IMG-04

CTDIvol

CTDIvol = (1/pitch)(⅓ CTDIc + ⅔ CTDIp). Weighted, pitch-corrected CT dose index.

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CT doseIEC CTDIAAPM TG-23

Governing equation

\mathrm{CTDI}_{vol}=\dfrac1p\left(\tfrac13\mathrm{CTDI}_c+\tfrac23\mathrm{CTDI}_p\right)

where

CTDI_c: Centre CTDI (mGy)
CTDI_p: Periphery CTDI (mGy)
p: Pitch (—)
CTDI_{vol}: CTDIvol (mGy)

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-04 — CTDIvol) is the form associated with IEC CTDI · AAPM TG-23. Working symbols: $CTDI_c$ , $CTDI_p$ , $p$ $\rightarrow$ $CTDI_{vol}$ . Centre and periphery of a 16 or 32 cm phantom. CTDIvol is a scanner output, not organ dose.

Purpose

Purpose: compute

CTDI_{vol}

from

CTDI_c

CTDI_p

p

in Medical imaging via

\mathrm{CTDI}_{vol}=\dfrac1p\left(\tfrac13\mathrm{CTDI}_c+\tfrac23\mathrm{CTDI}_p\right)

CTDIvol = (1/pitch)(⅓ CTDIc + ⅔ CTDIp). Weighted, pitch-corrected CT dose index. 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_c = 12.000\,\mathrm{mGy}

CTDI_p = 18.000\,\mathrm{mGy}

p = 1.000\,\mathrm{—}

, the governing relation

\mathrm{CTDI}_{vol}=\dfrac1p\left(\tfrac13\mathrm{CTDI}_c+\tfrac23\mathrm{CTDI}_p\right)

yields

CTDI_{vol} = 16.00\,\mathrm{mGy}

. A CTDI phantom, centre and rim chambers. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Centre CTDI CTDI_c12 mGyPeriphery CTDI CTDI_p18 mGyPitch p1 —

Outputs

CTDIvol CTDI_{vol}16.00 mGy

Reading speed

Watch on YouTube

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Narration of this film

A CTDI phantom, centre and rim chambers.

Centre and periphery of a 16 or 32 cm phantom. CTDIvol is a scanner output, not organ dose.

Reading speed

Watch on YouTube