CT (Computed Tomography) directs a beam of x-rays around the area of interest in a circular fashion. Some of the x-ray will be stopped (attenuated) by the body structures but some will pass through. The machine will detect the x-rays that have pass through and based on that will produce a map of tissue attenuation (approximately equal to density). Using this, very powerful computers and special software, images of the body part will be produced. Depending on the type and location of the scan, 3D images can also be obtained.
Some scans may require the use of intravenous radiographic contrast (X-ray dye). This specifically formulated agent is injected into a vein usually during or immediately before the scan. This is the same agent as used in angiograms. This contrast is used to opacify and highlight the vascular structures and other organs or tissues that have a good blood supply. As with all agents used in Medicine, there is a very small risk of an allergic reaction. Most of these will be minor requiring either no or simple treatments. More severe reaction can and do occur some of which may be life threatening but these are very rare.
The intravenous contrast agent is cleared from the body by the kidneys. If the kidneys are not working well, this can allow accumulation of the agent, which may be harmful. It is therefore important for the technician to be aware of any renal problems to adjust or possibly avoid intravenous contrast.
There can be a detrimental interaction between intravenous contrast and a particular diabetic medication; metformin. This drug is sold in Australia under the following trade names; Avandemet+, Diabex, Diabex XR, Diaformin, Diaformin XR, Formet, GenRx Metformin, Glucohexal, Glucomet, Glucophage, Glucovance+, Janumet+, Metex XR, Metforbell and Metformin-GA (this is not an exhaustive list and if there concern please contact us). Patients on this medication will be required to cease it for a short time after any imaging procedures using intravenous contrast.
During or immediately after the injection of contrast, there may be a warm flush feeling and or a funny metallic taste. This is a very common side effect of the contrast agent is not an allergic reaction. Very rarely nausea or vomiting can occur.
Some scans of the abdomen and pelvis may require the administration of oral contrast. This formulation contains a dilute iodine preparation or in the case of iodine or contrast allergy, a dilute barium solution can be substituted. The contrast is taken orally over 1 to 2 hours depending on the scan and patients will be asked to attend the practise earlier to accommodate this.
As with all radiation, there is a very small risk of harm. This risk however would need to weigh against the potential harm of not diagnosing or delaying the diagnosis of a medical condition. Your referring doctor would be aware of this when he/she ordered the scan.
At Lime Radiology, we use the latest GE CT scanners which have specifically been designed to reduce as much as possible the radiation dose whilst producing the very highest image quality scans. Our technicians are also always aware of dose considerations when they scan patients and adhere to the International Committee of Radiation Protection (ICRP) principle of As Low As Reasonably Achievable (ALARA).