CT Scan

 

Computed Tomography (CT) is an X-ray examination performed with a computerised X-ray scanning machine.

The CT scan looks at the body in cross section. Images are produced by a narrow beam of x-rays rotating around the part of your body that is being examined. The X-ray beam is monitored and recorded by an array of sensitive detectors which channel the signals to a large computer within the scanner. The computer then generates a visible image of the cross section of the body region being examined.

Preparation

The following CT scans require NO preparation:

  • Spine (cervical, thoracic, lumbosacral)
  • Extremity (hand, wrist, elbow, shoulder, hip, knee, ankle, foot)
  • Kidneys-Ureter-Bladder – “KUB” (looking for kidney stones)
  • Sinus/Facial Bones
  • Dental/Dentascan
  • Most brain scans
  • HRCT Chest (note: If a standard CT chest or CTPA is also requested, these latter two require X-ray dye and    hence the need to fast for 4 hours)

Unless otherwise specified at the time of booking, the following scans need X-ray dye (also known as contrast – see below) and therefore require fasting for 3 hours prior to the examination:

  • Neck
  • Chest
  • Abdomen and Pelvis (also must arrive 30 minutes before appointment to drink 1L of water).
  • This include CT examinations dedicated to liver (“triphasic liver”), pancreas and kidneys scans
  • All Angiograms

If you are to undergo an examination that requires X-ray dye in conjunction with another that does not (for example, a CT of the lumbar spine and CT of the abdomen and pelvis), then you must also fast for three hours.

Patients who have poor kidney function (renal impairment) will often not be given contrast so as not to worsen the condition. Diabetic patients who are to undergo a CT with contrast must let the clinic know if they are taking medications for their diabetes eg. Metformin. If this is the case, you will be given special instructions.

Information for female patients

If you are pregnant, or it is possible that you may be pregnant, then a CT scan is usually not performed unless it is an absolute medical necessity to do so. It is possible that another type of scan may provide provide similar information and therefore be used as a substitute. Please inform our clinic if this situation applies to you.

Procedure

  • Patients undergoing a CT angiogram, CT of the neck, chest, abdomen, pelvis and spine will be asked to be changed into a gown. Patients undergoing a brain, dental, facial bones, sinus, wrist, elbow, foot, ankle or  knee CT scan may not need to change.
  • You will then lie down on a bed that will position you within the scanner. You must lie still during the scan as movement will blur the images.
  • A series of planning scans will be performed at the start which will localise which body part is to be imaged.  The main part of the scan, which is when the images used for diagnosis are obtained, then follows and is  usually over within a minute or two, sometimes within several seconds.

Depending on your examination, you may be asked by an automated voice to hold your breath. An injection of X-ray dye or contrast may need to be administered through a small plastic cannula which has been inserted into a vein in your arm.

Contrast

If you are to be given contrast, you will be provided with an information sheet detailing the risks and benefits of the dye. This is then followed up by a brief questionnaire and patient consent. The contrast can provide valuable information by highlighting certain organs and blood vessels on the CT images. During the injection you may notice a brief sensation of warmth and a medicinal taste or smell. These subside rapidly.

All patients who have been administered dye need to wait for 10-15 minutes before leaving, in case there is a small chance of a delayed allergic reaction. Patients not administered contrast may leave immediately. Once you leave the clinic, you may resume normal activities and diet.

Please be sure to bring along any previous X-rays, CT scans, ultrasound or MRI examinations which you may have available. These films can often provide valuable additional information to our Radiologist.