A crucial point to be evaluated while selecting a probe is its shape and volume. Indeed, an optimal probe should represent the best compromise between the size, which should be small to allow its handling in deep and narrowed spaces, and the ultrasonographic scanning window, which should be large enough to provide a widest possible area of exploration in a single view; the adherence to the surface of the target organ should be high enough for enabling an adequate stability along its handling and for avoiding gas interposition, reducing the number of possible artefacts in organ exploration. The most frequently used probes are T-shaped with linear (Fig. 1.5a, b) or convex scanning head (Fig. 1.6a, b), interdigital (Fig. 1.7a, b), and microconvex (Fig. 1.8a, b). The microconvex probe provides the best solution regarding the aforementioned desirable criteria. Indeed, the T-shaped probe, while remaining more stable and being associated with higher image resolution, has a lower ratio between lateral length and ultrasonographic scanning window than the microconvex one. Linear transducers, with enlarged scanning windows, have more recently become available (trapezoid scanning window): these combine the stability of the linear probes and their higher image resolution with larger scanning windows and a limited volume (Figs. 1.4a–d, 1.9a, b). Another aspect to be considered in evaluating a probe is whether it can be used for surgical maneuvers as those described in Chap.​ 8 for which the echoprobe is acting as a kind of surgical instrument (see Fig. 1.10a–c).