Physics 2 test 2 Flashcards
1
Q
Quality Control is referring to
A
Equiptment
2
Q
Quality Asurance is referring to
A
Patients
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
4
Q
Began as a war against unacceptable repeat rates
A
Screen-Film Quality Control
5
Q
Equiptment oriented-image production, procesing, image evaluation & critique
A
Screen-Film Quality Control
6
Q
Planned, Continuous, Documented, Deomstrate adaptations
A
Screen-Film Quality Control
7
Q
Best possible image obtained with respect for patient safety
A
Screen-Film Quality Control
8
Q
Sort rejects on positioning, motion, density, etc.
A
Reject analysis (QC)
9
Q
Goal for reject analysis:
A
Less than 2% per 250 patients
10
Q
Who does quality control testing?
A
Physicist or designated technologist
11
Q
When and who does Acceptance testing?
A
Upon installation and it’s done independently
12
Q
PM
A
Preventative Maintenance
13
Q
Routine Performance Evaluation:
A
Periodic or upon major repair/part replacement
14
Q
Another reasons why Quality Control testing would be needed
A
Error Correction Consistency Reproducibility Predictability Confidence
15
Q
3 benchmarks for QC Guidelines
A
Tolerance
method
Frequency
16
Q
QC guidelines for Filtration
A
2.5 mm Al minimum
Tested by HVL
Annually
17
Q
QC guidelines for Collimation
A
Light field coincides withing 2% of SID
Test each size film
Semiannually
18
Q
QC guidelines for Effective Focal Spot
A
Tested with slit camera, pinhole camera or star pattern
Variance fairly large
Annually
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
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
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
22
Q
QC guidelines for Reproducibility
A
Appropriate denstiy & contrast for technique factors selected +/- 5%
half value layer
pieces of equiptment: step wedge, etc
23
Q
QC guidelines for Film contact
A
Wire mesh test
semi or annually
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
25
QC guidelines for Lead protective apparel
45-50 kVp range (not too much go right through-looking for a tear or whole in apron-will look black)
Annually
26
QC guidelines for Film Illuminators
*view box-light is measured in Lumens*
Measures averagle light intensity
Annually
27
Special QC for Fluro
| Exposure Rate
```
Cant exceed (but shouldn't need it anyway) 10 rad/min for ABS
5 rad/min for manual
```
28
Special QC for Fluro
| Spots
```
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
```
29
Special QC for Fluro
| AEC
Constant image brightnes
| Measured by seeing if input phosphor receives constant dose regardless of whats being penetrated
30
Conventional Tomography QC
| Tomo
Constant patient exposure
Cut height accurate +/- 5 mm
Patient movement between slices accurate +/- 2 mm
31
Computed Tomography QC
| CT
```
Ongoing Preventive Maintence
Periodic testing of noise/uniformity
Linearity
Contrast resolution
Slice thickness
Table incrementation
Light localization
Patient dose
```
32
`Processor QC-Radiographic film processor
DOCUMENTATION: No Doc, it didn't happen
33
Digital QC
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"
34
AAPM TG 18 Test
American Association of Physicians: Test patterns and related procedures-for digital display devices
35
Digital QC Display Resolution
Display separable images with high fidelity
36
Digital QC Display Noise
Fluctuations-quantified with a TB test pattern
37
Continuous Digital QC Program
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
Fluro Cones
Centrally located
Better for fine detail
Best in bright light
39
Fluro Rods
More abundant at periphery
Less acuity
Best in dim light/darkness
40
Fluor Image Intensifier Tubes
Convert the x-ray image into a small bright optical image, which can then be recorded using a TV camera.
41
Fluro Image Intensifier Tube Conversion
X-rays to light
Light to electrons (input phospher)
Electrons cross the tube crossing sides
Electrons convert to light (output phospher)
42
What is special about the image that is displayed from the tube?
It must be inverted to get an accurate anatomy.
43
Comparison of image quality between the input/output phosphors
DQE Detective Quantum Efficiencies:
want at least 60-70% quality
*what you lose from input to output*
44
Fluorscopy Intensifier Tube Sequence of events
| 1-3
1. Remnant Beam
2. Glass envelope of Image Intensifier
3. Input Phosphor-converted to visible light (Cesium Iodide-CsI)
45
Fluorscopy Intensifier Tube Sequence of events
| 4-6
4. Photocathode-think metal: Cesium and antimony compunds. Light here causes electron emission (photoemission) Many light photons required to produce one electron
5. Electrons are focused down 50 cm tube by electrostatic focusing lenses (electrodes of increasing voltage all along); accelerated by 25 kV potential difference
6. Electrons cross anode neck, inverting image
46
Fluorscopy Intensifier Tube Sequence of events
| 7-9
7. Through thin aluminum layer (allows electrons through but prevents light from output phosphor from going back toward cathode end of tube.
