Perioperative cerebral blood flow measured by arterial spin labeling with different postlabeling delay in patients undergoing carotid endarterectomy: a comparison study with CT perfusion

Background: Arterial spin labeling (ASL) is a non-invasive technique for measuring cerebral perfusion. Its accuracy is affected by the arterial transit time. This study aimed to (1) evaluate the accuracy of ASL in measuring the cerebral perfusion of patients who underwent carotid endarterectomy (CEA) and (2) determine a better postlabeling delay (PLD) for pre- and postoperative perfusion imaging between 1.5 and 2.0 s. Methods: A total of 24 patients scheduled for CEA due to severe carotid stenosis were included in this study. All patients underwent ASL with two PLDs (1.5 and 2.0 s) and computed tomography perfusion (CTP) before and after surgery. Cerebral blood flow (CBF) values were measured on the registered CBF images of ASL and CTP. The correlation in measuring perioperative relative CBF (rCBF) and difference ratio of CBF (DRCBF) between ASL with PLD of 1.5 s (ASL(1.5)) or 2.0 s (ASL(2.0)) and CTP were also determined. Results: There were no significant statistical differences in preoperative rCBF measurements between ASL(1.5) and CTP (p = 0.17) and between ASL(2.0) and CTP (p = 0.42). Similarly, no significant differences were found in rCBF between ASL(1.5) and CTP (p = 0.59) and between ASL(2.0) and CTP (p = 0.93) after CEA. The DRCBF measured by CTP was found to be marginally lower than that measured by ASL(2.0_ 1.5) (p = 0.06) and significantly lower than that measured by ASL(1.5_ 1.5) (p = 0.01), ASL(2.0_ 2.0) (p = 0.03), and ASL1(.5_ 2.0) (p = 0.007). There was a strong correlation in measuring perioperative rCBF and DRCBF between ASL and CTP (r = 0.67-0.85, p < 0.001). Using CTP as the reference standard, smaller bias can be achieved in measuring rCBF by ASL(2.0) (-0.02) than ASL(1.5) (-0.07) before CEA. In addition, the same bias (0.03) was obtained by ASL(2.0) and ASL(1.5) after CEA. The bias of ASL(2.0_ 2.0) (0.31) and ASL(2.0_ 1.5) (0.32) on DRCBF measurement was similar, and both were smaller than that of ASL(1.5_ 1.5) (0.60) and ASL(1.5_ 2.0) (0.60). Conclusion: Strong correlation can be found in assessing perioperative cerebral perfusion between ASL and CTP. During perioperative ASL imaging, the PLD of 2.0 s is better than 1.5 s for preoperative scan, and both 1.5 and 2.0 s are suitable for postoperative scan.