Flip Angle Optimization for Hepatobiliary Phase MRI at 0.55 T in Patients with Neuroendocrine Tumors

Motivation: The optimal flip angle for hepatobiliary phase imaging at 0.55T is not known. Goal(s): To determine the flip angle that maximizes liver enhancement and lesion contrast for hepatobiliary phase imaging at 0.55T. Approach: Fourteen patients with metastatic neuroendocrine tumors were imaged at 0.55T using a T1 VIBE research sequence systematically across a range of flip angles between 10 and 70 degrees. Normalized liver lesion contrast, liver vessel contrast, and liver signal intensity were computed. Results: Normalized liver-lesion and liver-vessel contrast is maximized at a flip angle of 30 degrees, while normalized liver signal intensity is maximized at 20 degrees. Impact: In patients with metastatic neuroendocrine tumors imaged at 0.55T, a flip angle of 30 degrees maximizes lesion contrast on the hepatobiliary phase. Improving hepatobiliary phase quality at 0.55T may improve MRI accessibility for patients with known or suspected liver lesions.