This paper presents the design and feasibility study of a very-high resolution gamma camera for detecting 27-35 keV X and gamma rays emitted by I-125 labelled radiotracers. This detector consists of a newly developed Electron-multiplying CCD (EMCCD) sensor and a de-magnifier tube coupled to a thin layer of scintillator. A prototype detector was developed and experimentally evaluated. This detector has a detection area of ~ 5 cm. It provided an intrinsic spatial resolution of < 60 µm FWHM and a high signal-to-noise ratio for detecting the 27-35 keV photons, which ensures an excellent counting efficiency. This detector will be used as the key component for a single photon emission microscope (SPEM) system that is under development.

This paper presents a comparison of three deconvolution techniques, Maximum Likelihood, Maximum Entropy and Linear Regularisation for the unconstrained deconvolution of gamma-ray spectra. These convert the raw energy-loss spectra obtained using a standard scintillation counter, into a good representation of the incident gamma-ray spectrum. This work is based on the use of an industry-standard 3x3 inch NaI detector. Both simulated and measured data have been deconvolved using the three algorithms to provide a direct comparison between the qualities of the deconvolved spectra. For applications in which it is important to derive an accurate estimate of the number of counts in a particular full-energy peak, the Maximum Likelihood Method has been shown to be superior.

This paper presents some initial experimental results obtained with a dual-head prototype single photon emission microscope system (SPEM) that is dedicated to mouse brain studies using I-125 labeled radiotracers. In particular, this system will be used for in vivo tacking of radiolabeled T cells in mouse brain. This system is based on the use of the intensified electron multiplying charge-coupled device (I-EMCCD) camera that offers the combination of an excellent intrinsic spatial resolution, a good signal-to-noise ratio, a large active area and a reasonable detection efficiency over an energy range between 27-140keV. In this study, the dual-head SPEM system was evaluated using both resolution phantoms and a mouse with locally injected T cells labelled with I-125. It was demonstrated that for a relatively concentrated source object, the current dual-head SPEM system is capable of visualizing the tiny amount of radioactivity (~12 nCi) carried by a very small number (<1000) of T cells. The current SPEM system design allows four or six camera heads to be installed in a stationary system configuration that offers a doubled or tripled sensitivity at a spatial resolution similar to that obtained with the dualhead system. This development would provide a powerful tool for in vivo and non-invasive tracking of radiolabeled T cells in mouse brain and potentially for other rodent brain imaging studies. Index TermsSingle photon emission microscope; T cell tracking

The authors have demonstrated the feasibility of these two novel approaches to XFCT imaging. While they use synchrotron radiation in this demonstration, the geometries could readily be translated to laboratory systems based on tube sources.