Chapter 22 Quality Assurance Flashcards
Quality assurance is important because
It validates the consistency of images and the accuracy of devices
Quality assurance is
The routine periodic evaluation of the system to guarantee optimal image quality
What are the 4 quality assurance requirements
Repairs, Assessment of system components, Preventative maintenance, Record keeping
Q.A. Goals
Proper operation of equipment, detect changes in performance, minimize downtime, reduce the # of non-diagnostic exams
Q.A. Devices
Tissue equivalent phantom, Doppler phantom, Beam profile/ slice thickness phantom
Q.A. is based on Objective Standards:
unbiased, factual, repeatable
Tissue Equivalent Phantom involves
box filled with medium with same PS speed and attenuates, scatters and present echogenicities similar to soft tissue
embedded in tissue equivalent phantom are
pins, mock cysts masses
the T.E. phantom is used to take performance measurements and to
evaluated grayscale/tissue texture
Doppler or Flow Phantoms are used to
evaluate Doppler systems
Modern Doppler Phantoms include
circulation pumps which propel fluid through vessels embedded in the tissue equivalent phantom
Other Doppler phantoms contain
vibrating strings or moving belts
Doppler phantoms assess characteristics of
all doppler modalities including PW, CW, color, and power mode
Slice Thickness Phantom is used to
specifically to evaluate slice thickness which determines elevational resolution
elevational resolution is most likely to degrade because
the imaging plane is thicker than either the beam width or pulse length
if the slice is not thin,
low contrast lesions can not be seen or cystic structures may appear filled in
A scattering plane in an anechioc medium is imaged at either ____ or ____ degree angle
45 or 90
The display of a Slice Thickness Phantom demonstrates
the beam geometry or thickness
Phantoms are used to
take performance measurements
Tissue Equivalent Phantom allow personnel to record
performance measurements
Performance measurement: Sensitivity is the ability of
the system to register low level echoes ( 2 levels are assessed – normal and maximum)
(performance measurement) normal sensitivity is the
gain, TGC, and power – where pins, cysts and masses are accurately displayed
(performance measurement) maximum sensitivity is evaluated by
setting the power and amplification to maximum and determining the maximum depth of tissue
(performance measurement) Dead zone
the region close to the probe where images are absent due to the time it takes to switch from transmit to receive
(performance measurement) when measuring the dead zone
a shallow series of pins at the top of the device are used to determine the depth at which uniform tissue texture appears
An increasing deeper dead zone may indicate a
a cracked crystal, detached backing material or longer pulse duration
Thinner dead zones are created from
higher frequency probes
(Dead zone)
An acoustic standoff
can be used to accurately image important superficial structures —dead zone would be at the level of the standoff
(performance measurement)
Registration Accuracy is the ability of
the system to place reflections in the proper positions
(registration accuracy)
range or vertical depth calibration describes
the systems accuracy in placing reflectors at correct depths
An error with Registration Accuracy could indicate
system malfunction or the PS in phantom fell off 1540 m/s
Registration Accuracy can evaluate
A mode, M mode and 2D
Horizontal calibration or registration accuracy is the ability to
place echoes in their correct position horizontally across the display (perpendicular to the sound beam)
(performance measurement)
Distance Measurement Accuracy
the distance between 2 vertical and horizontal pins should be measured to check the digital calipers
(performance measurement)
Focal Zone
the focus is adjusted ( depth and #) and the lateral resolution assessed in the region affected
(performance measurement)
axial resolution is evaluated by
scanning a set of closely spaced pins positioned front to back in the beam
(performance measurement)
lateral resolution is evaluated by
scanning a set of closely spaced pins positioned side by side in the beam —lateral resolution should be best at focus
(performance measurement)
compensation operation or uniformity
2 same reflectors in phantom are located at different depths. —TGCs are applied to ensure equal echodensities can be displayed
(performance measurement)
mock cysts and solid masses
tissue equivalent phantom is used to evaluate the dimension, texture, and fill-in of cysts
(performance measurement)
mock cysts and solid masses
tissue equivalent phantom is used to evaluate the dimension, texture, and fill-in of cysts
(performance measurement)
Display, Hardcopy Output, Grayscale dynamic range
power, gain, compress are adjusted and grayscale change evaluated
with monitor calibrated, the image displayed is compared against images on other output devices
adjusting contrast and brightness only affects the monitor not stored or archived images
True Positive
correctly predicted disease
False negative
incorrectly predicted no disease
Comparison test compares our test to
the Gold Standard
Comparison Test tells us
how good is ultrasound at detecting the presence or absence of disease
gold standard is
a diagnostic test or invasive procedure that is nearly perfect at detecting the presence or absence of disease
(performance measurement)
Sensitivity equation
TP / (TP + FN)
(performance measurement)
Specificity equation
TN / (TN + FP)
the ability of the comparison test to detect the absence of disease
(comparison test)
Accuracy is
the percentage of times the comparison test is right
(comparison test)
accuracy equation
(TP+TN) / (TP+FP+TN+FN)
(comparison test)
Positive Predictive Value is
the % of time the test correctly predicted the presence of disease relative to the total number of times the test predicted disease
(comparison test)
Positive Predictive Value equation
TP/(TP+FP)
(comparison test)
Negative Predictive Value is
the % of time the test correctly predicted the absence of disease relative to the total number of times the test predicted no disease
(comparison test)
Negative Predictive Value equation
TN/(TN+FN)
