Optimized visualization of focal liver lesions and vascular structures in real-time T1-weighted gradient echo sequences for magnetic resonance-guided liver procedures
Vanessa F. Schmidt, Olaf Dietrich, Philipp M. Kazmierczak, Max Seidensticker, Jens Ricke, Marco Armbruster
Abstract
PURPOSE: This study aimed to determine the optimal sequence parameters of a real-time T1-weighted (T1w) gradient echo (GRE) sequence for magnetic resonance (MR)-guided liver interventions. METHODS: We included 94 patients who underwent diagnostic liver MR imaging (MRI) and acquired additional real-time T1w GRE sequences with a closed 1.5-T MRI scanner 20 min after a liver-specific contrast agent was injected. In four measurement series, one of the following four sequence parameters was changed, and repeated scans with different values for this parameter were acquired: flip angle (FA) (10-90°), repetition time (TR) (5.47-8.58 ms), bandwidth (BW) (300-700 Hz/pixel), and matrix (96 × 96-256 × 256). Two readers rated the visualizations of the target and risk structures (7-point Likert scale) and the extent of artifacts (6-point Likert scale); they also quantified the lesion-liver contrast ratio, the lesion-liver contrast-to-noise ratio (CNR), and the liver signal-to-noise ratio (SNR). Substratification analyses were performed for differences in overall visual and quantitative assessments depending on the lesion size, type, and the presence of cirrhosis. RESULTS: = 0.032) were found. All results showed no significant correlation with lesion size. CONCLUSION: We recommend an FA of 30°-45° and a matrix size of 128 × 128-192 × 192 for MR-guided liver interventions with real-time T1w sequences to provide a balance between good visualizations of target and risk structures, high signal intensities, and low ghosting artifacts. The visualization of the target lesion may vary due to clinical conditions, such as lesion type or associated chronic liver disease.