Comparison of monopolar and bipolar diffusion weighted imaging sequences for detection of small hepatic metastases

Highlights: • The CNRwithBP showed significantly higher values than inMP. • TheSNRwasnot significantly different betweenthe twomethods. • The detection sensitivities ofthe threereaders were higher in the BP than in MP. • The lesion distortionreducein theBP groupthan inMP. • It is related in lesion detection sensitivity and lesion distortion. - Abstract: Objective: To compare monopolar (MP) and bipolar (BP) diffusion weighted imaging (DWI) in detecting small liver metastases. Materials and methods: Eighty-eight patients underwent 3-T MRI. The signal-to-noise ratios (SNR) of the liver parenchyma and lesions, the lesion-to-liver contrast-to-noise ratios (CNR), and the detection sensitivities were compared. The lesion distortion was scored (LDS) from 4 (no distortion) to 1 (excessive distortion), dichotomised as no-distortion and distortion, and the association between detected lesions for each reader in the MP or BP DWI group and the dichotomised lesion distortion degree was assessed. Result: Forty-six hepatic metastases were confirmed. The CNR with BP images showed significantly higher values than with MP (P = 0.017). The detection sensitivities of the three readers were higher in the BP sequence than in MP, and one reader detected significantly more hepatic lesions with BP images (P = 0.04). LDS was significantly improved with BP sequence (P = 0.002). In the no-distortion group, excluding the MP DWI assessments of one reader, detection sensitivities were significantly higher than in the distortion group (P < 0.001 and P = 0.002, respectively). Conclusion: Reduced lesion distortion improves the detection of small liver metastases, and BP is more sensitive in detecting small liver metastases than MP DWI