Positron Emission Tomography Summary

Introduction to PET Scan

Positron Emission Tomography or PET is a method which is used to detect the cellular activity of a structure along with Magnetic Resonance Imaging (MRI) and Computerized Tomography (CT) it is used to create multidimensional color images of inside working of the human body. It shows not only what an organ looks like, but how it is functioning.

Working Principle of a PET Scanner 

PET scan uses a scanning device which detects the positron particles emitted from the target tissue or organ the radiotracers used in PET scans are made by attaching a radioactive atom to chemical substances that are used naturally by the particular organ or tissue during its metabolic process. For example, the radioactive element is applied to glucose which works as the primary source of energy for almost each and every organ of human body. The radionucleotide of glucose is called Fluorodeoxyglucose (FDG).



Other molecules can also be used depending on the organ to be examined and its perfusion a the d main source of metabolism. Other molecules generally used are oxygen, gallium, carbon or nitrogen.

PET Scanner Shape

The CT scanner is typically a large, box-like machine with a round hole, that the patient can fit inside it, or short tunnel, in the center. The x-ray tube and the x-ray detector are rotating around the patient opposite to each other on a ring called gantry. The X-ray detector collects various images and these are compiled and the functioning of the organ is seen on the computer.

Procedures Using PET Scanners 

The patient is not allowed to have any food 4 to 6 hour before the procedure as it may act as another glucose source.The patient is also advised to drink plenty of water to flush out the glucose present in the body.

Caffeine has to be usually avoided 24 hours before the scan as it may hamper with the test results by causing diuresis of the ink or by causing tachycardia.

The radiotracer can be given to the patient by various means like:

• Venous root
• Inhalation
• Orally
• Direct injection into the organ

And depending on the organ involved it may take up to 60 to 90 minutes for the radiotracer to reach the target organ.

After the radiotracer has reached the organ the patient is made to go inside the scanner where depending on the body part involved various images of the part are taken and the process may take up to 30 more minutes.

Diseases For Which PET Scanner Can Be Used

• Epilepsy: To detect the part of the brain involved.

• Alzheimer's disease: Brain cells affected by the disease usually take up glucose slowly.

• Cancer: Cancer affected cells usually use more glucose than normal cells.

• Heart disease: To detect the part of the heart damaged or scarred.

Limitations of a PET Scanner

• The procedure is time-consuming and cumbersome.
• The procedure cannot be used for patients suffering from diabetes as radioactive glucose would enter their cells very slowly.
• The half-life of the radioactive glucose is very low so the patient has to be attended immediately after the radioactive material has reached the organ.

Precautions Needed Before Doing a PET Scanner

Precautions have to be taken in certain conditions before the pet scan these include:

• Pregnancy
• Breastfeeding Mothers
• Patients allergic to the radiotracer element