Reliability and precision of pseudo-continuous arterial spin labeling perfusion MRI on 3.0 T and comparison with 15O-water PET in elderly subjects at risk for Alzheimer's disease

Abstract

Arterial spin labeling (ASL) offers MRI measurement of cerebral blood flow (CBF) in vivo, and may offer clinical diagnostic utility in populations such as those with early Alzheimer's disease (AD). In the current study, we investigated the reliability and precision of a pseudo-continuous ASL (pcASL) sequence that was performed two or three times within one hour on eight young normal control subjects, and 14 elderly subjects including 11 with normal cognition, one with AD and two with Mild Cognitive Impairment (MCI). Six of these elderly subjects including one AD, two MCIs and three controls also received (15)O-water positron emission tomography (PET) scans 2 h before their pcASL MR scan. The instrumental reliability of pcASL was evaluated with the intraclass correlation coefficient (ICC). The ICCs were greater than 0.90 in pcASL global perfusion measurements for both the young and the elderly groups. The cross-modality perfusion imaging comparison yielded very good global and regional agreement in global gray matter and the posterior cingulate cortex. Significant negative correlation was found between age and the gray/white matter perfusion ratio (r = -0.62, p < 0.002). The AD and MCI patients showed the lowest gray/white matter perfusion ratio among all the subjects. The data suggest that pcASL provides a reliable whole brain CBF measurement in young and elderly adults whose results converge with those obtained with the traditional (15)O-water PET perfusion imaging method. pcASL perfusion MRI offers an alternative method for non-invasive in vivo examination of early pathophysiological changes in AD.

Figure 1

A: 3D pseudo-continuous arterial spin labeling (pcASL) pulse sequence paradigm. Presat: pre-saturation pulse; sat: saturation pulse; BS: background suppression. B: A set of cerebral blood flow (CBF) images from one 57-year old control subject with pcASL scan. The ASL perfusion image voxel size is 3.75 × 3.75 × 4 mm³. FSE acquisition: Fast Spin Echo acquisition.

Figure 2

A. Grand mean normalized regional CBF (rCBF) images from one 60-year old control with normal cognition using pcASL-MRI (upper row) and ¹⁵O-water PET (bottom row) method. The rCBF images are in the same ratio scale; B. Mask template shows GM in gray and PCC in blue (WFU PickAtlas Tool). WM ROI is manually drawn for each subject and shown in red. C. Bland-Altman plots show the agreement on rCBF from GM, WM and PCC measured by pcASL-MRI and ¹⁵O-water PET methods. D. In the scatter plot, significant correlations were shown in the CBF perfusion values from both the GM, WM and PCC ROIs.

Figure 3

Global Gray matter, white matter ROI CBF value and their ratios were plotted against age. No group difference was found in global gray matter and white matter perfusion values between the normal young and elderly subjects. The GM/WM ratio is significantly higher in young controls than the elderly subjects (p<0.009, t-test). There are weak correlations between age and global GM perfusion (CC= − 0.24, p<0.292), WM perfusion (CC= 0.17, p<0.457). Significant negative correlations was found between age and GM/WM perfusion ratio (CC = − 0.62, P<0.002).