A hand-held medical ultrasound apparatus (10), in particular for ultrasound computed tomography of the breast, comprises an ultrasound transducer (1), a reflector (2) and an indicator (311, 321, 312) enabling the indication of a relative position and/or orientation between the transducer and the reflector. In a first embodiment, the transducer and the reflector are attached to a mechanical structure comprising a first frame (33) and a second frame (34), which allow to adjust the distance (d) between the transducer and the reflector in order to adapt to the shape of the breast. In a second embodiment, the tranducer and the reflector are not mechanically connected and a position and/or orientation sensor is provided to determine a relative position and/or orientation between the transducer and the reflector. In a third embodiment, thin resonant reflector layers are applied to introduce acoustic signatures in the tracked reflector signals. The disclosure further relates to the processing for determining the tomographic image.