Quality Assurance Flashcards
What is Quality Assurance?
A program that ensures proper and consistent operation of imaging systems.
What does QA ensure? (6)
- Proper equipment operation
- Detection of gradual performance degradation
- Minimizes down time and misdiagnosis
- Ensures patient/employee safety
- Ensures cost efficiency
- Maintains standards
Who is responsible for QA?
Physicians, sonographers and service personnel (biomedical/manufacturer)
Who is the director of the QA program?
The physician
Who’s responsible for assessing the images for overall quality?
The radiologist
Who assesses images on the “front line”?
The sonographer
Besides assessing images, what other responsibilities do have sonographers have regarding QA?
- Perform routine testing
- Record keeping
- Routine maintenance
What routine maintenance do sonographers perform?
- Cleaning (filters)
2. Visual inspections
What does routine preventative maintenance include?
- Cleaning surfaces, recording devices and fan filters
- Film/image recording quality
- Assessing cables and transducer integrity
What are the types of service personnel?
- The manufacturer
2. The biomedical personel
What does the manufacturer provide?
Routine preventative maintenance and repairs.
What are the biomedical personnel responsible for?
Acceptance testing when a machine arrives on site to ensure patient/employee safety.
What is acceptance testing?
Testing that is done before a system is placed into operation.
What is tested during acceptance testing?
- Imaging performance
- Power output is measured
- Compatibility with ancillary equipment in department
What is the key to good QA?
Consistent routine performance testing and record keeping
What is routine performance testing?
Measuring the image performance and assessing for changes over time.
What is a TE phantom?
A tissue equivalent phantom that contain materials that simulate a body of tissue in its interaction with US.
What are TE phantoms used to assess? (8)
Everything;
- Deadzone measurement
- Detailed resolution (including dynamic range)
- Distance accuracy
- Image uniformity
- Depth of penetration
- Cyst imaging capabilities
- Attenuation (TGC)
- Sensitivity
How often is routine maintenance performed by the sonographer?
Daily, weekly, monthly
How often is routine preventative maintenance performed by the manufacturer?
2-3 times per year while the machine is under warrenty.
How often is routine performance testing done and what is used to do it?
A TE phantom is used on a yearly basis
What is the AIUM 100?
An older testing device in which a plastic case contains 0.75 mm steel rods arranged in groups.
What are AIUM 100’s filled with?
Water, 9% alcohol and algaecide.
What are the pros and cons of the AIUM 100?
Pro = Inexpensive
Con = Have no grayscale so cannot test contrast resolution or attenuation (TGC)
What can AIUM 100’s test?
- Resolution
- Calipers
- Deadzone
Can AIUM 100’s test for contrast resolution?
No, because they have no grayscale
What are TE phantoms made of?
A plastic case containing a gel mixed with graphite powder and rod groups plus solid and cystic lesions.
What are the pros and cons of TE phantoms?
Pros = Give better idea of performance because they allow the testing of grayscale, attenuation and the speed of sound.
Cons = Expensive
How do test objects compare to TE phantoms?
TE phantoms can test for everything, test objects can only test Deadzone, axial/lateral resolution and depth/length calibration accuracy.
What characteristics must a good phantom have in order to mimic soft tissue? (5)
- Similar attenuation coefficient
- Similar speed of sound
- Similar backscatter coefficent/relative contrast
- Similar elasticity
- Similar thermal properties
What is deadzone?
The area in the near field close to the transducer
What is the dead zone also known as?
The main bang or reverberation
What type of probes had a large dead zone?
Large mechanical probes
How does measuring the dead zone work?
Imaging the deadzone pins and observing a change in their resolution over time
What amount of change in the dead zone is acceptable over time?
Less than 15 mm (but this is an old #, technology is now better so it should be even less)
What are the other names for axial resolution?
- Longitudinal
- Range
- Depth
What is axial resolution?
The ability to separate reflectors along the path of the beam
What does axial resolution depend on and how is it calculated?
SPL (Better res = shorter SPL)
Axial resolution = 1/2 the SPL
What is the formula for SPL?
SPL = wavelength x Ringdown
What is the best axial resolution and when are objects in the axis of the beam demonstrated as a single echo?
0.5 mm = best
When objects are closer than 1/2 the SPL they will be one
What is lateral resolution?
The ability to separate reflectors perpendicular to the path of the beam
What does lateral resolution depend on?
The width of the beam (smaller width = better res)
What are the other names for lateral resolution?
Angular, Transverse and Azimuthal
What is elevational resolution?
The ability to separate reflectors perpendicular to the image plane of the beam
What does elevational resolution depend on?
The width of the beam in the Z-axis and the depth
What is another name for elevational resolution?
Slice thickness
What is contrast resolution?