8. Electrons stike the output phosphor (zinc cadmium sulfide crystals) each electron produces 50-75 x's the light required to produce it.
9. For every electron that strikes the Intensifier tube here 50-75 X's as many light photons are emitted
47
Intensifier Tube Flux gain, Minification gain, Brightness gain
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
Multifield Image Intensification
- 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
TV Camera Tube/Charge Coupled Devices (CCD's)
| *Conventional TV Camera Tube
* 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
Video capture is where on the tube?
Output Phosphor
51
Static is referring to...
Stationary Image
52
Spots in Fluro
mAs goes up as well as pt dose. Versus spots off the image intensifier
53
Chain of Mechanics of Image Intensified Fluoro
```
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
Coupling Devices
- Fiber optics
- Mirrors or Lenses
Fiber optics: only allows cassette loaded spot film
55
Digital Fluro
Smaller pixel size equals better spatial resolution
56
Comparison between conventional versus Digital
| digital
- 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
Image Wisely
Came first, reduce repeats
58
Image Gently
Came second, pediatric patients need less technical factors than adults
59
High Frequency Generators
Capable of switching on and off rapidly.
| have interrogation and extinction times of less than 1 ms
60
Interrogation Time
The time required for the x-ray tube to be switched on and reach selected levels of kVp and mA
61
Extinction Time
The time required for the x-ray tube to be switched off.
62
Duty Cycle
The fraction of time the x-ray tube is energized, what percentage of time the beam is ACTUALLY on
63
CCD replaces TV Camera Tube
| *Advantages
- 1024X1024 large matrix @ 10 lp/mm- Spatial resolution
| - Eliminates pin cushion/barrel artifact (curves at the edge)
64
CCD Compared to TV Camera Tube
- More DQE (light sensitivity) Quantum Efficiency
- Less noise
- More SNR (signal to noise ratio)
- More Contrast Resolution
- Less Patient Exposure
65
Flat Panel Image Receptor
- Small, light, flexible
- Insensitive to magnetism
- Shape match to Image Intensifier
66
FPIR's
- Need SNR 1000:1
- Progressive mode: e-beam sweep
- Signal from FPIR doesn't have to be digitized, it already is!
67
Digital Subtraction Angiography
Image before Contrast
Then contrast Image
computer superimposes the images and subtracts anything that is the same, removes it.
68
In Digital Subtraction the Mask is...
The original image
69
Subtraction TID
Time Interval Difference:
| Different masks required throughout the study, ie Cardiac
70
Subtraction Mis-registration
Patient motion between mask and acquisition (same pixel contains different anatomy)
71
Energy Subtraction
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
Roadmapping
Subtraction image following images with a catheter and a final/new "mask"
73
Patient Exposure in Digital Fluro
Beam is pulsed
Camera tube and CCD are more sensitive
Ease of acquisition makes "extra" images tempting
74
An acceptable QC program consists of three steps:
Acceptance testing
Routine performance monitoring
Maintenance
75
Misalignment must not exceed
2% of the SID
76
Three tools are used for measurement of focal-spot size:
Pinhole camera
Star pattern
Slit camera
77
Screen Film: Measured kVp should be within (blank) % of the indicated kVp
10%
78
Screen Film: Exposure timer accuracy should be within (blank) % of the indicated time for exposure times great than (blank) ms
5%
| 10 ms
79
Screen Film: Exposure linearity must be within (blank)% for adjacent mA stations
10%
80
Screen Film: Sequential radiation exposures should be reproducible to within
+- 5%
81
What measurements and observations should be instituted for all digital display devices
AAPM TG 18
82
Photometric evaluation of digital display devices and ambient light levels is essential to what QC
Digital QC
83
Coupling Devices
| -Mirrors or Lenses
Mirrors or Lenses, auxillary devices may be added here:
- Spot film camera (70 mm, 90 mm, 105 mm)
- Cine Camera (16 or 35 mm)
