Nonenhanced Extracranial Carotid MR Angiography Using Arterial Spin Labeling: Improved Performance With Pseudocontinuous Tagging

Purpose: To compare pulsed arterial spin labeling (PASL) and pseudocontinuous arterial spin labeling (PCASL) for nonenhanced extracranial carotid MR angiography (MRA). Materials and Methods: Parametric signal equations for PASL and PCASL MRA were formulated and compared. Volunteer imaging (n = 7) at 1.5 Tesla was performed to compare the methods over a broad range of repetition and labeling times. Empirical results were compared with theoretical predictions. The feasibility of the optimal method was investigated in patients (n = 2) with sonographically documented carotid artery disease. Results: In volunteers, PCASL provided significantly improved signal than PASL (range: 32-255% improvement; P < 0.01), and better supported the use of long labeling times and short repetition times. Excellent agreement between theory and experiment was found (intraclass correlation coefficient = 0.966; P < 0.001). PCASL provided excellent depiction of the carotid arteries in initial patient studies. Conclusion: Compared with pulsed tagging, pseudocontinuous tagging provides improved performance for nonenhanced extracranial carotid MRA and warrants further clinical investigation.