The ability to distinguish subtle differences in tissue gray scale.
What does contrast resolution depend on?
Bit depth (More bits = more shades of grey = more control over dynamic range)
What is attenuation coefficient?
The amount of attenuation that occurs per centimetre travelled.
What is the the attenuation coefficient in soft tissue?
1/2 frequency
How do we find the total attenuation?
TA = Attn Coef x path length in cm
How is axial resolution tested?
Measuring the smallest separation visible between the axial resolution pins at various depths and watching for changes over time.
Why are the axial resolution pins staggered?
To avoid the reverberation (comet tail artifact) due to the metal pins.
How is lateral resolution tested?
Measuring the lateral resolution pins and watching for changes over time.
What does the lateral resolution test depend on?
The focus and depth used.
What type of resolution is being tested when a ramp is used?
Elevational
How is elevational resolution quantitatively tested (with measurements)?
Using a spherical void phantom or beam profile phantom (RAMP)
How is elevational resolution qualitatively tested?
Using a regular phantom and assessing cysts (if they are filled in then slice thickness artifact is present = poor elevational resolution.
How are horizontal and vertical distance accuracy measured?
By measuring pins at a known distance with calipers and comparing the numbers.
Why is it important to measure over larger distances when testing distance accuracy?
To detect smaller margins of error
How are TGC characteristics tested?
Images are captured with different slide pod configurations under different conditions and then compared over time.
What type of test is TGC?
User specific, the results are based on the observations of the individual performing the test.
What does image uniformity test?
A linear arrays consistency along the array
When testing image uniformity what indicates degradation?
An inhomogenous region or area of non-uniformity (a vertical or horizontal band).
What does sensitivity test for?
A systems ability to pick up weak echoes
What is the maximum depth of visualization?
A common test of sensitivity where the power and gain are optimized for penetration and the observer records the depth where brightness starts to fade.
How is the dynamic range tested?
The number of shades of grey are measured by recording a specific image and then compared with other images over time to appreciate any changes in display.
What type of test is the dynamic range?
Subjective
What is the contrast resolution test?
Measures the ability to distinguish between simulated lesions of similar echogenicity by scanning solid, cystic, echogenic and hypoechoic lesions (varying decibel range or dynamic range) and then comparing with previous results.
What is Registration?
A test for older static B scanners to ensure arm positioning is accurate for image reconstruction.
How is Registration performed?
By scanning pins from 3 sides to see if the lines intersect at one point.
What are the two types of phantoms used for assessing doppler function?
- Flow
2. String or belt
What is the difference between flow and string/belt phantoms?
How the doppler shift is created
What type of doppler phantoms closely match the clinical experience but are expensive?
Flow or TE
What type of doppler phantoms do not match the clinical experience but are affordable?
String/Belt
What are string phantoms?
The phantoms move a string/belt in a water bath
What are doppler phantoms used to measure?
- Maximum depth
- Gate position accuracy
- Volume flow and velocity accuracy
- Colour flow penetration
- Image congruency test
Why does the axial resolution change with doppler on?
Because SPL increases (worse res) to allow for the receival of information over the entire cardiac cycle.
Besides QA, what can phantoms be used for?
- Demonstration
- Training
- Research and development
What different applications require specialty phantoms?
- Biopsy
- Mass
- 3 Dimensional
- Cyrosurgery (Liquid nitrogen)
- Brachytherapy (Radiation)
- HIFU (High intensity focused US)
- IVUS (intravascualar US)
Who evaluates the systems output?
Manufacturer or service personnel
What devices evaluate power output?
- Hydrophone
- Power (force) balencers
- Calorimeter
What is a hydrophone?
A small 1 mm transducer that produces a voltage proportional to the received acoustic wave.
What is used to produce a beam profile?
A hydrophone with a plotter.
What can a hydrophone measure when used with an oscilloscope? (5)
- SPL
- PD
- PRP
- PRF
- DF
What can a hydrophone measure when used with a spectrum analyzer? (4)
- Resonant “f”
- Bandwidth
- Fractional bandwidth
- Q Factor
What is a Force Balance?
A sensitive micro balance that is phased in the sound field and calibrated to measure acoustic power and intensity by watching how far the sound absorber moves into the water (measured on scale).
What is a Calorimeter?
A heat meter used to measure acoustic power by detecting temperature changes in a fluid container using a sensitive thermocouple (special thermometer).
What are two ways that phantoms can accommodate for advancing technology in US?
- Thin Film phantom targets
2. Smaller resolution point targets
What is a way that future machines may help with the subjectivity of manual QA evaluation?
Self-evaluation settings
A good TE phantom must have an attenuation coefficient equal to…?
One half the frequency times the path length
