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Physics > Physics 2 test 2 > Flashcards

Physics 2 test 2 Flashcards

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1
Q

Quality Control is referring to

A

Equiptment

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2
Q

Quality Asurance is referring to

A

Patients

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3
Q 
These are consistent with what "Quality"
People oriented
Necessary and appropriate procedures
Producing desired information
Accurately interpreted
with ALARA as the goal for exposure, cost and inconvenience:
scheduling
prep instructions
report accuracy & distribution
image interpretation
A

Quality Assurance

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4
Q

Began as a war against unacceptable repeat rates

A

Screen-Film Quality Control

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5
Q

Equiptment oriented-image production, procesing, image evaluation & critique

A

Screen-Film Quality Control

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6
Q

Planned, Continuous, Documented, Deomstrate adaptations

A

Screen-Film Quality Control

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7
Q

Best possible image obtained with respect for patient safety

A

Screen-Film Quality Control

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8
Q

Sort rejects on positioning, motion, density, etc.

A

Reject analysis (QC)

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9
Q

Goal for reject analysis:

A

Less than 2% per 250 patients

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10
Q

Who does quality control testing?

A

Physicist or designated technologist

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11
Q

When and who does Acceptance testing?

A

Upon installation and it’s done independently

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12
Q

PM

A

Preventative Maintenance

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13
Q

Routine Performance Evaluation:

A

Periodic or upon major repair/part replacement

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14
Q

Another reasons why Quality Control testing would be needed

A 
Error Correction
Consistency
Reproducibility
Predictability
Confidence
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15
Q

3 benchmarks for QC Guidelines

A

Tolerance
method
Frequency

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16
Q

QC guidelines for Filtration

A

2.5 mm Al minimum
Tested by HVL
Annually

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17
Q

QC guidelines for Collimation

A

Light field coincides withing 2% of SID
Test each size film
Semiannually

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18
Q

QC guidelines for Effective Focal Spot

A

Tested with slit camera, pinhole camera or star pattern
Variance fairly large
Annually

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19
Q

QC guidelines for kVp

A

+/- 10 kVp diagnostic (+/- 1 kVp mammo)
Dx: 3% kVp variance will alter image density, radiographic contrast, and patient exposure
Annually

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20
Q

QC guidelines for Exposure Control

A

Time has a big influence on patient exposure & radiographic density +/- 5%
Test actual time set and AEC systems
backup timer must stop exposure at 6 sec or 600 mAs
Annually

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21
Q

QC guidelines for Linearity

A

Constant output for any mA/sec resulting constant mAs +/- 10% (reciprocity law)
Measure mR/mAs by varying mA (so timer inaccuracy doesnt flaw test) *only want one variable
Annually

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22
Q

QC guidelines for Reproducibility

A

Appropriate denstiy & contrast for technique factors selected +/- 5%
half value layer
pieces of equiptment: step wedge, etc

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23
Q

QC guidelines for Film contact

A

Wire mesh test

semi or annually

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24
Q

QC guidelines for Scren film cleaning

A

Depends on volume (how many x-rays your performing)

Actually emtpy the cassets and clean them

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25
Q

QC guidelines for Lead protective apparel

A

45-50 kVp range (not too much go right through-looking for a tear or whole in apron-will look black)
Annually

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26
Q

QC guidelines for Film Illuminators

A

view box-light is measured in Lumens
Measures averagle light intensity
Annually

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27
Q

Special QC for Fluro

Exposure Rate

A 
Cant exceed (but shouldn't need it anyway) 10 rad/min for ABS
5 rad/min for manual
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28
Q

Special QC for Fluro

Spots

A 
Entrance skin does highest for cassette loaded spots- spots off image intensifier much less exposure
smaller mode (mag) image inensifier is highest patient dose
*Patient exposure increases from fluro to still spots
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29
Q

Special QC for Fluro

AEC

A

Constant image brightnes

Measured by seeing if input phosphor receives constant dose regardless of whats being penetrated

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30
Q

Conventional Tomography QC

Tomo

A

Constant patient exposure
Cut height accurate +/- 5 mm
Patient movement between slices accurate +/- 2 mm

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31
Q

Computed Tomography QC

CT

A 
Ongoing Preventive Maintence
Periodic testing of noise/uniformity
Linearity
Contrast resolution
Slice thickness
Table incrementation
Light localization
Patient dose
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32
Q

