Optical to Planar X-ray Mouse Image Mapping in Preclinical Nuclear Medicine Using Conditional Adversarial Networks.

In the current work, a pix2pix conditional generative adversarial network has been evaluated as a potential solution for generating adequately accurate synthesized morphological X-ray images by translating standard photographic images of mice. Such an approach will benefit 2D functional molecular imaging techniques, such as planar radioisotope and/or fluorescence/bioluminescence imaging, by providing high-resolution information for anatomical mapping, but not for diagnosis, using conventional photographic sensors. Planar functional imaging offers an efficient alternative to biodistribution ex vivo studies and/or 3D high-end molecular imaging systems since it can be effectively used to track new tracers and study the accumulation from zero point in time post-injection. The superimposition of functional information with an artificially produced X-ray image may enhance overall image information in such systems without added complexity and cost. The network has been trained in 700 input (photography)/ground truth (X-ray) paired mouse images and evaluated using a test dataset composed of 80 photographic images and 80 ground truth X-ray images. Performance metrics such as peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM) and Fréchet inception distance (FID) were used to quantitatively evaluate the proposed approach in the acquired dataset.

A prototype PET/SPECT/X-rays scanner dedicated for whole body small animal studies.

OBJECTIVE: To present a prototype tri-modal imaging system, consisting of a single photon emission computed tomography (SPET), a positron emission tomography (PET), and a computed tomography (CT) subsystem, evaluated in planar mode. MATERIALS AND METHODS: The subsystems are mounted on a rotating gantry, so as to be able to allow tomographic imaging in the future. The system, designed and constructed by our group, allows whole body mouse imaging of competent performance and is currently, to the best of our knowledge, unequaled in a national and regional level. The SPET camera is based on two Position Sensitive Photomultiplier Tubes (PSPMT), coupled to a pixilated Sodium Iodide activated with Thallium (NaI(Tl)) scintillator, having an active area of 5x10cm2. The dual head PET camera is also based on two pairs of PSPMT, coupled to pixelated berillium germanium oxide (BGO) scintillators, having an active area of 5x10cm2. The X-rays system consists of a micro focus X-rays tube and a complementary metal-oxide-semiconductor (CMOS) detector, having an active area of 12x12cm2. RESULTS: The scintigraphic mode has a spatial resolution of 1.88mm full width at half maximum (FWHM) and a sensitivity of 107.5cpm/0.037MBq at the collimator surface. The coincidence PET mode has an average spatial resolution of 3.5mm (FWHM) and a peak sensitivity of 29.9cpm/0.037MBq. The X-rays spatial resolution is 3.5lp/mm and the contrast discrimination function value is lower than 2%. CONCLUSION: A compact tri-modal system was successfully built and evaluated for planar mode operation. The system has an efficient performance, allowing accurate and informative anatomical and functional imaging, as well as semi-quantitative results. Compared to other available systems, it provides a moderate but comparable performance, at a fraction of the cost and complexity. It is fully open, scalable and its main purpose is to support groups on a national and regional level and provide an open technological platform to study different detector components and acquisition strategies.

Characterization of "γ-Eye": a Low-Cost Benchtop Mouse-Sized Gamma Camera for Dynamic and Static Imaging Studies.

PURPOSE: Several preclinical imaging systems are commercially available, but their purchase and maintenance costs make them unaffordable for the majority of small- and medium-sized groups. Taking into account the needs of average users, we developed "γ-eye", a mouse-sized, benchtop γ-camera suitable for in vivo scintigraphic imaging. PROCEDURES: The γ-eye is based on two position-sensitive photomultiplier tubes, coupled to a CsI(Na) pixelated scintillator and a low-energy lead collimator with parallel hexagonal holes. RESULTS: The spatial resolution of the system is 2 mm at 0 mm. The energy resolution is 26 % at 140 keV and the maximum recorded sensitivity 210 cps/MBq. The system was evaluated in a proof-of-concept animal study, using three different clinical Tc-99m-labeled radiopharmaceuticals. Phantom and animal studies demonstrate its ability to provide semiquantitative results even for short scans. CONCLUSIONS: Systems' performance, dimensions, and cost make γ-eye a unique solution for efficient whole-body mouse nuclear imaging.

λ-Eye: a high-sensitivity γ imaging probe for axillary sentinel lymph node mapping.

OBJECTIVE: The aim of this study is the construction and performance evaluation of 'λ-eye', a γ imaging probe, optimized in terms of sensitivity for sentinel lymph node mapping. The optimization of the probe is based on theoretical models and simulation results that were presented in a previous study of our group. In this work, the construction of the probe, the experimental confirmation of the simulation results, and the evaluation of its performance with phantoms and lymph node imaging in small animals are presented. METHODS: The system's spatial and energy resolution, sensitivity, and count rate performance were measured using phantoms. The values of the integral and differential uniformity in the useful field-of-view and in the central field-of-view were also calculated. Finally, a proof-of-concept animal experiment was conducted for the imaging of the lymph nodes of normal mice. RESULTS: The system's energy resolution was measured as 36±2% and the spatial resolution was 2.2 mm at 2 mm source-collimator distance. The values of the integral uniformity and differential uniformity in the useful field-of-view and in the central field-of-view were found to be 5.2, 2.1, 1.7, and 0.75%, respectively. Finally, the lymph nodes of normal mice were clearly imaged with a 10 s acquisition time. CONCLUSION: The 'λ-eye', used for sentinel lymph node mapping, provides a combination of high sensitivity (∼1.5 counts/s/kBq) and good spatial resolution (∼6 mm full-width of the half-maximum at 20 mm and ∼10 mm full-width of the half-maximum at 50 mm distance). Its compact size (40 mm×40 mm×70 mm) allows its use during surgery and/or for the detailed scan of a suspicious region.