What Physiologic Imaging of the Brain Is
Physiologic Imaging of the Brain is of great use when a stroke has occurred. Recent technological advances in CT and MRI scanning have made it easy to image the brain in detail never before possible. By quickly detecting a stroke and identifying its cause, doctors can more rapidly take action to limit, and potentially reverse, the damaging effects of stroke.
Multi-slice CT scanners provide the speed needed to determine the extent of brain tissue that has been deprived of its blood supply during the first few hours after the onset of a stroke. A technique called CT brain perfusion imaging consists of images acquired over a 60-75 second time span while x-ray contrast medium is rapidly injected. This yields images that show the circulation of blood through the brain. A radiologist can quickly evaluate any areas where the blood supply has been disrupted or decreased due to the narrowing or blockage of arteries.
An ultra-fast MRI technique called echo-planar imaging, or EPI, is used to generate images of the brain tissue and blood supply to the brain and can be used to evaluate acute and later phases of stroke. MRI diffusion imaging exploits the principle of microscopic water movement in the brain tissue. Under normal conditions, water in the brain tissues moves with relative freedom. When a disruption to the blood supply of the brain occurs, the tissue will swell. This swelling will decrease the freedom with which the water can move about and this restriction is visible on the MRI diffusion scans.
EPI is also used in MRI brain perfusion imaging. Very similar to CT brain perfusion imaging, MRI brain perfusion uses a rapid injection of a special MRI contrast medium called gadolinium, rather than an x-ray contrast medium. MRI diffusion done in concert with MRI brain perfusion yields information about the amount of brain tissue that has suffered irreversible damage and also the amount of tissue that is “at risk” of irreversible damage, but may still be salvageable.
The MR and CT techniques used to physiologically image the brain are often combined with three dimensional (3D) images of the cerebral vasculature to provide a comprehensive picture of the circulatory activity in the brain. When a 3D imaging technique is used in conjunction with CT brain perfusion, MR brain perfusion, and/or MR diffusion, the radiologist can see not only the area of the brain affected by the blood flow disruption, but also in many cases, the cause of the disruption itself. A team of physicians can then determine the best course of treatment to minimize the effects of stroke.
Physiologic imaging of the brain represents a powerful set of tools available to image
the brain and manage cerebral vascular disease. RIA radiologists interpret the results of these
complex exams at several Denver area hospitals.