Among other things, an anti-scatter collimator is provided including a first layer defining a first retaining member at a first surface. A second layer defines a second retaining member at a first surface that faces the first surface of the first layer. A septum is disposed between the first layer and the second layer and physically contacts the first retaining member and the second retaining member. The first retaining member and the second retaining member maintain a position of the septum relative to the first layer and the second layer. The septum has a third attenuation coefficient that is greater than a first attenuation coefficient of the first layer and a second attenuation coefficient of the second layer. An end support is attached to the first layer and to the second layer. The end support borders an end of the septum.