Today's physicians have a tremendous number of tools at their disposal to help them see what may be going on inside a patient's brain. But the same set of tools that makes them more informed than ever before can make patients more intimidated than ever before. Understanding a little about the scans a doctor may ask for, and what to expect from each, can make the patient's experience a lot more comfortable. As with any medical test, tell your doctor if you may be pregnant before agreeing to any scan.
CT Scan
One of the oldest technologies neurologists still heavily use, the computerized tomography scan builds a cross-section of the brain by combining X-rays from many angles. The CT (sometimes called the CAT scan) is the first scan many doctors will order, because can be quick and inexpensive. Almost no preparation is necessary, and the patient can return to normal activity immediately afterward. A CT scan may reveal evidence of a stroke, a skull fracture, or bleeding in the brain. It does not show the blood vessels of the brain, so it's common for doctors to need further scans, whether or not the CT has revealed anything.
CT Scan with Angiography
A physician may order a head CT scan with angiography (medical personnel simply call it a "CT angio"), in order to see the arteries and veins of a patient's brain. This scan uses the same technology as the CT scan, but with a contrast dye injected into a vein, which allows vessels to appear on the CT image. This scan is growing rare, as other scans may provide a better image of brain vasculature, but some doctors still find it useful. It requires a bit more preparation than an ordinary CT scan. The doctor may ask the patient not to eat or drink for several hours before the scan.
MRI
The magnetic resonance imaging scan has become one of the most commonly ordered scans in the neurologist's toolbox. This scan uses magnets and radio waves to reveal detailed images of the brain. It can show many types of tissue in very high resolution, making it more informative than the CT scan for many conditions. Doctors will often spot something on a CT scan, and, once they know where to look, will order an MRI to see it in more detail. According to the National Institutes of Health, an MRI can help reveal the extent of a stroke, study tumors, and diagnose multiple sclerosis. Your doctor may ask you to avoid eating or drinking for four to six hours before the test, depending on the area being studied, and you can return to normal activity immediately afterward. For many MRIs, the patient enters a tube for the imaging, so those with a fear of close spaces will want to discuss the test with their doctor. Some patients take a sedative before a long MRI.
MRI With Contrast
Doctors may order an MRI with contrast in order to make blood vessels stand out more clearly in the image. The contrast dye is usually injected shortly before the test. This is common before surgery, helping doctors to plan their approach in as much detail as possible. According to the National Institutes of Health, the dye used for an MRI with contrast is very safe, rarely causes allergic reactions, and side effects are rare.
MRA
Magnetic resonance angiography, or MRA, is closely related to MRI and, for the patient, offers essentially the same experience. The radiologist will use the MRI machine to perform a different set of tests during the MRA. It provides the most comprehensive, realistic images of brain vasculature, so doctors often use it to study aneurysms in detail.
Invasive Angiography
A newer technique that goes by many names (neuro-angiography and neurovascular angiography are two common terms, although you'll hear nurses simply call it "angio"), invasive angiography is a more involved scan often done only during a hospital stay. For this test, a radiologist will insert a catheter through a patient's femoral artery, and use it to precisely administer dye while scanning her with a CT scanner. It shows vessels in great detail, and is sometimes used to help place a stent to keep a vessel open, or to plan repair of an aneurysm. The patient is sedated for this procedure. Patients should not eat or drink after midnight the day before the procedure, and should plan to spend a day under observation afterward.
PET Scan
A positron emission tomography scan can show doctors temperature patterns in the brain, and track how the tissues are actually metabolizing oxygen and glucose. The Cleveland Clinic states it is particularly useful in studying Alzheimer's disease and Parkinson's disease, as well as cancerous tumors. Newer machines can perform the PET scan and CT scan at the same time. Patients may be asked not to eat or drink for several hours before the scan, but can resume normal activity immediately afterward.
