How it works: CT Perfusion evaluates how well blood is flowing to the brain. A small bolus of iodine based intravenous contrast is injected rapidly through a vein, and then multiple low dose CT scans are taken through the same area of the brain to evaluate how the contrast bolus flows through a portion of the brain over time. The data is then processed with advanced perfusion software.
Equipment: Perfusion studies are usually performed on a Philips 64 or 256 channel CT scanner. OHSU is an ACR accredited CT facility.
Benefits: CT Perfusion is a fast, minimally invasive method of evaluating cerebral perfusion. Reasons for the exam include evaluation of brain perfusion after stroke, temporary ischemic attack (TIA), and/or occlusion or narrowing of a major intracranial vessel.
Exam Preparation: Preparation for a CT perfusion study is the same as for a CT angiogram study. The technologist will interview you for contraindications to contrast such as allergy or kidney problems. If you have had an allergy to iodine based contrast in the past, you should discuss this with your physician before the study. In some situations, an alternative imaging method may be considered, or you may receive medication that needs to be taken before the study to reduce your risk of reaction. In some situations, kidney function labs may also be checked before your study. An IV will be placed, usually in the arm.
What to Expect: Once you are positioned on the table and the contrast injector tubing is attached to your IV, a localizer scan will be taken, which takes a few seconds. The actual perfusion scan then takes 50 seconds. It is very important that your head remains still during the scan time. The technologist will check the images before you leave the room. In some situations, a non contrast CT or CTA study will be performed first. If a CTA is performed first, you will have to wait about 10 minutes between CTA and perfusion scans, to let the first bolus of contrast dissipate. After you have left, the perfusion data will be processed and analyzed, and a board certified neuroradiologist will review the study.
Adverse reactions to contrast materials are uncommon, but can range from mild to severe. Severe reactions are very uncommon. Further information about the risks and benefits of x-rays and contrast material can be found at http://www.radiologyinfo.org/en/safety/index.cfm
Recent FDA publications have warned of the risks associated with high x-ray doses administered during CT perfusion exams at certain facilities. OHSU uses the latest technology to reduce the x-ray exposure as much as possible while maintaining a high quality examination.
Radiology 2004; 231:632-644