According to one aspect, the invention relates to a light guide which may
include a first surface which receives light, a second surface which
emits light, wherein the second surface is parallel to the first surface
and the second surface has a smaller area than the first surface, at
least one edge surface which extends between the first surface and the
second surface, and a light barrier which extends between the first
surface and the second surface, wherein the light barrier divides the
light guide into separate regions and reduces the propagation of light
between the separate regions. The light guide can be used in a positron
emission tomography scanner.