Case in Methods and Statistics
Arterial spin labeling (ASL) is an emerging magnetic resonance imaging (MRI) technique for the quantification of whole brain perfusion.
Due to the absence of an exogenous contrast agent, ASL is harmless, not hampered by the blood-brain barrier and can be performed as long and as frequent as required. Therefore, it is an attractive tool compared to former perfusion modalities, especially in studies with repeated measurements.
ASL can be applied in both in healthy volunteers (to study its reproducibility), as well as in specific patient populations. In healthy volunteers, we validated our ASL protocol to the gold standard, 15O Positron Emission Tomography (PET). We found that ASL methods provide quantitatively identical results as compared to cerebral blood flow (CBF) values of gray matter. Both methods can therefore be exchanged. Moreover, ASL data using Philips 3T MRI were compared with those obtained with a General Electric 3T and again produced similar results indicating that results obtained in multiple centers can be readily aggregated into meaningful imaging data.
Accordingly, our ASL protocol is now routinely used in the neurodegeneration research area. In collaboration with Dr. Edo Richard we participate in a multi-center research program to investigate perfusion patterns that correlate with disease severity in patients with cognitive deficits. In large samples of elderly with and without neurodegeneration, we successfully constructed whole brain arterial transit time maps and developed methods to measure white matter perfusion.
New developments include the value of ASL combined with other functional imaging modalities such as diffusion tensor imaging (DTI). These and forthcoming optimizations of ASL implementations will further expand the clinical and diagnostic use of ASL.