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Physics > Fluoroscopy > Flashcards

Fluoroscopy Flashcards

1
Q

Difference between fluoro and rads when discussing mA?

A

Fluoro: low mA (0-5) Rads: High mA (200-800)

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2
Q

Fluoro vs rads: spatial resolution

A

Rads are better

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3
Q

Fluoro vs rads: Contrast

A

Rads are better

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4
Q

Fluoro vs rads: Temporal resolution

A

Fluoro is better

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5
Q

Difference between “Spot hold” and “Last Image Hold”

A

Spot hold - like regular rad

Last image hold - more quantum mottle - just the last image of the fluoro image

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6
Q

Two types of fluoroscopic mechanism

A

1) Image intensifiers
2) Flat Panel Detectors

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7
Q

Source from above the table causes higher or low dose to technician?

A

Higher

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8
Q

Brightness gain is a combo of?

A

Flux gain - 50x (this stays pretty much the same and is caused by the difference between photocathode and anode) - This is how fast those fuckers are flying (electrons)

Minification gain - The image getting smaller at the out put phosphor concentrates photons

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9
Q

How does EM change in an image intensifier? Basically how is the x-ray signal transmitted through the system.

A

x-ray—-(Input phosphor) light—- (Photocathode) electrons—- Focusing electrodes (flux gain)—- (Smaller output phosphor) light

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10
Q

Electrons lens or Electrostatic focusing lens does what?

A
  1. Focuses the beam to a focal point (in control of electronic magnification)
  2. Speed up electrons
  3. Reserves and Inverted image
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11
Q

Why is the output phosphor made out of zinc-cadmium sulfide?

A

To keep the output phosphor thin and therefore maintain spatial res.

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12
Q

What are special characteristics of cesium iodide (CsI) in the input phosphor?

A

1) Packed tight together: more efficient at gathering electrons
2) Vertical orientation of crystal needles: Reduces lateral light diffusion
3) K-edge: more absorption
4) Thickness of CsI is also less than old ZnCdS and therefore improved spatial resolution

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13
Q

Conversion gain

A

New way to say brightness gain

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14
Q

What happens to conversion or brightness gain over time?

A

Loss of 10% over 1 year so Automatic brightness converter cranks technique and dose goes up

once 50% of previous it is time to throw away.

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15
Q

Spatial res for Image intensifier?

A

~4 Line pair/mm

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16
Q

What can you do if conversion gain sucks?

A

1) open up aperture at the cost of decreasing SNR
2) ABC increases dose
3) Replace

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17
Q

Brightness equation?

A

(D1/D2)2 = Brightness gain

(Diameter of input/diameter of output)2

As you can see making output smaller will increase you brightness, but making your input smaller you decrease you brightness

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18
Q

If output stays the same, but input is reduced in size.. what happens?

A

Minification increases

Decrease spatial resolution

Increase brightness

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19
Q

Having II close to patient does 3 things?

A
  1. Decrease patient dose by collecting more x-rays and not allowing ABC to increase technique
  2. Decrease scatter
  3. Increase image sharpness
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20
Q

Artifacts

A

Pincushion

S Distortion

Glare

Lag

Vignetting

Saturation

21
Q

Pincushion Artifact is created by?

A

Peripheral electrons do not strike output phosphor where they ideally should, nor do they focus well resulting in UNEQUAL magnification

Decrease FOV

22
Q

S distrotion created by?

A

Earth’s magnetic field having effect of electrons in I.I.

23
Q

Lag artifact happens because?

A

Persistence of luminescence after x-ray stimulation… 1ms in I.I. but now is more associated with TVs

24
Q

Vignetting is and what causes it?

A

Unequal magnification due to peripheral electrons not traveling where they should.. causing fall-off in brightness at the periphery.

25
Q

Two factors that diminish contrast or causing fog in I.I.?

A
  1. Incident electrons not absorbed by input screen and travel through I.I. and are absorbed by the output screen causing light
  2. Retrograde light flow from output screen coming back and activating photocathode in wrong position and then photocathode sends that signal back to the image
26
Q

What does the flat panel detector replace?

A

Output screen

27
Q

Saturation artifact happens when?

A

Happens when ABC cransk technique to get through very dense object (metal) and then saturates the rest of the image

28
Q

How to make s-distortion better?

A

“mu metal”

29
Q

Spatial resolutin in FPD?

A

2.5-3.0Lp/mm

30
Q

Artifacts with FPD

A
  1. Bad pixel
  2. Lag

DOES NOT HAVE PINCUSHION, VIGNETTING, GLARE, S-Distortion or Saturation!

31
Q

What is pitch when discussing FPD?

A

The deminsons of the FDP

32
Q

What is the “fill factor”

A

FDPs only have a part that is sensitive to light. So the fill factor is the

Sensitive area/(pitch2)

33
Q

As FDP gets smaller the spatial resolution improves T/F

A

True, but requires more radition.

34
Q

What is binning?

Advantages?

A

Taking several detector elements and averaging their signal together

  1. This reduces data and increases temporal resoultion.
  2. Maintains SNR
  3. Reduces dose
35
Q

What is frame averaging?

A

Adds several images together to increase SNR

Increases susceptibility to motion artifact

36
Q

Spatial resolution of FPD depends on what?

A

Matrix and matrix mismatch

37
Q

Spatial resolution of I.I. depends on?

A

Television display system

38
Q

Pulse Fluoro greatest advantage?

39
Q

For best image where is the receptor placed in relation to the patient and where is the tube?

A
  1. Tube is under the patient and as far away as possible
  2. Receptor is as close to the patient as possible
40
Q

What is the photocathode made out of?

A

Antimony

Alkali metals

Conversion effciency of 10-20%

41
Q

Difference between indirect and direct FPD?

A

Indirect: X-rays are converted to light

Direct: FPD absorbs straight x-rays (semiconductor - selenium)

42
Q

Why is the QDE (Quantum Detection Efficiency) better in FPD when compared to I.I.?

A

FPD use carbon fiber for cover on input rather than aluminum. This decreases thickness of material and attenuation of x-ray beam.

43
Q

Change FOV (input) from 30cm to 17cm will affect exposure rate how?

A

(30/17)2 = 3.1 times more exposure

44
Q

DSA (digital subtraction angiography) will not subtract moving parts. T/F

45
Q

What procedures would you need faster temporal resolution (60FPS)

46
Q

Best ways to reduce patient dose?

A
  1. Collimate
  2. Pulse
  3. Reduce total time
  4. Lead
47
Q

Regulatory dose limit for worker?

48
Q

Where is the best place to stand?

A

Next to the image detector/receptor

Most of the scatter is found on the side of the source

Physics (10 decks)

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