03 Nuclear
Counting efficiency
Well-counter or detector efficiency from count rate, activity, and yield.
Listen
Listen · English
Simulation
Counting efficiency — 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
ε
Efficiency
0.4775
ε
Efficiency
47.753%
Explanation
What it means
Counting efficiency ε = R / (A γ) is counts per photon emitted. A well counter for Tc-99m can exceed 80%; a gamma camera with a collimator is 100–200 cps/MBq (a few 10⁻⁴ as a fraction). 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
Convert A to Bq (here kBq→×1000). γ is photons per decay (0.89 for Tc-99m 140 keV). Use ε to convert a count rate back to activity. Change one input and watch the curve and the simulation follow.
Symbols
- RCount rate8,500 cps
- AActivity20 kBq
- γPhoton yield0.89
Worked example
A typical case from the default values: R = 8,500 cps (Count rate); A = 20 kBq (Activity); γ = 0.89 (Photon yield). Substituting into the relation gives ε = 0.4775; ε = 47.753 %. These are teaching numbers — align them with your machine.
Typical values give
- ε = 0.4775
- ε = 47.753%
Where it comes from
The displayed formula is the working relation. Well-counter or detector efficiency from count rate, activity, and yield. Usual reference: Cherry. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Cherry
Assumptions & limits
No background subtraction, pile-up or dead-time. Geometry (sample volume, well position) is baked into ε — re-measure if the geometry changes.
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. No background subtraction, pile-up or dead-time. Geometry (sample volume, well position) is baked into ε — re-measure if the geometry changes.
Keep this
A in Bq, R in cps, γ is photons per decay.
In this specialty