Comparison of susceptibility artifact on rectal DWI-MRI and rectal volume before and after ultrasound gel versus Microlax enema
Introduction: MRI is necessary for rectal cancer staging. Adding DWI sequence has various benefits. Air in rectum decreases images quality especially on DWI sequence. For this purpose, Rectal enema has been offered. Rectal enema could compress mucosa and potentially change T stage of cancer. Enema with ultrasound gel was compared with enema with Microlax according to their extent of decreased susceptibility artifact and extent of rectal distension. Material and Methods: 40 patients with known rectal cancer were enrolled. 20 patients had enema with Microlax, and 20 patients had enema with ultrasound gel. For each patient, rectal MRI before and after enema was taken, and susceptibility artifact of DWI images before and after enema and the volume inside rectal lumen before and after enema were calculated, and compared between two groups. Results: Mean Susceptibility artifact after enema with Microlax (1.77±1.47) and ultrasound gel (1.97±1.16) decreased significantly versus pre enema images ((3.325±1.35) for Microlax and (3.32±1.37) for ultrasound gel) (P value<0.001 for each group). Mean volume inside rectal lumen after enema with Microlax was (14.38±5.352 cm3), and after ultrasound gel enema was (31.33±9.494 cm3). Rectal distension with ultrasound gel enema was statistically more than enema with Microlax (P-value<0.001). Conclusion: Enema with about 60 cc of Microlax was offered before DWI MRI of rectum. This enema decreased susceptibility artifact. Furthermore, Microlax caused less rectal distension in comparison to ultrasound gel, so T-staging was more precise with Microlax versus ultrasound gel enema on MRI T2 Sequence.
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