03 Nuclear
Recovery coefficient
RC = C_measured / C_true. Partial-volume loss for lesions smaller than ~3× FWHM.
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Simulation
Recovery coefficient — Change the numbers; the scene follows.
Where it works
PET/CT
Patient / uptake
In the patient on the PET couch — activity concentration, SUV, and internal dose.
Open this machineFormula
Variables
Results
RC
Recovery coefficient
0.5
1/RC
Correction multiplier
2
Explanation
What it means
A sphere smaller than the reconstructed PSF spills counts into the background (spill-out) and the measured SUV underestimates truth. Recovery coefficient vs diameter is the NEMA image-quality curve: RC ≈ 0.3 at 10 mm, ≈ 0.8 at 22 mm, ≈ 1 at 37 mm on a typical TOF PET. Partial-volume correction multiplies by 1/RC or deconvolves the PSF. This is a working relation in Nuclear medicine.
Where it is used
Clinically it sits on the PET/CT — Patient / uptake. In the patient on the PET couch — activity concentration, SUV, and internal dose. 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.
PET/CT · Open this machineHow to use it
Enter measured and true concentration (or SUV). Read RC and the correction multiplier. A 13 mm sphere, C_meas=4, C_true=8 → RC=0.5 → multiply SUV by 2. Change one input and watch the curve and the simulation follow.
Symbols
- C_measMeasured concentration4
- C_trueTrue concentration8
Worked example
A typical case from the default values: C_meas = 4 (Measured concentration); C_true = 8 (True concentration). Substituting into the relation gives RC = 0.5; 1/RC = 2. These are teaching numbers — align them with your machine.
Typical values give
- RC = 0.5
- 1/RC = 2
Where it comes from
The displayed formula is the working relation. RC = C_measured / C_true. Partial-volume loss for lesions smaller than ~3× FWHM. Usual reference: NEMA NU 2 / Soret. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: NEMA NU 2 / Soret
Assumptions & limits
Hot sphere in cold (or uniform) background; spill-in from a hot background is the opposite problem. RC depends on reconstruction, filter, TOF, and the VOI rule (max vs mean vs 50% isocontour). Never apply a phantom RC blindly to a patient lesion of different shape.
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. Hot sphere in cold (or uniform) background; spill-in from a hot background is the opposite problem. RC depends on reconstruction, filter, TOF, and the VOI rule (max vs mean vs 50% isocontour). Never apply a phantom RC blindly to a patient lesion of different shape.
Keep this
Write the assay time next to every activity. Decay does the rest. Hot sphere in cold (or uniform) background; spill-in from a hot background is the opposite problem. RC depends on reconstruction, filter, TOF, and the VOI rule (max vs mean vs 50% isocontour). Never apply a phantom RC blindly to a patient lesion of different shape.
In this specialty