1 Detector head & component information
Select isotope and collimator energy for learning (match hints on collimators). Toggle PMT vs CZT for a full comparison. Fire a photon or click components for detail. In Section 2, use Free navigation to unlock isotope choice and pick phantom shapes on the live slice (scoring stays frozen).
- Detection chain: gamma → visible light (crystal) → electrons (PMT) — two conversion steps
- Position encoding: ~40–90 PMTs (most modern large-field heads use about 59) share each flash; nearest tubes dominate the centroid
- Strengths: mature, lower capital cost, general-purpose SPECT workhorse
- Limits: broader photopeak (more accepted scatter), pulse pile-up / dead time at high rates, bulkier gantries
Orbit · zoom · pan (touch: one finger orbit, two finger zoom/pan). Tap a SPECT or CT part for a teaching note. Housings are a cut-away view.
Cardiac SPECT needs a 180° acquisition arc from RAO to LPO. In 90° L-mode each head covers 90° of that arc, so the gantry only rotates 90° for the full set — about half the acquisition time of a 180° H-mode orbit — while both heads stay close to the chest. L-mode works only with low-energy collimators (LEHR, LEUHR, ELEGP).
SPECT collimator holes enlarged ~10× for visibility. CT bore 75 cm; 40 mm coverage (teaching scale).
3D model shows Aurora-style dual NaI/PMT Anger heads; CZT is a different detector technology that replaces the crystal, light guide and PMTs with pixelated CZT modules.
Select a component in the diagram to read how it works and its role in image acquisition.
2 Acquisition & image quality
Tune dose, time, AC, collimator, and hole shape. In mystery mode the isotope is locked and you can score the hidden phantom. Turn on free navigation to pick any isotope and choose which phantom shape is shown — scoring stays frozen until free nav is off.
Simulated reconstructed slice
Tc-99m · LEHR · hexagonal · PMT/NaI · AC on
Mystery phantom — which shape is hidden in the counts?
Icon phantom for teaching count statistics. Low dose/time hides the shape in noise; better acquisition (and match) reveals it.
Hole shapes
Parallel-hole collimators are the camera’s mechanical lens. Click a hole geometry — packing efficiency and septal-penetration artifact shape update the live image. Hexagonal is the modern clinical standard.
Round (circular) holes
Circular channels leave dead lead between holes, so open area (sensitivity) is lower for a given septal thickness. When high-energy photons penetrate thin septa, mislocalized counts form a multi-ray star artifact around hot foci.
Square holes
Improved packing over round holes with simpler casting. Mild directional resolution along hole walls. Under-specified septa produce an orthogonal cross artifact (0°/90° arms) rather than a multi-spoke star — artifact shape tracks hole geometry.
Hexagonal holes
Honeycomb tiling maximizes open area for a given septal thickness — highest practical sensitivity and nearly isotropic response. Default on modern LEHR/LEAP/ME/HE parallel-hole collimators. Penetration yields the classic 6-spoke star around hot foci.
3 PMT/NaI vs CZT — the numbers
The column matching your selected detector is highlighted. These are the board-relevant contrasts between the conventional scintillation camera and modern solid-state detectors.
| Feature | PMT / NaI(Tl) | CZT (solid-state) | Why it matters clinically |
|---|
4 Check yourself — ABR-style quiz
22 board-style questions in the spirit of the ABR core/certifying exam. One at a time — pick an answer to see the explanation, then advance. Questions and answer choices shuffle each session.