Quality Assurance Flashcards
Parameter
The whole population
Statistic
Sample of the population
Population
set of homogeneous items or events that is of interest for some question or experiment.
Sample
A sample is a smaller group of members of a population selected as a representative of the population.
Sample is biased
Random Sample
Randomly means that every member of the target population has an identical chance of being included in the sample. In other words, the method you use for selecting your sample can not be biased.
quality
Documented data use of statisticial calculations to compare lab data against other confirmed means of testing
what are the 2 medicine statistical tests
Reference test (Gold standard) Comparison test (Procedure to be validated)
when does a test become gold standard?
When it is the most consistent and most accurate test for a particular disease
What is a comparison test
Any other testing procedure, competing technology or variation from the gold standard
Making statistical indices more intuitive
Realize that all indices start with a presumption that the Gold Standard is perfect
Pay particular attention to the English of the statistical terminology
Pay close attention to the labels and layout of any table of data
Golden rule
For all purposes of statistical indices, the assumption is that the gold standard s perfect
If the results of a test match the results of a gold standard
Test=true
If the results of a test do not match the results of a gold standard test
Test=false
Both comparison and gold standard test are attempting to do what?
Predict the presence of disease
If the result is positive
it means that the test predicted the presence of disease
If the result was negative
Test predicted the absence of disease
True
is when the test results match the gold standard
False
is when the test results do not match the gold standard
True Positive
The test is correct (T) because it matches the gold standard and the test is positive for disease (P)
True Negative
The test is correct (T) because it matches the gold standard and the test is negative for disease (N)
False Positive
The test is incorrect (F) because it does not match the gold standard and the test is positive for disease (P)
False negative
The test is incorrect (F) because it does not match the gold standard and the test is negative for disease (N)
Gold standard
Assumed to be perfect
Number of tested Patients with disease
Have disease=TP+FN
Patients without disease
No disease=TN+FP
Number of tested patients in the population that the test predicts to have the disease
Test positive: TP+FP
Number of tested patients in the population that the test predicts do not have the disease
Test negative: TN+FN
Sensitivity
Implies the ability of a test to detect disease
Times the test correctly predicted disease divided by al of the the times the disease really does exist
Sensitivity equation
TP/TP+FN (*100%)
Specificity
Refers to the ablity of a test to detect the absence of disease relative to the number of people who in reality do not have disease
Specificity equation
TN/TN+FP (*100%)
Accuracy
Percentage of times the test is correct relative to the gold standard
Accuracy equation
TP+TN/TP+FN+TN+FP (*100%)
positive predictive value
Is a value of how often the test is correct when positive for disease as a percentage of the total times the test is positive for disease
Positive predictive value equation
PPV = TP/TP+FP (x100%) - notice only positive terms
Negative predictive value
is a measure of how often the test is correct when negative for disease as a percentage of the total times the test is negative for disease
Negative predictive value equation
NPP = TN/TN+FN (x100%) - notice only negative terms
Accuracy defintion
Overall measure includes both a cacualtion for when the test was correct when positive for disease and when the test was correct when negative for the disease
Accuracy must be….
Between the sensitivity and specificity
The accuracy must also be between
Negative predictive value and positive predictive value
Sensitivity is…
The ability of a test to detect disease
Specificity is…
Ability of a test to detect the absence of disease
Accuracy is
The percentage of times the test is correct
Accuracy=TP+TN/All tests
Positive predictive value is
Percentage of times the test was correct when it predicted presence of disease
how is positive predictive value determined
How many times the test correctly predicted the presence of disease divided by the total number of times the test predicted that there was disease.
negative predictive value is…
Percentage of times the test was correct when it predicted absence of disease
How is negative predictive value determined
How many times the test correctly predicted the absence of disease divided by the total number of times the test predicted that there was no disease
The perfect test….
