US FUNDAMENTALS: B-MODE AND DOPPLER MACHINE SETTINGS

MSUS BASIC US: 2-20 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

MSUS BASIS 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.

MSUS BASIS 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. Bone Fluid

MSUS BASIC 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 MACHINE SET UP

The choice of transducer frequency is dependant on the joint, body habitus and age of a patient A higher frequency transducer (e.g MHz) is preferable for the assessment of superficial lying anatomical structures e.g. for the MCPJ. Generally > 18MHz used for skin and very superficial structures. A lower frequency transducer (e.g MHz) is preferably for deeper lying structures e.g. for the shoulder FREQUENCY OF TRANSDUCER

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 FOOTPRINT OF TRANSDUCER

IMAGE OPTIMIZATION: GENERAL Grey scale 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

Doppler 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. GENERAL CONSIDERATIONS

Recommended settings for colour and power Doppler in rheumatology Doppler frequencyLowest or highest depending on machine Pulse repetition frequencyLowest possible* Colour priorityAll priority to colour Wall filterLowest possible* PersistenceLowest possible GainOn the threshold to noise FocusPlaced 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:

–Always observe the full extent of joint space (capsule) proximally and distally IMAGE PRESENTATION

–Ensure colour box captures whole joint and that box reaches skin surface IMAGE PRESENTATION

–Always ensure pathology observed in both longitudinal and transverse views SCORING PATHOLOGY