Elongated arrays of individual ultrasonic transducer elements at spaced locations emit wedge-shaped beams of ultrasonic energy such that energy emitted by corresponding elements of the arrays travels into a common region of the object to be imaged. Energy emitted by the elements of both arrays is reflected by the same structure within the object. The relative distances of the reflecting structure from the corresponding elements of the arrays are compared to determine the elevation of the reflecting points with respect to an image plane, and a three-dimensional image of the reflectors is generated. A virtual image including information responsive to the elevation of the points can be derived, and used to recalculate the visible display corresponding to a user-selected image plane. The transducer may include a parallel pair of arrays.