Abstract: A SPECT system includes three gam camera heads (22a), (22b), (22c) which are mounted to a gantry (20) for rotation about a subject (12). The subject is injected with a source of emission radiation, which emission radiation is received by the camera heads. Camera head (22a) has a fan-beam collimator (24a) mounted on a radiation receiving face and generates fan-beam data indicative of the received emission radiation. The camera heads (22b) and (22c) each have a cone-beam collimator (24b), (24c) mounted respectively on their radiation receiving face and generate cone-beam data indicative of the received emission radiation. A transmission radiation source (26) is mounted opposite the camera head (22a) having the fan-beam collimator (24a). The fan-beam detector head (22a) further receives transmission radiation and generates fan-beam transmission radiation indicative thereof. A transmission data reconstruction processor (50) reconstructs the fan-beam transmission data.