Computed Tomography

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DURING THE CT & MRI ARTHROGRAM PERFORMED BY HILL MEDICAL

What does the equipment look like?

The equipment typically used for this examination consists of a CT table, an x-ray tube and a television-like monitor that is located in the examining room. Fluoroscopy, which converts x-rays into video images, is used to watch and guide progress of the procedure. The video is produced by the CT machine on fluoroscopy mode as the patient is lying down on the CT bed and passes through the machine.

The MRI unit is a large cylinder-shaped tube surrounded by a circular magnet. You will lie on a moveable examination table that slides into the center of the magnet.

The computer workstation that processes the imaging information is located in a separate room from the scanner.

Other equipment necessary for performing arthrography include a variety of needles, syringes and contrast material.

How does the procedure work?

Fluoroscopy uses a continuous or pulsed x-ray beam to create a sequence of images that are projected onto a fluorescent screen, or television-like monitor. When used with a contrast material, which clearly defines the area being examined by making it appear bright white, this special x-ray technique makes it possible for the physician to view joints or internal organs in motion. Still images are also captured and stored electronically on a computer.

Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not depend on ionizing radiation. Instead, while in the magnet, radio waves redirect the axes of spinning protons, which are the nuclei of hydrogen atoms, in a strong magnetic field.

The magnetic field is produced by passing an electric current through wire coils in most MRI units. Other coils, located in the machine and in some cases, placed around the part of the body being imaged, send and receive radio waves, producing signals that are detected by the coils.

A computer then processes the signals and generates a series of images each of which shows a thin slice of the body. The images can then be studied from different angles by the interpreting radiologist.

Frequently, the differentiation of abnormal (diseased) tissue from normal tissues is better with MRI than with other imaging modalities such as x-ray, CT and ultrasound.

How is the procedure performed?

The patient is positioned on the examination table and x-rays are taken of the joint to be compared later with the arthrograms. If recent x-rays are available, the physician may choose to use these for reference.

Next, the skin around the joint is cleansed with antiseptic and a local anesthetic is injected into the area.

Your physician will numb the area with a local anesthetic.

The area where the needle is to be inserted will be sterilized and covered with a surgical drape.

A needle is then inserted into the joint. The radiologist, a physician specifically trained to supervise and interpret radiology examinations, will use a syringe to inject the contrast material into the joint space and the needle is removed. The patient will be asked to move the affected joint to distribute the contrast material throughout the space.

The conventional arthrography exam is usually completed within 30 minutes. Exams involving MRI may take more than one hour.

What will I experience during the procedure?

You will experience a slight pinprick and may feel a momentary burning if a local anesthesia is used to numb the joint area.

You may feel a fullness as the joint is filled and hear gurgling when the joint is moved.

If your arthrography exam involves MR imaging:

It is normal for the area of your body being imaged to feel slightly warm, but if it bothers you, notify the radiologist or technologist. It is important that you remain perfectly still while the images are being recorded, which is typically only a few seconds to a few minutes at a time. For some types of exams, you may be asked to hold your breath. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that generate the radiofrequency pulses are activated. You will be able to relax between imaging sequences, but will be asked to maintain your position without movement as much as possible.

You will usually be alone in the exam room during the MRI procedure. However, the technologist will be able to see, hear and speak with you at all times using a two-way intercom. Many MRI centers allow a friend or parent to stay in the room as long as they are also screened for safety in the magnetic environment.You may be offered or you may request earplugs to reduce the noise of the MRI scanner, which produces loud thumping and humming noises during imaging.

When the contrast material is injected, it is normal to feel coolness and a flushing sensation for a minute or two. The intravenous needle may cause you some discomfort when it is inserted and once it is removed, you may experience some bruising. There is also a very small chance of irritation of your skin at the site of the IV tube insertion. Some patients may sense a metallic taste in their mouth after the contrast injection.


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