A mechanism and method for performing transmission and emission scanning sessions with two line sources and two detectors wherein two sliding transmission detection windows are employed to differentiate between transmission and emission photons. Transmission and emission data can be collected simultaneously. This system provides that the dual transmission detection windows are each associated with a particular line source and move in synchronization with the associated line source. Further, the two line sources and the two detector windows all move in synchronization in the direction of the long axis of the object being scanned and at any given position all are within a given spatial plane that is transverse to the long axis of the object. In this configuration, the system can effectively reduce the amount of cross-talk detected by a detector (e.g., cross-talk being scattered photon radiation detected by a given detector but not originating from the detector's associated line source). The configuration of this system also effectively operates in conjunction with systems employing tracking zoom regions across detector surfaces (e.g., used for cardiac studies).