What is the procedure?
CT (Computed Tomography, commonly called a Cat Scan) imaging uses a ring shaped x-ray detector to obtain x-ray images of the body at multiple angles around the body. Using complex mathematical reconstructions, a computer is then able to create a cross-sectional image (tomogram) of the body, much like a slice through the body. The computer generates multiple images, slices which could be stacked up to recreate the whole region scanned.

The interpreting radiologist then reviews the images at a digital workstation, dictating a report which is provided to the ordering physician.

What are some common uses for the procedure?
Extremity CT is most often used for assessment of bony abnormalities, usually bony injuries. This provides much better evaluation of complex anatomy and fractures than routine x-rays. It can also be used for assessment of joints, arthritis, or even to find loose bodies (bone or cartilage fragments) within joints.

For soft tissue masses, infections, or tumors, MRI generally provides better soft tissue discrimination, but some patients are not candidates for MRI (claustrophobia, pain or excessive motion during the longer MRI exam, metallic devices such as pacemakers which are incompatible with the MRI magnet). In these instances, CT can be used.

How should I prepare for the procedure?
The procedure doesn't require any specific pre-procedural preparation.

What does the equipment look like?
The CT scanner is a ring of imaging equipment inside a square block-like housing which contains electronics, the x-ray generator and detectors, and the mechanical instrumentation to move the imaging components. The apparatus is relatively like a square doughnut. The patient lays on a cart or table which slides into the x-ray ring, but the ring is relatively thin and open at both ends so it should not present any problems for claustrophobic patients.

How is the procedure performed?

•  Imaging is generally done with the patient lying on his/her back, occasionally on the side or stomach for certain areas. Motion obscures detail on the pictures, and so your cooperation will be necessary. You will be asked to lie completely still. The technologist will be able to see and hear you and also speak to you throughout the exam.

•  Most extremity CT's do not require contrast (x-ray dye) which is given intravenously. However, if the exam is assessing soft tissue questions, contrast may be utilized. If this is necessary, an IV will be placed before the exam to allow injection, most frequently in front of the elbow.

•  Some joint exams require placement or contrast and/or air into joints to allow better visualization of the joint lining and contents. This is done in a separate x-ray procedure room immediately preceding the CT. Under x-ray guidance, following sterilization of the area and local anesthetic (numbing), a needle is advanced into the joint and injection is performed followed by removal of the needle. Any injected air or contrast is absorbed naturally in the coming hours. Allergies, as noted above, are much more rare with contrast in joints than in the bloodstream.

What should I expect during the procedure?
While the unit is scanning the images, the CT gantry rotates in a circle to allow the x-ray tube to image from all angles. There is whirring and clicking in the CT unit while the tube is rotating for the pictures. The table will slowly slide through the ring to allow the machine to cover the necessary segment of the body.
If contrast is used, this can normally cause a warm flushing feeling through the body and a metallic taste in the mouth.

What are the benefits and risks?

Benefits:

CT scanning of the extremities provides excellent anatomic detail to assist orthopedic evaluation. Complicated fractures can be thoroughly evaluated to allow appropriate surgical planning for fixation, or to assess adequacy of fixation. Joint relationships and contents can be studied.

Risks:

The radiation dose for this exam is about 2-4mSv (milliSievert). Over about one year, most people would get equivalent radiation exposure from natural background radiation. Radiation exposure should be limited during pregnancy.
Allergic reactions to contrast can occur, rarely severe ones. Trained physicians and nurses with necessary medications and equipment will be available to treat any reaction.

What are the limitations of the procedure?
CT has limited ability to distinguish between soft tissue types, making it less optimal for assessment of soft tissue masses, infection, etc, although it can be useful if the patient is incompatible for MRI.