Measuring Cerebral Blood Flow Using Pseudo-continuous Arterial Spin Labeling Perfusion Magnetic Resonance Imaging

Cerebral blood flow (CBF) represents an important physiological parameter for the diagnosis and management of multiple brain disorders. The clinical need for CBF measurements is further complicated by the desire to have a non-invasive method with high temporal resolution that can measure CBF over a wide range of blood flows and in a wide range of patients. Numerous techniques are available to measure CBF. Nuclear medicine approaches, such as single positron emission computed tomography (SPECT) and positron emission tomography (PET) rely on radioisotopes which can be problematic in the pediatric population. In contrast, MRI-based methods are non-invasive and the CBF information can be obtained in conjunction with other MRI techniques (i.e. diffusion weighted imaging or spectroscopy) which allows for a combined longitudinal assessment of CBF, morphology, and metabolism, to provide a more complete understanding of the developing pathophysiological mechanisms. Arterial spin labeling (ASL) perfusion imaging uses arterial blood water as an endogenous diffusible tracer where radiofrequency (RF) pulses magnetically label the moving spins in flowing blood without the use of a contrast agent. After a time delay allowing for the magnetically labeled blow to flow into the brain, "labeled" images are acquired. Separate control images are also acquired, without labeling and the difference between the two sets of imaged provides a measure of perfusion. Since gadolinium-based contrast agents are not required, the ASL perfusion technique is completely non-invasive. In addition, ASL techniques are insensitive to blood-brain barrier permeability changes, which can occur after strokes or with tumors. Because gadolinium-based contrast is not used, the ASL technique has an inherently lower sensitivity than DSC-PWI. To date, there are a number of commercially available ASL techniques that differ in their labeling schemes, which has contributed to the difficulty in obtaining consistent results across different patient populations (pediatric, elderly, stroke, tumors). A number of recent reports using pseudo-continuous ASL (pCASL) have been published and show increased reliability across different patient populations. Moreover, a recent consensus statement published by the International Society of Magnetic Resonance in Medicine Perfusion Study Group recommends the use of pCASL labeling strategies for clinical applications. The objectives of this study is to determine the accuracy and reliability of a newly developed pCASL sequence and post-processing software across multiple patient populations (neonate to elderly) and pathological processes.