1. An apparatus for imaging mechanical properties of a tissue region from within an endocavity of a patient, the apparatus comprising: (a) an ultrasound probe insertable inside the endocavity and having a distal end contactable against the tissue region to be imaged, the distal end comprising at least one transducer array to acquire ultrasound images in an imaging plane of the transducer; (b) a vibration assembly translationally coupled to a proximal end of the probe and operable to vibrate the probe along a direction essentially parallel to the imaging plane, thereby causing deformational excitation of the tissue region contacted by the probe; and (c) a rotation assembly rotationally coupled to the vibration assembly and operable to rotate the probe and vibration assembly such that the imaging plane is rotated about a selected rotational range.