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Anger gamma camera structure & detection chain

Cross-section of an Anger gamma camera drawn bottom to top: gamma photons from the patient pass a parallel-hole lead collimator that accepts only near-parallel photons (direction, not energy), reach the sodium iodide scintillation crystal where they produce light, which travels through a light guide to an array of photomultiplier tubes that convert light to photoelectrons and amplify it via a dynode chain. The electrical pulses feed position and energy logic, then a pulse-height analyser whose energy window of about plus or minus ten percent around the 140 keV photopeak rejects lower-energy Compton scatter.

Gamma camera cross-section and signal path Cross-section of an Anger gamma camera drawn bottom to top: gamma photons from the patient pass a parallel-hole lead collimator that accepts only near-parallel photons (direction, not energy), reach the sodium iodide scintillation crystal where they produce light, which travels through a light guide to an array of photomultiplier tubes that convert light to photoelectrons and amplify it via a dynode chain. The electrical pulses feed position and energy logic, then a pulse-height analyser whose energy window of about plus or minus ten percent around the 140 keV photopeak rejects lower-energy Compton scatter. signal path pulse-height analyser (PHA) energy window rejects lower-energy scatter ±10% window scatter (rejected) 140 keV energy x, y position + energy position (x, y) & energy (z) logic Anger logic locates each event electrical pulses NaI(Tl) gamma photons from patient photomultiplier tubes light → photoelectrons, then dynode-chain gain ~10⁵–10⁷ light guide NaI(Tl) scintillation crystal gamma photon → visible light parallel-hole lead collimator accepts near-parallel photons — gives direction, not energy
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