DQE , NPS and MTF Clearly Explained (Detective Quantum Efficiency)

DQE , NPS and MTF are related quantities to quantify the image quality in medical imaging such as x-ray and CT.
The Detective Quantum Efficiency (DQE) is related to the Modulation Transfer Function (MTF) and the Noise Power Spectrum.
The DQE is more foundationally defined as the SNR_in (signal to noise input) divided by the SNR_out (signal to noise output).