Computerized tomography (CT) scanning uses special X-ray technology to obtain image data from different angles around the body and then uses computer processing of the information to show a cross section of body tissues and organs. Radiologists interpreting the images can then view the organs in cross section. In addition, some studies will be performed with computer-generated, three-dimensional images of the organ systems to give added information. This type of three-dimensional imaging is typically done to view vessels, bones or particular organ systems such as the liver or kidneys. CT technology has advanced to the point that it is possible to use computer reconstruction of the coronary arteries to give physicians important information about coronary artery disease.
At Lahey, we are constantly updating our technology to bring patients state-of-the-art equipment that offers the most efficient and accurate diagnostic imaging studies possible. With the latest in CT technology, we can now scan the body in less than one minute. Some patients, however, require more complex studies entailing multiple scans. The total amount of time a patient might spend on the CT table for one of the more complex studies could be a total of 30 minutes, although most studies are completed in 15 to 20 minutes.
Your doctor might request a CT scan to better determine the cause of symptoms you are having. CT imaging gives a very detailed look at the internal structures and can help with rapid diagnosis of infection, tumors, inflammatory processes or abnormalities involving vessels. CT's ability to give rapid and accurate information about the body also makes it very useful in the evaluation of trauma-related injuries. Both soft tissue and bone injuries, as well as vascular injuries, can be evaluated with CT.
CT imaging is painless. Depending on the type of scan to be performed, the radiologist could request that you drink contrast material prior to the scan to allow for better visualization of your gastrointestinal tract. This is typically done for evaluations of the abdominal and/or pelvic cavity. In addition, many of the CT studies are performed with the benefit of intravenous contrast, or dye, as it permits better visualization of the internal organs and vessels and gives added information to assist in the diagnosis of your condition. The contrast is injected through an intravenous line that the technologist will place in your arm prior to the study. Patients commonly experience a slight burning sensation in the arm as the dye is injected. Patients also commonly experience a flushed feeling, or even momentary nausea and a metallic taste in the mouth. These are normal side effects that pass after a moment or two. During the scan you will be asked to lie still, and you may need to hold your breath for a brief period. The technologist will work with you to keep you comfortable while taking the best possible images.
We ask all patients to let us know about any allergies they might have. If you know you are allergic to IV contrast or iodine, please tell your doctor so that you can be given a special preparation before your exam in order to have IV contrast given to you safely. If during or just after the injection of IV contrast you experience sneezing, vomiting, itching or hives, please alert the technologist so that treatment can be given immediately. If you experience minor symptoms, the doctor could keep you for a short period of observation. Rarely, some patients may experience a more severe reaction and develop difficulty breathing. This could be a life-threatening reaction, and again, alerting the technologist immediately is very important so the test can be stopped and appropriate treatment can be provided.
Patients taking certain glucose lowering medications such as Glucophage or another metformin preparation may need to have special lab tests ordered or medication adjustments if an IV contrast study is to be performed. Diabetic patients should discuss the procedure with their doctor prior to the exam so that the proper monitoring or medication adjustments can be arranged.
Since IV contrast is excreted by the kidneys, patients with kidney insufficiency or failure might require special hydration or dialysis for the IV contrast study to be performed safely. Alternatively, patients with kidney disease are occasionally not given IV contrast at all, when potential risks are felt to outweigh the benefits of contrast administration. Because of the potential impact of IV contrast on the kidneys, laboratory studies are often performed on patients prior to CT imaging, if such studies were not recently performed. This may lengthen the time that a patient spends in the department, but is often necessary to ensure that IV contrast can be given safely.
At Lahey, CT screening examinations are available to patients who are referred by their physicians. The exact tests performed depend on the patient and his or her medical history or concerns. CT body scanning can cover almost any part of the body, but the most frequent requests are for evaluations of the chest (for lung cancer), cardiac calcium screening (cardiac scoring), or abdominal and pelvic studies. Virtual colonoscopy is also available as a screening test. Some patients request head and neck CT imaging, which are also available. CT body scans at Lahey are often performed with IV contrast to enhance the sensitivity of the test for early detection of tumors or abnormalities. For that reason, it may be necessary to perform laboratory tests and place an intravenous line prior to the CT examination being performed. Although this may seem like an inconvenience to the patient, the increased sensitivity of the test with IV contrast is worth the extra preparation. These screening examinations are not yet considered standard for the general population. They are typically reserved for patients who are either at risk for underlying disease or have, in the view of their physicians, other reasons to undergo the test. For this reason, Lahey does not currently accept self-referrals. Instead, patients are encouraged to discuss the indications and possible risks of CT screening examinations with their doctors, who then may refer them to the Radiology Department.
This is a specialized CT examination of the chest that obtains images of the coronary arteries of the heart. Using a special interactive computer analysis, the images are reviewed for calcium in the walls of the coronary arteries. Although this study does not give anatomic information in the same way as the diagnostic arteriogram performed routinely by cardiologists, this information can be used in conjunction with other risk factors to determine an overall risk for heart disease. Patients should understand that this study is not currently reimbursed under Medicare or other health care plans and is typically billable directly to the patient.
This is a CT examination of the abdomen and pelvis that is performed in conjunction with insufflation of air into the colon. During the procedure, a tube is placed in the rectum while the patient is on the CT table, and air is cautiously administered via the tube to expand the colon. Then imaging is obtained with the patient lying both face down and also on his or her back. After the imaging is complete, the patient may leave the department. This test does require a special diet and oral preparation to ensure that the best possible images of the colon are obtained. Following the procedure, an extensive interactive analysis and special reconstruction of the images of the patient's colon are performed to create a "virtual colonoscopy." A radiologist then reviews these images to determine if there are any polyps or lesions of the colon. Unlike a traditional colonoscopy performed by a gastroenterologist, the virtual colonoscopy requires no sedation. Also, since the procedure is a computer-generated "virtual tour" of the colon that does not require putting any device inside the colon, polyps cannot be removed or biopsied during the virtual colonoscopy as they can during a traditional colonoscopy. For some patients-particularly those who are hesitant to have a traditional colonoscopy-this is an extremely useful screening tool in the detection of colon cancer.
Some drainage and biopsy procedures, which involve the removal of tissue from the body to establish a diagnosis, require imaging guidance to be performed accurately and safely. When an abnormality can be viewed well with CT imaging, it is often desirable to perform the procedure with CT guidance. This permits visual confirmation that the needle or medical device advances to the desired location. Depending on the nature of the procedure being performed, local anesthetic with or without conscious sedation will be given. The type of anesthesia will be discussed in advance with the patient. At the start of the exam, an initial CT image or series of images will be obtained so that the radiologist can plan the procedure's approach. The exam will then proceed in a step-by-step fashion, with the radiologist advancing the needle or medical device into the area to be biopsied while intermittently obtaining additional CT images. It is not unusual for the radiologist to check the area several times with additional CT images in order to ensure the accuracy and safety of the procedure.