Computed diffusion weighted imaging (cDWI) and voxelwise-computed diffusion weighted imaging (vcDWI) for oncologic liver imaging: A pilot study

OBJECTIVE: Aim of the study was to evaluate the influence of the selection of measured b-values on the precision of cDWI in the upper abdomen as well as on the lesion contrast of PET-positive liver metastases in cDWI and vcDWI. METHODS: We performed a retrospective analysis of 10 patients (4 m, 63.5 ± 12.9 y/o) with PET-positive liver metastases examined in 3 T-PET/MRI with b = 100,600,800,1000 and 1500s/mm(2). cDWI (cb1000/cb1500) and vcDWI were computed based on following combinations: i) b = 100/600 s/mm(2), ii) b = 100/800 s/mm(2), iii) b = 100/1000s/mm(2), iv) b = 100/600/1000s/mm(2) v) all measured b-values. Mean signal intensity (SI) and standard deviation (SD) in the liver, spleen, kidney, bone marrow and in liver lesions were acquired. The coefficient of variation (CV = SD/SI), the differences of SI between measured and calculated high b-value images and the lesion contrast (SI lesion/liver) were computed. RESULTS: With increasing upper measured b-values, the CV in cDWI and vcDWI decreased (CV in the liver in cb1500: 0.42 with b100/600 s/mm(2) and 0.28 with b100/b1000s/mm(2)) while the differences of measured and calculated b-value images decreased (in the liver in cb1500: 30.7% with b = 100/600 s/mm(2), 19.7% with b100/b1000s/mm(2)). In diffusion-restricted lesions, lesion contrast was at least 1.6 in cb1000 and 1.4 in cb1500, respectively, with an upper measured b-value of b = 800 s/mm(2) and 2.1 for vcDWI with an upper measured b-value of b = 1000s/mm(2). Overall, the lesion contrast was superior in cb1500 and vcDWI compared to cb1000 (15% and 11%, respectively). CONCLUSION: Measuring higher upper b-values seems to lead to more precise computed high b-value images and a decrease of CV. vcDWI provides a comparable lesion contrast to b = 1500s/mm(2) and offers additionally the reduction of T2 shine-through effects. For vcDWI, measuring b = 1000s/mm(2) as upper b-value seems to be necessary to guarantee good lesion visibility in the liver based on our preliminary results.