1.3 X-ray Detection

Question 1

x-ray detection methods

Answer 1

analog and digital

Question 2

x-ray detection constraints

Answer 2

intensity/flux
spatial resolution
x-ray energy
energy resolution

Question 3

intensity/flux unit ?

Answer 3

photons/sec/surface area

Question 4

the resolution is fully characterized by:

Answer 4

point spread function or line spread function

Question 5

psf/lsf describes

Answer 5

detector response to a single point/line shaped illumination function

Question 6

fourier of psf

Answer 6

MTF
modulation transfer function

Question 7

mtf plot axis names

Answer 7

x: spatial frequency (line pairs/milimeter)
y: contrast

Question 8

psf plot axis names

Answer 8

x: intensity
position(mm)

Question 9

for better resolution FWHM should be

Answer 9

low

Question 10

dynamic range is defined as

Answer 10

ratio of the maximum to minimum signal flux which can be detected at the linear range of the detector

Question 11

minimum signal is typically given by

Answer 11

read-out or detector noise
NOT poisson limited

Question 12

maximum signal is limited by

Answer 12

saturation of the signal

Question 13

Quantum Efficiency (QE)

Answer 13

the fraction of x-ray photons that are
absorbed in the detection layer

Question 14

Detective Quantum Efficiency (DQE):

Answer 14

ratio of the detected signal-to-noise ratio (typically not Poisson) to the incoming signal-to-noise ratio (typically Poisson).

Question 15

analog imaging detectors:

digital imaging detectors:

Answer 15

Analogue imaging detectors:
* photographic film (x-ray modified)

Digital imaging detectors :
* „charge-coupled devices“ (CCDs)
* flat-panel detectors
* future: photon-counting spectral pixel detectors

Question 16

photographic film working principle

Answer 16

x-ray absorption leads to splitting of AgBr crystal into ions the oxidized silver develops and appears black on screen

Question 17

digital detectors working principle

Answer 17

photons create electron hole pairs, we can

measure average current
measure integrated charge per unit time
count single photons:
count single photons and measure individual changes

Question 18

avg current detection is not

Answer 18

efficient

Question 19

integrated charge detection examples

Answer 19

x-ray film(ANALOGUE)
CCD
flat-panel