• Neville D Gai and John A Butman.
• Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA.
• J Magn Reson Imaging. 2019 Sep 1; 50 (3): 951-960.

BackgroundArterial spin labeling with 3D acquisition requires determining a single postlabeling delay (PLD) value. PLD affects the signal-to-noise ratio (SNR) per unit time as well as quantitative cerebral blood flow (CBF) values due to its bearing on the presence of a vascular signal.PurposeTo search for an optimal PLD for pseudocontinuous arterial spin labeling (pCASL) using patient-specific carotid artery blood velocity measurements.Study TypeProspective.SubjectsA control group of 11 volunteers with no known pathology. Corroboration was through a separate group of six volunteers and a noncontrol group of five sickle cell disease (SCD) patients.Field Strength/SequencePseudocontinuous arterial spin labeling with 3D nonsegmented echo planar imaging acquisition at 3T.AssessmentA perfusion-based measure was determined over a range of PLDs for each of 11 volunteers. A third-order polynomial was used to find the optimal PLD where the defined measure was maximum. This was plotted against the corresponding carotid artery velocity to determine a relationship between the perfusion measure and velocity. Corroboration was done using a group of six volunteers and a noncontrol group of five patients with SCD. PLD was determined from the carotid artery velocity and derived relationship and compared with optimal PLD obtained from measured perfusion over a range of PLD values. Error between the perfusion measure at predicted and measured optimal PLD was determined.Statistical TestsChi-squared goodness of fit; Pearson correlation; Bland-Altman.ResultsCarotid artery velocity was 63.8 ± 6.6 cm/s (53.1 ≤ v ≤ 72.3 cm/s) while optimal PLD was 1374 ± 226.5 msec (1102 ≤ PLD ≤ 1787 msec) across the 11 volunteers. PLD as a function of carotid velocity was determined to be PLD = -31.94. v + 3410 msec (Pearson correlation -0.93). In six volunteers, mean error between the perfusion measure at predicted and measured optimal PLD was 1.35%. Pearson correlation between the perfusion measure at the predicted PLD and the measure obtained experimentally was r = 0.96 (P < 0.001). Bland-Altman revealed a slight bias of 1.3%. For the test case of five SCD patients, the mean error was 1.3%.Data ConclusionCarotid artery velocity was used to determine optimal PLD for pCASL with 3D acquisition. The derived relationship was used to predict optimal PLD and the associated perfusion measure, which was found to be accurate when compared with its measured counterpart.Level Of Evidence2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:951-960.Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

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