CdTe-DSD SPECT-I: An Ultrahigh-Resolution Multi-Isotope Tomographic Imager for Mice

Multi-isotope imaging in vivo is an appealing molecular imaging approach that provides extensive information about molecular pathways that cannot be accessed in usual imaging methods with a single radioactive probe. However, conventional imaging systems have limited energy resolution; as a result, the images obtained from multi-isotope imaging are associated with problems, such as nonnegligible noise and spectral crosstalk, owing to the photons emitted from radioisotopes being simultaneously used in the experiments. This study proposes a novel small-animal SPECT system, called CdTe-DSD SPECT-I, based on the cadmium telluride double-sided strip detector (CdTe-DSD), which was originally developed to observe high-energy X-rays and gamma rays in space. The detector has an energy resolution of 1-2 keV (FWHM) in 10-100 keV and 1.6% (FWHM) at 140 keV, which is approximately three times better than those of currently available high-grade semiconductor SPECT systems. Through imaging with phantoms, we demonstrate that the proposed system achieves an ultrahigh spatial resolution of over 0.35 mm for several radioisotopes. Furthermore, we demonstrate via animal experiments that the high-energy resolution and the crosstalk-subtraction method work effectively to suppress image noise and spectral crosstalk. We believe that the proposed system will allow investigators to choose various combinations of radioisotopes in their multi-isotope studies without much concern regarding potential spectral contaminations. Simultaneous visualization of drugs and probes distributed in small volumes in a mouse is possible with it.