Arterial spin labeling (ASL) is a powerful MRI-based technique for the measurement of tissue blood flow, and is widely used to study the brain. In ASL, radiofrequency pulses are used to modify the longitudinal magnetization of arterial blood, generating an endogenous tag that decays away with a time constant given by the T1 relaxation time. After a delay to allow tagged blood to flow into the target tissue, an image is acquired that reflects the inflow of tagged blood as well as static tissue. A second (control) image is then acquired in the absence of a preceding tag pulse. The difference between these images reflects the amount of tagged blood that has been delivered to the imaging region. ASL techniques applied to cardiac perfusion have several potential advantages over contrast-based methods. The most important is that ASL does not require any contrast agents, making it safer and cheaper. For example, cardiac ASL could be safely applied in patients with ESRD who are not candidates for alternative techniques.
The images below show (left) ASL perfusion reserve maps and (right) x-ray angiograms from two patients in our initial clinical study. (A, B) is from a patient with total occlusion of the left anterior descending coronary artery; (C, D) is from a patient with total occlusion of their right coronary artery. Regions of heart muscle with low perfusion reserve are consistent with the territories of the blocked vessels (arrows).
Selected References:
- F Kober, T Jao, T Troalen, KS Nayak, Myocardial Arterial Spin Labeling. Journal of Cardiovascular Magnetic Resonance. 2016, 18:22. April 2016. PDF JNRL
- T Jao, KS Nayak. Demonstration of velocity selective myocardial arterial spin labeling perfusion imaging in humans. Magnetic Resonance in Medicine. 80(1):272-278. July 2018. PDF JRNL
- Z Zun, P Varadarajan, RG Pai, EC Wong, KS Nayak. Arterial Spin Labeling Cardiac Magnetic Resonance Detects Clinically Relevant Increases in Myocardial Blood Flow With Vasodilation. Journal of the American College of Cardiology: Cardiovascular Imaging 4(12):1253-1261. December 2011. PDF JRNL Editorial Comment JRNL
- Z Zun, EC Wong and KS Nayak. Assessment of myocardial blood flow in humans using arterial spin labeling: feasibility and SNR requirements. Magnetic Resonance in Medicine 62(4):975-83. October 2009. PDF JRNL