Comparison of test-retest reliability of BOLD and pCASL fMRI in a two-center study

Abstract

Background: The establishment of test-retest reliability and reproducibility (TRR) is an important part of validating any research tool, including functional magnetic resonance imaging (fMRI). The primary objective of this study is to investigate the reliability of pseudo-Continuous Arterial Spin Labeling (pCASL) and Blood Oxygen Level Dependent (BOLD) fMRI data acquired across two different scanners in a sample of healthy adults. While single site/single scanner studies have shown acceptable repeatability, TRR of both in a practical multisite study occurring in two facilities spread out across the country with weeks to months between scans is critically needed.

Methods: Ten subjects were imaged with similar 3 T MRI scanners at the University of Pittsburgh and Massachusetts General Hospital. Finger-tapping and Resting-state data were acquired for both techniques. Analysis of the resting state data for functional connectivity was performed with the Functional Connectivity Toolbox, while analysis of the finger tapping data was accomplished with FSL. pCASL Blood flow data was generated using AST Toolbox. Activated areas and networks were identified via pre-defined atlases and dual-regression techniques. Analysis for TRR was conducted by comparing pCASL and BOLD images in terms of Intraclass correlation coefficients, Dice Similarity Coefficients, and repeated measures ANOVA.

Results: Both BOLD and pCASL scans showed strong activation and correlation between the two locations for the finger tapping tasks. Functional connectivity analyses identified elements of the default mode network in all resting scans at both locations. Multivariate repeated measures ANOVA showed significant variability between subjects, but no significant variability for location. Global CBF was very similar between the two scanning locations, and repeated measures ANOVA showed no significant differences between the two scanning locations.

Conclusions: The results of this study show that when similar scanner hardware and software is coupled with identical data analysis protocols, consistent and reproducible functional brain images can be acquired across sites. The variability seen in the activation maps is greater for pCASL versus BOLD images, as expected, however groups maps are remarkably similar despite the low number of subjects. This demonstrates that multi-site fMRI studies of task-based and resting state brain activity is feasible.

Keywords: Blood oxygen level dependent; Finger tapping; Functional magnetic resonance imaging; Pseudo-continuous arterial spin labeling; Resting state functional connectivity; Test–retest reliability.

Fig. 1

Activation measured in BOLD and pCASL finger-tapping scans at PIT and MGH scanning locations. Rendered Z-statistic images for each subject at each location for BOLD (a) and pCASL perfusion activation (b). Negative perfusion change is shown in blue, and positive is shown in red/yellow. Both BOLD and pCASL scan sequences showed activation in the motor cortex, and group mean images at each location were very similar. Signal changes for BOLD scans (c) at each location (PIT = blue, MGH = black) were significantly correlated between the two locations and with the finger-tapping task, shown in gray. Individual subject Pearson correlations with the task and within-subject are shown to the right, demonstrating excellent repeatability. Signal changes for pCASL scans (d) were significantly correlated with the tapping task at PIT and at MGH, and were significantly correlated between the two scanning locations, again as shown to the right

Fig. 2

Default mode network functional connectivity in BOLD and pCASL scans at both scanning locations. Functional connectivity maps with PCC as the seed region are shown for each subject at each location for BOLD (a) and pCASL (b) resting state scans. Inter- and intra-subject variability expressed as mean standard deviations, intraclass correlation coefficients (ICC) and Dice Similarity Coefficients (DSC) for BOLD (c) and pCASL (d) resting state scans are shown for the DMN subregions MPFC, PCC, LLP, and RLP as the seed regions and the PCC, LLP, RLP, ACC, and left and right insula as the ROIs. Inter- and intra-subject variability were not significantly different for both BOLD and pCASL scans. Both the BOLD and pCASL functional connectivity maps showed high intraclass correlation in at least one DMN pathway, but the pathways showing the highest ICC values differed between the two scan sequences

Fig. 3

Dual regression default mode network functional connectivity for pCASL scans at both scanning locations. Functional connectivity maps with the ICA defined PCC as the seed region are shown for each subject at each location for pCASL (a) resting state scans. Inter- and intra-subject variability expressed as mean standard deviations, intraclass correlation coefficients (ICC) and Dice Similarity Coefficients (DSC) for pCASL (b) resting state scans are shown for the DMN subregions MPFC, PCC, LLP, and RLP as the seed regions and the PCC, LLP, RLP, ACC, and left and right insula as the ROIs. Overall the intraclass correlations increased as a result of the ICA ROI selection, with specific improvements in the DMN pathways

Fig. 4

Global and regional cerebral blood flow (CBF) measured at the two scanning locations. Mean CBF maps for each subject at each location for resting state scans (a) and for finger-tapping scans (b). CBF maps for the finger-tapping scans are shown separately for the tapping and resting portions of the scans. Mean global CBF and regional flow values in the motor cortex compared with paired-samples t-tests (c) were not significantly different between the two scanning locations for the resting state scans or for the tapping and resting portions of the finger-tapping scans