Towards in vivo nuclear microscopy: iodine-125 imaging in mice using micro-pinholes

Position-sensitive gamma-radiation detectors equipped with collimators have been used for in vivo im- aging of the distribution of radiolabelled molecules in laboratory animals and humans for several decades. To date, the best image resolution achieved in a rodent is on the order of 1 mm. Here we demonstrate how a basic and compact gamma camera can be constructed for in vivo radionuclide imaging in small animals, at much higher spatial resolution. Resolution improvements were ob- tained by combining dense, shaped, micro-pinhole aper- tures with iodine-125, an isotope with low energy emis- sions, ease of incorporation into a wide range of mole- cules, and straightforward translation into the clinic via other isotopes of iodine that are suitable for nuclear med- icine imaging. 125 I images of test distributions and a mouse thyroid have been obtained at a resolution of as high as 200 µm using this simple bench-top camera. Pos- sible future applications and extension to ultra-high-res- olution emission tomography are discussed.