03 Nuclear

Pediatric activity (Clark)

Scale adult administered activity by body weight.

Play lecture Cast to TV

Listen

Listen · English

Simulation

Pediatric activity (Clark) — Change the numbers; the scene follows.

Where it works

Hot lab

Dose calibrator

In the dose calibrator well — assayed activity, decay between two times, Marinelli.

Open this machine

Formula

A_{\mathrm{child}} = A_{\mathrm{adult}}\cdot\frac{m}{70}

Variables

A_ad · Adult activityMBqm · Child weightkgm_ref · Reference weightkg

Results

A_ch
Child activity
105.7MBq

Explanation

A_{\mathrm{child}} = A_{\mathrm{adult}}\cdot\frac{m}{70}

What it means

Clark’s rule scales adult activity by child/adult weight (reference 70 kg). It is a starting point only — EANM and SNMMI paediatric cards use more sophisticated (often class/weight) schedules and minima. This is a working relation in Nuclear medicine.

Where it is used

Clinically it sits on the Hot lab — Dose calibrator. In the dose calibrator well — assayed activity, decay between two times, Marinelli. 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.

Hot lab · Open this machine

How to use it

Enter adult activity and child weight. Always check the procedure-specific card (e.g. EANM dosage card 2016) and a minimum activity so the scan remains diagnostic. Change one input and watch the curve and the simulation follow.

Symbols

A_adAdult activity370 MBq
mChild weight20 kg
m_refReference weight70 kg

Worked example

A typical case from the default values: A_ad = 370 MBq (Adult activity); m = 20 kg (Child weight); m_ref = 70 kg (Reference weight). Substituting into the relation gives A_ch = 105.7 MBq. These are teaching numbers — align them with your machine.

Typical values give

A_ch = 105.7MBq

Where it comes from

The displayed formula is the working relation. Scale adult administered activity by body weight. Usual reference: Clark's rule / EANM paediatric dosage card. Derive it in the specialty lesson, then return here to pin the numbers.

Reference: Clark's rule / EANM paediatric dosage card

Assumptions & limits

Linear with weight; ignores organ fraction, photon energy, and the fact that smaller patients need relatively more activity for comparable counts. Not for therapy (I-131, Lu-177).

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. Linear with weight; ignores organ fraction, photon energy, and the fact that smaller patients need relatively more activity for comparable counts. Not for therapy (I-131, Lu-177).

Keep this

Rule of thumb. Use EANM/SNMMI paediatric guidelines per study.

In this specialty

Nuclear medicine