Transit delay and flow quantification in muscle with continuous arterial spin labeling perfusion-MRI

Purpose: To test the hypothesis that flow measurements using continuous arterial spin labeling (CASL) magnetic resonance imaging (MRI) in muscle depend upon transit delay, and examine the repeatability of CASL measurements. Materials and Methods: A total of 23 healthy subjects underwent CASL imaging of the calf, foot, and forearm with varying postlabeling delay (PLD = 1000, 1500, and 1900 msec). Experiments were conducted on a 3.0T system. An orthopedic tourniquet system was employed to create a five-minute period of ischemia followed by a transient hyperernic flow. Imaging commenced two minutes prior to cuff inflation and ended three minutes after cuff release. Results: CASL was found able to well resolve the time course of the hyperemic flow pattern with an effective TR of 16 seconds, although we were unable to establish that a plateau had been reached in the flow measurements even at a PLD as long as 1900 msec. Peak hyperemic flow measurements compared favorably with those obtained with contrast-enhanced (CE) MRI following a similar period of ischemia. Region-of-interest (ROI)-based repeated measurements varied by approximately 20% over a period of one hour. Conclusion: In all anatomic regions studied, flow measurements were found to increase with PLD, suggesting the prolonged transit delay in muscle.