Topic 3 System Optimisation Flashcards
What is a quality ultrasound image?
An image that clearly and accurately displays anatomy and pathology with minimal to no artefact
What is spatial resolution?
The ability to define two separate objects as distinct from each other rather than a single larger object. Relates to frequency and a focal point.
What is contrast resolution?
Defines the various shades of grey. Pure black represents no ultrasound reflection whereas pure white represents structures that reflect all or nearly all of the sound.
What is temporal resolution?
The ability to view moving objects in real time. Monitored by frame rate.
What is the dynamic range?
Dynamic range is the ratio in dB of the maximum input signal that can be displayed without reaching saturation to the smallest input signal that can be visually seen above noise level
What is compound imaging?
allows the image to be created from multiple directions to reduce noise artefact, but can eliminate subtle detail such as arterial or venous thrombus
How can you change sensitivity to improve image quality?
- Increase sensitivity to gain more data from slow flow or smaller diameter vessels (change the setting to low)
- increasing sensitivity to reduce frame rate
- changing the sensitivity to medium/high will reduce the time needed to capture colour info
How can you change the scale to improve image quality?
scale settings change the PRF therefore this controls the level of slower or faster velocities that will be displayed and the velocity at which aliasing will begin
How can you change colour box size to improve image quality?
the colour box controls the width and depth of a colour display on the b-mode image. It primarily affects frame rate. If the width is too large, it will significantly slow the frame rate. This is because the wider the box, the more lines of site that must be transmitted and received
How can you change angle of insonation to improve image quality?
Angle of insonation has a significant effect on the presence of aliasing. Colour boxes can be steered so that the image of the vessel can be parallel with the transducer. Heel-toeing can be done to tilt the image to increase or decrease the angle of the artery
How does the wall filter affect image quality?
Vessel wall motion can interfere with the clarity of colour and increasing the wall filter will eliminate the low frequency components associated with colour flash in the tissue outside the vessel. Filter can also remove some of the low velocity signal from the vessel and produce anechoic areas within the lumen.
How does changing the baseline affect image quality?
Changing the baseline will change the velocity at which the forward and reverse flow will start to aliase. Increasing the baseline will reduce the level of aliasing for flow towards the probe. Lowering the baseline will reduce the aliasing velocity away from the transducer
How does gate size affect spectral quality?
size of the gate determines the area that will be sampled to create the waveform. keeping the gate small so that the central area of the vessel can be sampled without other velocities being included that will contribute to unwanted noise. In vessels with little to no flow, larger gates can be used to ensure velocities are not missed by a smaller gate
How does transducer frequency affect spectral quality?
Transducer frequency changes the velocity at which aliasing occurs. High frequency transducer will be more sensitive to slower flow and give a high frequency shift. Lower frequency transducers will increase the velocities that can be recorded before aliasing occurs.
How does the angle of insonation affect spectral quality?
Decreasing the angle of the vessel to the beam will increase the frequency shift. Aliasing will occur at a lower level than at higher angles
