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Physics > Physics Test 2 > Flashcards

Physics Test 2 Flashcards

1
Q

quality assurance

A
  • people oriented
  • necessary and appropriate procedures
  • producing desired information
  • accurately interpreted
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2
Q

with ALARA as the goal for exposure, cost, and inconvenience

A
  • scheduling
  • prep instructions
  • report accuracy & distribution
  • image interpretation
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3
Q

Screen-Film QC

A
  • began as a war into unacceptable repeat rates and evolved into more
  • planned, continuous, documented, demonstrate adaptations
  • equipment oriented
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4
Q

equipment orientation (Screen film QC)

A

image production, processing, image evaluation and critique.

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5
Q

reject analysis (screen film QC)

A
  • sort rejects on positioning, motion, density, etc.
  • for 250 patients, goal is less than 2%
  • increase in any category must be investigated
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6
Q

when is dose optimized for reject analysis

A

if NO repeats are caused by equipment

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7
Q

Quality Control testing

A
  • usually by physicist or designated technologist
  • acceptance testing
  • Routine Performance Evaluation
  • Error Correction
  • consistency
  • reproducibility
  • predictability
  • confidence
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8
Q

Acceptance Testing

A

Independently upon installation (new equipment)

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9
Q

Routine Performance Evaluation

A

periodic or upon major repair/part replacement

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10
Q

Guidelines for QC Frequency/Tolerance

A
  • Filtration
  • Collimation
  • Effective focal spot
  • kvp +/- 10 kvp diagnostic
  • exposure control
  • linearity
  • reproducibility
  • film contact
  • screen film cleaning
  • lead protective apparel
  • film illuminators
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11
Q

Filtration

A

2.5 mm AL minimum. tested by HVL annually

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12
Q

Collimation

A

light field coincides within 2% of SID. test for each size film. semiannually

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13
Q

effective focal spot

A

tested with slit camera, pinhole camera or star pattern. variance is large, annually

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14
Q

kvp +/- kvp diagnostic (+/- 1 kvp mammo)

A

dx: 3% kvp variance will alter image density, radiographic contrast, and patient exposure. annually

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15
Q

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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16
Q

linearity

A

constant output for any mA/sec resulting in constant mAs +/- 10%

  • measure mR/mAs by varying mA (so timer inaccuracy does not flaw test)
  • annually
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17
Q

reproductibility

A

appropriate density & contrast for technique factors selected
-annually

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18
Q

film contact

A

(wire mesh test) semi or annually

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19
Q

screen film cleaning

A

depends on volume

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20
Q

lead protective apparel evaluation

A

annually

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21
Q

film illuminators

A

measure average light intensity (unity is Lumens) annually

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22
Q

Special Quality Control for Fluoro

A
  • exposure rates
  • SPOTS
  • AEC
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23
Q

exposure rates

A

cant exceed 10 rad/min for ABS (manual 5 rad/min)

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24
Q

SPOTS

A

entrance skin dose highest for cassette loaded spots.

-spots off image intensifier much less (smaller mode on Image intensifier is highest patient dose)

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25
Q

AEC

A

constant image brightness

-measured by seeing if input phosphor receives constant dose regardless of what’s being penetrated.

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26
Q

conventional tomography quality control

A
  • constant patient exposure
  • cut height accurate +_ 5mm
  • patient movement between slices accurate+-2mm
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27
Q

Computed Tomography Quality Assurance

A

-ongoing preventive maintenance
-periodic testing of noise/uniformarity
-linearity
-contrast resolution
-slice thickness
-table incrementation
-light localization
-patient dose
-

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28
Q

Processor QC

A
  • activity
  • processor cleaning
  • schedule maintenance
  • processor monitoring
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29
Q

activity

A

procedure or item- schedule

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30
Q

processor cleaning

A
  • crossover racks- daily

- entire rack assembly and processing ranks- daily

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31
Q

scheduled maintenance

A
  • observation of belts, pulleys, and gears- weekly

- lubrication- weekly or monthly

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32
Q

processor monitoring

A
  • planned parts replacement- regularly
  • check developer temp-daily
  • check wash water temp- daily
  • check replenishment - daily
  • sensitometry and densitometry- daily
33
Q

Digital Quality Control (look at chart in book)

A
  • SMPTE pattern adopted by ACR for evaluation of digital monitors
  • Digital Imaging and Communication (DICOM) standards developed by ACR and Nat’l Electrical Manufacturers Assoc (NEMA)
34
Q

Digital Quality Control (look at chart in book)

A
  • DIN 2001: “Image quality assurance in diagnositcs; acceptance testing for imaging display devices” Joint performance evaluation of imaging modality and digital display
  • AAPM TG 18: test patterns and related procedures (Task Group Report for digital display devices.)
35
Q

display resolution (Digital QC)

A

display separable images with high fidelity

36
Q

Display noise (digital QC)

A

fluctuations- quantified w/ a TG test pattern.

37
Q

Continuous QC program (digital)

A
  • 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

human eye/vision cones

A
  • centrally located
  • better for fine detail
  • best in bright light
39
Q

rods

A
  • more abundant at periphery
  • less acuity
  • best in dim light/darkness
40
Q

Image intensifier tubes convert what?

