Nuclear medicine consists of the use of small, safe amounts of radioactive substances (radiopharmaceuticals) to diagnose, evaluate, and treat diseases. It is an effective tool to assess and treat the biochemical abnormalities in the cells of the disease-affected region. Unlike primary radiological techniques like CT or MRI, nuclear medicine focuses on the functional activities of the organ rather than its anatomical structure.
PET stands for Positron Emission Tomography. This is a specialized subcategory of nuclear medicine. It consists of diagnosing, staging, monitoring, and guiding the treatment of diseases by evaluating the metabolic, biochemical, and molecular processes inside the body. The core principle of PET imaging is to identify the metabolic and biochemical changes at the cellular level, rather than the outer anatomical changes, which surface much later. It utilizes positron-emitting tracers that mimic the functions of natural biochemical molecules. When these tracers are sent into the body, they follow the same pathway as that of the natural substances. This gives insights into the metabolic activities of the cells and tissues.
This category consists of tumors, masses, and other types of malignancies. These conditions are caused by the uncontrolled growth of cells, known as cancer cells. Cancer cells are characterized by large amounts of glucose metabolism and altered biochemical pathways. Conventional radiological techniques like CT or MRI may not be effective in detecting such changes or assessing the response of cancer cells to the treatment. PET imaging facilitates the observation of metabolic activities in the cell, thus revealing unique characteristics os the cancer cells.
Several neurological disorders are caused by metabolic changes that might not be easily detected by typical radiological tests. PET imaging effectively analyzes changes like cerebral glucose metabolism, neurotransmitter activity, hypometabolism, or hypermetabolism. It makes use of disease-specific markers to increase diagnostic accuracy.
In ischemic heart disease, the myocardium might be alive, but may not function at all. It may also be irreversibly damaged with diagnostic transparency to conventional methods. PET imaging is useful in analyzing myocardial perfusion and metabolism, preserved glucose uptake, absolute myocardial blood flow, etc.
The advantages of nuclear medicine/PET imaging are listed below:
Detection of conditions at an early, metabolic-changes stage.
High sensitivity due to assessment of physiology, biochemistry, receptor expression, and metabolism.
Analysis of the complete boldly in a single assessment.
PET imaging helps differentiate active disease from inactive tissues.
Evaluates the metabolic response, which is essential to assess the response to the treatment.
This method is an effective tool to compare metabolic changes over time.
PET imaging is an excellent tool for multiple fields such as oncology, cardiology, neurology, etc.
It reduces the requirement for unnecessarily invasive procedures.
Radiation exposure
Limited insights into anatomic details
High cost of equipment and
False positive results due to infections, inflammation, etc.
False negatives due to low-grade, slow-growing, or low-metabolic tumors
Longer, more complex imaging protocols
Radiological tracer-related limitations
Contraindications in pregnant and lactating women
Suitable for limited clinical questions
1. Gamma Camera (Planar Scintigraphy)
Basic nuclear medicine imaging
Detects gamma rays from radiotracers
Produces 2D images
Common studies:
->Thyroid scan
->Bone scan
->Renal scan
->Liver–spleen scan
2. SPECT (Single Photon Emission Computed Tomography)
Uses a rotating gamma camera
Produces 3D functional images
Better localization than planar imaging
Common uses:
->Cardiac perfusion imaging
->Brain perfusion studies
->Bone SPECT
3. PET (Positron Emission Tomography)
Uses positron-emitting tracers (e.g., FDG)
Detects annihilation photons
Provides high-resolution metabolic images
Widely used in oncology, neurology, cardiology
4. PET-CT
Combines PET (function) + CT (anatomy)
Most commonly used PET modality
Accurate lesion localization & attenuation correction
5. PET-MRI
Combines PET (metabolism) + MRI (soft tissue)
Lower radiation than PET-CT
Excellent for brain, pelvis, pediatric imaging
6. SPECT-CT
Combines SPECT + CT
Improves anatomical localization
Common in bone & cardiac imaging