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What are the risks associated with Cardiac CT?

Radiation Exposure:

Many Medical Imaging examinations involve exposure to ionsing radiation. The radiation exposure (dose) of a dual source Cardiac CT varies depending on the chest volume scanned, your weight/build and your heart rate at the time of the scan, as well as whether any functional imaging is required by your Doctor. At San Radiology the radiation dose will range for a Cardiac CT from 0.06 - 5mSv, with an average recorded dose of approximately 2mSv.

In comparison the:

  • Natural annual background radiation exposure in Australia is 1.5mSv
  • The radiation exposure for invasive coronary catheter angiography is in the range of 3-8 mSv

There is a theoretical risk of any medical radiation causing cancer later in a person’s life. This risk has to be weighed up against the benefits of the examination and also the “natural” incidence/risk of developing cancer. The latter is usually several hundred to thousand times higher than the risk of developing cancer from CT. This risk is higher for younger patients (because they live for a longer period of time before they would otherwise succumb to unrelated causes). In order to limit any potential risk to an individual, it is recommended to avoid Cardiac CT under the age of 45 unless there is a strong indication to undergo the examination.

X-ray Dye:

All intravenous (IV) contrast agents for CT contain iodine (including non-ionic dyes). Like any medical substance, IV contrast may cause an allergic reaction. Reactions will vary from a transient skin rash or asthma to severe anaphylaxis. Severe reactions occur in less than 1:10000 cases. Being located in a hospital, San Radiology is fully equipped to instantly respond to any allergic reaction with high-level medical and nursing care. Minor side effects of IV contrast may include a hot flush, metallic taste, sneezing and nausea. These side effects usually resolve within seconds or minutes following onset.

Viagra:

Viagra or similar substances must be withheld for 48 hours prior to a Cardiac CT as it may interact with the nitrate spray administered during the scan and lead to a drop in blood pressure.

Betablockers:

Depending on your heart rate on the day of the examination you may be given beta-blocker medication to slow your heart rate down (to minimise CT radiation exposure). In order to avoid any side effects you will be asked whether you take other regular medications and to provide a brief history of any abnormal heart rhythms or illnesses (e.g. Asthma) which may be a contraindication.

Precautions:

If you suffer from impaired kidney function, there is a potential risk of worsening the kidney function with administering IV contrast. Usually this effect is temporary, however, with marked kidney impairment contrast administration should be avoided. In addition, diabetes, multiple myeloma, polycythaemia vera, phaeochromocytoma, heart disease or asthma may also be contraindications to IV contrast administration and should be discussed with your doctor prior to your scan.

Why dual source CT?

The ability to obtain sharp pictures of the heart blood vessels (coronary arteries) depends largely on true temporal resolution (similar to the “shutter speed” in a camera). The better the temporal resolution the better the ability to freeze the heart motion. This can be achieved by increasing the speed at which the CT tube rotates around a patient by increasing the number of CT tubes producing the images per rotation. Dual Source CT (dual = two tubes) improves the temporal resolution by a factor of 2 over a Single Source CT. At San Radiology the Siemens FORCE CT (384-slice) is a Dual Source CT which enables us to scan patients at any heart rate, including irregular heart rhythms (e.g. Atrial fibrillation), which is usually not often achievable with most Single Source CT machines.

Does this mean I am exposed to twice the radiation?

No. Because the information from both tubes adds up to one image, each tube emits only enough radiation to produce one combined diagnostic picture. In fact, Dual Source CT is proven to expose patients to much lower radiation dose in the normal heart rate range.

Is a CT with "more slices" better?

The number of slices produced by a CT per rotation is similar to increasing the angle of a lens on a film camera. The larger the number of the slices the larger the volume of the heart captured per rotation. With lower slice numbers (16-64), multiple pictures of the heart are combined to produce an image of the whole heart (like a collage). At San Radiology the Siemens FORCE is a 384 slice scanner which enables the whole heart volume to be captured in a single rotation, which coupled with the superior temporal resolution enables extremely high quality diagnostic images of a heart and its blood supply.

 

Booking a Cardiac CT

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