Quality Assurance

Chapter 22

Quality assurance:

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

How often should QA be performed?

periodically and routinely according to your specific lab

Who is responsible for implementing a quality assurance action plan?

the sonographer

What are the 4 requirements of QA?

1. Assessment of system components

2. Repairs

3. Preventative maintenance

4. Record keeping

Are technique and protocols a part of QA?

No

What are the 4 QA devices?

1. AIUM 100 mm test object (first ever device; no longer used)

2. Tissue equivalent phantom

3. Doppler phantom

4. Beam profile/slice thickness phantom

Methods for QA:

• Test under known conditions

• Use constant instrument settings

• Use a phantom with measurable characteristics

• Image in an identical environment

An objective statement is…

completely unbiased

A subjective statement is…

one that is influenced by an individual’s experience, beliefs, or assumption

QA programs should be based on _____ standards

objective

Tissue equivalent phantom is used to…

evaluate characteristics such as gray scale, tissue texture, multi focus & adjustable focus phased array transducers

Tissue equivalent phantoms are similar to soft tissue in the 4 following ways:

1. Speed of sound

2. Attenuation

3. Scattering characteristics

4. Echogenecity

Gray scale is evaluated because it contains _____ that act like soft tissue

small scatterers

Structures embedded in the phantom mimic what?

hollow cysts and solid masses

What may be embedded in the phantom to produce reflections at strategic locations

nylon strings

Evaluated when the pins in the test object are parallel to the sound beam’s main axis

axial resolution

Evaluated when the pins in the test object are perpendicular to the sound beam

lateral resolution

Evaluated by comparing the distances between reflections on the display with the actual distances in the test object

electronic caliper accuracy

Evaluated by scanning the pins located at the top of the test object very close to the transducer

dead zone

Doppler/flow phantom is used for…

evaluating Doppler systems

Includes a circulation pump to propel fluid through vessels embedded in a tissue equivalent phantom

Doppler phantom

Other Doppler phantoms contain…

vibrating strings or moving belts

Doppler modalities:

• Pulsed

• Continuous wave

• Color

• Power mode

Slice thickness phantom evaluates…

elevational resolution

Slice thickness phantom:

assesses the slice thickness and its effect upon image accuracy

Slice thickness is most likely to…

degrade image quality because the imaging plane is thicker than either the beam width or the pulse length

When the ultrasound beam is overly thick…

cystic structures may appear filled in

Thicker slices diminish…

spatial resolution and reduce the ability to visualize small, low contrast reflectors

Contains a diffuse scattering plane that is at an angle to the incident beam & measures the beam geometry perpendicular to the imaging plance

slice thickness phantom

Sensitivity:

refers to the ability of a system to display low level echoes (weak echoes)

What are the 2 forms of sensitivity?

normal and maximum

Normal sensitivity:

those at which all the pins, solid masses, and cystic structures in the test phantom are accurately displayed

Maximum sensitivity:

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

Maximum sensitivity is used with…

a tissue equivalent phantom

Dead zone:

is the region closest to the transducer to the shallowest depth and results from transducer ringing and the time it takes the system to switch from the transmit to the receive mode

Information within the dead zone is…

unreliable and may not be used for diagnostic setting

Higher frequency transducers have a ____ dead zone than lower frequency transducers

thinner

Increasing dead zone may indicate…

a cracked crystal, detached backing material, or a longer pulse duration

What allows for accurate imaging of important superficial structures?

a stand off pad

Registration accuracy:

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

Range accuracy or Vertical depth calibration:

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

The accuracy of reflector depth positioning

depth calibration

Horizontal calibration:

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

Focal zone:

surrounds the focus (the depth at which intensity is the highest and the beam is narrowest)

______ resolution is excellent in the focal zone because the beam is narrow

Lateral

The focus of phased array transducers is…

sonographer controlled

Systems with dynamic receive focusing should produce…

narrow reflections over a wide range of depths

Axial resolution:

the smallest distance at which two pins parallel to the sound beam are displayed as two distinct echoes

Axial resolution is evaluated by…

scanning a set of closely spaced pins within the phantom

Lateral resolution:

the minimum distance that two side by side rods are displayed as two distinct images

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

What phantom is used to evaluate the dimension, texture, and fill in of cysts

tissue equivalent

A tissue equivalent phantom system should accurately display hollow structures as ____ and solid structures as ____

anechoic, hyperechoic

Adjusting the systems output power and amplification should produce changes in the…

grayscale display

The strength of the reflection is related to the characteristics of…

the tissue creating the reflection

Direction of the flow =

color map

Sample volume =

accuracy of sample volume placement

Velocity =

accuracy of velocity estimation

Vertical length =

axial

Width =

lateral

What results in better elevational resolution?

a shorter, thinner beam

What is elevational resolution determined by

the height of the ultrasound beam