Computed tomography (CT) scan / Computerized axial tomography (CAT) scan
A CT or CAT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce horizontal, or axial, images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, organs, and blood vessels. CT scans are more detailed than standard X-rays.
In standard X-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can be obtained from a regular X-ray, a lot of detail about internal organs and other structures is not available.
In CT, the X-ray beam moves in a circle around the body. This allows many different views of the same organ or structure and provides much greater detail. The X-ray information is sent to a computer that interprets the X-ray data and displays it in two-dimensional form on a monitor. Newer technology and computer software makes three-dimensional (3-D) images possible.
CT scans may be done with or without contrast. "Contrast" refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require the patient to fast for a certain period of time before the procedure. A doctor will notify the patient of this prior to the procedure.
CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage.
Research shows CT screening may detect lung cancer in its earliest and most treatable stages. When it’s found early, lung cancer has cure rates of up to 92 percent.
Lung cancer screening uses low-dose computed tomography (CT) with reduced radiation to identify lung nodules, some of which may be cancerous. CT or CAT (computerized axial tomography) scans are more likely than routine chest X-rays to show lung tumors.
Preparing for a CT scan
To prepare for a CT scan, Northwell suggests the following:
- If a patient has diabetes, the patient should have his or her recent (six months or less) BUN and Creatinine levels available.
- If the patient is currently taking Metformin (ex: Glulcophage, Glucovance, Avandammet, Metaglip), he or she should notify the location where they will receive the exam at least three days in advance for special instructions.
- If the patient requires iodinated contrast for the CT scan, Metformin should not be taken for 48 hours following the contrast injection. The patient’s doctor must recheck blood levels of BUN and Creatinine before the patient restarts medication.
- If a patient is allergic to iodinated contrast (iodine dye) or has a history of multiple allergic reactions, he or she should notify the office where they will receive the CT scan at least three days in advance for special instructions.
Preparations for specific types of CT scans include:
- Coronary CTA - No coffee, tea, Viagra, Levitra, or Cialis for 12 hours before study. No food three hours before study. Patients should drink two to three glasses of water prior to arrival.
- Cardiac calcium scoring - No caffeine on day of exam.
- CT with injected/IV contrast - No food four hours before study. Patients should drink two to three glasses of water prior to arrival.
- CT without injected/IV contrast - No preparation required.