An apparatus, comprising: an ultrasonic transducer element configured to generate ultrasonic energy to be directed into tissue of a subject and configured to receive a portion of the ultrasonic energy reflected by a predominantly specular-reflecting target, the ultrasonic transducer element comprising a surface configured to provide and receive the ultrasonic energy, the surface including an area of greater than or equal to about 4λ 2, where λ is an acoustic wavelength corresponding to a center frequency of the generated ultrasonic energy, the surface at least approximately symmetrical in two axes; a processor circuit configured to control the ultrasonic transducer element to generate and receive ultrasonic energy, and configured to obtain information indicative of the ultrasonic energy reflected by the target; and a position tracking circuit configured to provide information indicative of a motion of the ultrasonic transducer element; and a display configured to present information about one or more of a location, orientation, or shape of the target, the information about the location, orientation, or shape determined by the processor circuit using the obtained information indicative of the ultrasonic energy reflected by the target and the information indicative of the motion of the ultrasonic transducer element; characterized by a housing sized and shaped to be held or manipulated using one hand of a user, the housing including the processor circuit, the position tracking circuit, and the display; wherein the ultrasonic transducer is located on or within the housing, wherein the target comprises bone, wherein the processor is configured to estimate one or more of a location, a shape, or orientation of the bone by fitting echo data to a system model describing hypothetical echoes from different hypothetical bone surfaces corresponding to at least one hypothetical target, the echo data indicative of the ultrasonic energy reflected by the target. an ultrasonic transducer element configured to generate ultrasonic energy to be directed into tissue of a subject and configured to receive a portion of the ultrasonic energy reflected by a predominantly specular-reflecting target, the ultrasonic transducer element comprising a surface configured to provide and receive the ultrasonic energy, the surface including an area of greater than or equal to about 4λ 2, where λ is an acoustic wavelength corresponding to a center frequency of the generated ultrasonic energy, the surface at least approximately symmetrical in two axes; a processor circuit configured to control the ultrasonic transducer element to generate and receive ultrasonic energy, and configured to obtain information indicative of the ultrasonic energy reflected by the target; and a position tracking circuit configured to provide information indicative of a motion of the ultrasonic transducer element; and a display configured to present information about one or more of a location, orientation, or shape of the target, the information about the location, orientation, or shape determined by the processor circuit using the obtained information indicative of the ultrasonic energy reflected by the target and the information indicative of the motion of the ultrasonic transducer element; characterized by a housing sized and shaped to be held or manipulated using one hand of a user, the housing including the processor circuit, the position tracking circuit, and the display; wherein the ultrasonic transducer is located on or within the housing, wherein the target comprises bone, wherein the processor is configured to estimate one or more of a location, a shape, or orientation of the bone by fitting echo data to a system model describing hypothetical echoes from different hypothetical bone surfaces corresponding to at least one hypothetical target, the echo data indicative of the ultrasonic energy reflected by the target.