An x-ray-based nonintrusive inspection apparatus has a collimator shield. An
adjusting
actuator is actuable to move the collimator shield between a pre-scanning position
and a CT scanning position, in the pre-scanning position, the collimator shield
exposing a smaller portion of a respective crystal to the x-rays than in the CT
scanning position. A controller is connected to a gantry motor and the adjusting
actuator. The controller controls the motor and the adjusting actuator such that
the collimator shield is in the pre-scanning position when a gantry is stationary
and in the CT scanning position when the gantry is rotating.
