Evaluation of Optimal Parameters for Non-Contrast-Enhanced Non-Breath-Holding Pulmonary Artery MRA Using 3D-FSE Imaging with Variable Flip Angle Echo Trains

Abstract

Purpose: The aim of this study was to find the optimal acquisition parameters of non-contrast-enhanced non-breath-holding pulmonary artery MRA using 3D-FSE imaging with variable flip angle echo trains. Materials and Methods: The 3D-FSE imaging method with variable flip angle echo trains (CUBE) was employed in this study. Pulmonary artery MRA was performed in five healthy volunteers using a 1.5 tesla (T) and a 3 T clinical scanner with multi-channel torso coils. The institutional review boards approved the study, and informed consent was obtained from all subjects. Prior to the CUBE studies, ECG-gated single-shot FSE scans were performed to determine the timing of systole and diastole. After that, CUBE scans with systolic timing and three adjusted (early, middle and delayed) diastolic timings using both ECG and respiratory gating were performed and subtracted images between systolic and diastolic images were calculated. Subtracted intensities of both lung parenchyma and pulmonary arteries were evaluated using the region of interest (ROI) function. Maximum intensity projection (MIP) images with six different scan parameters (three timings and two static magnetic fields) were processed for evaluation by the ranking method with visual assessment. Three observers each scored all six images and a statistical analysis based on the variation of ratings was performed. Results: The subtracted intensities of pulmonary arteries and lung parenchyma with middle diastolic timing were higher than that with both early and delayed systolic timing. The same tendency was shown in both 1.5 T and 3 T images. Though the subtracted intensity of 3 T was higher than that of 1.5 T, the contrast ratio between lung parenchyma and pulmonary artery of 1.5 T was higher than that of 3 T. The MIP image using the 1.5 T scanner with middle diastolic timing obtained the best score by the visual assessment using the ranking methods. The middle diastolic timing using the 1.5 T scanner provides the best non-contrast-enhanced non-breath-holding pulmonary artery MRA.