NMD-11

Gamma-camera sensitivity

S = C / (A t). Counts per second per MBq in air.

Reading speed

Gamma cameraNEMA NU-1

Governing equation

S=C/(A t)

$A \in \left[0.5, 200\right]$

where

C: Counts (—)
A: Activity (MBq)
t: Live time (s)
S: Sensitivity (cps/MBq)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

S=C/(A t)

$A \in \left[0.5, 200\right]$

$A = 0.5$ $S = 8333.3$

Along the curve

②

Domain of the variable — blue

A_{\min} = 0.5,\quad A_{\max} = 200

$A \in \left[0.5, 200\right]$

$A = 0.5$ $A = 0.5$

Along the curve

③

Response curve — green

S=C/(A t)

$A \in \left[0.5, 200\right]$

$A = 0.5$ $S = 8333.3$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}S}{\mathrm{d}A}

$A \in \left[0.5, 200\right]$

$A = 1.755$ $S^{\prime} = -2769.1$

Along the curve

Lecture brief

Historical brief

MIRD schema, in-vivo decay, uptake fractions and PET coincidence turned unsealed sources into organ dose. The sheets compute activity, residence and well-counter geometry. This sheet (NMD-11 — Gamma-camera sensitivity) is the form associated with NEMA NU-1. Working symbols: $C$ , $A$ , $t$ $\rightarrow$ $S$ . LEHR collimators run ~70–100 cps/MBq. Sensitivity and resolution trade through hole geometry.

Purpose

Purpose: compute

S

from

C

A

t

in Nuclear medicine via

S=C/(A t)

S = C / (A t). Counts per second per MBq in air. Use it when a real nuclear medicine question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

C = 250000.000\,\mathrm{—}

A = 20.000\,\mathrm{MBq}

t = 60.000\,\mathrm{s}

, the governing relation

S=C/(A t)

yields

S = 208.3\,\mathrm{cps/MBq}

. A flood or point source, a count total, a sensitivity. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Counts C250000 —Activity A20 MBqLive time t60 s

Outputs

Sensitivity S208.3 cps/MBq

Reading speed

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Narration of this film

A flood or point source, a count total, a sensitivity.

LEHR collimators run ~70–100 cps/MBq. Sensitivity and resolution trade through hole geometry.

Reading speed

Watch on YouTube