Computerized tomography (CT) uses a combination of x-ray techniques and computer technology to provide highly detailed images of internal structures. The CT scanner uses an x-ray source similar to that used to obtain ordinary chest x-rays, however, the x-ray beam is so tightly focused that portions of the body outside of the scanned region get relatively little x-ray exposure.
The CT scanner acquires multiple thin “slices” through the portion of the body requested. Depending on the part of the body scanned, between 20 and 1000 separate slices will be generated. Most studies are completed within about 5 to 10 minutes. The acquired information is processed by a computer and then made available to the radiologist for interpretation. The results are then sent to the referring physician.
CT Contraindications & Screening
Patients who are pregnant or could be pregnant will have to discuss with their referring physician and one of our radiologists whether or not they should have this exam.
For certain CT studies, the use of intravenous dye (contrast) is required. Patients meeting the conditions listed below will need to have their BUN and creatinine (blood test) measured before they can be scanned. Patients that are:
•over 60 years of age
•have chronic kidney disease – including nephrectomy patients
•long-term daily users of nephrotoxic medicines including NSAIDS (Aleve, Advil, Motrin, Anaprox, Naprosyn).
•receiving or have received Chemotherapy within the last 6 months – if taking Platinol and Cisplatin, bloodwork must be drawn within 1 week of the CT scan
•Multiple Myeloma patients
All tests for these patients must be performed during the 6-weeks prior to the scheduled CT exam. Patients currently receiving Platinol and Cisplatin will need to take the renal function tests within one week of the exam. Patients with renal failure undergoing dialysis do not require renal function tests.
There is usually no preparation required unless the CT scan is of the Abdomen or Pelvis. For those studies, the patient must obtain two doses of oral contrast and a prep sheet with instructions for the exam from the University Radiology Group. After arriving at our office for the exam, the patient will receive an additional dose of oral contrast. This oral contrast improves the visualization of the bowel on CT studies.
Frequently, CT requires IV contrast for an optimum study. For those CT examinations, a non-ionic contrast agent is injected intravenously to aid in diagnosis. If the patient has a very strong allergic history or has experienced a reaction to contrast material during a previous study, the patient should be premedicated on the day before the CT exam. The intravenous dyes help evaluate the blood vessels and highlights regions of abnormality.