Intra- and multicenter reproducibility of pulsed, continuous and pseudo-continuous arterial spin labeling methods for measuring cerebral perfusion

Abstract

Intra- and multicenter reproducibility of currently used arterial spin labeling (ASL) methods were assessed at three imaging centers in the Netherlands, equipped with Philips 3TMR scanners. Six healthy participants were scanned twice at each site. The imaging protocol consisted of continuous ASL (CASL), pseudo-continuous ASL (p-CASL) with and without background suppression, pulsed ASL (PASL) with single and multiple inversion times (TIs), and selective ASL for segmentation. Reproducibility was expressed in terms of the coefficient of repeatability and the repeatability index. Voxelwise analysis of variance was performed, yielding brain maps that reflected regional variability. Intra- and multicenter reproducibility were comparable for all methods, except for single TI PASL, with better intracenter reproducibility (F-test of equality of two variances, P<0.05). Pseudo-continuous ASL and multi TI PASL varied least between sites. Variability maps of all methods showed most variability near brain-feeding arteries within sessions and in gray matter between sessions. On the basis of the results of this study, one could consider the use of reference values in clinical routine, with whole-brain p-CASL perfusion varying <20% over repeated measurements within the same individuals considered to be normal. Knowledge on regional variability allows for the use of perfusion-weighted images in the assessment of local cerebral pathology.

Figure 1

Voxel-based analysis of variability. ANOVA, analysis of variance; CBF, cerebral blood flow; s.d, standard deviation.

Figure 2

Flow territories, as defined by planning-free selective arterial spin labeling (ASL; first row) and perfusion-weighted images obtained by pseudo-continuous ASL (p-CASL) with and without background suppression, single inversion time pulsed ASL (TI PASL), multi TI PASL and continuous ASL (CASL).

Figure 3

Mean cerebral blood flow (CBF) per arterial spin labeling (ASL) method and imaging site. Error bars represent corresponding standard deviations (s.d.). A significant difference between perfusion values measured at one site and the other two sites was found for continuous ASL (CASL) and single inversion time pulsed ASL (TI PASL; as indicated by the double asterisk). A significant difference between perfusion values measured at one site and one other site was found for pseudo-continuous ASL (p-CASL) with background suppression and multi TI PASL (as indicated by the single asterisk).

Figure 4

Bland–Altman plots showing the difference between intracenter repeated cerebral blood flow (CBF) measurements and mean CBF (mL per 100 g/min). Dotted lines indicate the mean CBF difference to be ±1.96 s.d. of the difference between repeated measurements (i.e., the confidence interval for the difference between repeated measurements). Of the differences between repeated measurements, 95% will be between the dotted lines. CASL, continuous arterial spin labeling; p-CASL, pseudo-continuous arterial spin labeling; s.d., standard deviation; TI PASL, inversion time pulsed arterial spin labeling.

Figure 5

Test–retest perfusion values measured using different arterial spin labeling (ASL) sequences (mL per 100 g/min). Values are centered around the line of equality, indicating good correlation between two measurements. CASL, continuous ASL; p-CASL, pseudo-continuous ASL; TI PASL, inversion time pulsed ASL.

Figure 6

Perfusion images registered to standard space with corresponding s.d. maps reflecting regional perfusion variability within and between imaging sessions. CASL, continuous arterial spin labeling; p-CASL, pseudo-continuous arterial spin labeling; s.d., standard deviation; TI PASL, inversion time pulsed arterial spin labeling.