Ch. 22 Quality Assurance Flashcards
Quality Assurance
the routine, periodic evaluation of an ultrasound system to guarantee optimal image quality
How often should quality assurance be performed
periodically and routinely
What are the 4 requirements for a QA program?
-assessment of system components
-repairs
-preventative maintenance
-record keeping
What are the goals of a QA program
-guarantee proper operation of the system
-detect gradual changes
-minimize downtime
-reduce the number of non-diagnostic exams
-reduce the number of repeat scans
What devices are used in QA?
-Tissue equivalent phantom
-Doppler phantom
-Beam profile/slice thickness phantom
Objective standards
factual, repeatable, quantitative information
Subjective standards
influenced by an individual’s experiences or beliefs
What type of standards should be used in a QA program?
Objective
What are tissue equivalent phantoms used to evaluate?
gray scale, tissue texture, speed calculation, multi-focus transducers, and adjustable focus phased array transducers
How are tissue equivalent phantoms similar to soft tissue?
-speed of sound(1540 m/s)
-attenuation
-scattering characteristics
-echogenicity
What is embedded in a tissue-equivalent phantom?
structures that mimic hollow cysts and solid masses (hyper and hypoechoic)
What are the different types of Doppler phantoms?
vibrating string, moving belt, flow phantom
What do Doppler phantoms assess?
All Doppler modalities, including pulsed, continuous wave, color, ad power mode
Slice thickness determines…
elevational resolution
Why is slice thickness most likely to degrade image quality?
the imaging plane is thicker than either the beam width or the pulse length
What does the slice thickness phantom mimic?
Slice thickness
Thicker slices…
diminish spatial resolution and reduce the ability to visualize small, low contrast reflectors
Sensitivity
the ability of a system to display low-level echoes
What are the 2 types of sensitivity
normal and maximal
Normal sensitivity settings
All the pins, solid masses, and cystic structures in a test phantom are accurately displayed with normal power, gain, and TGC
What is adjusted to establish normal sensitivity?
Output power, TGC, and amplification
Normal sensitivity settings should…
Not vary from one routine evaluation to the next
How is maximum sensitivity evaluated?
With the output power and amplification of the system set to the maximum practical levels
________ is used to assess sensitivity and should not differ from one routine eval to the next
Maximum visualization depth
How else is sensitivity assessed?
when the sonographer adjusts the system controls to change echo brightness from barely visible to full brightness (saturation)
Dead zone
the region close to the transducer where images are inaccurate
Where is the dead zone
It extends from the transducer to the shallowest depth from which meaningful reflections appear
What causes the dead zone?
the transducer ringing and the time it takes the system to switch from transmit to receive mode
How is frequency related to dead zone?
higher frequency transducers have a thinner dead zone than lower frequency transducers
How is the dead zone assessed?
The shallowest series of pins in a test object
How can you better image superficial structures?
an acoustic standoff or gel pad
What does an increasingly deep dead zone indicate?
A cracked crystal, detached backing material, or a longer PD
Registration accuracy
the ability of the system to place reflections in proper positions while imaging from different orientations
What is another name for range accuracy
vertical depth calibration, axial resolution
vertical depth calibration/range accuracy
describes the system’s accuracy in placing reflectors at correct depths located parallel to the sound beam
Horizontal calibration
the system’s ability to place echoes in their correct position when the reflectors are perpendicular to the sound beam (lateral resolution)
How do we evaluate distance measurement accuracy
By evaluating the digital calipers in both vertical and horizontal directions
Axial resolution is evaluated by
scanning sets of successively closer spaced pins within the phantom
Lateral resolution is evaluated by
measuring the width of reflections on the display that are created by point targets in the phantom. This approximates the beam diameter at that depth.
Uniformity
the system’s ability ability to display similar reflectors in the phantom with echoes of equal brightness
It is important to compare the relationship between the image on the system’s screen with
the output display of all other devices, such as remote viewing stations
Adjustments to output power and amplification should…
alter the appearance of the image on the system’s display and all output devices
Adjustments on a single-display device (like brightness or contrast)…
alter the image on that device only
minimum sensitivity
assess the weakest echo signal that is accurately displayed, setting system gain to minimum and then increasing until the deep rod is displayed
What does the AIUM test object evaluate?
axial resolution, lateral resolution, caliper accuracy, and the dead zone
AIUM 100 mm test object
fluid filled tank that has the speed of soft tissue that does not attenuate
AIUM 100 mm test object does not evaluate
gray scale
