Planar x-ray Imaging

Question 1

Define: Contrast Resolution

Answer 1

Ability to discriminate a structure from the surrounding background

Question 2

Define: Spacial Resolution

Answer 2

The ability to discriminate structures that are close together

Question 3

Recall: the equation for contrast

Answer 3

C = |Mout - Min| / Max(Min, Mout)

Question 4

Recall: the signal to noise ration

Answer 4

SNR = |Tout - Tin| / sigma_out

Question 5

Define: Tin

Answer 5

Tin = Min * detail surface area

Question 6

Define: the point spread function

Answer 6

The response of the system to a point-like system (Poissonian)

Question 7

Recall: the equation for MTF

Answer 7

MTF = output Amp / Input amp

Question 8

Describe the relationship between the MTF and PSF

Answer 8

The MTF is the Fourier transform of the PSF

MTF goes to higher frequencies for sharper PSFs

Question 9

Describe the relationship between energy and dose

Answer 9

Low energy = high dose

Question 10

Recall: the X-ray specific contrast equation

Answer 10

C = (1 - e^(-mu x)) / (1 + R)

Question 11

Name the spruces of noise in planar X-ray imaging

Answer 11

Quantum noise (poissonian stats)
Noise in the detector

Question 12

Name the desirable characteristics in X-ray imaging

Answer 12

Max SNR
High efficiency
Low noise
Linear response
High spacial resolution
Low cost

Question 13

Define: pixel pitch

Answer 13

Distance between pixel centres

Question 14

Define: pixel size

Answer 14

Dimensions of detectors active pixel area

Question 15

Define: Alaising

Answer 15

Incorrect reproduction of signal frequency/period due to a too high step

Question 16

Recall: Nyquists theorem

Answer 16

The frequency at which alaising occurs
f = 1/ (2p)

Question 17

Define: angiography

Answer 17

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

Question 18

Define: Fluroscopy

Answer 18

Real-time acquisition of a sequence of low dose images to highlight dynamics or aid medical procedures
Contrast medium required

Question 19

Define: phase contrast imaging

Answer 19

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