Physiologic Imaging of the Brain

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.

This page contains the following information about physiologic imaging of the brain:

Reasons for Having Physiologic Imaging of the Brain

CT perfusion imaging and MR diffusion and perfusion imaging can be helpful in the decision making process for managing acute stroke and non acute cerebral vascular disease.

Risks Involved in Physiologic Imaging of the Brain

With CT perfusion imaging, there is the risk of radiation exposure; however, it is well below the level that generally causes adverse affects. There is a very small possibility that you could have an allergic reaction to the contrast used for the exam. Also, if you have impaired kidney function, contrast can aggravate your condition.

Since some MRI scanners are enclosed, claustrophobic patients may be uncomfortable. It is also possible that undetected metal implants can be affected by the magnetic field or that they can interfere with the readability of the images. Patients are thoroughly screened before every MR exam to help prevent these problems.

MRI contrast, gadolinium, has an extremely low incidence of documented allergic reactions. MRI contrast also is not known to have any adverse effects on kidney function.

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Conditions to Let Our Doctor Know About

Physiologic imaging of the brain is often done in emergency situations. If it’s possible, in advance of your exam, let your Invision Sally Jobe radiologist or technologist know if any of the following circumstances apply to you:

CT Brain Perfusion

MR Diffusion or Brain Perfusion

Insurance Coverage for Physiologic Imaging of the Brain

CT and MRI exams, especially those done as an emergency, are usually covered by insurance. Please contact your insurance company to check your coverage for these exams and emergency room visits.

Exam Locations

Physiologic imaging of the brain is performed by Invision Sally Jobe radiologists at the following Invision Sally Jobe partner hospitals:

Please note:

Invision Sally Jobe is partially owned by Radiology Imaging Associates (RIA); consequently, your radiologist’s lab coat and your bill, if you receive one, will say RIA rather than Invision Sally Jobe.

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What to Expect During Your Exam

After answering any questions you have, a technologist will position you on a table. He or she will start an intravenous (IV) line in your arm. From here, experiences for CT and MR exams vary slightly.

CT Brain Perfusion

For a CT brain perfusion exam, you will be placed on the CT scanner table and your head will be moved into the machine. X-ray contrast medium will be administered through the IV. It is not unusual to feel a sensation of warmth in your chest, stomach and groin during the contrast injection. It is also possible that the contrast injection may cause you to experience a metallic taste in your mouth. These feelings dissipate once the injection is completed.

It is important to remain still during the CT exam to avoid blurring the pictures. The technologist will not stay in the room during the scan, but you can speak with him or her throughout the exam by intercom. The exam typically takes less than 15 minutes to complete.

MR Diffusion or Brain Perfusion

For an MRI diffusion or perfusion exam, you will be placed on the MRI scanner table and you will be moved into the machine so that your head is in the center. MRI contrast medium will be administered through the IV. It is possible that you will feel some warmth from the injection of the contrast; however, it is more likely that you will feel coolness in the arm with the IV. This dissipates as soon as the injection is complete.

It is very important to remain still during the MRI exam to avoid blurring the pictures. The technologist will not stay in the room during the scan, but you can speak with him or her throughout the exam by intercom. The exam typically takes less than 30 minutes to complete.

Getting Your Exam Results

CT and MR physiologic brain studies are interpreted by radiologists who are specially trained in the interpretation of these types of exams. They review the images as soon as they are acquired and report the results immediately to the emergency room physician and members of the stroke alert team. This allows for the most appropriate course of treatment to begin as quickly as possible.

CT perfusion image of the brain MR diffusion image of a brain suffering a stroke