`Processor QC-Radiographic film processor

A

DOCUMENTATION: No Doc, it didn’t happen

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33
Q

Digital QC

A

SMPTE pattern adopted by ACR for evaluation of digital monitors
DICOM Digital Imagning Communication
Line pairs per millimeter
blank spot and line together is a “line pair”

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34
Q

AAPM TG 18 Test

A

American Association of Physicians: Test patterns and related procedures-for digital display devices

35
Q

Digital QC Display Resolution

A

Display separable images with high fidelity

36
Q

Digital QC Display Noise

A

Fluctuations-quantified with a TB test pattern

37
Q

Continuous Digital QC Program

A

State has to approve for usage
Acceptance testing
Routine use of TG 18-QC test pattern by QC Tech
Periodic review by Medical Physicist
Annual and Post-Repair Performance evaluations

38
Q

Fluro Cones

A

Centrally located
Better for fine detail
Best in bright light

39
Q

Fluro Rods

A

More abundant at periphery
Less acuity
Best in dim light/darkness

40
Q

Fluor Image Intensifier Tubes

A

Convert the x-ray image into a small bright optical image, which can then be recorded using a TV camera.

41
Q

Fluro Image Intensifier Tube Conversion

A

X-rays to light
Light to electrons (input phospher)
Electrons cross the tube crossing sides
Electrons convert to light (output phospher)

42
Q

What is special about the image that is displayed from the tube?

A

It must be inverted to get an accurate anatomy.

43
Q

Comparison of image quality between the input/output phosphors

A

DQE Detective Quantum Efficiencies:
want at least 60-70% quality
what you lose from input to output

44
Q

Fluorscopy Intensifier Tube Sequence of events

1-3

A
  1. Remnant Beam
  2. Glass envelope of Image Intensifier
  3. Input Phosphor-converted to visible light (Cesium Iodide-CsI)
45
Q

Fluorscopy Intensifier Tube Sequence of events

4-6

A
  1. Photocathode-think metal: Cesium and antimony compunds. Light here causes electron emission (photoemission) Many light photons required to produce one electron
  2. Electrons are focused down 50 cm tube by electrostatic focusing lenses (electrodes of increasing voltage all along); accelerated by 25 kV potential difference
  3. Electrons cross anode neck, inverting image
46
Q

Fluorscopy Intensifier Tube Sequence of events

7-9

A
  1. Through thin aluminum layer (allows electrons through but prevents light from output phosphor from going back toward cathode end of tube.
  2. Electrons stike the output phosphor (zinc cadmium sulfide crystals) each electron produces 50-75 x’s the light required to produce it.
  3. For every electron that strikes the Intensifier tube here 50-75 X’s as many light photons are emitted
47
Q

Intensifier Tube Flux gain, Minification gain, Brightness gain

A

Flux gain: # of light photons at output phosphor/ # of x-ray photons at input phosphor x-ray photons to electrons-lose gain

Minification gain: (input size)2/(output size)2 how many light photons get from # of electrons-gain

Brightness gain: Minification gain X’s Flux gain # >1

48
Q

Multifield Image Intensification

A
  • May be operated using full or partial input phosphor
  • In less than full field modes: Reduced field of view, magnified image and increased patient dose to THAT anatomy
  • Amount of magnification: base/top
  • Amount of patient dose: base/top squared
49
Q

TV Camera Tube/Charge Coupled Devices (CCD’s)

*Conventional TV Camera Tube

A
  • i.e. Vidicon, Plumbicon*
  • Light from the output phosphor of image-intensifier tube strikes window
  • Light goes through window
  • Light goes through signal plate to target (photoconductive layer)
  • Electron beam from cathode strikes illuminated portion of target, electrons are conducted, video signal goes out. If photoconductive layer is not illuminated, no video signal is produced.
  • Electronic scanning converts imge into electronic signal which is transmitted to TV monitor
50
Q

Video capture is where on the tube?

