quality assurance

quality assurance

the routine, periodic evaluation of an ultrasound system to guarantee optimal image quality

how often should quality assurance evaluations be performed?

periodically and routinely

what are the 4 requirements for a quality assurance program?

• assessment of system components

• repairs

• preventive maintenance

• record keeping

perfomance testing

scheduled activities that evaluate the accuracy of the system’s imaging capabilities

proper methods for quality assurance programs include:

• test under known, defined conditions

• use constant instrument settings

• use a phantom with measurable characteristics

• image in an identical environment

devices 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

devices that test the operation of the instrument (anatomic imaging and flow evaluation performance):

• this group takes into account the operation of the entire instrument

• imaging and doppler performance are important in evaluating the instrument as a diagnostic tool

• the acoustic output of an instrument is important when considering bioeffects, risk and safety

what are the 2 types of commercially available devices that test imaging performance?

• tissue-equivalent phantoms

• test objects

tissue-equivalent phantoms

simulate tissue properties, allowing assessment of detail and contrast resolutions, penetrations, dynamic range, and time-gain-compensation operation

what are tissue-equivalent phantoms made out of?

• graphite-filled aqueous gels or urethane rubber materials

• graphite particles act as ultrasound scatterers in materials

test objects

• DO NOT simulate tissue characteristics but do provide some specific measure of instrument performance

• the beam-profile slice-thickness test object contains a thin, scattering layer in an echo-free material

• the object can be used to show beam width in the scan plane or perpendicular to it (section thickness)

doppler testing phantom

• evaluates the doppler capabilities of imaging systems

• utilize physical moving structure, such as a vibrating string, a moving belt, or a circulation pump that moves blood-simulating fluid through the phantom

what can be evaluated using a doppler testing phantom?

• doppler sensitivity

• depth resolution

• volume flow

• velocity accuracy

slice thickness phantom

• evaluates the elevational plane to the thickness portion of the sound beam perpendicular to the imaging plane

• contains a diffuse scattering plane that is at an angle to the incident sound beam

• mimics soft tissue

sensitivity

refers to the ability of a system to display low-level echoes

what are the two forms of sensitivity?

• normal

• maximum

normal sensitivity

with these settings, all the pins, solid masses, and cystic structures in the test phantom are accurately displayed

what is adjusted to establish normal sensitivity?

• output power

• TGC

• amplification

all subsequent quality assurance and performance measurements are made at what form of sensitivity?

normal sensitivity

maximum sensitivity

with these settings, a tissue equivalent phantom is imaged and the depth of tissue-like texture on the display is measured

what is maximum sensitivity evaluated with?

evaluated with the output power and amplification of the system set to the maximum practical levels

dead zone

the region close to the transducer where images are inaccurate

the dead zone extends from the transducer to the:

shallowest depth from which meaningful reflections appear

information within the dead zone is:

unreliable and may not be used in the diagnostic setting

the dead zone is assessed with:

the shallowest series of pins in the test object

in a tissue equivalent phantom, the dead zone is the:

shallowest depth at which uniform tissue texture appears

what type of transducer frequency has a thinner dead zone?

higher frequency transducers

registration accuracy

the ability of the system to place reflections in proper positions while imaging from different orientations

range accuracy/vertical depth calibration

describes the system’s accuracy in placing reflectors at correct depths located parallel to the sound beam

if differences appear between the ultrasound scan and the actual pin locations in the test object, the error may be caused by:

• system malfunction

• the speed of sound in the phantom is different than 1,540 m/s

horizontal calibration

the system’s ability to place echoes in their correct position when the reflectors are perpendicular to the sound beam

distance measurement accuracy

• components of the ultrasound system used to measure distances require periodic evaluation

• digital calipers should be checked in both vertical and horizontal directions

focal zone

• surround the focus

• lateral resolution is excellent because the beam is narrow

• the focus of phased array transducers must be carefully evaluated

axial resolution

evaluated by scanning sets of successively closer spaced pins within the phantom

lateral resolution

evaluated by measuring the width of reflections on the display created by the point targets in the phantom

compensation operation or uniformity

• describes the system’s ability to display similar reflectors in the phantom with echoes of equal brightness

• with proper TGC, identical reflectors should have the same appearance on the monitor regardless of their depth

mock cysts and solid masses

• tissue-equivalent phantoms are used to evaluate dimension, texture and fill-in of cysts

• the system should accurately display hollow structures as anechoic and solid structures as hyperechoic

display, hardcopy output and gray scale dynamic range

• adjustments to the output power and amplification of the system should alter the appearance of the image on the display and all output devices

• adjustments on a single display device (such as the brightness or contrast of a monitor) alter the image on that particular device only