Lirong Yan and Yan Zhuofrom the State Key Laboratory of Brain and Cognitive Science, in collaboration with JJ Wang’s group in the University of Pennsylvania, as well as researchers from Siemens Mindit Magnetic Resonance (Shenzhen) and Beijing Tiantan Hospital, have recently developed a technique called TrueSTAR which shows promise for the clinical evaluation of dynamic blood flow in cerebrovascular disorders such as arteriovenous malformation (AVM), steno-occlusive disease and cerebral aneurysm.

The evaluation of the dynamic flow patterns within the cerebral vasculature is useful for a number of clinical diagnosis. Intra-arterial digital subtraction angiography(DSA) is currently the reference standard for vascular imaging procedures. This method, however, is invasive and requires the use of ionizing radiation and iodinated contrast agents, with all their associated risks of side-effects. Time-resolved contrast enhanced magnetic resonance angiography (CE-MRA) has emerged as an alternative for vascular imaging. However, the temporal resolution of CE-MRA is on the order of seconds, and it requires intravenous injection of a contrast agent. Yan et al. described a novel non-contrast enhanced time-resolved MRA technique named TrueSTAR, which combines spin tagging with alternating radiofrequency (STAR) with a segmented multiphase trueFISP (true fast imaging with steady-state precession), in a paper published recently in Radiology¹. Compared to the previous spin-labeling-based dynamic MR angiography based on turbo FLASH or Look-locker sequence, TrueSTAR offers both high temporal resolution (in the order of tens of milliseconds) and spatial resolution (a few cubic millimeters) with high signal-to-noise (SNR) ratio.

Yan et al. described the application of TrueSTAR to the evaluation of cerebral blood flow in AVM patients. It was successfully able to delineate the dynamic course of labeled blood flowing through feeding arteries into the nidus and draining veins, providing spatial resolution of a few cubic millimeters and temporal resolution of 50-100 msec, and allowing clear temporal separation of the feeding arteries from the draining veins. The SNR and contrast-to-noise ratio (CNR) of TrueSTAR dynamic MR angiography images were 29% and 39% higher, respectively, than those acquired using a standard Look-Locker echo-planar imaging sequence.

TrueSTAR dynamic MR angiography imaging is thus a promising unenhanced dynamic MR angiography technique for clinical evaluation of cerebrovascular disorders. It offers improved SNR and CNR, and 3D imaging protocols with an imaging time of 6-7 minutes have been developed for clinical use.

1. Lirong Yan, Sumei Wang, Yan Zhuo, Ronald L. Wolf, Michael F. Stiefel, Jing An,

Yongquan Ye, Qian Zhang, Elias R. Melhem & Danny J. J. Wang (2010) Unenhanced Dynamic MR Angiography: High Spatial and Temporal Resolution by Using True FISP–based Spin Tagging with Alternating Radiofrequency. Radiology 256: 270-279