CT uses x-rays to collect images of your heart which are then reconstructed to produce images of your arteries.
At North Shore Radiology, we have a powerful scanner which reduces radiation dose of up to 80% from the conventional scanner1.
The time for this examination varies depending on your heart rate, but most scans take 30 minutes. If your heart rate is too fast we may have to give you more preparation before the scan, and this can delay the time until we can do the scan. Please allow yourself plenty of time.
1 Prospectively Gated Axial CT Coronary Angiography: Preliminary Experiences With A Novel Low-Dose Technique. Klass O, Jeltsch M, Feuerlein S, Brunner H, Nagel HD, Walker MJ, Brambs HJ, Hoffmann MH., Eur Radiol. 2008, Nov 15.
We do ask you have someone accompany you and drive you to and from the examination, as this will help you arrive in a rested state.
As the heart moves, we need to collect data during the quiet time of heart activity, called diastole (when the heart is not pumping) as this provides the best images. We want your heart rate (pulse) to be slow, therefore we ask that you do not have any chocolate or drinks with caffeine (tea, coffee, fizzy drinks/coke etc.) for 12 hours before the test. You must also fast for 2 hours before your scan and ensure you are well hydrated with water.
We may arrange for you to take a drug called a β blocker the night before and the morning of the test or after you arrive for your appointment. This helps in slowing down your heart rate and enables a quality scan.
Please bring your previous relevant imaging, particularly CT’s. Details of your cardiac medications and previous heart surgery eg: by-passes, will be required.
Continue to take all usual medication.
Upon arrival you are taken to nurses’ trolley bay. You will have your blood pressure and heart rate measured.
If your heart rate is too fast, you may be given additional medication to slow it down.
You will be asked to fill out a questionnaire to make sure you are not allergic to the Intravenous Contrast (X-ray dye) we use for the CT and to check you have no other problems. You will also be asked to sign a consent for administration of the x-ray contrast. After you have entered the CT room, you will be positioned on the padded scanner table. This table will move you so that your heart is in the middle of the scanner. The radiographer controls the examination from a separate room next to the scanner. You will be able to talk to him/her at all times.
A needle will be placed in a vein, usually in the right arm to give the contrast (x-ray dye). A spray of glyceryl tri-nitrate will be given under your tongue to help dilate the coronary vessels and highlight these vessels for us to see.
It is important to let the staff know if you are on
- Cialis or
- Other similar medications
prior to the glyceryl tri-nitrate as it cannot safely be given with these drugs. Sometimes the spray may give you a short term headache.
Each scan will take only a few seconds to complete. You will be asked to hold your breath for the scans. It is important to obey any instructions given. During the scan you will be able to hear the sound of the machine moving around you.
Intravenous contrast (X-Ray dye) is used to show the arteries during the injection. You may feel slightly warm or have a flushing sensation, or have a metallic taste in the mouth. Some patients even briefly feel as though they have urinated. These sensations are normal and are no cause for concern.
Reactions to the dye are a very rare occurrence, but our staff are fully trained to provide the treatment required, should such a reaction occur.
The cannula in your arm will be removed by our nursing staff/radiographers and you will be able to change into your clothes. You should feel no after affects, and no further care is required after your examination has finished.
You may resume your normal diet immediately, and you are able to resume your normal activities, although we do ask that you avoid rigorous exercise for 24 hours following the test. Please also ensure you have someone with you to drive you home following the procedure.
The injection of intravenous contrast (X-Ray dye) you received is excreted through your urine over the next 24-48 hours following you test. We do suggest you increase your water intake over this period to assist the excretion of dye from your kidneys.
What About the Results?
The Radiologist and Cardiologist will study your films and prepare a written report. Please allow 2 working days for these results to be available.