3. Radiation Detection
Nuclear medicine requires specialized detectors to convert radiation into measurable signals.
Learning Objectives
- Compare different detector types and their applications
- Explain scintillation detection principles
- Describe the role of photomultiplier tubes
- Understand modern solid-state detectors
Detector Types Overview
| Detector Type | Principle | Application |
|---|---|---|
| Gas-filled | Ionization | Survey meters, dose calibrators |
| Scintillators | Light emission | Gamma cameras, PET |
| Semiconductor | Electron-hole pairs | CZT cameras, high-resolution imaging |
Scintillation Detectors
NaI(Tl) Crystals
The workhorse of nuclear medicine:
- Thallium-activated sodium iodide
- High light output
- Good detection efficiency for 140 keV
- Energy resolution: ~10%
Other Scintillators
- BGO (Bismuth Germanate): Dense, good for PET
- LSO/LYSO: Fast timing, modern PET
- CsI: Compact gamma cameras
Photomultiplier Tubes
Convert scintillation light to electrical signal:
- Photocathode converts light → electrons
- Dynodes multiply electrons (10⁶ gain)
- Anode collects signal
Semiconductor Detectors
CZT (Cadmium Zinc Telluride)
- Direct conversion of gamma rays
- Superior energy resolution (~5%)
- Compact, no PMTs required
- Used in dedicated cardiac cameras
Content under development: Electronics, pulse processing, dead time