Imaging 2 M1L4

• modulation transfer function: Measures the ability of the detector to transfer it’s spatial resolution characteristics to the image. quantifies the loss or gain of resolution
• an MTF of zero means no image is recorded
• a MTF of 1 means perfect image is recorded. There was no loss of information
• spatial resolution is described by the “modulation transfer function”
• MTF is measured separately for each component in the recording system (monitor, detector, cables and wires etc). Total MTF is the product of all the subcomponents.
• MTF graph: the flatter the line, the lower the MTF
• DR has a higher MTF for small objects due to its wide dynamic range and high DQE
• Signal-to-noise ratio is a measure of contrast resolution
• High signal to noise ratio is ideal
• Digital imaging systems SNR 1000:1
• Spatial Resolution for DR: Is determined by size of detector elements (pixels). Size is limited due to requirements of electronics. decrease pixel size = decreased light/photon absorption.
• Fill factor = ratio of light sensitive area to the entire area of the detector element
• How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency.
• DQE = SNR2out / SNR2in
• DQE: value range from 0-1.
• A perfect system would have a DQE of 1 (no information is lost between detector input and detector output)
• SNR = signal (useful info)/ noise (erratic info)
• High SNR captures the greatest amount of useful image info
• Advantages of high DQE: Lower dose, increase ability to visualize small low contrast objects
• Direct method has increased spatial resolution over indirect due to no divergence of light.
• direct DR has best DQE, while film has the lowest