Sensitivity, specificity, accuracy, positive predictive value and negative predictive value would all be 100%
In the real world
-No garuntee that the gold standard is perfect
Good match to good standard
Good test
Good match to bad standard
Bad test
bad match to a good standard
Bad test
bad match to a bad standard
Not a whole lot of information
Testing can be preformed by the
Ultrasound manufacture, regulatory bodies or within the ultrasound lab
Purpose of testing
To assess performance differences between different ultrasound system designs
To assess a system’s performance and/or manufacturing
To minimize artifacts
what does testing include
- Routine maintenance of ultrasound equipment
- Routine maintenance of lab equipment
- Individual certification
- Accreditation
- Statistical processing to compare a testing procedure against the gold standard
- QA meetings
- Overall accuracy of studies
- peer review
Why is testing needed
Make certain that the system performance is adequate
How do we test the system?
Use of test objects and test phantoms is an attempt to provide a constant reference frame so that a standard can be developed and so that changes over time can be identified
Certain phantoms
Stable means by which to calibrate and compare performance over time
Ability to mimic characteristics and complexities of tissues….
Limited
Part of the system most likely to break/degrade
Transducer
Getting repeatable test results
Take careful preparation and great system knowledge
Transducer Care
Don’t drop the probe
No kinks, crimps or excessive force should be placed on the cord (RUNNING OVER CORD WITH MACHINE)
probe leakage tests
Determine the mechanical integrity and ensure patient safety
Why are probe leakage tests done
Mechanical discontinuities and fissures represent a potential electrical safety hazard
Small mechanical deformities can reduce efficacy of cleaning and disinfecting procedures with microbial formation in breaches
Transducer general cleaning
Soap and water with a soft cloth to remove residual gel or biological related residues
Disinfecting Wipes after each use
Transducer disinfection and sterilization
Sterilization
High-level disinfection
Intermediate-level disinfection
Low-level disinfection
Sterilization
Complete elimination of all forms of microbial life including spores and viruses
Required when using a device considered ‘critical’-penetrates the skin or mucous membrane and is used without protective covering or if it is compromised
NOT AUTOCLAVING
Low level disinfection
Destruction of most bacteria, some viruses and some fungi
Low level disinfection=not enough to inactivate TB or spores
Use of germicide
Transducer is sprayed or immersed in germicide nd then rinsed with sterile water
General cleaning should be employed prior to this type of care
High level disinfection
Destruction/removal of all micro-organisms except bacterial spores
Intended for probes which makes the spread of disease more likely because of contact with blood or other bodily fluids
Trans-esophageal
Trans-rectal
Trans-vaginal
Process for high level disinfection
Perform general cleaning
Ensure compatibility of disinfecting solution with transducer
Immerse transducer following specific disinfecting guidelines (20 minutes in CIDEX)
Rinse with sterile water (10 minutes)
Allow probe to dry
Examine probe for structural damage
what are the two groups of 2D/Doppler testing
Those that measure the acoustic output of the instrument
Those that test the operation of the instrument
Those that measure the acoustic output of the instrument
This group considers only the beam former and the transducer acting together as a source of ultrasound
Those that test the operation of the instrument (anatomic images and flow evaluation performance):
This group takes into account the operation of the entire instrument. Imaging and Doppler performance are important for evaluating the instrument as a diagnostic tool. The acoustic output of an instrument is important when considering bioeffects and safety
Doppler testing
Doppler testing presents extraordinary challenges since mimicking the properties of blood in a consistent fashion is extremely difficult. As a result, many different types of Doppler phantoms have been created
Doppler Phantoms
Flow phantoms
Non-flow/String phantoms
Vibrating Plate (sensitivity) phantoms
Blood mimicking fluids
Flow phantoms may provide continuous or pulsatile flow
Water based suspension fluid
Doppler flow phantom consists of
an imaging face a medium a flow conduit a pump Reservoir a blood mimicking fluid
Non-flow/String phantoms
-Created because of difficulty creating a stable flow pattern
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