Overview of the principles, history, and applications of nuclear medicine imaging in healthcare, including the use of radioactive tracers and detectors.
Introduction to Nuclear Medicine Imaging
Core concepts, techniques, and clinical relevance
| Aspect | Description |
|---|---|
| Definition | A diagnostic (and therapeutic) specialty that uses small amounts of radioactive material (radiopharmaceuticals) to visualize physiological processes in the body. |
| Key Principle | Detects gamma photons emitted from radionuclides inside the patient and reconstructs images that reflect tissue function, not just anatomy. |
| Main Modalities | • Scintigraphy (planar imaging) • Single‑Photon Emission Computed Tomography (SPECT) • Positron Emission Tomography (PET) |
| Typical Uses | • Oncology (tumor detection, staging, therapy monitoring) • Cardiology (myocardial perfusion, viability) • Neurology (brain metabolism, receptor imaging) • Endocrinology (thyroid, adrenal, bone metabolism) |
| Component | Details |
|---|---|
| Radionuclide | Emits detectable radiation (γ‑rays for SPECT, positrons for PET). Common examples: • Technetium‑99m (⁹⁹ᵐTc) – γ emitter, half‑life 6 h (SPECT) • Fluorine‑18 (¹⁸F) – positron emitter, half‑life 110 min (PET) |
| Carrier Molecule | Determines biological target (e.g., glucose analogue, phosphate, antibodies). |
| Administration | Usually intravenous; occasional oral, inhalation, or intrathecal routes. |
| Dosimetry | Patient radiation dose is low (comparable to a few chest X‑rays); doses are optimized for image quality vs. safety. |
| Concept | SPECT | PET |
|---|---|---|
| Radiation Detected | Single γ photons (usually 140 keV for ⁹⁹ᵐTc) | Coincident 511 keV photons from positron annihilation |
| Detectors | NaI(Tl) crystals coupled to photomultiplier tubes (PMTs) or solid‑state detectors | LSO/LYSO scintillators coupled to avalanche photodiodes or PMTs |
| Acquisition | Rotating camera acquires multiple 2‑D projections → tomographic reconstruction (filtered back‑projection or iterative) | Ring of detectors records simultaneous photon pairs → direct 3‑D reconstruction |
| Spatial Resolution | ~6–10 mm (depends on collimator) | ~4–5 mm (better due to coincidence detection) |
| Attenuation Correction | Usually via transmission scan (e.g., CT) or uniform correction factors | Integrated CT (PET/CT) provides accurate attenuation maps |
| Study | Radiopharmaceutical | Typical Dose | Imaging Timeline |
|---|---|---|---|
| Myocardial Perfusion SPECT | ⁹⁹ᵐTc‑sestamibi or tetrofosmin | 10–30 mCi (370–1110 MBq) | Rest → stress (pharmacologic or exercise) → 30‑60 min post‑injection |
| Bone Scan |