IMG-05

Dose–length product

DLP = CTDIvol × L. The scan-length integral used for DRL audits.

Reading speed

CT doseDLPEUR 16262

Governing equation

\mathrm{DLP}=\mathrm{CTDI}_{vol}\,L

$L \in \left[5, 80\right]$

where

CTDI_{vol}: CTDIvol (mGy)
L: Scan length (cm)
DLP: Dose–length product (mGy·cm)

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{DLP}=\mathrm{CTDI}_{vol}\,L

$L \in \left[5, 80\right]$

$L = 5$ $DLP = 50$

Along the curve

②

Domain of the variable — blue

L_{\min} = 5,\quad L_{\max} = 80

$L \in \left[5, 80\right]$

$L = 5$ $L = 5$

Along the curve

③

Response curve — green

\mathrm{DLP}=\mathrm{CTDI}_{vol}\,L

$L \in \left[5, 80\right]$

$L = 5$ $DLP = 50$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}DLP}{\mathrm{d}L}

$L \in \left[5, 80\right]$

$L = 5.472$ $DLP^{\prime} = 10$

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-05 — Dose–length product) is the form associated with DLP · EUR 16262. Working symbols: $CTDI_{vol}$ , $L$ $\rightarrow$ $DLP$ . Effective dose ≈ k × DLP with k a body-region coefficient (e.g. 0.014 mSv/mGy·cm chest).

Purpose

Purpose: compute

DLP

from

CTDI_{vol}

L

in Medical imaging via

\mathrm{DLP}=\mathrm{CTDI}_{vol}\,L

DLP = CTDIvol × L. The scan-length integral used for DRL audits. 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

CTDI_{vol} = 10.000\,\mathrm{mGy}

L = 30.000\,\mathrm{cm}

, the governing relation

\mathrm{DLP}=\mathrm{CTDI}_{vol}\,L

yields

DLP = 300.0\,\mathrm{mGy·cm}

. A helical scan, a length L, a DLP bar. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

CTDIvol CTDI_{vol}10 mGyScan length L30 cm

Outputs

Dose–length product DLP300.0 mGy·cm

Reading speed

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Narration of this film

A helical scan, a length L, a DLP bar.

Effective dose ≈ k × DLP with k a body-region coefficient (e.g. 0.014 mSv/mGy·cm chest).

Reading speed

Watch on YouTube