DR systems Flashcards

1
Q

what are some advantages of Digital Radiography

A

wide latitude
ability to window image to exploit this dynamic range
ability to process and store the images on the computer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

the thin film transistor array (TFT) is common to both indirect and direct DR systems. True or False

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what does the detector element consist of?

A

TFT
charge collection electrode
charge collection capacitor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what connects the TFT and the capacitor

A

the gate and drain lines connect the TFT and the capacitor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

the TFT is ____ during exposure, allowing the charge that is produced to be stored in the ____

A

the TFT is closed during exposure, allowing the charge that is produced to be stored in the capacitor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

when the X-Ray exposure is terminated, one gate line at a time is set to a ___ _____ which activates the ___ along that row

A

when the x-ray exposure is terminated, one gate line at a time is set to a high voltage which activates the TFTs along that row

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

charge flows from the ____ to the transistors and down the ____ in parallel

A

charge flows from the capacitors to the transistors and down the drain lines in parallel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the charge met with at the column of each matrix

A

output charge amplifiers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what effect does deactivating the gate line have?

A

deactivating the gate line will reset the TFTs for the next exposure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the fill factor

A

the percentage of the detector element that collects the charge from the energy deposited by the photons in the converter material
- basically the area of the detector that can take X-Rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

name some dead areas of the detector

A

the TFT
the capacitor
the gate and drain connections

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the effect of a smaller detector element on fill factor and DQE

A

as detector element gets smaller, the fill factor and DQE gets smaller

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is a typical range for a fill factor

A

0.5-0.8

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is used as the detector material in direct conversion systems

A

amorphous selenium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

in direct systems, where in relation to the TFT layer is the photoconductor

A

it is on top of the TFT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what does the large voltage placed between the two electrodes (between selenium) have

A

this reduces the spread of ion pairs and prevents recombination

17
Q

advantages of direct conversion systems

A

simpler TFT structure with no photodiode
high intrinsic spatial resolution due to high voltage ion spread
selenium plates are easy to manufacture

18
Q

disadvantages of direct conversion systems

A

charge trapping in thick selenium layer reducing absorption efficiency, increases signal retention and causes greater lag
can damage TFT due to over charging caused by high x-ray exposures

19
Q

difference between direct and indirect DR systems

A

indirect DR systems have the addition of an amorphous silicon photodiode and a scintillator made of CsI on top of the TFT

20
Q

what does the photodiode and scintillator do

A

converts x-ray photons to light photons proportional to the incident x-ray intensity

21
Q

what happens to the light photons in indirect DR

A

The light photons are converted to an electric charge by the amorphous silicon photodiode

22
Q

how is the light spread in the scintillator reduced

A

the light spread in the scintillator is reduced by structuring the scintillator CsI into crystal needles

23
Q

spatial resolution is determined by ___ in DR systems

A

spatial resolution is determined by pixel size in DR systems

24
Q

what determines pixel size in DR systems

A

pixel size is determined by the size of the detector element

25
Q

what is the spatial resolution for DR systems

A

2.5-5lp/mm

26
Q

DR vs CR

A

More rapid image production in DR, higher DQE, similar spatial resolution