Detective quantum efficiency

Last revised by Mostafa El-Feky on 24 Jan 2023

Detective quantum efficiency (DQE) is one of the fundamental physical variables related to image quality in radiography and refers to the efficiency of a detector in converting incident x-ray energy into an image signal.

The words "quantum efficiency" have a precise meaning, because the DQE measures the quantum efficiency of an equivalent virtual detector which produces at its output the same signal-to-noise ratio (SNR) of the real detector even when the input signal is the same.

The DQE is generally defined by the ratio of the squared output signal-to-noise ratio (SNRo)2 to the  squared input signal-to-noise ratio (SNRi)2 of the imaging detector.

DQE is dependent on radiation exposure, spatial frequency, modulation transfer function (MTF), and detector material. The quality (voltage and current) of the radiation applied is also an important influence on DQE.

DQE is therefore directly proportional to the MTF of a detector; as an imaging system, however, adds noise to the output information, the DQE is also in relation to SNR, with inverse proportionality. Thus, the DQE measures the SNR and MTF at various spatial frequencies.

High DQE values indicate that less radiation is needed to achieve identical image quality; increasing the DQE and leaving radiation exposure constant will improve image quality. The ideal detector would have a DQE of 1 (DQE 100% at all spatial frequencies), meaning that all the radiation energy is absorbed and converted into image information. In practice, a system loses efficiency on the high spatial frequencies (details), reaching values ​​between 40% and 50% (DQE 0,45) at low spatial frequencies (background).

In 2003, the IEC62220–1 standard was introduced to standardize DQE measurements and make them comparable.

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