A

Output Phosphor

51
Q

Static is referring to…

A

Stationary Image

52
Q

Spots in Fluro

A

mAs goes up as well as pt dose. Versus spots off the image intensifier

53
Q

Chain of Mechanics of Image Intensified Fluoro

A 
xray tube
Patient
Cassette loaded spot film device (optional)
Image intensifier
Coupling Device (fiber optics, mirrors or lenses)
TV Camera tube/CCD (Vidicon/Plumbicon)
TV Picture Tube (CRT)
Image on Fluorescent Screen
54
Q

Coupling Devices

  • Fiber optics
  • Mirrors or Lenses
A

Fiber optics: only allows cassette loaded spot film

55
Q

Digital Fluro

A

Smaller pixel size equals better spatial resolution

56
Q

Comparison between conventional versus Digital

digital

A
  • Faster image acquisition
  • More post-processing enhancement options
  • mA in the 100s versus 4-5 mA conventional
  • Pulse progressive fluro in digital versus conventional
  • Flat panel image receptor versus Image Intensifier in conventional, flat panerl much better less distortion smaller pixels and better spatial resolution
57
Q

Image Wisely

A

Came first, reduce repeats

58
Q

Image Gently

A

Came second, pediatric patients need less technical factors than adults

59
Q

High Frequency Generators

A

Capable of switching on and off rapidly.

have interrogation and extinction times of less than 1 ms

60
Q

Interrogation Time

A

The time required for the x-ray tube to be switched on and reach selected levels of kVp and mA

61
Q

Extinction Time

A

The time required for the x-ray tube to be switched off.

62
Q

Duty Cycle

A

The fraction of time the x-ray tube is energized, what percentage of time the beam is ACTUALLY on

63
Q

CCD replaces TV Camera Tube

*Advantages

A
  • 1024X1024 large matrix @ 10 lp/mm- Spatial resolution

- Eliminates pin cushion/barrel artifact (curves at the edge)

64
Q

CCD Compared to TV Camera Tube

A
  • More DQE (light sensitivity) Quantum Efficiency
  • Less noise
  • More SNR (signal to noise ratio)
  • More Contrast Resolution
  • Less Patient Exposure
65
Q

Flat Panel Image Receptor

A
  • Small, light, flexible
  • Insensitive to magnetism
  • Shape match to Image Intensifier
66
Q

FPIR’s

A
  • Need SNR 1000:1
  • Progressive mode: e-beam sweep
  • Signal from FPIR doesn’t have to be digitized, it already is!
67
Q

Digital Subtraction Angiography

A

Image before Contrast
Then contrast Image
computer superimposes the images and subtracts anything that is the same, removes it.

68
Q

In Digital Subtraction the Mask is…

A

The original image

69
Q

Subtraction TID

A

Time Interval Difference:

Different masks required throughout the study, ie Cardiac

70
Q

Subtraction Mis-registration

A

Patient motion between mask and acquisition (same pixel contains different anatomy)

71
Q

Energy Subtraction

A

Using x-ray beams of alternating energy (pulse energy) to take advantage of the k-edge absorption difference for contrast media (est. 33 keV)

Beams are not Monoenergetic

Hybrid: energy subtraction 1st followed by temporal subraction

72
Q

Roadmapping

A

Subtraction image following images with a catheter and a final/new “mask”

73
Q

Patient Exposure in Digital Fluro

A

Beam is pulsed
Camera tube and CCD are more sensitive
Ease of acquisition makes “extra” images tempting

74
Q

An acceptable QC program consists of three steps:

A

Acceptance testing
Routine performance monitoring
Maintenance

75
Q

Misalignment must not exceed

A

2% of the SID

76
Q

Three tools are used for measurement of focal-spot size:

A

Pinhole camera
Star pattern
Slit camera

77
Q

Screen Film: Measured kVp should be within (blank) % of the indicated kVp

A

10%

78
Q

Screen Film: Exposure timer accuracy should be within (blank) % of the indicated time for exposure times great than (blank) ms

A

5%

10 ms

79
Q

Screen Film: Exposure linearity must be within (blank)% for adjacent mA stations

A

10%

80
Q

Screen Film: Sequential radiation exposures should be reproducible to within

A

+- 5%

81
Q

What measurements and observations should be instituted for all digital display devices

A

AAPM TG 18

82
Q

Photometric evaluation of digital display devices and ambient light levels is essential to what QC

A

Digital QC

83
Q

Coupling Devices

-Mirrors or Lenses

A

Mirrors or Lenses, auxillary devices may be added here:

  • Spot film camera (70 mm, 90 mm, 105 mm)
  • Cine Camera (16 or 35 mm)

Physics (7 decks)

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