detector characteristics

contrast resolution is determined by

bit depth

spatial resolution is determined by

pixel size

what determines noise

signal-to-noise ratio

image data exists as

sinusoidal waves

smaller objects have what wave frequency

higher frequency

larger objects have what wave frequency

lower wave frequency

what is spatial frequency

number of repetitions per unit of space

as spatial frequency goes up

structure size goes down

spatial frequency measurement

cycles per mm

What is nyquist frequency

max spatial resolution a detector can yield

ina PSP the pixel size is determiend by

sampling frequency

nyquist frequency equation

½ of pixel density

pixel density measurement

pixels/mm

Nyquist frequency is measured in

lp/mm

the highest pixel density means

highest spatial resolution

What is nyquist criterion

if the sampling frequency 2 times nyquist frequency an image can be accurately reconstructed

if the Nyquist frequency is 2 cycles/mm, the sampling rate must be what to get from having noise

4 pixels/mm

oversampling

if the sampling is significantly more than 2x per wave cycle

result of oversampling

longer processing time and larger file size

undersampling

sampling less than 2 times per cycle

result of under sampling

aliasing

what is aliasing

an inaccurate representation of structures and objects

what kind os structures are more likely to have noise due to undersampling

high frequency / small structures

wave amplitude represents

contrast

amplitude decrease is larger with

high-frequency signals (small structures)

MTF

modulation transfer function

what is modulation transfer function

objective measure of detector spatial resolution

How does MTF objectively measure spatial resolution

measures the detector’s ability to transfer the signal (maintain contrast from the object)

a high MTF yeilds

high spatial resolution

DQE stands for

detective quantum efficiency

What is detective quantum efficiency?

objective measure of how well a detector holds on to data (reduces noise)

DQE is an indicator of

dose required to produce a high quality image