Hitoshi Kanazawa

Flow-Dependent Noncontrast MR Angiography

Noncontrast MR angiography (NC-MRA) techniques such as time-of-flight (TOF) and phase contrast (PC) have been available since the early days of MRI development. However, long scan times and various artifacts have limited their use in the clinical setting over contrast-enhanced (CE) MRA techniques, introduced first around the mid-1990s. At the present time, three-dimensional (3D) TOF remains the main technique for intracranial MRA, while PC has been used as an angiogram technique as well as flow functional technique in various regions of the body. In other regions of the body like the chest, abdomen, and peripheral regions, CE MRA became the main MR technique in those areas. Rapid development of CE MRA was facilitated by various developments in system hardware, parallel imaging, sequence improvements, and the introduction of time-resolved MRA. Since the recent FDA black-box warning associated with the use of gadolinium-base contrast agent in 2007 and the risk of developing nephrogenic systemic fibrosis (NSF), there is renewed interest in NC-MRA as an alternative to CE MRA.

2111 Recent progress on non-contrast-enhanced MRA techniques

Methods All experiments were performed on 1.5-T clinical imagers. A flow-spoiled fresh blood imaging (FS-FBI) technique, ECG-gated 3D partial Fourier FSE, allows separation of arteries from veins by applying appropriate flow spoiling gradient pulses in the read-out (RO) direction. To find suitable ECG delay time, ECG-prep scan, single-slice multiple phases, is applied to acquire single shot images with different ECG delay times. The application of the ECGprep technique can be used as non-contrast time-resolved MRA like images by acquiring multiple phases across small incremental trigger delay times during the period of steep signal changes from systolic to diastolic phase. The renal artery examinations using non-contrast MRA techniques are a must for patients with renal insufficiency and vascular disease. In order to depict the multiple directional vasculatures of renal arteries, respiratory-gated balanced SSFP with an arterial spin labeling (time-spatial labeling inversion pulse; time-SLIP) technique was applied to gain superior in-flow effect using an axial scan. The marked blood by the time-SLIP traveled from the aorta to renal branches was acquired using balanced SSFP readout. The time-SLIP pulse was optimized to have good contrast between blood and background cortex and medulla. An inferior sat-band pulse was placed to eliminate venous flow.