Arterial Spin Labeling at Ultra-High Field: All That Glitters is Not Gold

In the past decade, MRI perfusion imaging has become increasingly important in the radiological clinic. Herein, arterial spin labeling (ASL) represents a truly noninvasive method for assessment of hemodynamic changes. Recently, whole body scanners that operate at a field strength of 7 Testa or above have become available, carrying the promise of higher signal to noise ratio. In this article, we discuss the basic ASL methods that are available today and the problems that may be encountered when implementing ASL on a high field scanner. Particularly, B-0 and B-1 field inhomogeneities and fluctuations in precession frequency due to respiration were measured at the level of the brain feeding arteries. The effect of these disturbances on ASL is being discussed as are other issues such as specific absorption rate and relaxation rates. It can be concluded that implementation of ASL on MRI systems with high field strength is not trivial, although the feasibility of ASL measurements has been demonstrated at 7 Testa. Further improvements can be expected, for example by the use of local labeling coils and improved shimming and preparation methods. (C) 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 62-70, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20218