A PET scan uses radiation, or nuclear medicine imaging, to produce three-dimensional, color images of the functional processes within the human body. PET stands for Positron Emission Tomography. The machine detects pairs of gamma rays which are emitted indirectly by a tracer (positron-emitting radionuclide) which is placed in the body on a biologically active molecule. The images are reconstructed by computer analysis. Modern machines often use a CT X-ray scan which is performed on the patient at the same time in the same machine.
PET scans can be used to diagnose a health condition, as well as for finding out how an existing condition is developing. PET scans are often used to see how effective an ongoing treatment is.
How a PET Scan Works
Radiotracer – Before carrying out a PET scan, a radioactive medicine is produced in a cyclotron (a type of machine). The radioactive medicine is then tagged to a natural chemical. This natural chemical could be glucose, water, or ammonia. The tagged natural chemical is known as a radiotracer. The radiotracer is then inserted into the human body. When it is inside, the radiotracer will go to areas inside the body that use the natural chemical. For example, FDG (fluorodeoxyglucose – a radioactive drug) is tagged to glucose to make a radiotracer. The glucose goes into those parts of the body that use glucose for energy. Cancers, for example, use glucose differently from normal tissue, so FDG can show cancers.
Detecting Positrons – A PET scan detects the energy emitted by positively-charge particles (positrons). As the radiotracer is broken down inside the patient’s body, positrons are made. This energy appears as a three-dimensional image on a computer monitor.
The Image – The image reveals how parts of the patients body function by the way they break down the radiotracer. A PET image will display different levels of positrons according to brightness and color.
When the image is complete, it will be examined by a radiologist who reports his/her findings to a doctor. A radiologist is a doctor who specializes in interpreting these types of images, as well as MRI scan, CT scan, Ultrasound and X-ray images.
Why PET Scans Are Required
PET scans are generally used alongside X-rays or MRI (magnetic resonance imaging) scans. Doctors use PET scans as a complementary test to these main ones. They are used to make a diagnosis or to get more data about a health condition. As mentioned above, they are also useful in finding out how effective current treatment is. One study revealed that the use of combined imaging technologies may hold the key to stopping — and even preventing — heart attacks.
PET scans are commonly used to investigate the following conditions:
- Alzheimer’s disease
- Heart disease
What Happens During a PET Scan
In most cases, the patient does not have to spend the night in the hospital when he/she comes in for a PET scan.
The majority of patients will be told not to consume any food for at least four to six hours before the scan, but to drink plenty of water. Some will be asked to refrain from consuming caffeine for at least 24 hours prior to the PET scan.
A small quantity of radiotracer will either be injected into the patient’s arm or breathed in as a gas. The radiotracer may take 30 to 90 minutes to reach the targeted part of the body. While waiting for the radiotracer to reach its destination, the patient will normally be asked to stay still and not talk. Some patients may be given some medication, such as diazepam, to relax.
When the patient is ready, he/she will be taken to the room where the PET scan is and will lie down on a cushioned examination table. The machine has a large hole that the table slides into. Then images of the body are taken.
In many centers the patient will be able to listen to music during the scan.
While the scan is in process it is vital that the patient keep as still as possible. Depending on which part of the body is being scanned, the whole process takes from about 30 to 60 minutes.
If the patient feels unwell he/she can press a buzzer which alerts the staff. During the whole process the patient is being watched by staff.
The process is not painful.
Most patients can go home as soon as the scan has been done. Doctors advise people to consume lots of liquids to flush the radioactive drugs out of their system more quickly. Experts say the radiotracers should have left the body completely within three to four hours after entering the body.
To schedule a PET/CT scan, please call 732-744-5527.