Diagnostic Methods in Medicine

Medical Tracers

• Definition: Radioactive substances absorbed by tissues to study organ structure and function.
• Common Isotopes:
  • Technetium-99m:
    • Binds to organic molecules like glucose.
    • Emits gamma radiation, decays into stable isotopes.
    • Half-life: 6 hours.
  • Fluorine-18:
    • Used in PET scanning as fluorodeoxyglucose.
    • Emits a positron (beta-plus decay).
    • Half-life: 110 minutes.
• Application:
  • Injected or swallowed to flow through the body.
  • Absorption by tissues indicates disease progress and treatment effectiveness.
  • Used for cancer diagnosis, heart, blood flow issues, brain injuries.

Worked Example: Nuclear Decay Equation

• Fluorine-18 Decay:
  • Reactants: Fluorine-18 (( ^{18}9F )) and positron (( ^{0}{1} \beta^+ )).
  • Products: Oxygen-18 (( ^{18}_8O )) and gamma ray.
  • Equation: ( ^{18}_9F \rightarrow ^{18}8O + ^{0}{1} \beta^+ + \gamma ).

Gamma vs. Beta-emitting Tracers

• Gamma Radiation:
  • Long range, easy to detect.
  • Less ionizing, safer for patients.
• Beta Particles:
  • Short range, not easily detected.
  • Highly ionizing, more cellular damage.

Gamma Camera

• Components:
  • Collimator, Scintillator, Photomultiplier tubes, Computer & Display.
• Collimator:
  • Absorbs non-parallel photons.
  • Ensures high-resolution images.
• Scintillator:
  • Converts gamma to visible light photons.
  • Excites electrons which emit light when returning to ground state.
• Photomultiplier Tubes:
  • Amplify faint light from scintillator.
  • Converts light to electrical signal.
• Image Formation:
  • Detectors capture gamma rays to create image.
  • Bright points indicate high tracer concentration.

PET Scans (Positron Emission Tomography)

• Definition: Imaging tissues/organs by measuring metabolic activity.
• Process:
  • Injection of beta-plus emitting isotope, usually fluorine-18.
  • Annihilation of positron and electron produces gamma photons.
  • Detected by gamma cameras.
• Annihilation:
  • Positron collides with electron, converting mass into energy (gamma rays).
  • Energy (E = hf = mc^2).
• Image Formation:
  • Photomultiplier signals used for imaging.
  • Tracer concentration indicated by photon density at points.

Worked Example: Positron-Annihilation Calculations

• Energy Calculation:
  • Mass of electron/positron: (9.11 \times 10^{-31}) kg.
  • Total energy from mass-energy equivalence: (E = 2m c^2).
• Frequency and Momentum Calculations:
  • Use Planck's constant and known photon equations.

Diagnosis with PET

• Advantages:
  • Short half-life reduces radiation exposure.
  • Requires quick scanning due to isotope decay.
  • Used for detecting cancer, brain function, and metabolic activity.