SCIENCE TO PRACTICE Radiology: Volume 265: Number 2—November 2012 n radiology.rsna.org 325 The Setting During the past decade there have been about 600 articles published per year on the topic of magnetic resonance (MR) angiography. The relative popularity of MR angiography and MR-based flow mea- surement is due to their use of radiofre- quency irradiation rather than ionizing radiation to construct images. Before gadolinium-induced nephrogenic systemic fibrosis was reported (1), the authors of most of these studies used a gadolinium- based contrast agent to enhance the signal-to-noise ratio and contrast of MR angiograms. After the reports of neph- rogenic systemic fibrosis, several non- contrast material–enhanced MR angio- graphic methods were developed to avoid the potential of adverse reactions to gadolinium-based contrast agents (2). Conflicts of interest are listed at the end of this article. q RSNA, 2012 Science to Practice: Can Hyperpolarized Water Be Used to Enhance MR Angiography and Flow Measurement? Robert E. Lenkinski, PhD Department of Radiology UT Southwestern Medical Center 5323 Harry Hines Blvd, Dallas TX 75390-9061 robert.lenkinski@utsouthwestern.edu See page 418 Summary: The method described by Lingwood et al is a continuously flowing system rather than the discrete batch approach of the dissolution dynamic nuclear polarization method, which means the hyperpolarized molecule can be continu- ously available for injection on demand. Despite the advantageous safety aspects of MR angiography and the major tech- nical advances that have shortened acqui- sition time, conventional MR angiography still has relatively poor signal-to-noise and signal-to-background ratios and longer acquisition times than its primary com- petitor, computed tomographic (CT) an- giography. Awareness of these short- comings has provided an impetus for developing new technical approaches to increasing the signal-to-noise ratio of MR angiographic examinations. One direct MR method to improve the signal-to noise ratio is performing the MR angiography at 3 T rather than 1.5 T because the thermal polarization of the protons in water increases linearly with field strength, resulting in a potential improvement of a factor of two in the signal-to-noise ratio of the study. An ex- tension of the idea of using higher mag- netic fields to increase the signal in MR angiography was patented by Dumoulin and Souza (U.S. patent no. 5,603,320; 1997). In this method, water is polar- ized in a small high-field-strength magnet (15 T), then this highly polarized water is injected though a catheter and images are acquired at a lower field strength, such as 1.5 T. Another class of approaches, which is broadly called hyperpolarization, em- ploys a variety of methods to increase the MR signal by transiently increasing the number of nuclei aligned with the applied magnetic field. The basis for these methods will be explained more fully in the following section. Most of these hy- perpolarization techniques involve the Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at www.rsna.org/rsnarights.