Prepare for Procedure

Prepare for a Procedure

Carotid Doppler Ultrasound
This is another ultrasound test similar to Transcranial Doppler, but uses a different machine to study the carotid artery in the neck. Since carotid artery disease in the neck is a significant but treatable cause for stroke, accurate detection and measurement of narrowing in this vessel is an important part of vascular evaluation. Ultrasound is a simple, non-invasive test that can give estimates of the degree of narrowing. In some patients who do not require intervention, repeated ultrasound measurements may be recommended to follow for progressive changes from year to year. No preparation is required for this test.

Cerebral Angiography
Cerebral angiography is considered the “gold standard” in the assessment of cerebral vessels. It produces very detailed pictures of the arteries in the neck and inside the head, and is useful in determining the layout of an aneurysm or an AVM, and can show subtle changes in the arteries in conditions like vasculitis or arterial dissection. Cerebral angiography can reveal abnormalities that can be easily missed by other non-invasive studies.

The disadvantage of cerebral angiography is that it is invasive and carries a small degree of risk. At Johns Hopkins, however, cerebral angiography is performed by highly-specialized neuroradiologists who are extensively experienced in this technique. As a result, the complication rate from cerebral angiography has been exceedingly low, even in patients with extensive vascular disease.

Patients will meet with the neuroradiologist immediately prior to the procedure. An intravenous sedative is administered after the patient has been positioned on the back on the x-ray table. The neuroradiologist then will give an injection of a local anesthetic into the groin. With the injection, the patient will feel a slight pressure and burning. A small incision is then made to allow passage of a small, flexible tube called a catheter through the skin into the femoral artery in the groin.

The catheter will be guided painlessly into the vessels to be examined. Passage of the catheter from one position to another within the blood vessels is performed with the aid of an x-ray system, called fluoroscopy, which provides a television-like viewing of the inside of the body.

After the catheter is positioned within a specific blood vessel, x-rays are taken while x-ray dye is injected through the catheter. At this time, the patient will notice a very warm feeling lasting approximately ten to twenty seconds. At the same time the patient experiences the warm feeling, the patient will also hear noise as the x-ray machine takes pictures of the dye's passage through the blood vessels. It is very important that the patient remain motionless during this process.

Although the length of the picture-taking process can be as brief as fifteen minutes, the actual time it takes will depend on the number of blood vessels that need to be examined. Most patients can anticipate lying on the x-ray table for one to two hours.

At the end of the test, the catheter will be removed. The blood vessel from which the catheter is removed must be compressed for ten to fifteen minutes until clotting at the entry site forms a firm seal to prevent leakage. The patient will feel the pressure as a member of the radiology team presses on this area. A small bandage will be placed on the site; no stitches are required.

The patient will stay in the Neuroradiology Department four to five hours after which the patient will be able to go home accompanied by a companion. Because of use of sedatives, the patient will not be able to drive home alone. The patient may want to bring a book or a radio with earphones to help pass the time. Written instructions for home care will be given to the patient before leaving the hospital.

The patient and family should inform the nurse or physician of any discomfort or unusual symptoms during or after the procedure. After the test, the injection site may be tender and bruised. Ice packs may be applied and the leg elevated with a pillow to ease discomfort.

Although the test has proven safe, the patient's physician will discuss possible complications prior to the procedure. Again, if the patient has allergies or is sensitive to drugs such as sleeping pills, barbiturates, local anesthesia, x-ray dye, etc., the patient must inform nurses and doctors beforehand, so that they can be prepared to avoid complications.

Computed Tomography – CT Scan
Computed Tomography (CT or “CAT” scan) uses a rotating X-ray machine and computer reconstruction to produce pictures of the brain in a very short period of time. Current generation of CT scanners can scan the entire brain within minutes. In some patients, use of an iodine-based IV dye injection is helpful to improve the picture. Patients who are allergic to iodine or have allergic reactions to seafood should alert the technician and doctor. Patients with significant kidney disease should do so as well, since the dye can cause problems in patients with poor kidney function. CT angiography is a technique where IV dye is also used, but to show pictures of the arteries. In general, no preparation is required for this test. For patients with iodine allergy or kidney disease who require IV dye, your doctor may prescribe specific medications before and after the CT scan.

