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Pittfalls of MRI measurement of white matter perfusion based on arterial spin labeling
P van Gelderen1, J A de Zwart, J H Duyn
1Advanced MRI, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1065, USA. gelderen@nih.gov
Abstract:
Although arterial spin labeling (ASL) MRI has been successfully applied to measure gray matter (GM) perfusion in vivo, accurate detection of white matter (WM) perfusion has proven difficult. Reported literature values are not consistent with each other or with perfusion measured with other modalities. In this work, the cause of these inconsistencies is investigated. The results suggest that WM perfusion values are substantially affected by the limited image resolution and by signal losses caused by the long transit times in WM, which significantly affect the label. From gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) bolus-tracking experiments (N=6), it is estimated that the transit time can be several seconds long in deep WM. Furthermore, simulations show that even at a spatial resolution of 7 microl voxel size, contamination by the GM signals can exceed 40% of the actual WM signal. From 10-min long flow-sensitive alternating inversion recovery ASL (FAIR-ASL) measurements at 3T in normal subjects (N=7), using highly sensitive detectors, it is shown that single-voxel (7 mul) deep WM perfusion values have an signal-to-noise ratio (SNR) less than 1. The poor sensitivity and heterogeneous transit time limit the applicability of ASL for measurement of perfusion in WM.
Insights
Arterial Spin Labeling (ASL) MRI struggles to accurately measure white matter (WM) perfusion due to low resolution and signal loss. These factors, including long transit times and gray matter (GM) signal contamination, limit ASL
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Radiology
Background:
- Arterial Spin Labeling (ASL) MRI is established for gray matter (GM) perfusion measurement.
- Accurate quantification of white matter (WM) perfusion using ASL remains challenging.
- Existing literature values for WM perfusion are inconsistent.
Purpose of the Study:
- Investigate the causes of inconsistencies in WM perfusion measurements using ASL.
- Identify factors limiting the accuracy and reliability of ASL in WM.
Main Methods:
- Performed gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) bolus-tracking experiments (N=6) to assess transit times.
- Conducted simulations to evaluate GM signal contamination at varying spatial resolutions.
- Acquired 10-min flow-sensitive alternating inversion recovery ASL (FAIR-ASL) data at 3T in healthy subjects (N=7).
Main Results:
- WM transit times were found to be several seconds long in deep WM.
- GM signal contamination exceeded 40% of the WM signal even at 7 microl voxel size.
- Single-voxel (7 mul) deep WM perfusion measurements exhibited a signal-to-noise ratio (SNR) less than 1.
Conclusions:
- Limited image resolution and signal loss due to long transit times significantly impact WM perfusion quantification.
- GM signal contamination further compromises WM perfusion accuracy.
- Poor sensitivity and heterogeneous transit times restrict the application of ASL for WM perfusion assessment.
