Fluoroscopy (Diagnostic Radiology) Flashcards Preview

Medical Physics 2nd Semester > Fluoroscopy (Diagnostic Radiology) > Flashcards

Flashcards in Fluoroscopy (Diagnostic Radiology) Deck (38)
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1

Exposure differences between radiograph and fluroscopy

Radiograph has a larger exposure rate, but is instant.

Fluroscopy has lower exposure rate, but is held for longer. Overall two orders of magnitude larger.

2

Approximately how much does the image intensifier amplify the brightness by?

~10,000

3

Why is the input screen curved?

For accurate electron focusing

4

What is the function of the input phosphor in the image intensifier?

Converts x-rays into scintillation photons

Then, the scintillation photons are converted to electrons

5

Minification gain equation

Areainput / Areaoutput

6

Signal density (increases or decreases) with minification gain?

Increases

7

True or false

When entering magnification mode, minifaction will decrease

True

8

Regarding the Output phosphor what is the...

Input:

Output:

Input: Accelerated electrons

Output: Multiple photons

 

1 electron emits ~ 1000 light photons

9

What is the term called for a fall off in brightness at the periphery of an image?

 

Occurs from scatter form periphery contributing to center

There is no scatter outside active image to contribute to periphery

Vignetting

10

What is a concern of a high x-ray flux impinging on a region of the II?

Brightness saturation

Yields a maximum level of brightness and display can't be any more bright if radiation increases. Gray scale won't display

11

Nice diagram of conversion steps of image intensifier

12

What is a quantum sink

Result of quanta at next step being less than current step

 

Ex. x-rays absorbed by input screen of image intensifier

13

Equation for brightness gain

BG = Flux gain x minification gain

14

What is flux gain defined as?

light photons at output / light photons at input

15

A smaller area into input phosphor means that brightness gain will decrease.

 

Because of this, the automatic brightness control needs to compensate for the dimmer image by boosting the x-ray exposure rate (by increasing kV, mA or both).

 

How much does exposure rate change when cutting FOV in half?

Increases by factor of 4

16

When dealing with the automatic brightness control,

Increasing mA will _______ dose and ________ contrast.

increase and increase

17

When dealing with the automatic brightness control,

Increasing kVp will _______ dose and ________ contrast.

decrease and decrease

18

What is typically the limiting component of the imaging chain in terms of spatial resolution degradation?

The television display!

19

For thin film transistor replacing image intensifier,

 

Smaller detector elements sizes would ________ the spatial resolution but __________ noise. It would also _______ dose.

improve

create more

increase dose (since noise is increased, more dose is required)

20

What are some benefits to using flat panel detectors over image intensifiers?

All around higher QDE at all kV energies

Directly records real time image

Compact

Similar or better resolution

Can correct pixel sensitivities

 

Biggest con: expensive

21

What conversion occurs during the intermediate step of indirect detection fluroscopy?

X-ray converted to light photons

22

Binning detector elements will,

______ data bandwidth

_______ SNR

_______ spatial resolution

Reduce

Increase

Reduce

23

What is the limiting factor of the spatial resolution in a flat panel detector (FPD)?

DEL size

24

What is the main limiting factor of spatial resolution in image intensifier / TV system?

Video system

(can be improved with magnification, smaller FOV)

25

Moving anatomy closer to image receptor will ______ focal spot blur and ______ patient dose.

Decrease

Decrease

26

Frame averaging may produce __________ and introduce _____________

Ghost artifact

motion blur

 

(in whichever order)

27

Why is contrast resolution of fluroscopy lower compared to radiography?

Due to the lower exposure per fram (low SNR)

28

Benefits of pulsed fluoroscopy

Reduce motion blur

Provide better spatial resolution

29

Frame averagin can be used in fluoro to reduce _______

Quantum noise

30

Approximately what fraction of the dose is delivered in the first 3-5 cm of tissue?

1/2