NMD-13

Scatter fraction

SF = S / (T + S). Scatter over trues-plus-scatter.

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ScatterScatter fraction

Governing equation

\mathrm{SF}=S/(T+S)

$S \in \left[0, 200\right]$

where

T: Trues (kcps)
S: Scatter (kcps)
SF: Scatter fraction (—)

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

\mathrm{SF}=S/(T+S)

$S \in \left[0, 200\right]$

$S = 0$ $SF = 0$

Along the curve

②

Domain of the variable — blue

S_{\min} = 0,\quad S_{\max} = 200

$S \in \left[0, 200\right]$

$S = 0$ $S = 0$

Along the curve

③

Response curve — green

\mathrm{SF}=S/(T+S)

$S \in \left[0, 200\right]$

$S = 0$ $SF = 0$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}SF}{\mathrm{d}S}

$S \in \left[0, 200\right]$

$S = 1.258$ $SF^{\prime} = 0.012$

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-13 — Scatter fraction) is the form associated with Scatter fraction. Working symbols: $T$ , $S$ $\rightarrow$ $SF$ . PET SF is ~30–40 % in 3D, less in 2D with septa. SPECT SF depends on the energy window and patient size.

Purpose

Purpose: compute

SF

from

T

S

in Nuclear medicine via

\mathrm{SF}=S/(T+S)

SF = S / (T + S). Scatter over trues-plus-scatter. 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

T = 80.000\,\mathrm{kcps}

S = 35.000\,\mathrm{kcps}

, the governing relation

\mathrm{SF}=S/(T+S)

yields

SF = 0.304\,\mathrm{—}

. Two count pools, a ratio. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Trues T80 kcpsScatter S35 kcps

Outputs

Scatter fraction SF0.304 —

Reading speed

Watch on YouTube

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Narration of this film

Two count pools, a ratio.

PET SF is ~30–40 % in 3D, less in 2D with septa. SPECT SF depends on the energy window and patient size.

Reading speed

Watch on YouTube