03 Nuclear
Gamma-camera spatial resolution
System FWHM from intrinsic and collimator (geometric) terms.
Listen
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Simulation
Gamma-camera spatial resolution — Change the numbers; the scene follows.
Where it works
Gamma camera
Detector head
In the gamma-camera crystal and PMTs — counts, dead time, energy window, resolution.
Open this machineFormula
Variables
Results
R_s
System resolution
8.8566mm
Explanation
What it means
System spatial resolution of a gamma camera combines intrinsic (crystal + electronics) and collimator geometric resolution in quadrature: R_s = √(R_i² + R_g²). Collimator term usually dominates at 10 cm. This is a working relation in Nuclear medicine.
Where it is used
Clinically it sits on the Gamma camera — Detector head. In the gamma-camera crystal and PMTs — counts, dead time, energy window, resolution. Nuclear-medicine relations sit in the hot lab, on the camera, and in the voxel: decay, SUV, TOF, and counting statistics. They decide whether an uptake is real or a clock error.
Gamma camera · Open this machineHow to use it
Typical R_i ≈ 3.5–4.5 mm at 140 keV. Add R_g from the collimator calculator. FWHM is what manufacturers quote; FWTM ≈ 2× FWHM for a Gaussian. Change one input and watch the curve and the simulation follow.
Symbols
- R_iIntrinsic resolution3.8 mm
- R_gCollimator resolution8 mm
Worked example
A typical case from the default values: R_i = 3.8 mm (Intrinsic resolution); R_g = 8 mm (Collimator resolution). Substituting into the relation gives R_s = 8.8566 mm. These are teaching numbers — align them with your machine.
Typical values give
- R_s = 8.8566mm
Where it comes from
The displayed formula is the working relation. System FWHM from intrinsic and collimator (geometric) terms. Usual reference: Cherry. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Cherry
Assumptions & limits
FWHM addition in quadrature assumes Gaussian shapes. Scatter, septal penetration (I-131, high-energy collimators) broaden the real PSF beyond this.
Pitfalls
Activity is not counts. SUV needs the true injected activity, the residual, and the correct decay time — a clock off by 10 min on ¹⁸F is a several-percent error. Do not compare SUVs across reconstructions. FWHM addition in quadrature assumes Gaussian shapes. Scatter, septal penetration (I-131, high-energy collimators) broaden the real PSF beyond this.
Keep this
Write the assay time next to every activity. Decay does the rest. FWHM addition in quadrature assumes Gaussian shapes. Scatter, septal penetration (I-131, high-energy collimators) broaden the real PSF beyond this.
In this specialty