IMG-21

Mean glandular dose

MGD = DgN × K. Conversion from entrance air kerma.

Reading speed

MammographyDance MGD

Governing equation

\mathrm{MGD}=D_{gN}K

$K \in \left[1, 20\right]$

where

D_{gN}: Conversion DgN (mGy/mGy)
K: Entrance air kerma (mGy)
MGD: Mean glandular dose (mGy)

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{MGD}=D_{gN}K

$K \in \left[1, 20\right]$

$K = 1$ $MGD = 0.2$

Along the curve

②

Domain of the variable — blue

K_{\min} = 1,\quad K_{\max} = 20

$K \in \left[1, 20\right]$

$K = 1$ $K = 1$

Along the curve

③

Response curve — green

\mathrm{MGD}=D_{gN}K

$K \in \left[1, 20\right]$

$K = 1$ $MGD = 0.2$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}MGD}{\mathrm{d}K}

$K \in \left[1, 20\right]$

$K = 1.119$ $MGD^{\prime} = 0.2$

Along the curve

Lecture brief

Historical brief

Larmor precession, CT Beer projections, SNR and Nyquist sampling are why MRI and CT images exist as numbers. The lab computes frequency, dose and resolution limits. This sheet (IMG-21 — Mean glandular dose) is the form associated with Dance MGD. Working symbols: $D_{gN}$ , $K$ $\rightarrow$ $MGD$ . Dance: MGD = K g c s, with g HVL, c glandularity, s spectrum. Typical MGD 1–2 mGy per view.

Purpose

Purpose: compute

MGD

from

D_{gN}

K

in Medical imaging via

\mathrm{MGD}=D_{gN}K

MGD = DgN × K. Conversion from entrance air kerma. Use it when a real medical imaging question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

D_{gN} = 0.200\,\mathrm{mGy/mGy}

K = 8.000\,\mathrm{mGy}

, the governing relation

\mathrm{MGD}=D_{gN}K

yields

MGD = 1.600\,\mathrm{mGy}

. A compressed breast and a glandular-dose bar. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Conversion DgN D_{gN}0.2 mGy/mGyEntrance air kerma K8 mGy

Outputs

Mean glandular dose MGD1.600 mGy

Reading speed

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Narration of this film

A compressed breast and a glandular-dose bar.

Dance: MGD = K g c s, with g HVL, c glandularity, s spectrum. Typical MGD 1–2 mGy per view.

Reading speed

Watch on YouTube