03 Nuclear
Percent uptake
Organ uptake as a percentage of injected activity, decay-corrected.
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Simulation
Percent uptake — 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
A_corr
Decay-corrected organ activity
43.6105MBq
%UA
Percent uptake
11.79%
Explanation
What it means
Percent uptake is the decay-corrected organ activity as a fraction of injected activity. Classic thyroid uptake uses a probe at 24 h for I-131 or 4–6 h / 24 h for I-123. 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
A_org should already be geometry-calibrated (neck phantom). The calculator applies e^{+λt} to bring the organ assay back to injection time. Change one input and watch the curve and the simulation follow.
Symbols
- A_orgMeasured organ activity40 MBq
- A_injInjected activity370 MBq
- T½Half-life192.5 h
- tTime of measurement24 h
Worked example
A typical case from the default values: A_org = 40 MBq (Measured organ activity); A_inj = 370 MBq (Injected activity); T½ = 192.5 h (Half-life); t = 24 h (Time of measurement). Substituting into the relation gives A_corr = 43.6105 MBq; %UA = 11.79 %. These are teaching numbers — align them with your machine.
Typical values give
- A_corr = 43.6105MBq
- %UA = 11.79%
Where it comes from
The displayed formula is the working relation. Organ uptake as a percentage of injected activity, decay-corrected. Usual reference: Cherry / thyroid uptake. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Cherry / thyroid uptake
Assumptions & limits
Does not subtract thigh/background or apply a phantom standard. Therapy planning (Gy to thyroid) needs extra mass and S-value steps.
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. Does not subtract thigh/background or apply a phantom standard. Therapy planning (Gy to thyroid) needs extra mass and S-value steps.
Keep this
Write the assay time next to every activity. Decay does the rest. Does not subtract thigh/background or apply a phantom standard. Therapy planning (Gy to thyroid) needs extra mass and S-value steps.
In this specialty