PET Scan

Have you suffered from a bone injury before? Did you get an X-ray taken? An X-ray would show structures like bones inside your body, and a doctor might use this information to diagnose bone-related injuries like fractures.

If we can see our bones through an X-ray, is there a way to see how much Blood is flowing to our heart or how much oxygen is being used in our brain? A PET scan allows us to get this kind of information, and doctors would use this for various reasons, including diagnosing Cancer.

• First, we will discuss what a PET scan is and how it is typically used in different fields.
• Then, we will distinguish between a PET scan and another imaging procedure called a CT scan.
• Finally, we will discuss some risks and considerations related to the PET scan.

PET Scan Meaning

Let's start by looking at the meaning of PET scan. A positron emission tomography (PET) scan is an imaging test that uses radioactive substances called tracers to examine Blood flow, metabolism, and chemical composition (for example, oxygen concentration) in specific body tissues or organs.

It is a procedure that is typically performed to identify specific conditions or assess how the treatment of certain diseases is working.

PET Scan Procedures and Interpretation

A small amount of tracer is either injected into a patient intravenously (through a vein), swallowed, or inhaled, depending on what area of the body is being examined. After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity.

The patient would lie down and slide through the central hole of the PET scanner (Fig. 1). Then, the PET scanner would be positioned at the region of the body that will be scanned.

The PET scanner has a special type of camera that detects positrons released by the tracer in the organ or tissue under study. A computer reconstructs the signals into three-dimensional images and displays them on a monitor.

The radioactive tracers attach to a chemical substance–such as glucose, carbon, or oxygen–that a specific organ or tissue uses during metabolism.

The specific tracer used during the procedure depends on the target organ or tissue. For example, suppose the PET scan aims to look at blood flow and circulation in an organ. In that case, the radionuclide is likely a type of radioactive oxygen, carbon, nitrogen, or gallium.

The first images taken by the PET scanner are used to determine if the machine is positioned correctly. To avoid producing blurry photos and causing errors, the patient must stay still and even hold their breath. The scan can take 30 minutes to an hour, depending on the body part being scanned.

When the images are taken, areas with higher uptake and brighter spots would generally be interpreted as having more activity.

PET Scan vs. CT Scan

If you have seen some medical dramas on TV, you may have heard of another imaging procedure called the CT scan.

Signals produced by this procedure are processed by a computer, generating cross-sectional images of the body. Once it has collected enough photos, the computer stacks these together to form a three-dimensional image of the patient.

While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues (Fig. 2).

How a PET Scan is Used to Detect Various Types of Diseases

A PET scan is typically performed to assess organs or tissues for the presence of diseases or other conditions. However, there are other reasons for administering a PET scan, including:

• Diagnosing neurological conditions like Alzheimer's disease, epilepsy, and stroke.

• Locating cancerous regions that need to be treated during brain surgery.

• Detecting how Cancer is spreading from the original site to other parts of the body.

• Assessing blood flow to The Heart to determine if there is a need for treatment.

• Evaluating the effectiveness of cancer treatment.

• Verifying lesions or masses in the lungs that were detected in a chest x-ray or chest CT scan.

• Mapping normal human brain and heart function.

Let's look at how a PET scan would be administered and interpreted.

Fluorine-18 (18F) fluoro-deoxyglucose (FDG), often referred to as [18F] FDG PET, is a tracer commonly used for cancer imaging. It is a compound resembling glucose, except its oxygen molecule is replaced with a positron-emitting Fluorine-18. FDG is taken up much like glucose, except it is trapped and retained in tumors after being phosphorylated by an enzyme called hexokinase.

Due to the high metabolic activity in cancerous tissues, a significant amount of glucose is absorbed there. This means that 18F-FDG is also taken up heavily in these areas, resulting in a bright spot on the PET scan.

In this way, FDG PET can be used to diagnose, stage, and monitor cancers, most notably Hodgkin's lymphoma, non-Hodgkin lymphoma, and lung cancer. On the other hand, given that Alzheimer's disease manifests in decreased glucose and oxygen metabolism in the brain, FDG PET can also be used to differentiate between Alzheimer's and other forms of dementia.

PET Scan Side Effects and Other Considerations

A PET scan uses only a little amount of radiation, so there is no need to worry about radiation exposure; a PET scan typically exposes the patient to the same amount of radiation as a conventional CT scan. Moreover, the radiation does not stay in the patient's body for very long.

However, pregnant or breastfeeding women must notify their doctor before undergoing this test. Because their organs are still developing, infants developing in the womb are more vulnerable to the effects of radiation.

Some patients may also experience discomfort, redness, or swelling at the site where they got injected. There is also a small chance of an allergic reaction to the radioactive tracer. For this reason, it is vital to inform the healthcare provider about any allergies or sensitivities to medications, contrast dyes, iodine, or latex.

There is also a possibility of getting less accurate results from the PET scan due to certain factors or conditions, including:

• High blood sugar or Insulin levels in diabetics.

• Medicines such as sedatives and tranquilizers.

• Caffeine, alcohol, or tobacco consumption.

• Excessive movement or inability to lie still.