A

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

41
Q

conversion of x-ray energy to light is in what screen

A

phosphor screen (CsI)

42
Q

Antimony

A

emission of low-energy electrons by photoemissive layer

43
Q

Acceleration (to enhance brightness) and focusing of electrons on

A

output phosphor screen (ZnCdS)

44
Q

Quantum detection effciencies

A

~60%-70% @59 keV

45
Q

Flouroscopy intensifier tube sequence of events

A
  • remnant beam
  • glass envelope of image intensifier tube
  • input phosphor-converted to visible light (CsI)
  • Photocathode
  • elecrons are focused down by electrostatic focusing lenses;accelerated by 25 kV potential difference
  • electrons cross at anode neck (inverting image)
  • thru thin al layer (allows e- thru but prevents light from output phosphor from going back toward cathode)
  • e- strike the output phosphor (zinc cadmium sulfide crystals) each e- produces 50-75 X’s the light required to produce it.
46
Q

what happens at the photocathode?

A

thin metal: cesium & antimony compounds- light here causes electron emission (photoemission) many light photons required to produce one electron

47
Q

flux gain

A

of light photons @ output phosphor/#of x-ray photons @ input phosphor

48
Q

minification gain

A

(input size)^2/(output size)^2

49
Q

brightness gain

A

minification gain X flux gain

50
Q

multifield image intensification

A
  • II may be operated using full or partial input phosphor
  • in less than full field modes
  • amt of magnification
  • amt of patient dose increase
51
Q

In less than full field modes…

A

reduced field of view, magnified image, increased patient dose

52
Q

amt of magnification

A

25/15= in 15 cm mode, image is 1.7 x’s larger than in 25 cm mode

53
Q

amt of patient dose increase

A

25^2/15^2= patient dose is 2.8 x’s greater in 15 cm mode than in 25 cm mode

54
Q

TV camera tube/CCDs examples

A

ex. Vidicon, Plumbicon

55
Q

TV camer tube/CCDs

A
  • light from output phosphor of image-intensifier tube strikes window
  • light goes through window
  • light goes through signal plate to target (photoconductive layer)
  • when e- beam from cathode strikes illuminated portion of target e-s are conducted and a video signal goes out; if area of photoconductive layer is not illuminated no video signal is produced
  • electronic scanning convert image into electronic signal which is transmitted to TV monitor
56
Q

TV Monitor

A

has electron gun which repeats 525 line scanning pattern onto the fluorescent screen of TV monitor’s picture tube (bright spots are areas of greater electrical charge)

57
Q

chain of mechanics of image intensified fluoroscopy

A
  • x-ray tube
  • patient
  • cassette loaded spot film device (optional)
  • image intensifier
  • coupling device
  • TV camera tube/CCD (Vidicon/Plumbicon)
  • Tv picture Tube (CRT)
  • Image on Fluorescent screen
58
Q

Coupling device

A

fiber optics or mirrors or lenses)(fiber optics only allows cassette loaded spot film)

59
Q

IF mirrors or lenses auxillary devices may be added here:

A
  • spot film camer (70mm, 90 mm, 105 mm)

- Cine Camera (16 mm or 35 mm)

60
Q

digital fluoro

A
  • pixel size
  • charged coupled device
  • flat panel image receptor
  • temporal/energy subtraction
61
Q

what are some advantages to digital fluoro

A

-faster image acquisition
-more post-processing enhancement options
-mA in the 100s (vs. 4-5 mA)
-pule progressive fluoro
=flat panel image receptor

62
Q

high frequency generators

A
  • interrogation time
  • extinction time
  • <1 ms
  • duty cycle
63
Q

interrogation time

A

x-ray tube time to “on” at desired kVp/mA

64
Q

extinction time

A

switch the tube off

65
Q

duty cycle

A

% beam on time (0.1 sec per sec =10%) for pt exposure, duty cycle needs to be ALAP

66
Q

CCD replaces tv camera tube

A
  • viewing the light output from the II

- generates electrical charge when illuminated

67
Q

What are some CCD advantages

A
  • 1024 matrix-10 lp/mm spatial resolution

- eliminates pin cusion/barrel artifact

68
Q

compared to tv camera tube, ccd..

A 
\+DQE (light sensitivity)
-noise
\+SNR
\+contrast resolution
- patient exposure
69
Q

flat panel IR

A
  • Small-light-flexible
  • insensitive to magnetism
  • shape match to II output
70
Q

Display Flat Panel (FPIR)

A
  • need SNR 1000:1
  • Progressive mode: e-beam sweep
  • signal from FPIR doesn’t have to be digitized..it already is
71
Q

digital subtraction angiography

A

can use multiple video frames to create images w/less noise.

72
Q

Subtraction

A
  • Time interval difference

- Mis-registration

73
Q

TID

A

different masks required throughout the study i.e.cardiac

74
Q

Mis-registration

A

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

75
Q

energy subtraction

A
  • using x-ray beams alternating energy
  • beams are NOT monoenergetic
  • hybrid
76
Q

using x-ray beams alternating energy

A

to take advantage of k-edge absorption difference for contrast media.(33 Kev)

77
Q

beams are NOT monoenergetic

A

can insert different filters alternately to “shape” beam energy

78
Q

Hybrid

A

energy subtraction (1st) followed by temporal subtraction

79
Q

patient exposure

A
  • df beam is pulsed
  • tv camera tube and ccd are more sensitive
  • ease of acquisition makes “extra” images tempting.

Physics (3 decks)

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