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Computed tomography is better known as CT scan or CAT scan. CT scanning uses highly sophisticated x-ray equipment to obtain images that are essentially slices through the body. This is a highly effective way of “seeing inside the body”. CT scanners initially obtained images a slice at a time, and the process was fairly time consuming. Newer CT scanners, called multi-slice scanners, can acquire multiple slices at one time and can even acquire volume images. This allows us to look at pictures of the body in a variety of two-dimensional planes and even as three-dimensional images.
Clinical Radiologists has been at the forefront of CT scanning since its inception. Clinical Radiologists, at Memorial Medical Center in Springfield, used the second brain CT scanner operating in the United States. We also had one of the first body CT scanners in the country. We have continued to lead the way, introducing multislice scanning, three-dimensional imaging, and a variety of new applications, such as CT angiography and CT of the heart, to Central Illinois. We have also been leaders in electronic transmission of CT images, so that our radiologists in Springfield can view CT scans from any of our sites, any time, night or day.
All radiologists receive extensive training in interpretations of CT scans during their residencies. Clinical Radiologists has several radiologists with advanced fellowship training in CT of the nervous system; CT of the chest, abdomen and pelvis; CT of the heart and blood vessels; CT of the musculoskeletal system; and pediatric CT scanning.
What preparation is needed?
Some CT scans do not require any special preparation. For some examinations, you will be asked to fast prior to the CT scan. For some abdominal or pelvic CT scans you will be asked to drink water or an oral contrast agent. The oral contrast agent will allow us to evaluate the bowel and some other abdominal structures. Please visit our section on exam preparation for additional information.
What happens during the examination?
You will be positioned comfortably on the scanner table, usually on your back. The picture-taking portion of the scanner looks like a giant donut. The table will slide through the “donut” as images are obtained. For most CT scans you will be asked to hold your breath during the exam. You will need to hold as still as possible, since movement can result in poor quality images.
Many examinations will be performed with the injection of a contrast agent (x-ray dye) through an IV. The dye may cause a warm sensation throughout your body and a metallic taste. The contrast is safe, but reactions do rarely occur. If you have any discomfort other than a warm sensation and metallic taste, let the CT technologist know. The technologist will monitor the first part of the dye injection and will observe the entire exam from the adjacent control room. The contrast agent may not be safe for some patients with kidney disease; you will be given a questionnaire prior to receiving any x-ray dye. If necessary, you may be asked to have a blood test to check kidney function prior to receiving the dye. People taking some oral medicines for diabetes will be asked to withhold those medicines for 48 hours after receiving the contrast. If you have any questions or concerns regarding the contrast agent, ask the technologist or the radiologist can address any concerns.
CT angiography refers to the use of CT scanning to study arteries throughout the body. Clinical Radiologists has been performing CT angiography (CTA) for years and has performed thousands of CTA exams. We use CTA to investigate arteries in the head, neck, chest, heart, abdomen, pelvis and extremities. CTA can be used to investigate all types of arterial disease, including blockages, aneurysms, dissections, emboli (clots) and injuries from trauma.
For CTA, we inject a contrast agent (x-ray dye) into an IV and then perform a rapid CT scan of the area of interest at a time when the contrast agent is in the arteries. To a patient, the CTA exam feels like any other CT scan. After the scan, the radiologist will look at all the image data with powerful computers. The computers allow us to look at the image data as slices of the body (like regular CT scans) as well as making a variety of two dimensional and three dimensional pictures of the blood vessels.
CTA allows us to get information about arteries that was once available only by placing a catheter directly into the artery and injecting the dye into the artery. CTA can often give the same information with less cost, fewer risks/complications and less time in the radiology department and hospital.
Coronary artery CTA refers to the use of CTA to evaluate the arteries of the heart. Clinical Radiologists has radiologists with special training in CT of the heart and we have been performing CTA of the coronary arteries for several years. We were one of the first two groups in the state of Illinois to use 64 row CT scanners for performing coronary artery CTA and now have several of these scanners in our practice.
CORONARY ARTERY CALCIUM SCORING
Coronary artery calcium scoring refers to the use of CT scanning to evaluate the arteries of the heart for calcium. Calcium is found in some atherosclerotic plaques in the coronary arteries. (Atherosclerotic plaques cause what is sometimes referred to as “hardening of the arteries”.) Calcium scoring does not involve the injection of a contrast agent and does not give as much information as coronary artery CTA. However, it is useful in some situations. Clinical Radiologists was the first group in central Illinois to offer coronary calcium scoring.
CT Enterography (CTE) is a relatively new technique used to evaluate a variety of small bowel diseases, such as Crohn disease (inflammatory bowel disease), small bowel tumors, unexplained bleeding from the gastrointestinal tract, etc. CTE is most commonly used to evaluate patients with known or suspected Crohn disease. CTE is very helpful in determining whether patients with this condition have active disease (requiring specific treatment) or any complications of the disease.
CTE involves drinking a special, flavored oral contrast agent prior to the CT scan. CTE also involves injection of a contrast agent (x-ray dye) through an IV. To a patient, CTE feels like a routine CT scan.
Clinical Radiologists has several radiologists with advanced fellowship training in CT scanning and abdominal imaging with expertise in interpreting CTE exams.
CT Urography (CTU) is a relatively new and evolving technique for evaluating the urinary tract (kidneys, ureters and bladder), usually in patients with hematuria or patients with a history of tumors of the bladder or ureter.
CTU involves a CT scan of the abdomen and pelvis before and after administration of a contrast agent (x-ray dye) through an IV. To a patient, the exam feels like a regular CT scan. The radiologist then uses the image data to look for kidney stones, tumors, blockages, blood clots, etc., involving the urinary tract.
