FULL PAPER Noncontrast-Enhanced Three-Dimensional (3D) Intracranial MR Angiography Using Pseudocontinuous Arterial Spin Labeling and Accelerated 3D Radial Acquisition Huimin Wu, 1 * Walter F. Block, 1–3 Patrick A. Turski, 2 Charles A. Mistretta, 1,2 and Kevin M. Johnson 1 Pseudocontinuous arterial spin labeling (PCASL) can be used to generate noncontrast magnetic resonance angiograms of the cerebrovascular structures. Previously described PCASL- based angiography techniques were limited to two-dimen- sional projection images or relatively low-resolution three- dimensional (3D) imaging due to long acquisition time. This work proposes a new PCASL-based 3D magnetic resonance angiography method that uses an accelerated 3D radial ac- quisition technique (VIPR, spoiled gradient echo) as the read- out. Benefiting from the sparsity provided by PCASL and noise-like artifacts of VIPR, this new method is able to obtain submillimeter 3D isotropic resolution and whole head cover- age with a 8-min scan. Intracranial angiography feasibility studies in healthy (N 5 5) and diseased (N 5 5) subjects show reduced saturation artifacts in PCASL-VIPR compared with a standard time-of-flight protocol. These initial results show great promise for PCASL-VIPR for static, dynamic, and vessel selective 3D intracranial angiography. Magn Reson Med 000:000–000, 2012. V C 2012 Wiley Periodicals, Inc. Key words: magnetic resonance angiography; pseudocontinuous arterial spin labeling; cerebrovascular disease; VIPR 5 vastly undersampled isotropic projection reconstruction; three- dimensional imaging INTRODUCTION Cerebrovascular disease is the third leading cause of mortality in the United States accounting for approxi- mately 200,000 deaths in the US each year as well as considerable neurologic morbidity (1). Imaging of the cerebral vasculature system is paramount for both diag- nosis and treatment planning. X-ray digital subtraction angiography (DSA) has long been considered the refer- ence standard for cerebral angiography with modern pro- tocols now allowing for extremely high resolution, three- dimensional (3D) static imaging as well as vessel selec- tive, dynamic two-dimensional (2D) projection imaging. However, X-ray DSA poses risk to patients due to the need for invasive access, ionizing radiation, and iodin- ated contrast agents. Additionally, X-ray DSA provides an incomplete assessment of tissue damage. Magnetic resonance imaging is capable of assessing disease markers including tissue viability (2), perfusion (3), and hemorrhage (4). Unfortunately, magnetic resonance angi- ography (MRA) is severely lacking compared with X-ray DSA. Intracranial MRA is most frequently performed with 3D time-of-flight (TOF) with multiple overlapping thin slabs (5). This technique provides relatively high spatial resolution; however, it is limited by the satura- tion of spins in slow, complex, or in-plane flow (6) and provides limited information of vessel filling patterns. Developing techniques hold the potential to signifi- cantly improve intracranial MRA. Contrast-enhanced MRA, which has proven to be robust in the extracranial vasculature, is highly challenging in the cerebral vascu- lature due to the rapid passage of blood from arteries to veins. However, contrast-enhanced MRA has reaped the benefits of accelerated imaging strategies (7–9) and is now feasible for intracranial imaging, albeit at relatively low spatial resolutions compared with X-ray DSA. Non- contrast-enhanced technique has seen renewed develop- ment since the discovery of nephrogenic systemic fibro- sis (10,11). One of these techniques, arterial spin labeling (ASL), is of particular interest for intracranial applications. Similar to TOF, ASL relies on the inflow of blood into the imaging volume; however, ASL uses sepa- rate sequences to label and image inflowing spins. By subtracting the images with different labeling sequences, angiography can be obtained with near zero background, vessel selectivity, and inflow dynamics similar to X-ray DSA. Although ASL has been in development since 1987 (12), its use in angiography has been limited due to low signal-to-noise ratio (SNR), long scan times, and difficul- ties in practical implementation. ASL magnetic resonance imaging can be divided into two basic types: pulsed ASL (PASL) and continuous ASL (CASL). PASL uses a single inversion pulse and has been popular in the last decades due to its easy imple- mentation. With recent improvements in accelerated 1 Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA. 2 Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA. 3 Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA. Grant sponsor: NIH; Grant number: R01NS066982. *Correspondence to: Huimin Wu, M.S., Department of Medical Physics, Wisconsin Institutes Medical Research, 1111 Highland Avenue, Room 1005, Madison, WI 53705-2275. E-mail: hwu7@wisc.edu Received 23 January 2012; revised 16 March 2012; accepted 27 March 2012. DOI 10.1002/mrm.24298 Published online in Wiley Online Library (wileyonlinelibrary.com). Magnetic Resonance in Medicine 000:000–000 (2012) V C 2012 Wiley Periodicals, Inc. 1