Sunday, September 12, 2010

PET/CT Scan/| PET Scan Procedure

PET is a nuclear medicine technique using a camera, which captures powerful images of the human body's function and reveals information of health and disease. Compounds normally existing in the body, like simple sugars, are labeled with radioactive tracers, which emit signals and are injected into the body intravenously. The scanner records the signals that the tracer emits as it journeys through the body and as it collects in targeted organs. A powerful computer reassembles the signals into actual images, which then show biological maps of normal organ function and failure of organ systems in disease.

A PET scan uses radiation, or nuclear medicine imaging, to produce 3-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 does a PET scan work?

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 up 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 3-dimensional image on a computer monitor.

The reason why PET is so successful is that no other imaging technique shows the internal chemistry of the body so well. Conventional imaging techniques such as X-ray, CAT scans, and Magnetic Imaging Resonance shows anatomy. PET detects chemical and metabolic changes in disease states, such as cancer, before anatomic and structural changes (detected by conventional imaging) have time to develop. Therefore PET can detect diseases when anatomic imaging studies are still normal, and may be informative in differentiating benign from malignant process. PET evaluation of tissue metabolism can indicate the probable presence or absence of malignancy based on differences of biological activity, where as anatomic imaging depends on size and radiographic characteristics of lesions to determine the likelihood of malignancy. In addition, whole body imaging with PET provides a means to examine all the organ systems in the entire body for both primary and metastatic disease in one procedure.

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 are PET scans 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. The use of combined imaging technologies may hold the key to stopping - and even preventing - heart attacks, a study revealed.


The preparation for a PET/CT is very specific in what you can andcannot do prior to your appointment. The preparation requirements are dependant on the reason for your scan. A detailed preparation sheet will be given to you when you make your appointment.


On arriving at the PET/CT Centre, present any previous imagingyou have had to clerical staff. A technologist will confirm that you have undertaken the correct preparation for your scan and make sure you understand the procedure fully. A Nurse will go through a questionnaire with you and a glucose check will be performed via a finger pin prick. A needle will be placed in your arm and the tracer is injected through the needle. After the injection you must wait a minimum of 1 hour prior to your scan. During this 1 hour period you will be resting quietly in a dimly lit room. It is very important during this time to relax, avoid talking, and avoid any significant movement.

Examination and Reporting Time

The PET scanner detects the radiation released from the radioactive sugar injection and uses this to create pictures of your body. The CT scan will image the anatomy and alterations in structure related to disease. The scan process will involve you lying on your back with your arms raised above the head. The scan will take approximately 20 minutes. The PET and CT images are combined and displayed on a computer screen or photographic fi lm.
We recommend that you resume your normal diet after the examination. You should drink plenty of fl uids for the next few days. This will help clear any remaining tracer from your body.
When the scan is complete, the images will be reviewed by a Radiologist and specialist in Nuclear Medicine, specially trained in reporting these scans. All your images will be correlated with any previous studies that you may have had. The results of your PET/CT scan will usually be available the next business day.

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