Planar x-ray Imaging Flashcards
Define: Contrast Resolution
Ability to discriminate a structure from the surrounding background
Define: Spacial Resolution
The ability to discriminate structures that are close together
Recall: the equation for contrast
C = |Mout - Min| / Max(Min, Mout)
Recall: the signal to noise ration
SNR = |Tout - Tin| / sigma_out
Define: Tin
Tin = Min * detail surface area
Define: the point spread function
The response of the system to a point-like system (Poissonian)
Recall: the equation for MTF
MTF = output Amp / Input amp
Describe the relationship between the MTF and PSF
The MTF is the Fourier transform of the PSF
MTF goes to higher frequencies for sharper PSFs
Describe the relationship between energy and dose
Low energy = high dose
Recall: the X-ray specific contrast equation
C = (1 - e^(-mu x)) / (1 + R)
Name the spruces of noise in planar X-ray imaging
Quantum noise (poissonian stats)
Noise in the detector
Name the desirable characteristics in X-ray imaging
Max SNR
High efficiency
Low noise
Linear response
High spacial resolution
Low cost
Define: pixel pitch
Distance between pixel centres
Define: pixel size
Dimensions of detectors active pixel area
Define: Alaising
Incorrect reproduction of signal frequency/period due to a too high step
Recall: Nyquists theorem
The frequency at which alaising occurs
f = 1/ (2p)
Define: angiography
Anatomical structures reduce visibility of blood vessels even when a contrast is used
“Mask” acquired before medium injection and a second image acquired after
Mask logarithmically subtracted from the second image
Define: Fluroscopy
Real-time acquisition of a sequence of low dose images to highlight dynamics or aid medical procedures
Contrast medium required
Define: phase contrast imaging
X-rays produce interface patterns
When crossing an object there’s a phase shift
Interference occurs between perturbed and unperturbed wave
Need spatially coherent source
