The design, the hardware, the software, and the performances of a computer-controlled multi-head scanner are described. The scanning machine is linked to a process computer for data control and elaboration. The system is capable of optimizing both scan domain and duration. Mechanical drawbacks like disuniform head velocity, phase shift, and scalloping error are corrected on-line. Decay correction for short-lived radioisotopes is made and on-line display of raw data and preelaborated images is produced in real time. The system is currently used for clinical research, in the field of lung perfusion, adrenal, and thyroid imaging. (auth)