Ultrasound transducers
For general ultrasound use the most frequently used probes are curvilinear, linear and phased array transducers (see figure 15 below). Other more specialised probes are cavity (gynaecology), hockey stick and TOE (both cardiology) transducers.

The linear probe is a high frequency transducer (>7 MHz, small wavelength), which has excellent resolution superficially, however secondary to the high frequencies the absorption of ultrasound is high and so the ultrasound depth is small (usually less than 9 cm). It is used for the visualisation of superficial structures (i.e. nerves, muscles, arteries, veins, thyroid, breast and testes) and needle guidance for biopsies, nerve blocks and vascular access.

The curvilinear probe is a low frequency transducer with a relatively good superficial resolution and a great depth (up to 30 cm). It is used for thoracic and abdominal ultrasound and can be used for the same purposes of the linear probe if greater depth is required. It has a relatively large footprint.

The phased array probe is a low frequency probe with a small footprint. Superficial resolution is extremely poor. It is ideal for echocardiography with great depth (up to 30 cm), and the right pulse repetition to assess muscle and valvular movement.