IMG-27

Detective quantum efficiency

DQE = MTF² / (q NPS). How well the detector uses incoming quanta.

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Image qualityIEC 62220 DQE

Governing equation

\mathrm{DQE}=\mathrm{MTF}^{2}/(q\,\mathrm{NPS})

$MTF \in \left[0.05, 1\right]$

where

MTF: MTF at f (—)
q: Incident quanta q (1/mm²)
NPS: Noise power NPS (mm²)
DQE: Detective QE (—)

The figure, part by part

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①

Governing law — red

\mathrm{DQE}=\mathrm{MTF}^{2}/(q\,\mathrm{NPS})

$MTF \in \left[0.05, 1\right]$

$MTF = 0.05$ $DQE = 0.003$

Along the curve

②

Domain of the variable — blue

MTF_{\min} = 0.05,\quad MTF_{\max} = 1

$MTF \in \left[0.05, 1\right]$

$MTF = 0.05$ $MTF = 0.05$

Along the curve

③

Response curve — green

\mathrm{DQE}=\mathrm{MTF}^{2}/(q\,\mathrm{NPS})

$MTF \in \left[0.05, 1\right]$

$MTF = 0.05$ $DQE = 0.003$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}DQE}{\mathrm{d}MTF}

$MTF \in \left[0.05, 1\right]$

$MTF = 0.056$ $DQE^{\prime} = 0.112$

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-27 — Detective quantum efficiency) is the form associated with IEC 62220 DQE. Working symbols: $MTF$ , $q$ , $NPS$ $\rightarrow$ $DQE$ . DQE(0) ≤ absorption efficiency. A good flat panel is 0.6–0.7 at low f; film/screen was ~0.2.

Purpose

Purpose: compute

DQE

from

MTF

q

NPS

in Medical imaging via

\mathrm{DQE}=\mathrm{MTF}^{2}/(q\,\mathrm{NPS})

DQE = MTF² / (q NPS). How well the detector uses incoming quanta. 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

MTF = 0.500\,\mathrm{—}

q = 50000.000\,\mathrm{1/mm^{2}}

NPS = 2.000e-5\,\mathrm{mm^{2}}

, the governing relation

\mathrm{DQE}=\mathrm{MTF}^{2}/(q\,\mathrm{NPS})

yields

DQE = 0.250\,\mathrm{—}

. An input fluence, an output NPS, a DQE bar. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

MTF at f MTF0.5 —Incident quanta q q50000 1/mm²Noise power NPS NPS0.00002 mm²

Outputs

Detective QE DQE0.250 —

Reading speed

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Narration of this film

An input fluence, an output NPS, a DQE bar.

DQE(0) ≤ absorption efficiency. A good flat panel is 0.6–0.7 at low f; film/screen was ~0.2.

Reading speed

Watch on YouTube