Arterial Spin Labeling Perfusion MRI in Alzheimer's Disease

Although nuclear medicine imaging methods such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) were the first to show a distinctive pattern of hypometabolism and hypoperfusion in patients with Alzheimer's disease (AD), large-scale application of these methods is hampered by invasiveness, high costs, low spatial resolution and availability. Recent findings that hemodynamic changes precede cortical thinning have resulted in a strong interest in developing a non-invasive alternative for measuring the hemodynamic status. Magnetic resonance imaging (MRI) provides a non-invasive measurement of cerebral blood flow by magnetically labeling the blood in the main brain-feeding arteries and subsequently detecting the labeled spins in the cerebral tissue after a delay. This technique has been dubbed "Arterial spin labeling (ASL)". Image quality of ASL has been considerably improved in recent years, owing to the development of medium and high field MRI scanners, improved methods to suppress physiological noise, and improved labeling sequences. In this review article the technique of ASL MRI is introduced and an overview of studies that employ ASL in AD is provided. A common finding over these studies is that CBF is reduced in bilateral precunei, parietal and temporal lobes, frontal areas, and occipital areas. These findings are in line with PET and SPECT findings, but ASL studies have also shown new results that were not previously observed in nuclear medicine studies. The most interesting finding is probably the observed increase in CBF (after atrophy correction) in the hippocampus.