggered diffusion-weighted MR imaging (DWI) in the characterization of small (≤10 mm) focal liver lesions (FLL). Materials and methods: A total of 185 FLL (76 metastases, 11 HCCs, 71 cysts, 18 hemangiomas, 6 focal nodular hyperplasias, 3 adenomas) were retrospectively analyzed in 77 patients. DWI was performed at 1.5 T using a respiratory- triggered single-shot echo-planar imaging (SSEPI) sequence (b values: 50, 300, 600 s/mm²). Diffusion-weighted images were evaluated by two independent observers and apparent diffusion coefficient (ADC) values were determined. Reference standard of diagnosis was obtained by two other radiologists correlating DWI with histopathologic findings, standard MR sequences and imaging follow-up. Receiver operating characteristic curve analysis was performed to evaluate the utility of ADC values for the diagnosis of malignancy. Results: Accuracy for characterizing FLL was 93.0% for reader 1 and 91.9% for reader 2. Interobserver agreement was excellent between both readers (κ = 0.88). Sensitivity and specificity for diagnosing malignancy were 90.8% and 89.9% using a threshold ADC of 1.41 × 10^-3 mm²/s. Conclusion: DWI using the respiratory-triggered SSEPI sequence can help to characterize FLL, even when the diameter of lesions is 10 mm or less.