Acquisition Time and Reproducibility of Continuous Arterial Spin-Labeling Perfusion Imaging at 3T

Abstract

SUMMARY:Arterial spin-labeling (ASL) is a relatively new and noninvasive MR imaging technique, used to measure cerebral blood flow (CBF). Scanning time and reproducibility remain important issues in the clinical applicability of ASL. We expected both to benefit from higher field strengths. We describe that when performing ASL at 3T, 20 averages suffice to obtain steady and reproducible CBF values. Scanning time can be as short as 3 minutes.A rterial spin labeling (ASL) is a noninvasive MR imaging technique, used for visualization and quantification of cerebral perfusion. Cerebral blood flow (CBF) values measured by ASL are comparable with CBF values measured by conventional techniques (eg, positron-emission tomography or susceptibility-weighted MR imaging). ASL is based on magnetic labeling of arterial blood water protons, which are used as an endogenous tracer of flow. Magnetic inversion takes place in a plane proximal to the brain. The decay rate of the labeled spins is sufficiently long to visualize perfusion of brain vasculature and microvasculature. Perfusion images are obtained by subtraction of successively acquired labeled and nonlabeled control images. In general, 40 to 60 paired acquisitions are averaged to improve perfusion signal intensity. ASL sequences differ in the way magnetic labeling is applied and are commonly classified as continuous or pulsed ASL (CASL or PASL, respectively). In CASL, continuous adiabatic inversion of spins is applied. In PASL, labeling is performed at once over a wide spatial range. Pseudocontinuous ASL (pCASL) has been introduced recently and uses a series of discrete labeling pulses. 1-8Despite its advantages, scanning time and reproducibility remain important issues in the clinical applicability of ASL. The use of higher-field strengths could overcome these issues because of increased signal-to-noise ratio, prolonged T1-weighted relaxation time of labeled blood, and better spatial and temporal resolution. 7,9 We hypothesized that scanning time of the CASL sequence can be reduced at 3T because fewer averages might suffice to obtain steady and reproducible CBF values. Our primary objective was to assess the number of averages needed to obtain steady and reproducible CBF values with use of 3T CASL.Also, we hypothesized that acquisition-related reproducibility of ASL will improve at higher-field strengths, whereas physiology-related reproducibility will not change. Previous CASL reproducibility studies were performed at 1.5T with test-retest timeframes of at least 1 hour. 4,6,10 Measurement of reproducibility within scans would be more valuable to assess physiologic variations. Our secondary objective was to assess 3T CASL reproducibility within scans (intrascan Ϸ 4 minutes), within sessions (intrasession Ϸ 10 minutes), and between sessions (intersession Ϸ 1 to 3 weeks). TechniqueAfter approval of the local ethics committee and written informed consent from all volunteers, we scanned 10 volunteers (5 men; age range, 25-33 years) without known cerebrovascular disease during 3...

Age‐related cerebral perfusion changes in the parietal and temporal lobes measured by pulsed arterial spin labeling

“…Based on the coefficient of variation which was 7.9 % in the global GM ROI, we conclude that the reproducibility of our measurements lies well in the range reported for other pulsed (28)(29)(30) and continuous ASL (31)(32)(33)(34) methods. A recent multi center study at 3T including 28 sites (29) using a PASL method termed QUASAR (35,36) reported values for SD w in GM between 3.01 and 8.12 ml/100 g/min, which suggests that the reproducibility of our measurements is quite high.…”

Intra- and Multicenter Reproducibility of Pulsed, Continuous and Pseudo-Continuous Arterial Spin Labeling Methods for Measuring Cerebral Perfusion

“…CASL, continuous arterial spin labeling; p-CASL, pseudo-continuous arterial spin labeling; s.d., standard deviation; TI PASL, inversion time pulsed arterial spin labeling. on reproducibility of these techniques (Floyd et al, 2003;Gevers et al, 2009a;Hermes et al, 2007;Jahng et al, 2005;Parkes et al, 2004). Looking at mean CBF values and the amount of data dispersion, as indicated by the CVs, we noticed that CASL and single TI PASL data from one site were largely responsible for this discrepancy.…”

Test-retest reliability of cerebral blood flow in healthy individuals using arterial spin labeling: Findings from the EMBARC study

“…We calculated ICCs for both aCBF and rCBF images; however, it should be noted that previous work showed higher reliability for rCBF measures [21,55,56]. A comparison of aCBF and rCBF was considered to be significant if confidence intervals (95%) for ICCs did not overlap with each other [18]. …”

“…Based on previous findings indicating that intra-class correlation coefficients of ASL measures may differ between scans acquired a few hours apart from those acquired several days apart [18,19,21,23,25–29,32] and limited information on possible effects of data acquisition using different scans platforms, we aimed to determine the test-retest reliability of ASL measures in these networks across sites/platforms on scans acquired one week apart.…”