What the practising rheumatologist needs to know about the technical fundamentals of ultrasonography.

A transducer generates ultrasound waves and emits them into the body. Boundaries in or between tissues reflect the waves, and the transducer receives the reflected waves. A computer converts the information into images that are displayed on a monitor. Image resolution is greater with higher frequencies, and penetration is greater with lower frequencies. Linear probes with frequencies between 5 and 20 MHz are mainly used for musculoskeletal ultrasound. Image quality and resolution have improved significantly. Tissue harmonic imaging and cross-beam technology aid in differentiating between anatomical structures, although borders appear artificially thickened. Three-dimensional ultrasound provides additional coronary planes, and contrast agents increase the sensitivity for synovial blood flow in inflamed joints. This chapter provides further information regarding which ultrasound technology is the best for purchase by a rheumatology unit, how to organize ultrasound clinics, and how best to perform ultrasonography in daily practice, including the most important indications for ultrasound in rheumatology.