As you would expect, Clinical Radiologists has several radiologists with advanced fellowship training in CT scanning with expertise in interpreting CTU exams. Clinical Radiologists also has one of only a handful of radiologists in the state who belong to the Society of Uroradiologists (a national group of radiologists with a special interest in imaging the urinary tract).
CT COLONOGRAPHY (VIRTUAL COLONOSCOPY)
Colon cancer is the second most common cause of cancer deaths among both men and women in the United States. About 135,000 new cases of colorectal cancer will be detected each year and about 57,000 deaths are expected from the disease each year. The risk of developing colon cancer is increased in people with a family history of colon cancer in a first degree relative, patients with a personal history of colon cancer, polyps, inflammatory bowel disease and certain hereditary syndromes. Other risk factors include high fat and low fiber diets, obesity and inactivity, alcohol consumption, red meat consumption and possibly cigarette smoking. Over half of colon cancers occur in patients without a family history, inflammatory bowel disease or hereditary condition.
Most cancers of the colon arise from polyps. Polyps are small growths that arise from the lining of the colon and generally look like bumps sticking in the lumen of the colon. Polyps are uncommon in young people but are found more commonly as people age. Certain polyps, called adenomatous polyps, can increase in size and eventually become malignant tumors (cancers). The chance of cancer being found in a polyp seems to be directly related to the size of the polyp. Cancer is very rare in adenomatous polyps that are less than one centimeter in size but is seen in almost half of polyps that are 2.5 centimeters (one inch) in size. The process of polyp growth and development of cancer within a polyp is slow.
Because colon cancer is a common disease, and because it usually develops from slowly growing polyps, it seems reasonable that screening patients for colon polyps or small colon cancers may reduce the number of colon cancers and the number of patients dying from colon cancer. The American Cancer Society and other organizations have therefore developed guidelines for screening for colon cancers and polyps. Screening tests include flexible sigmoidoscopy or barium enema every 5 years or colonoscopy every 10 years beginning at age 50. Colonoscopy is generally acknowledged to be the best colorectal screening test. Colonoscopy allows detection of almost all polyps larger than one centimeter; polyps can also be removed at the time of colonoscopy.
CT colonography (CTC or virtual colonoscopy) is relatively new test that may be useful for colon screening. CT colonography refers to a CT scan of the abdomen and pelvis done after colon cleansing and distending the colon with air. The exam takes about 20 minutes. No sedation is needed. CT colonography can be performed in patients who cannot undergo colonoscopy because of various medical conditions, patients who are unable to schedule colonoscopy and those who prefer not have a colonoscopy. Screening of the colon with CT colonography is generally recommended only for patients with an average risk of developing colon polyps and cancer (no family or personal history, no hereditary disease predisposing to colon cancer, etc.)
CT colonography, like any other means of visualizing the colon, requires thorough cleansing of the colon, usually with dietary modification for a couple days, along with laxative agents. This cleansing or preparation of the colon is unpleasant, but necessary. CT colonography also requires the colon to be well distended with air. The distention of the colon will result in some pain during the course of the procedure, although a medication called glucagons will often be administered to try to minimize the discomfort.
CT colonography is quick and safe and patients can leave the x-ray department right after the exam.
If the CT colonography exam is negative, that is, no polyps are seen, then periodic screening with a repeat CT colonography in 5 years or with other tests like sigmoidoscopy, barium enema or colonoscopy, will be recommended. If the CT colonography exam shows a polyp above a certain size, then colonoscopy will be needed to biopsy or remove the polyp. In some cases some retained stool or a normal part of the colong may look like a polyp. In these cases, colonoscopy may be performed but no polyp be found. If a very small polyp is found, colonoscopy may not be needed, but a repeat CT colonography in only three years may be recommended. In about 12% of patients, the CT colonography exam will show an important finding unrelated to the colon, including things such as aneurysms, kidney masses, etc. These findings may require additional tests for complete evaluation.
We expect CT colonography to detect between 80% and 90% of one-centimeter polyps that would be detected by colonoscopy. In order to have the best possible exam, it is imperative to follow the instructions regarding diet and colon cleansing. The colon cleansing instructions must be followed completely; stool remaining in the colon can make the test impossible to perform or inaccurate to read. In order to have the best possible exam it is also imperative to have the colon as distended as possible. It is important to do your best to allow air to be put into the colon and to hold on to the air during the short time of the examination.
The CT colonography exam does not allow us to evaluate the lower rectum and anus. It is therefore important to have your doctor perform a rectal exam in order to evaluate those areas. CT colonography may be covered by insurance companies in some instances, such as when colonoscopy cannot be performed. However, most CT colonography exams performed for screening will not be covered by insurance and will be paid for by the patient.
Clinical Radiologists performs CT colonography in Springfield and Quincy. CT colonography is not available at our other sites.
Summary Points
- Almost all colon cancers develop from polyps. Removal of colon polyps one centimeter in size or larger is believed to significantly reduce the risk of colon cancer.
- CT colonography will not detect all colon polyps and masses. We expect CTC to show 80%-90% of one centimeter polyps that would be seen by colonoscopy.
- Stool and some normal structures can look like polyps at CTC. In some cases CTC will seem to show a polyp, but colonoscopy may be normal.
- It is VERY IMPORTANT to have a thoroughly cleansed colon for a quality CTC exam. You must follow all instructions regarding diet and laxatives and complete the full prep.
- It is VERY IMPORTANT to have the colon distended with air for CT colonography. Although it may be uncomfortable, do your best to let your colon be filled with air as much as possible.