A Detailed Look Inside the Human Body

Simple, safe, and swift...Computed Tomography (or CT scanning) is a common radiologic test that has revolutionized the way doctors diagnose and evaluate diseases, examine abnormalities, and detect internal damage. CT scanning provides an unparalleled window to the inside of the body by combining X-rays and computers. Using a highly focused X-ray beam, CT scans create a set of wafer-thin, cross-sectional images of the body’s internal organs, tissues, and structures--much like slices of bread. Accurate to within millimeters in resolution, these 2-dimensional X-ray images are displayed in 3-D on a computer screen for in-depth clinical evaluations.

Unmatched for detail, speed, and consistency, CT scanning is a vital tool in the diagnosis and management of a host of medical problems. At  Bryn Mawr, Lankenau, and Paoli Hospitals and at the Main Line Health Centers in Exton and Lawrence Park, Main Line Health Imaging utilizes GE LightSpeed 16-Slice CT Scanners—the most powerful, sophisticated and patient-friendly devices of their kind available today. Unlike the early CT scanners that required patients to lie still for long periods, these newer devices can complete a head-to-toe body scan in just 90 seconds (compared with 30 minutes on older machines)! Even patients who are critically ill, in pain, are very young, or have trouble holding still can undergo successful scans. The test is completely painless (although patients having certain studies may be injected with or be asked to drink a contrast material).

Data from the CT scanners is sent electronically to radiology reading rooms at the three hospitals for every study. Through our Picture Archiving and Communications System (PACS) all Main Line Health hospitals and outpatient centers are digitally interconnected, allowing radiologists across the Main Line Health sytem to consult with each other to make the most accurate diagnosis.

In addition, many CT scans require intravenous contrast. For these scans, a technologist or nurse must place an IV before the examination. During the scanning, iodine containing contrast is injected through the IV. This IV contrast provides a dramatic improvement in overall quality of the CT images, particularly when evaluating the abdominal organs such as the liver, pancreas, and kidneys. Intravenous contrast is also often used for CT scanning of the neck, chest, pelvis, and head.  While scanning of these areas can be done without the IV contrast, the lack of contrast limits the quality of these scans.

• There is a potential risk of damage to the kidneys in patients with renal insufficiency. The risk of damage is small but real and increases with the severity of pre-existing kidney disease. For these patients, a recent creatinine blood test may be required before the CT examination. For high-risk patients, the radiologist (often in consultation with the referring doctor) makes a decision whether to administer or withhold the IV contrast.

• Intravenous contrast rarely can cause an allergic response in the patient. When it occurs, it is usually mild, such as itching or hives. (Flushing or warmth during the injection is normal and is not considered an allergic reaction.) Very rarely, an acute allergic reaction may occur. In these instances, there is often a history of a previous mild allergic reaction where the body became “sensitized” to the contrast agent. Therefore, if you have ever experienced a reaction to the IV contrast, you should inform your doctor before the scan. CT technologists also routinely ask patients about a prior contrast reaction before the scan. If you do experience an allergic reaction, even a mild one, you must take great care in the future to inform your doctor before having any other IV contrast injection that contains iodinated contrast.

• For patients that have had an allergic contrast reaction in the past, pre-medication with a short-term immunosuppressant can greatly reduce the risk of another (and possibly more severe) contrast reaction. This pre-medication preparation consists of 3 divided doses of oral steroid (Prednisone) given for 24 hours before the IV contrast injection. Your doctor will write you a prescription for the medication with more detailed instructions.

• The oral anti-diabetic agent Glucophage poses a special problem. There is a known risk of delayed allergic response for 48 hours after having the IV iodinated contrast injection, and the Glucophage must not be taken for these two days. The CT technologist will also ask you if you take Glucophage before the IV injection.