Evaluation of Appropriate Readout Sequence for Renal MRI Perfusion Using ASTAR (ASL) Technique

The aim of this study was to compare true-steady state free precession (True-SSFP) with fast field echo (FFE) as readout imaging sequences for renal arterial spin labeling (ASL), and to optimize the imaging condition. Renal ASL perfusion images were acquired using signal targeting with alternated radio frequency using asymmetric inversion slab (ASTAR) technique with respiratory triggering at 3T MRI system, using either 3D True-SSFP or FFE as the readout sequence. Inversion time (TI) varied from 800 to 2400 ms. Appropriate flip angles were estimated for each sequence by simulating signal intensity (SI). The SI of the renal cortex, vertebral body, and intestinal tract were measured, and the contrast ratio of the cortex (CR_cortex) or intestine (CR_intestine) related to vertebra was calculated. The image quality of the kidneys, background signal suppression, and misregistration were evaluated by four-point scales. As a result, in quantitative evaluation, the average of CR_cortex of each TI (800, 1200, 1600, 2000, and 2400 msec) were 0.49, 0.57, 0.63, 0.63, and 0.56 in FFE, and 0.59, 0.71, 0.73, 0.73, and 0.68 in True-SSFP, respectively. IN qualitative evaluation, ASL images with True-SSFP readout were significantly better than those with FFE readout. In conclusion, True-SSFP sequences will be recommended as read out imaging sequence for obtaining ASL image compared with FFE image.