SPI II - Quality Assurance

Quality assurance

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

Annually

AIUM recommends that all equipment should be evaluated and calibrated

ensure optimal imaging, ensure operator and patient safety, and legal reasons

Who’s is quality assurance important

QA Requirements

• assess system components

• Repairs as needed

• Preventative maintenance

• Record keeping

QA goals

1. Guarantee proper operations of the system

2. Detect gradual changes

3. Minimize downtime

4. Reduce the number of non-diagnostic exams

5. Reduce the number of repeat scans

QA methods

1. Test under known, defined conditions

2. Use constant imaging settings

3. Use a phantom with measurable characteristics

4. Image in an identical environment

Objective

Unbiased, not affected by ones past experience, preference or taste

Factual, repeatable, and counted

Objective information is

Subjective

Influenced by ones experience or beliefs and can’t be verified by facts/figures

Affected by opinion, belief, and assumption

Subjective information is

Tissue equivalent phantoms

Used to evaluate gray scale and tissue texture, multi-focus and adjustable focus phased arrays

Doppler phantom (flow phantom)

Tissue equivalent material with simulated “vessels” embedded in gel to mimic all Doppler modalities

Types of Doppler phantoms

1. Vibrating string

2. Moving belt

3. Flow phantom

Slice thickness phantom

Assesses the slice thickness (thickness perpendicular to scanning beam) and gives cysts a filled-in appearance

Elevational resolution

Slice thickness determines

Spatial resolution and low contrast reflectors

Thicker slices diminished

Slice thickness phantom

Contains diffuse scattering plane that is at an angle to the incident sound beam

Imaging place is thicker than beam width (lateral) or pulse length (axial)

When is slice thickness more likely to degrade image quality?

Sensitivity

ability of a system to display low level echos

Minimum sensitivity

minimum weakness (weak amplitude echoes) of a reflection that can be displayed by the system

Normal sensitivity

occurs with settings in which all the pins, solid masses, and cystic structures in the phantom are displayed and accurate.

Should not

Normal sensitivity ______ vary from evaluation to evaluation

Maximum sensitivity

sets output power and amplification (gain) to the maximum practical levels showing maximum depth of phantom and normal tissue starts to fade

Dead zone

Part of the image closest to the transducer where images are inaccurate

System ringing and switching from send to receive

Why is there a dead zone?

High frequency transducers

Which transducer had a thinner dead zone?

Deep dead zone

could mean cracked crystal, detached backing

material, or longer pulse duration

standoff pad or gel pad

can be used to ensure accurate evaluation of very superficial structures

Registration accuracy

Ability of the system to place reflections in proper position while imaging from different orientations

Range accuracy (vertical depth calibration)

Systems accuracy in placing reflectors at correct depths located parallel to the sound beam

Speed isn’t 1540 or system malfunction

Discrepancies in range accuracy could mean

Horizontal calibration

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

Distance measure accuracy

Evaluation of system components used to measure distances (calipers) both horizontal and vertical

Lateral resolution

What resolution is best in the focus?

Dynamic receive focusing

should have a narrow beam at a wide range of depths

Axial resolution

Smallest distance between two objects placed parallel to sound beam can be distinguished as two echoes

Lateral resolution

ability to distinguish two closely spaced structures that lie side by side or perpendicular to the sound beam

Lateral resolution

Can be assessed by measuring the width of reflections on the display created by targets in the phantom

Uniformity

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

Hyperechoic

Solid structures should be displayed as

Anechoic

Hollow structures should be displayed as

Positive

the test predicted disease

Negative

the test predicted the absence of disease

True positive

comparison test is correct; both are positive for disease

True negative

comparison test is correct; both are negative

for disease

False positive

test says there is disease when there is not

False negative

test says there is no disease when there is

Sensitivity is ability of a test to detect disease specificity is ability of a test to detect the absence of disease

What is the difference between sensitivity and specificity?

Positive predictive value

how often the test is correct when positive for disease

Negative predictive value

how often the test is correct with negative for diseases

True Positive + True Negative/TP+TN+FP+FN

Accuracy/gold standard equation