Evaluation of liver diffusion isotropy and characterization of focal hepatic lesions with two single-shot echo-planar MR imaging sequences: Prospective study in 66 patients

PURPOSE: To (a) evaluate liver diffusion isotropy, (b) compare two diffusion-weighted magnetic resonance (MR) imaging sequences for the characterization of focal hepatic lesions by using two or four b values, and (c) determine an apparent diffusion coefficient (ADC) threshold value to differentiate benign from malignant lesions. MATERIALS AND METHODS: Sixty-six patients were examined with two single-shot echo-planar diffusion-weighted MR sequences. In the first sequence, liver diffusion isotropy was evaluated by using diffusion gradients in three directions with two b values. In the second sequence a unidirectional diffusion gradient was used, with four b values. ADCs were measured in 43 patients with 52 focal hepatic lesions more than I cm in diameter and in 23 patients with 14 normal and nine cirrhotic livers and were compared by using nonparametric tests. RESULTS: Diffusion in the liver parenchyma was isotropic. ADCs of focal hepatic lesions were significantly different between sequences (P < .01). The mean (+/-SD) ADCs in the first sequence were 0.94 X 10(-3) mm(2)/sec +/- 0.60 for metastases, 1.33 X 10(-3) mm(2)/sec +/- 0.13 for HCCs, 1.75 X 10(-3) mm(2)/sec +/- 0.46 for benign hepatocellular lesions, 2.95 X 10(-3) mm(2)/sec +/- 0.67 for hemangiomas, and 3.63 X 10(-3) mm(2)/sec +/- 0.56 for cysts. There was a significant difference between benign (2.45 X 10(-3) mm(2)/sec +/- 0.96, isotropic value) and malignant (1.08 X 10(-3) mm(2)/sec +/- 0.50) lesions (P < .01 for both sequences). CONCLUSION: Diffusion-weighted MR imaging can help differentiate benign from malignant hepatic lesions. The use of two b values in one direction could be sufficient for the design of MR sequences in the liver. (C) RSNA, 2002.