Physics Test 2 Flashcards
(79 cards)
1
Q
quality assurance
A
- people oriented
- necessary and appropriate procedures
- producing desired information
- accurately interpreted
2
Q
with ALARA as the goal for exposure, cost, and inconvenience
A
- scheduling
- prep instructions
- report accuracy & distribution
- image interpretation
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
4
Q
equipment orientation (Screen film QC)
A
image production, processing, image evaluation and critique.
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
6
Q
when is dose optimized for reject analysis
A
if NO repeats are caused by equipment
7
Q
Quality Control testing
A
- usually by physicist or designated technologist
- acceptance testing
- Routine Performance Evaluation
- Error Correction
- consistency
- reproducibility
- predictability
- confidence
8
Q
Acceptance Testing
A
Independently upon installation (new equipment)
9
Q
Routine Performance Evaluation
A
periodic or upon major repair/part replacement
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
11
Q
Filtration
A
2.5 mm AL minimum. tested by HVL annually
12
Q
Collimation
A
light field coincides within 2% of SID. test for each size film. semiannually
13
Q
effective focal spot
A
tested with slit camera, pinhole camera or star pattern. variance is large, annually
14
Q
kvp +/- kvp diagnostic (+/- 1 kvp mammo)
A
dx: 3% kvp variance will alter image density, radiographic contrast, and patient exposure. annually
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
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
17
Q
reproductibility
A
appropriate density & contrast for technique factors selected
-annually
18
Q
film contact
A
(wire mesh test) semi or annually
19
Q
screen film cleaning
A
depends on volume
20
Q
lead protective apparel evaluation
A
annually
21
Q
film illuminators
A
measure average light intensity (unity is Lumens) annually
22
Q
Special Quality Control for Fluoro
A
- exposure rates
- SPOTS
- AEC
23
Q
exposure rates
A
cant exceed 10 rad/min for ABS (manual 5 rad/min)
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)
25
AEC
constant image brightness
| -measured by seeing if input phosphor receives constant dose regardless of what's being penetrated.
26
conventional tomography quality control
- constant patient exposure
- cut height accurate +_ 5mm
- patient movement between slices accurate+-2mm
27
Computed Tomography Quality Assurance
-ongoing preventive maintenance
-periodic testing of noise/uniformarity
-linearity
-contrast resolution
-slice thickness
-table incrementation
-light localization
-patient dose
-
28
Processor QC
- activity
- processor cleaning
- schedule maintenance
- processor monitoring
29
activity
procedure or item- schedule
30
processor cleaning
- crossover racks- daily
| - entire rack assembly and processing ranks- daily
31
scheduled maintenance
- observation of belts, pulleys, and gears- weekly
| - lubrication- weekly or monthly
32
processor monitoring
- planned parts replacement- regularly
- check developer temp-daily
- check wash water temp- daily
- check replenishment - daily
- sensitometry and densitometry- daily
33
Digital Quality Control (look at chart in book)
- 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
Digital Quality Control (look at chart in book)
- 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
display resolution (Digital QC)
display separable images with high fidelity
36
Display noise (digital QC)
fluctuations- quantified w/ a TG test pattern.
37
Continuous QC program (digital)
- 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
human eye/vision cones
- centrally located
- better for fine detail
- best in bright light
39
rods
- more abundant at periphery
- less acuity
- best in dim light/darkness
40
Image intensifier tubes convert what?
the x-ray image into a small bright optical image, which can then be recorded using a tv camera.
41
conversion of x-ray energy to light is in what screen
phosphor screen (CsI)
42
Antimony
emission of low-energy electrons by photoemissive layer
43
Acceleration (to enhance brightness) and focusing of electrons on
output phosphor screen (ZnCdS)
44
Quantum detection effciencies
~60%-70% @59 keV
45
Flouroscopy intensifier tube sequence of events
- 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
what happens at the photocathode?
thin metal: cesium & antimony compounds- light here causes electron emission (photoemission) many light photons required to produce one electron
47
flux gain
#of light photons @ output phosphor/#of x-ray photons @ input phosphor
48
minification gain
(input size)^2/(output size)^2
49
brightness gain
minification gain X flux gain
50
multifield image intensification
- 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
In less than full field modes...
reduced field of view, magnified image, increased patient dose
52
amt of magnification
25/15= in 15 cm mode, image is 1.7 x's larger than in 25 cm mode
53
amt of patient dose increase
25^2/15^2= patient dose is 2.8 x's greater in 15 cm mode than in 25 cm mode
54
TV camera tube/CCDs examples
ex. Vidicon, Plumbicon
55
TV camer tube/CCDs
- 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
TV Monitor
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
chain of mechanics of image intensified fluoroscopy
- 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
Coupling device
fiber optics or mirrors or lenses)(fiber optics only allows cassette loaded spot film)
59
IF mirrors or lenses auxillary devices may be added here:
- spot film camer (70mm, 90 mm, 105 mm)
| - Cine Camera (16 mm or 35 mm)
60
digital fluoro
- pixel size
- charged coupled device
- flat panel image receptor
- temporal/energy subtraction
61
what are some advantages to digital fluoro
-faster image acquisition
-more post-processing enhancement options
-mA in the 100s (vs. 4-5 mA)
-pule progressive fluoro
=flat panel image receptor
62
high frequency generators
- interrogation time
- extinction time
- <1 ms
- duty cycle
63
interrogation time
x-ray tube time to "on" at desired kVp/mA
64
extinction time
switch the tube off
65
duty cycle
% beam on time (0.1 sec per sec =10%) for pt exposure, duty cycle needs to be ALAP
66
CCD replaces tv camera tube
- viewing the light output from the II
| - generates electrical charge when illuminated
67
What are some CCD advantages
- 1024 matrix-10 lp/mm spatial resolution
| - eliminates pin cusion/barrel artifact
68
compared to tv camera tube, ccd..
```
+DQE (light sensitivity)
-noise
+SNR
+contrast resolution
- patient exposure
```
69
flat panel IR
- Small-light-flexible
- insensitive to magnetism
- shape match to II output
70
Display Flat Panel (FPIR)
- need SNR 1000:1
- Progressive mode: e-beam sweep
- signal from FPIR doesn't have to be digitized..it already is
71
digital subtraction angiography
can use multiple video frames to create images w/less noise.
72
Subtraction
- Time interval difference
| - Mis-registration
73
TID
different masks required throughout the study i.e.cardiac
74
Mis-registration
patient motion between mask and acquisition (same pixel contains different anatomy)
75
energy subtraction
- using x-ray beams alternating energy
- beams are NOT monoenergetic
- hybrid
76
using x-ray beams alternating energy
to take advantage of k-edge absorption difference for contrast media.(33 Kev)
77
beams are NOT monoenergetic
can insert different filters alternately to "shape" beam energy
78
Hybrid
energy subtraction (1st) followed by temporal subtraction
79
patient exposure
- df beam is pulsed
- tv camera tube and ccd are more sensitive
- ease of acquisition makes "extra" images tempting.
