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

Fluoroscopy (Diagnostic Radiology) Flashcards

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1
Q

Exposure differences between radiograph and fluroscopy

A

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.

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2
Q

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

A

~10,000

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3
Q

Why is the input screen curved?

A

For accurate electron focusing

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4
Q

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

A

Converts x-rays into scintillation photons

Then, the scintillation photons are converted to electrons

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5
Q

Minification gain equation

A

Areainput / Areaoutput

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6
Q

Signal density (increases or decreases) with minification gain?

A

Increases

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7
Q

True or false

When entering magnification mode, minifaction will decrease

A

True

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8
Q

Regarding the Output phosphor what is the…

Input:

Output:

A

Input: Accelerated electrons

Output: Multiple photons

1 electron emits ~ 1000 light photons

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9
Q

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

A

Vignetting

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10
Q

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

A

Brightness saturation

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

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11
Q

Nice diagram of conversion steps of image intensifier

A
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12
Q

What is a quantum sink

A

Result of quanta at next step being less than current step

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

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13
Q

Equation for brightness gain

A

BG = Flux gain x minification gain

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14
Q

What is flux gain defined as?

A

light photons at output / light photons at input

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15
Q

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?

A

Increases by factor of 4

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16
Q

When dealing with the automatic brightness control,

Increasing mA will _______ dose and ________ contrast.

A

increase and increase

17
Q

When dealing with the automatic brightness control,

Increasing kVp will _______ dose and ________ contrast.

A

decrease and decrease

18
Q

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

A

The television display!

19
Q

For thin film transistor replacing image intensifier,

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

A

improve

create more

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

20
Q

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

A

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
Q

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

A

X-ray converted to light photons

22
Q

Binning detector elements will,

______ data bandwidth

_______ SNR

_______ spatial resolution

A

Reduce

Increase

Reduce

23
Q

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

A

DEL size

24
Q

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

A

Video system

(can be improved with magnification, smaller FOV)

25
Q

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

A

Decrease

Decrease

26
Q

Frame averaging may produce __________ and introduce _____________

A

Ghost artifact

motion blur

(in whichever order)

27
Q

Why is contrast resolution of fluroscopy lower compared to radiography?

A

Due to the lower exposure per fram (low SNR)

28
Q

Benefits of pulsed fluoroscopy

A

Reduce motion blur

Provide better spatial resolution

29
Q

Frame averagin can be used in fluoro to reduce _______

A

Quantum noise

30
Q

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

A

1/2

31
Q

Where is dose rate measured for a GI unit, and for a C-arm unit?

A

GI - 1 cm above table

C-arm: 15 cm from isocenter towards source

32
Q

Which of the following when increased, will increase patient dose?

  1. kVp
  2. beam current
  3. Fluro time
  4. Beam filtration
  5. Collimation
  6. grid
  7. ABC
  8. Magnification
  9. Pulsed fluoro
A
  1. No
  2. Yes
  3. Yes
  4. No
  5. No
  6. Yes
  7. Yes or No
  8. Yes (total brightness gain falls, image is dimmer, ABC compensates by raising dose)
  9. No
33
Q

What is the optimal way to position the patient to reduce dose and improve spatial resolution?

A

Close to image receptor, far from x-ray source

34
Q

Increasing OID will have what changes to…

  • Magnification
  • Dose
  • Scatter to image receptor
  • Scatter to medical staff
  • Focal spot blurring
A
  • Magnification - increase
  • Dose - increase
  • Scatter to image receptor - reduce
  • Scatter to medical staff - increase
  • Focal spot blurring - increase
35
Q

Approximately how much does scattered radiation drop for every 1 meter distance from patient?

A

Drops to 0.001

Ex. 3 meters away, drops to 0.0013 of original entrance

36
Q

What is the approximate skin dose threshold for fluoro?

A

2 Gy

37
Q

How does dose area product change with increased distance from source?

A

It doesn’t change.

DAP is the product of dose over some area. Moving away will decrease dose by inverse square law, but increase area by inverse square law.

Product remains constant

38
Q

Assuming ABC maintains brightness going from FOV1 to FOV2 what is the ratio of DFOV1 to DFOV2

A

(FOV1/FOV2)2

Medical Physics 2nd Semester (7 decks)

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