What Is a PET-CT Scan? - What Are The Side Effects Of PET Scan? - How Is PET Scan Performed?
What is a PET-CT scan? How does a PET scan work? How to prepare for a PET scan test and how the test is performed? Positron emission tomography or PET scan as it is called is a very commonly advised scan in medical practice. Watch as Dr. Pallavi Patil, a nuclear medicine specialist,
Discusses the basics of the different types of applications of nuclear medicine scans especially the PET scan?
WHAT IS NUCLEAR MEDICINE?
It is a modality where we use radioactive elements tagged with organ-specific compounds for diagnostic and therapeutic purposes. Conventional radiological scans image the anatomy or structure of the body. Nuclear medicine images the physiology or function of the organs.
These compounds are also known as radioactive pharmaceuticals/ radiopharmaceuticals for short. They are also sometimes referred to as radiotracers or simply tracers.
These tracers can be injected, ingested, or inhaled depending on the nature of the procedure performed. This results in the emission of radiation from the patient's body. Special types of scanners called gamma cameras are used to image these emissions. This is where it is different compared to conventional X-Ray or CT imaging. The source of radiation is within the patient and the camera simply captures the emissions and generates the images.
The applications of nuclear medicine can be broadly classified under 3 headings:
Diagnostic,
Therapeutic,
and Theranostic
1- Diagnostic: Commonly used for detection, staging, and response assessment during work-up for cancers or to find recurrences with PET/CT.
There are many non-oncological utilities of Nuclear scans as well. eg: assessment of thyroid or kidney function. Your cardiologist may advise you to undergo a nuclear scan to assess whether or not you have coronary artery disease (in cases of an indeterminate TMT result) and whether you are likely to benefit from cardiac intervention therapies.
Nuclear scans can detect the earliest changes in neurodegenerative diseases like AD, Parkinson's. A nuclear brain perfusion scan is also useful in surgical planning in cases of epilepsy.
2. Therapeutic: In the beginning of the session we discussed radioactive alpha and beta particles. These particles have high energies and are capable of causing tissue destruction. We utilize this knowledge to our advantage by using selective tracers to cause "internal radiation" in target organs. This is extremely useful in treating various thyroid conditions like Grave's disease and thyroid cancer.
3. Theranostics: It is a combination of the words Therapeutic & Diagnostic. It's used to describe a combination of radiopharmaceuticals, 1 of which is used for identifying & localizing the tumor sites, and the 2nd one is used to deliver therapy.
WHAT TO EXPECT DURING THE SCAN?
The doctor will review your case history, explain the nature of the test, and obtain consent from you. The nursing staff will check your vitals to make sure everything is in order. They will check your blood sugar levels before a PET scan. An intravenous line is then inserted and secured which is used to administer the radiopharmaceuticals. The technologist proceeds to administer the radioactive tracer and then we wait for the tracer to accumulate in the target organs. Typically the waiting time is 1 hour but can vary depending on the organ of interest. After the uptake period, you will be asked to lie down on the scanner. The imaging is done approximately in 20 minutes and you are expected to lie still during the duration of the process. An additional radiographic contrast may be administered at this stage to obtain a diagnostic CT image.
POST-PROCEDURE INSTRUCTIONS
You will be asked to hydrate yourself over the coming 24 hours to encourage excretion of the radiotracer through the urinary route. A distance of 1 meter has to be maintained from others, especially pregnant ladies and young children. Lactating women need to stop breastfeeding for 1 day. There are no particular dietary or medical restrictions. All non-emergency surgical procedures are deferred by 1 day to allow for radioactive decay.
ADVANTAGES OF NUCLEAR SCANS
They are extremely sensitive and can detect changes at the cellular level even before apparent structural changes are noticed in conventional scans.
The radiation exposure for diagnostic scans is within acceptable limits.
Nuclear scans can be safely performed in patients even with renal or hepatic failure as the radiotracers do not aggravate any existing pathology.
DISADVANTAGES
Cost & availability are the most limiting factors.