PET-CT SCAN

What is a PET scan?

PET stands for Positron Emission Tomography. PET imaging is a diagnostic imaging tool. PET imaging is a process

by which the biological functions of the body are scanned. By using a small amount of a biological marker, the PET scan procedure can assess areas of abnormal metabolism in the body. The workhorse tracer used in PET-CT imaging is a glucose (sugar) analogue abbreviated as ¹⁸F-FDG, which stands for fluorodeoxyglucose. As with regular sugar (glucose), cancers, especially fast-growing aggressive cancers, rely solely on sugar for energy. Similarly, infections (requiring more energy) take up more FDG than the surrounding normal tissues. The low-dose emitted radiation is detected using a special machine called a PET scanner.

We see this change in the glucose use in cancer before a physical change is seen on a CT or MRI scan. The latest advancements in imaging have combined the PET scan procedure with a CT scan (PET-CT), allowing areas of interest to be more accurately localized. We can also manually fuse PET to an MRI scan, especially of clinical use in children.

Other tracers utilizing the physical properties of 18F but with a different substrate (e.g. 18F-DOPA are available that bind to specific infective sites, cancers or tumours or to bone. We will inform you when using one of these other tracers.

It is helpful to help in the diagnosis of:

Oncology—to determine the location of tumours and the extent of tumour growth

Neurology—to aid in the diagnosis of Alzheimer’s disease, dementia, stroke, brain tumours and seizures

Cardiology—to determine the viability of the heart muscle

PET scan procedure:

At the beginning of the PET scan procedure, you will sit in a chair and receive an injection of a small amount of radioactive material called FDG in a vein in your arm. You will not feel differently at all.

You will be asked to sit quietly for a while, usually about 30-60 minutes.

During this time, you must sit and relax and will not get up and walk around, talk to friends, or read. This allows the tracer to travel throughout your body while it is in a relaxed state. Excessive movement, eye movement, vocal use, et cetera divert the FDG to areas it is not wanted, e.g., muscles.

You will lie down on a table that will move you through the PET-CT scanner. The machine has a larger opening than an MRI, and it does not make any significant sound. A PET-CT scan procedure takes about an hour to complete, excluding the report.

PET scan preparation & diet:

When scheduling a PET scan, it’s essential to remember that your physician will require you to follow a strict PET scan preparation diet up to 12 hours before your appointment. A typical PET scan diet is as follows:

12 hours before your procedure:
- Eat a low carbohydrate diet. Allowed foods include:
  - Meat
  - Hard cheese
  - Tofu
  - Eggs
  - Butter
  - Vegetables with no starch.
- Some foods that are NOT allowed include:
  - Cereal
  - Pasta
  - Milk
  - Bread
  - Sugar
- If you are scheduled in the late afternoon and can eat breakfast before the scan, it must be a low carbohydrate diet.
6 hours before your appointment:
- Stop eating 6 hours before your appointment; however, you may continue to drink water.
- Bring copies of any recent CT scans or MRI scans done outside of our unit—it is possible to fuse the PET data with the other imaging modalities.
If you have diabetes, please inform us on the day of your booking:
- You will also be required to fast.
- You may take a slice of toast on the morning of your test.
- You may use any oral anti-diabetic medications as long as you inform us of the fact.
- If you are insulin-dependent, you may use half your usual insulin dose.
- We will test your blood sugar before scanning. We will bring it under control before scanning if it is too high.

What can I expect to happen next?

Conventional PET-CT:

We will inject you with a low-dose radioactive tracer upon arrival in the unit. You will wait while the tissues take up the tracer – approximately 60-90 minutes. After that, we will scan you. This takes approximately 30 minutes.

A diabetic patient may require multiple insulin injections before tracer administration, as elevated blood sugar can affect the scan findings.

Cardiac viability study:

Glucose-rich (sugar-rich) meal is administered upon arrival to force the heart to use glucose instead of fatty acids for energy. Acipimox (a substance that prevents free fatty acid availability in the blood) and Aspirin (to control side effects to the Acipimox) are administered.

However, if you are allergic to Aspirin, the Acipimox can be administered alone. One hour later, another dose of Acipimox is given. We will then inject the tracer. Forty minutes after the tracer injection, we will perform a scan lasting approximately 30 minutes. After the study, the patient can eat again.

High blood glucose can cause spurious scan results. Diabetic patients may require multiple insulin injections until blood sugar is under control. Forty minutes afterwards, a scan of 30 minutes is performed. After the study, you may receive a meal.

Does insurance cover the cost of the test?

Medical schemes and private insurance companies usually cover PET-CT imaging, especially cancer staging. Medical schemes usually follow the prescribed minimum benefit guidelines. Still, many will cover other indications for a PET-CT scan either as part of the oncology benefit or the imaging benefit. Contact your insurance for further information. We can help motivate for the scan if needed.