US FUNDAMENTALS: B-MODE AND DOPPLER MACHINE SETTINGS. MSUS BASIC. US: emission and reception of mechanical sound waves with a frequency greater than the human hearing frequency range ( 15-20 MHz).
US: emission and reception of mechanical sound waves with a frequency greater than the human hearing frequency range (15-20 MHz)
Sound waves produced and captured by piezoelectric material located inside the transducer or probe
US: 2-20 MHz
The degree of reflection of an ultrasound wave depends on the body tissue being assessed. Each tissue has its own acoustic properties (density and resistance) which determine its ‘acoustic impedance’. Reflections occurs at interfaces between tissues of different acoustic interfaces.
Gray scale (GS) ultrasound refers to the black and white images that are generated. Gray scale defines the morphology of a tissue. The whiter a structure appears, the more reflective it is. e.g. bone or calcification will appear white. The darker a structure is, the less reflective it is. As water is the best transmitter of sound, fluid e.g. blood, synovial fluid, cysts generally appear black on the image as sound is not reflected back and registered on the screen.
Doppler technique detects movement of red blood cells in vessels
The Clinical Application Specialist from the ultrasound company for your machine will assist in setting up appropriate settings for the assessment of synovitis (and other joint structures) as these will vary from machine to machine
The footprint of the transducer is the surface area of the
transducer that is physically in contact with the skin.
An image this is acquired should contain all the information
required to make a valued assessment
For small structures e.g. MCPJ, this may be achieved with a smaller footprint (e.g. hockey stick style transducer) whilst larger structures e.g. shoulder and hip may require a larger footprint to capture the full field of view.
Small transducers may be useful if there are deformities or for guiding interventional procedures
Use a minimal number of focal points (on average 2 are used)
Ensure focus points are at level of region of interest
Adjust the depth so that region of interest at least half way down screen
Adjust B-mode or 2D gain to optimize image brightness
There are other modifiable parameters on some machines such as dynamic range. This ‘contrast control’ may be adjusted for personal preference but we would advise discussing this (and others) with clinical applications specialist according to your machine
Most scans for the assessment of joint inflammation are performed using Power Doppler or Colour Doppler displays
After choosing either option, the Doppler box should be adjusted to cover the whole joint (or specific region of interest). It should encompass the joint proximally and distally and also reach the skin surface.
Recommended settings for colour and power Doppler in rheumatology
Doppler frequency Lowest or highest depending on machine
Pulse repetition frequency Lowest possible*
Colour priority All priority to colour
Wall filter Lowest possible*
Persistence Lowest possible
Gain On the threshold to noise
Focus Placed where highest sensitivity is required
*Lowest possible where motion artifacts are avoided most of the time.
From: Torp-Pedersen ST, Terslev L Settings and artefacts relevant in colour/power Doppler ultrasound in rheumatology. Ann Rheum Dis. 2008;67:143-9.
– Always observe the full extent of joint space (capsule) proximally and distally
– Ensure colour box captures whole joint and that box reaches skin surface
– Always ensure pathology observed in both longitudinal and transverse views