Diagnostic Benefit of High b-Value Computed Diffusion-Weighted Imaging in Patients with Hepatic Metastasis

Diffusion-weighted imaging (DWI) has rapidly become an essential tool for the detection of malignant liver lesions. The aim of this study was to investigate the usefulness of high b-value computed DWI (c-DWI) in comparison to standard DWI in patients with hepatic metastases. In total, 92 patients with histopathologic confirmed primary tumors with hepatic metastasis were retrospectively analyzed by two readers. DWI was obtained with b-values of 50, 400 and 800 or 1000 s/mm(2) on a 1.5 T magnetic resonance imaging (MRI) scanner. C-DWI was calculated with a monoexponential model with high b-values of 1000, 2000, 3000, 4000 and 5000 s/mm(2). All c-DWI images with high b-values were compared to the acquired DWI sequence at a b-value of 800 or 1000 s/mm(2) in terms of volume, lesion detectability and image quality. In the group of a b-value of 800 from a b-value of 2000 s/mm(2), hepatic lesion sizes were significantly smaller than on acquired DWI (metastases lesion sizes b = 800 vs. b 2000 s/mm(2): mean 25 cm(3) (range 10-60 cm(3)) vs. mean 17.5 cm(3) (range 5-35 cm(3)), p < 0.01). In the second group at a high b-value of 1500 s/mm(2), liver metastases were larger than on c-DWI at higher b-values (b = 1500 vs. b 2000 s/mm(2), mean 10 cm(3) (range 4-24 cm(3)) vs. mean 9 cm(3) (range 5-19 cm(3)), p < 0.01). In both groups, there was a clear reduction in lesion detectability at b = 2000 s/mm(2), with hepatic metastases being less visible compared to c-DWI images at b = 1500 s/mm(2) in at least 80% of all patients. Image quality dropped significantly starting from c-DWI at b = 3000 s/mm(2). In both groups, almost all high b-values images at b = 4000 s/mm(2) and 5000 s/mm(2) were not diagnostic due to poor image quality. High c-DWI b-values up to b = 1500 s/mm(2) offer comparable detectability for hepatic metastases compared to standard DWI. Higher b-value images over 2000 s/mm(2) lead to a noticeable reduction in imaging quality, which could hamper diagnosis.