Ultrasound QA

Question 1

What are the general conditions for scanner settings in US QA?

Answer 1

Representability - The setting should represent a typical clinical application for the probe.
Sensitivity - The setting should be such that subtle changes in the tested parameter can be easily revealed.
Reproducibility - The setting should be easily and exactly reproduced.

Question 2

How is element drop-out tested?

Answer 2

• A “wire tool” (e.g. paper clip) is run over the scanner membrane coupled with a thin layer of gel or water.
• Reverberations within the wire are shown as a string of echoes.
• Reverberations will not be present if an element has stopped working.

Question 3

How should the scanner be optimised for the Wire-Tool Test?

Answer 3

• Scanner settings need to be optimised to form a plain, linear scan at a high frequency.
• THI, Compound Imaging, Post-Processing Off.
• No beam steering.
• Single frequency, Highest Frequency.
• Depth: min.
• Focus: Single at the top.

Question 4

What are the three methods for assessing image uniformity?

Answer 4

• Phantom Test.
• In-Air Exposure Test.
• Metal Wire Test.

Question 5

How does the phantom test assess uniformity?

Answer 5

• A homogenous region of the phantom is scanned with uniform grey scales. Any signal out or dark bands constitute a possible fault.
• Must be scanned with general considerations, suitable TCG, gain and power.

Question 6

How does the in air exposure test assess uniformity?

Answer 6

• The reverberations pattern when the transducer is exposed to air should be laterally uniform (linear and curvilinear transducer only).

Question 7

How is the assessment of image uniformity optimised for the in air exposure method?

Answer 7

• General considerations.
• Depth: min.
• Focus: Single at the top.
• Harmonics off.
• Highest Frequency.
• Compounding off.

Question 8

What is the definition of system sensitivity?

Answer 8

The weakest ultrasound signal that can be detected by the scanner.

Question 9

What is the definition of system sensitivity in characterising B-Mode imaging?

Answer 9

The lowest signal level that can be visualised on an image, perceived by an observer in normal clinical settings.

Question 10

What factors can affect system sensitivity?

Answer 10

• Scanner settings.

- Background lighting conditions.

Question 11

What are the three methods for assessing scanner sensitivity?

Answer 11

• Phantom test
• Reflecting block Test
• in air exposure test.

Question 12

How does the phantom test assess system sensitivity?

Answer 12

• Measurement of the maximum depth of visualisation (i.e. the depth of the speckle seen on the phantom image)
• The action level for this is 10mm.

Question 13

How is the scanner optimised in the phantom sensitivity test?

Answer 13

• General considerations.
• Power, gain, TGC to obtain speckle from as deep a depth as possible
• Compounding off.

Question 14

How does the reflecting block test measure system sensitivity?

Answer 14

• Reverberation pattern from reflecting block is monitored and gain is turned down until the monitored plane disappears.
• Gain at which this occurs is recorded.

Question 15

How does the in air exposure test measure system sensitivity?

Answer 15

• Measurement of the depth of the last reverb.

- The action level is the loss of 1 reverb.

Question 16

How is the scanner optimised in the in air exposure sensitivity test?

Answer 16

• Depth: min
• Focus: Single at the top
• Harmonics off
• Highest frequency
• Compounding off.

Question 17

Define system noise.

Answer 17

System noise refers to the imaging noise oriented from electrical noises in both ultrasound emission and receiving parts.
This can be represented by the noise level in the electrical circuits, but it is usually visual imaging noise that is examined.

Question 18

What are the two methods of measuring system noise?

Answer 18

• In Air Exposure method

- Computer-assisted imaging analysis method

Question 19

How is the in air exposure method used to assess system noise?

Answer 19

• The gain is slowly reduced until there is no visible noise on the image
• The action level is two gain levels.

Question 20

How is the scanner optimised for the in air exposure test for system noise?

Answer 20

• General considerations
• Transducer dry and clean
• Power at max
• Time and frame averaging, persistence and compounding off.

Question 21

How is computer-assisted analysis used in the measurement of system noise?

Answer 21

• Multiple phantom images are taken and statistical features are examined to calculate SNR.

Question 22

What are the three methods to determine spatial resolution?

Answer 22

• Phantom methods (resolution or point targets)
• Beam width determination
• Point Spread Function method

Question 23

What is the difference between the resolution targets and the point targets in a US Test Object?

Answer 23

• Resolution targets are staggered in spacing both laterally and axially.
• Resolution is measured by determining the closest pair that can be resolved by eye.
• Point targets are evenly spaced axial and laterally in the phantom.
• Resolution is measured by measuring (either manually or with computer automation) their depth and width.
• This can also be used to measure slice thickness if the probe is at 45deg to the targets.

Question 24

What two devices can be used to measure calliper accuracy?

Answer 24

Phantom or Open-Top Test Object

Question 25

What general considerations apply when making calliper accuracy measurements?

Answer 25

• Scanner should be in an appropriate clinical preset.
• Largest Magnification should be used.
• Measurements should be made on targets at clinically relevant distances and depths.
• Scanner settings should be optimised (depth, write zoom, read zoom, gain, TGC, power)
• Callipers should be placed in a repeatable position on the target (centre or edge).

Question 26

What are the tolerances for calliper accuracy?

Answer 26

• Axial and lateral measurements: +/- 2%
• 3D or Z measurements: +/- 5%
• Circumference and Area measurements: +/- 5%