Abstract: A data acquisition head for an ultrasonic imaging system which employs a plurality of transducers is disclosed. The transducers are rotated in a liquid filled chamber at a constant rate, each about an axis perpendicular to its transmission axis. The transducers are sequentially activated as their transmission axes cross a semi-rigid membrane which is in contact with the body. The acoustic impedance of the liquid and membrane, and the thickness of the membrane, are matched to enhance transmission. In one embodiment, the membrane is one-half or a full wavelength thick and comprises a low density polyethylene and the liquid has an acoustic impedance approximately equal to that of the polyethylene.