PET CT

Positron Emission Tomography (PET) and Computerized Tomography (CT) are both standard imaging tools that allow physicians to pinpoint the location of cancer within the body before making treatment recommendations.

The highly sensitive PET scan detects the metabolic signal of actively growing cancer cells in the body and the CT scan provides a detailed picture of the internal anatomy that reveals the location, size and shape of abnormal cancerous growths.

Alone, each imaging test has particular benefits and limitations but when the results of PET and CT scans are "fused" together, the combined image provides complete information on cancer location and metabolism. The bottom line is that you can have both scans - PET and CT - done at the same time.

Positron Emission Tomography (PET) demonstrates biochemical activity of various tissues within the body. An administered radioactive substance tagged to a natural compound accumulates in areas of altered metabolism (such as cancerous areas). As the radioactive substance decays emitted positrons produce gamma rays which are detected by special sensors. Images are constructed using complex computer processing.

Computed Tomography (CT) uses x-rays and complex computing to provide precise anatomical information in three planes about the size, shape and location of the organs of the body. 2 dimensional or 3 dimensional images of internal structures can be generated.

PET-CT combines the two state of the art imaging modalities of PET and CT. The functional information from PET is merged with the anatomical information from CT into a single image providing the most comprehensive diagnostic scan currently available to the cancer specialist.

Clinical Applications

1. Cancer
2. Brain disorders
3. Heart disease

How PET/CT Works

While a CT scan provides anatomical detail (size and location of the tumor, mass, etc.), a PET scan provides metabolic detail (cellular activity of the tumor, mass, etc.). Combined PET/CT is more accurate than PET and CT alone.

Anatomical : CT scanners send x-rays through the body, which are then measured by detectors in the CT scanner. A computer algorithm then processes those measurements to produce pictures of the body's internal structures.

Metabolic : PET images begin with an injection of fluorodeoxyglucose (FDG), an analog of glucose that is tagged to the radionuclide F18. Metabolically active organs or tumors consume sugar at high rates, and as the tagged sugar starts to decay, it emits positrons. These positrons then collide with electrons, giving off gamma rays, and a computer converts the gamma rays into images. These images indicate metabolic "hot spots," often indicating rapidly growing tumors (because cancerous cells generally consume more sugar/energy than other organs or tumors).

The entire examination usually takes less than 30 minutes, providing comprehensive diagnostic information to your health care team very quickly. The PET/CT system provides exceptional image quality and accuracy of diagnostic information.

Benefits of PET/CT

There are tremendous benefits of having a combined PET/CT scan :

1. Earlier diagnosis
2. Accurate staging and localization
3. Precise treatment and monitoring

With the high-tech images that the PET/CT scanner provides, patients are given a better chance at a good outcome and avoid unnecessary procedures. A PET/CT image also provides early detection of the recurrence of cancer, revealing tumors that might otherwise be obscured by scar tissue that results from surgery and radiation therapy,particularly in the head and neck. In the past, difficulties arose from trying to interpret the results of a CT scan done at a different time and location than a PET scan, due to the fact that the patient's body position had changed. The combination PET/CT provides physicians a more complete picture of what is occurring in the body - both anatomically and metabolically - at the same time.

Cancer Staging

In one continuous full-body scan (usually about 30 minutes), PET captures images of miniscule changes in the body's metabolism caused by the growth of abnormal cells, while CT images simultaneously allow physicians to pinpoint the exact location, size and shape of the diseased tissue or tumor. Essentially, small lesions or tumors are detected with PET and then precisely located with CT.

A cyclotron is used to produce a radioactive substance which is tagged to a normal body compound. The most commonly used radioactive compound is an analogue of glucose, called fluorodeoxyglucose (FDG); when this is injected into the body it is taken up by areas of high glucose metabolism. Cancer cells use more glucose than most normal healthy tissues thus the FDG accumulates in cancerous areas (and organs of normal high glucose metabolism such as the heart and the brain). Areas of high metabolism (which are emitting positrons) are detected by the scan sensors - in this way it is possible to demonstrate cancers and sites of cancer spread.

Early Detection of Cancer

Cancer diagnosis and treatment planning are the main uses for PET-CT, which may :

• Identify cancer earlier than other imaging technologies
• Distinguish between malignant and benign tumors
• Determine the location and extent of cancer indicating spread to other areas of the body such as lymph nodes, liver or bones (metastatic disease)
• Identify recurrent cancer distinguishing it from scar tissue or fibrosis
• Demonstrate the cancers response to a particular treatment

Treatment process

When you arrive at our diagnostic imaging centre you will be registered at our front desk and we will review your clinical details. For the PET portion of the PET-CT scan you will receive an injection of the radiopharmaceutical or tracer. This contains a small dose of radioactive tracer. It is necessary to allow the radiopharmaceutical to distribute itself around the body before the scan is undertaken – this can take up to 1 hour. You will be asked to relax in a quiet, partly darkened room. You will be asked not to move too much and not to talk as this can affect the localization of the radioactivity. You will then be transferred to the PET-CT scanner where you will lie down on the examination scan table.

The scanner looks like a large doughnut within which are multiple detectors that register and record the energy from the radiopharmaceutical – which by now has reached the area of interest. The total scan (CT and PET) usually takes 30-45 minutes. You may notice a quiet electrical hum but otherwise there are no affects.

There is a small dose of radiation associated with both the CT and PET components of the test, so you should let us know if you may be pregnant. After the examination you can go home and return to a normal diet and normal medication. The radioactive substance only lasts for a very short time and does not limit any normal interactions with other people. Drinking plenty of water helps to flush out the radioactivity from the system.

The images are interpreted by a Consultant Radiologist who has a specialist training in Nuclear Medicine and PET-CT. The reports are sent back to your referring doctor usually within a few days.