Magnetic Resonance testing (MRI)
Magnetic Resonance Imaging (MRI) provides physicians a means by which a physician can see a patient's internal body structures without using x-rays. This technology enables physicians to detect developing diseases or abnormalities earlier than ever before. Basically, MRI involves a powerful but harmless magnetic field and radiowaves like the kind that transmit FM music. The combination of radiowaves and magnetic field produces very clear images of body structures such as the brain, the spine and other vital organs. Magnetic resonance angiography is a variant of MRI using the same machine, but to produce pictures of the arteries. Newer techniques, such as perfusion MRI, are increasingly being used in routine MRI studies.

What Kinds of Machines Are Used to Perform MRI? - The patient's scan will be performed in a room containing "the magnet." The MRI unit looks like a large box with an open-ended tunnel running through the middle. Many different kinds are in use, but they all work in the same way. The patient will be asked to lie on a comfortable, padded table that is gently moved into the opening of the magnet where the scanning is performed. Sometimes a "coil," which is really just a special radio receiver, will be placed around the body part being scanned (the patient's head or neck). The data from the scan is fed into computers which compose very clear pictures that the physician will use to make a diagnosis.

What Happens the Day of the Exam? - The patient should allow about two hours for the MRI exam, although most scans take an hour or less.

Unless the patient's doctor indicates otherwise, the patient can eat normally the day of the exam. The patient should not wear any makeup, since some brands contain metallic components. On arrival at the MRI center, the patient will be asked to put on a gown and to remove all personal possessions such as jewelry, wallet, car keys or metallic items such as dentures, pins, etc.

It's very important not to take anything that could be affected by a magnet into the examining room. For example, the information on credit cards could be erased if the patient has them in a pocket during the exam!

While the vast majority of people can undergo an MRI exam with no problems, some cannot. The radiologist or the staff at the MRI center will probably ask the patient questions like the following:

• Does the patient weigh more than 300 pounds?
• Can the patient lie flat for an extended period of time?
• Does the patient suffer from claustrophobia?
• Is the patient pregnant?
Since the MRI Scan involves the use of a powerful magnet, the patient will also be asked the following kinds of questions:
• Does the patient have any implanted devices such as a cardiac pacemaker, a cerebral aneurysm clip, a neurostimulator, or a hearing aid?
• Does the patient have any metal shrapnel in the body or any metal fragments in the eyes?
After providing all of the necessary information, the patient should feel free to air any concerns about the upcoming examination. Radiologists and their technologists expect questions and part of their job is answering them.

What Happens During the Actual Exam? - The patient will be escorted into the room containing the "magnet" by a technologist and will be asked to lie down on the padded table. The technologist will position the patient inside the magnet so that the appropriate part of the patient's body is ready to be scanned. During the exam, the patient will be able to talk with the people conducting the exam by means of an intercom and they will be able to watch the patient through a glass window.

The patient may hear very loud clanking and thumping sounds which the machine makes as the technologists adjust the radio frequencies and other controls. These sounds are completely normal.

Sometimes a radiologist, nurse, or technologist may come into the scanning room to inject an enhancement agent to help the radiologist interpret the pictures taken during the exam.

Side Effects - Since MRI uses harmless radiowaves and magnetization instead of x-rays, it is considered to be safer than other radiologic techniques. There are no known side effects. In cases where a dye injection is required for the study, the dye used is called gadolinium. Allergic reactions to gadolinium are rare.

Transcranial Doppler
Transcranial Doppler (TCD) is a non-invasive ultrasound test to study the blood flow inside the head. During the procedure, a small ultrasound device is placed over the temples (where the skull is thin) and over the back of the neck (where the spinal cord enters the skull) to sense flow in the major intracranial vessels. In special cases, the physician may request a contrast TCD study. Contrast TCD (“bubble” TCD) monitors blood flow in the head while microbubbles are injected into a vein in the arm. Appearance of microbubbles inside the head can be used to diagnose a patent foramen ovale. (The microbubbles are harmless and are quickly dissolved in the blood stream.). No preparation is required for this test.