An optical CT scanner for small laboratory animals comprises a housing having a vertical through opening through which a test subject is passed through during a scanning session, the housing including a peripheral slot disposed around the perimeter of the opening; a movable horizontal table disposed through the opening, the table being split with a horizontal slot aligned with the peripheral slot; a light beam directed toward the peripheral slot and orbitable around the opening; a plurality of collimators directed toward the peripheral slot and orbitable around the opening together with the light beam; a plurality of main photodetectors to detect the light beam after passing through the test subject and the collimators; a perimeter photodetector adapted to provide perimeter data of the test subject during a scanning session; and a first computer programmed to reconstruct an image of the test subject from the output of the perimeter and main photodetectors.