Topic 2: Basic Principles in Radionuclide Diagnostics. Apparatus – Planar Gamma Camera, SPECT Gamma Camera, SPECT/CT, PET/CT – Basic Principles
Radionuclide diagnostics is a branch of nuclear medicine that uses radiopharmaceuticals to evaluate the physiological, biochemical, and metabolic function of organs and tissues by detecting radiation emitted from inside the patient's body.
Unlike CT or MRI, which mainly show anatomy, radionuclide imaging primarily shows function.
Principle of Radionuclide Imaging
The principle consists of five basic steps:
Step 1: Administration of Radiopharmaceutical
A radiopharmaceutical consists of:
- Radionuclide → emits radiation.
- Carrier molecule (pharmaceutical) → directs the radionuclide to a specific organ or tissue.
Routes of administration:
- Intravenous (most common)
- Oral (e.g., radioiodine)
- Inhalation (ventilation scan)
- Subcutaneous (lymphoscintigraphy)
Step 2: Biodistribution
After administration, the tracer is distributed according to:
- Blood flow
- Cellular metabolism
- Receptor expression
- Organ function
Examples:
99mTc-MDP → accumulates in bone.
99mTc-MIBI → myocardium, parathyroid, tumors.
18F-FDG → tissues with high glucose metabolism.
Step 3: Emission of Radiation
The radionuclide emits radiation:
Diagnostic imaging mainly uses:
- Gamma photons
- Positrons (PET)
The emitted photons leave the patient's body.
Step 4: Detection
Special cameras detect emitted photons.
Examples:
- Gamma camera
- SPECT
- PET
The patient becomes the source of radiation.
Step 5: Image Formation
Computer software reconstructs images.
Images demonstrate:
- Organ function
- Perfusion
- Metabolism
- Receptor activity