Physiological Modulations in Arterial Spin Labeling Perfusion Magnetic Resonance Imaging

Abstract

The purpose of this study is to evaluate cardiac and respiratory modulations in the signals of arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) using RETROICOR, an image domain based retrospective correction method. Systematic comparisons were conducted for tagging schemes, pulsed (PASL) versus frequency-modulated continuous (CASL) methods, and the use of background suppression (BGS). Results showed that cardiac pulsation accounted for more signal fluctuation in PASL than in CASL (two-tailed paired Student's t-test, p < 10(-3)), whereas no significant difference was found in the effect of respiratory motion ( p=0.55) on the two tagging schemes studied. For PASL, significantly more improvement was achieved by the inclusion of cardiac pulsation than respiratory motion in RETROICOR ( p < 0.01). On the contrary, the inclusion of respiratory motion offers more improvement for CASL ( p < 0.02). BGS effectively improved the temporal signal-to-noise ratio (tSNR) as previous studies reported, but no significant difference was measured in the spectral power of physiological modulations relative to the entire spectrum of PASL signals before and after the superimposition of BGS ( p=0.63 for cardiac component, p=0.67 for respiratory component). Thus, we conclude that BGS reduces noise without spectral selectivity, and the improvements of tSNR from RETROICOR and BGS are additive. CASL with a labeling duration at a multiple of an R-R interval can be used to minimize signal fluctuation originating from cardiac pulsation.

Arterial spin labeling MRI

“…Pseudocontinuous ASL (pCASL) represents a hybrid of these approaches in which many short pulses simulate the continuous labeling of CASL (39, 40). Continuous inversion allows labeling throughout the cardiac cycle, greatly reducing cardiac noise (41). This difference results in a significant SNR and test-retest reliability advantage for pCASL relative to PASL; the latter being commercially available on a number of scanner platforms [(41, 42)].…”

“…Continuous inversion allows labeling throughout the cardiac cycle, greatly reducing cardiac noise (41). This difference results in a significant SNR and test-retest reliability advantage for pCASL relative to PASL; the latter being commercially available on a number of scanner platforms [(41, 42)]. This reproducibility advantage for pCASL occurs at a whole grey matter level, but also includes regions of interest (ROIs) that may be particularly relevant to AD, including the posterior cingulate and hippocampus (42).…”

MRI patterns of atrophy and hypoperfusion associations across brain regions in frontotemporal dementia

“…The resulting mean control image was subtracted from the mean labeled image, yielding raw perfusion-weighted image. This was followed by the intensity normalization of the raw perfusion-weighted image by the overall mean cASL image (i.e., average of mean labeled and mean control images) as approximation for arterial water density (Wen-Chau et al, 2009), and for elimination of spurious signal contributions of very high intensity from arterial vessels. The intensity normalization also reduced the intensity inhomogeneity in EPI.…”

Joint analysis of structural and perfusion MRI for cognitive assessment and classification of Alzheimer's disease and normal aging

“…This was followed by the normalization of the raw perfusion-weighted images by the overall mean cASL image (i.e., average of mean labeled and mean reference images) as an approximation for arterial water density (Wen-Chau et al, 2009), and for elimination of spurious signal contributions of very high intensity from arterial vessels. The intensity normalization also reduced the intensity inhomogeneity in EPI.…”