Diffusion-Weighted MR Imaging before and after Contrast Enhancement with Superparamagnetic Iron Oxide for Assessment of Hepatic Metastasis

PURPOSE The purpose of our study was to validate diffusion-weighted MRI (DWI) before and after superparamagnetic iron oxide (SPIO) injection for assessment of hepatic metastases. MATERIALS AND METHODS Eighty-six hepatic metastases (size range, 0.3-4.7 cm; mean, 1.5 cm) verified pathologically or by follow-up imaging studies in 22 consecutive patients (17 men and 5 women; 44-83 years; mean age, 60 years) during a 13-month period were enrolled. Hepatic MRI, including DWI (b-factors=50, 400, 800 s/mm²) with breath-holding technique of single-shot spin-echo echo-planar imaging (TR/TE=1000/69 ms, average=2) before and after SPIO administration, were retrospectively reviewed by two independent radiologists with a 5-point scale confidence score for each hepatic lesion on pre-contrast DWI (pre-DWI), SPIO-enhanced DWI (SPIO-DWI), and SPIO-enhanced T2*-weighted imaging (SPIO-T2*wI). RESULTS For all lesions, SPIO-T2*wI showed significantly higher confidence score in the diagnosis of hepatic metastases than pre-contrast or SPIO-DWI regardless of the size of b-factors (p<0.05) with only one exception; using b-factor=50 s/mm², the score of SPIO-T2*wI was still higher than SPIO-DWI but there was no statistical significance given by observer 1 (p=0.730). For the subcentimeter lesions (n=37), SPIO-T2*wI showed the highest score, and using b-factor= 50 or 400 s/mm² SPIO-DWI showed similar confidence scores to SPIO-T2*wI by both observers (p>0.05). Pre-DWI using b-factor=50 sec/mm² was also comparable with SPIO-T2*wI by observer 1 (p=0.060). CONCLUSION Pre-DWI has a limited value for the assessment of hepatic metastases, however, the repetition of DWI after SPIO injection using small b-factors could complement SPIO-T2*wI, especially for subcentimeter lesions.