Toward a Medipix2 coded aperture gamma microscope

We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low energy gamma-rays as from 125I (27-35 keV). The system imaging optics features a high resolution coded aperture mask and a fine pitch silicon hybrid pixel detector of the Medipix2 series (55 μm pitch). The coded aperture (no-two-holes-touching MURA 62×62) had 70 μm holes in 75 μm tungsten, and was used in a 2:1 magnification for a field of view of about 7 mm. Laboratory tests with a 109Cd 22-keV source and in vivo mouse thyroid imaging tests with 125I show a system resolution of about 110 μm. This low energy, semiconductor-based, compact gamma camera is the basic imaging unit of a small animal single photon emission computed tomography system with deep sub-millimeter resolution.