Quality Assurance

What is quality assurance

the routine (regular scheduled 6-12months) periodic evaluation of the US system to guarantee optimal image quality

Requirements

multiple evaluations of the system’s components

repairs

preventative maintenance

record keeping

Goals

proper equipment operation

detect gradual changes

minimize downtime

reduce number of repeat scans

Methods

test under known, defined conditions

constant instrument settings

use phantom with measurable characteristics

image in identical environment

what is a phantom

an objective standard (eliminates opinion) medical/legal: a must for every laboratory (in theory)

Who is responsible for performing quality assurance

service engineer may be involved but ultimate responsibility of the sonographer

AIUM 100mm test object

Water-filled phantom. commercially available, array of strategically located pins

Attenuation

does NOT have attenuation properties of soft tissue, cannot evaluate gray scale

know the pattern of the pin set

dead zone, longitudinal resolution (transducer on top) vs lateral resolution (transducer on side), lateral resolution (transducer on oblique corner, horizontal registration, vertical registration, all pins=registration

Tissue equivalent phantom

commercially available, contains a medium similar to soft tissue (mimics soft tissue). Strategically located pins, structures that mimic cysts and solid masses are embedded in the phantom. Metal/nylon pins. Made of aqueous gel and graphite particles

attenuation for tissue equivalent phantom

attenuation coefficient similar to soft tissue. EVALUATES gray scale since this phantom attenuates like soft tissue

Doppler phantom

commercially available, contains static simulated vessels as well as dynamic simulated vessels at variety of angles. assesses the accuracy of pulsed, CW and color flow systems.

what 2 pieces may be used to evaluate doppler systems

vibrating string and moving belt phantoms

Performance testing

unbiased factual representation of the machine performance

subjective

opinion

objective

facts

Minimum sensitivity

increasing the gain from minimum value to the point when an echo displayed. Sensitivity is the ability to detect low level echoes in the far field

Normal sensitivity

gain setting where all of the pins in the AIUM test object are displayed. Found at HIGHER gain than minimum all other performance measurements are made here

sensitivity

when adjustments make changes in display or echo brightness from visible to fully saturated sensitivity is being assessed

Dead zone

using series of shallow pins while scanning from the top of the AIUM test object. The distance close to the transducer that can’t produce an image. (results from time between switching from T/R switch)

acoustic standoff

aka gel pad, eliminates the dead zone

range accuracy

aka VERTICAL depth calibration. machine’s ability to display echoes in proper depth

registration accuracy

place echoes in proper positions while imaging from different orientations

horizontal calibration

position echoes in their correct position along a distance perpendicular to the beam

longitudinal resolution

parallel/ front to back to sound beam

Gold Standard

a perfect technique. a sensitivity and specificity of 100%

3 main sonography labs accreditation agencies

american college of radiology (ACR)

american institue of ultrasound in medicine (AIUM)

intersocietal accreditation commission (IAC)

hydrophone

evaluates acoustic output and pressure in a sound beam

sensitivity

correctly identify those with the condition (true positives)

specificity

correctly identify those without the condition (true negatives)

accuracy

overall ability of ultrasounnd to identify both true positives and true negatives

reliability

consistency or repeatability of ultrasound results when repeated under the same conditions. Assessed using interobserver or intraobserver agreement

Positive Predictive Value (PPV)

probability that a person with a positive ultrasound result actually has the condition

Negative Predictive value (NPV)

probability that a person with a negative ultrasound result truly does not have the condition

Epidemiological studies

requires large numbers of patients when the occurence rate of the measure effect is small (randomized studies require large sets) using this method has shown no adverse effects on fetal outcome or other measurements

best study is

prospective

randomized

limitations of epidemiologic studies

retrospective, ambiguities, other risk factors

what is the value of calculating specificity

it tells you how often a positive ultrasound exam is correct

what evaluates all types of procedures performed within the ultrasound laboratory on an ongoing basis

CQI (continuous quality improvement)