02 Imaging

Detective quantum efficiency DQE

DQE(f) = SNR_out² / SNR_in² = MTF²(f) / (u² NPS) × (incident quanta).

Play lecture Cast to TV

Listen

Listen · English

Simulation

Detective quantum efficiency DQE — Change the numbers; the scene follows.

Where it works

Radiography room

Bucky / detector

In the Bucky / detector: grid, AEC, DQE, and the pixel that samples the image.

Open this machine

Formula

\mathrm{DQE}(0)=\frac{\mathrm{SNR}_{\mathrm{out}}^2}{\mathrm{SNR}_{\mathrm{in}}^2}

Variables

SNR_out · Output SNRSNR_in · Input SNR

Results

DQE(0)
Detective quantum efficiency
0.64
DQE
DQE
64%

Explanation

\mathrm{DQE}(0)=\frac{\mathrm{SNR}_{\mathrm{out}}^2}{\mathrm{SNR}_{\mathrm{in}}^2}

What it means

DQE is the fraction of incoming Poisson information that the detector actually uses. A perfect detector has DQE=1; a real CsI DR panel is 0.6–0.7 at low frequency and falls with MTF². CR is ~0.2–0.3. Raising DQE is how manufacturers cut dose at equal image quality — it is the number to ask for, not just pixel size. This is a working relation in Diagnostic imaging.

Where it is used

Clinically it sits on the Radiography room — Bucky / detector. In the Bucky / detector: grid, AEC, DQE, and the pixel that samples the image. Diagnostic equations live on the tube, the detector, and the patient: magnification, air kerma, CTDI, and why bone lights up at 70 kV. They turn a technique chart into physics you can defend.

Radiography room · Open this machine

How to use it

Enter SNR_out and SNR_in (or incident quanta and measured SNR). DQE at f=0 is this ratio of squares. A panel with SNR_in = 100 (from √N) and SNR_out = 80 has DQE(0) = 0.64. Change one input and watch the curve and the simulation follow.

Symbols

SNR_outOutput SNR80
SNR_inInput SNR100

Worked example

A typical case from the default values: SNR_out = 80 (Output SNR); SNR_in = 100 (Input SNR). Substituting into the relation gives DQE(0) = 0.64; DQE = 64 %. These are teaching numbers — align them with your machine.

Typical values give

DQE(0) = 0.64
DQE = 64%

Where it comes from

The displayed formula is the working relation. DQE(f) = SNR_out² / SNR_in² = MTF²(f) / (u² NPS) × (incident quanta). Usual reference: IEC 62220 / Bushberg. Derive it in the specialty lesson, then return here to pin the numbers.

Reference: IEC 62220 / Bushberg

Assumptions & limits

Zero-frequency DQE only. Full DQE(f) needs measured MTF and NPS (IEC 62220). Additive electronic noise makes DQE dose-dependent at low exposure.

Pitfalls

kVp is not the same as effective energy. CTDI is not patient dose — SSDE and organ dose come after. Do not quote DLP as if it were effective dose without a k-factor. Zero-frequency DQE only. Full DQE(f) needs measured MTF and NPS (IEC 62220). Additive electronic noise makes DQE dose-dependent at low exposure.

Keep this

Technique is physics: kV sets contrast, mAs sets noise, filtration sets the spectrum. Zero-frequency DQE only. Full DQE(f) needs measured MTF and NPS (IEC 62220). Additive electronic noise makes DQE dose-dependent at low exposure.

In this specialty

Diagnostic imaging