An X-ray detector system for determining the contents of an item, the system comprising: an X-ray emitter configured for emitting X-ray radiation; an imaging detector comprising a receiving surface, the imaging detector configured to receive the X-ray radiation and to generate one or more intensity signals indicative of an intensity of the received X-ray radiation at each of a plurality of locations on the receiving surface; an X-ray penetration grid comprising a first grid structure comprising a perimeter surrounding the X-ray penetration grid having at least a first side oriented in a first primary direction, a first plurality of parallel grid members each having a first end and a second end, and a second plurality of parallel grid members each having a first end and a second end; wherein the system further comprises a conveying mechanism configured for conveying the item and the X-ray penetration grid in a second primary direction to a location between the X-ray emitter and the imaging detector, said second primary direction being substantially the same as the first primary direction: characterized in, that the first plurality of parallel grid members are coincident with a first plane, the second plurality of parallel grid members are coincident with a second plane, the first plane and the second plane are parallel and the first plane is spaced a distance apart from the second plane, the first plurality of parallel grid members crosses the second plurality of grid members at an angle γ, the first end and the second end of each of the first plurality of parallel grid members intersects the perimeter at an angle such that the first plurality of parallel grid members are neither parallel nor perpendicular to the first side of the perimeter, and the first end and the second end of each of the second plurality of parallel grid members intersects the perimeter at an angle such that the second plurality of parallel grid members are neither parallel nor perpendicular to the first side of the perimeter. an X-ray emitter configured for emitting X-ray radiation; an imaging detector comprising a receiving surface, the imaging detector configured to receive the X-ray radiation and to generate one or more intensity signals indicative of an intensity of the received X-ray radiation at each of a plurality of locations on the receiving surface; an X-ray penetration grid comprising a first grid structure comprising a perimeter surrounding the X-ray penetration grid having at least a first side oriented in a first primary direction, a first plurality of parallel grid members each having a first end and a second end, and a second plurality of parallel grid members each having a first end and a second end; wherein the system further comprises a conveying mechanism configured for conveying the item and the X-ray penetration grid in a second primary direction to a location between the X-ray emitter and the imaging detector, said second primary direction being substantially the same as the first primary direction: characterized in, that the first plurality of parallel grid members are coincident with a first plane, the second plurality of parallel grid members are coincident with a second plane, the first plane and the second plane are parallel and the first plane is spaced a distance apart from the second plane, the first plurality of parallel grid members crosses the second plurality of grid members at an angle γ, the first end and the second end of each of the first plurality of parallel grid members intersects the perimeter at an angle such that the first plurality of parallel grid members are neither parallel nor perpendicular to the first side of the perimeter, and the first end and the second end of each of the second plurality of parallel grid members intersects the perimeter at an angle such that the second plurality of parallel grid members are neither parallel nor perpendicular to the first side of the perimeter.