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CAT (computer aided tomography) scan is a machine that uses a moving x-ray tube and detectors to send information to a computer which reconstructs an image that looks like a cross sectional “slice” through the body. The CAT scan machine is only able to take pictures in the axial plane, but coronal, sagital and 3D images are able to be reconstructed. CAT scan is best for imaging chest, abdomen, and bony structures. For most exams the patient lies on their back with arms resting on the pillow above their head. Many exams require the patient to hold their breath for usually no longer than 15 seconds. Exam times are relatively short and therefore are not as sensitive to motion as MRI. However, movement and metal both still cause image degradation.
Exams that are commonly done at our facility are:
- Sinus/Facial bones
- Chest/Pulmonary Angio
- Extremities (elbow, knees, etc.)
- Virtual colonography
- Bone Mineral Density (BMD)
- Biopsy/Abscess aspiration
Some CAT scans are done with oral or IV contrast, or both. When contrast is used it is asked that you be fasting before the exam (follow the instructions given for your specific exam). Oral contrast follows the path of the digestive tract while IV contrast is injected into a vein and travels everywhere there is blood supply. This greatly improves the ability of the radiologist to visualize pathology and helps make an accurate diagnosis. Oral contrast can be the white barium that is drank the night before the exam or gastrographin which is used in more emergent cases.
IV contrast is an iodine based contrast that is injected into the bloodstream. Before receiving this contrast every patient is required to fill out a consent form (see below) which asks about allergies and various medical conditions. It is very important to inform your doctor if you are allergic to iodine or if you have ever had an allergic reaction where you have had difficulty breathing or swelling of the mouth or throat. If you have had these symptoms your doctor will need to prescribe pills for you to take to prevent an allergic reaction during the CAT scan. Also, if you have asthma and use an inhaler it is important that you bring it with you to the appointment in case of an asthma attack. (If you do not bring your inhaler, you will be required to be premedicated which means you will have to be rescheduled.)