Calculation and experimental observation of two-dimensional multiferroic CuCrP₂S₆.

Using a sample of $14\times {10}^6$ $\psi (2S)$ events accumulated with the BES II detector, evidence for $f_0(980)f_0(980)$ production in ${\chi }_{c0}$ decays is obtained for the first time; the branching ratio is determined to be $\mathcal{B}[{\chi }_{c0}\to f_0(980)f_0(980)\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}]=[7.6\pm 1.9(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 1.6(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\times {10}^{-4}$. The significance of the $f_0(980)$ signal is about 4.6$\sigma$.

With the goal of developing a total-body small-animal PET system with a high spatial resolution of ∼0.5 mm and a high sensitivity >10% for mouse/rat studies, we simulated four scanners using the graphical processing unit-based Monte Carlo simulation package (gPET) and compared their performance in terms of spatial resolution and sensitivity. We also investigated the effect of depth-of-interaction (DOI) resolution on the spatial resolution. All the scanners are built upon 128 DOI encoding dual-ended readout detectors with lutetium yttrium oxyorthosilicate (LYSO) arrays arranged in 8 detector rings. The solid angle coverages of the four scanners are all ∼0.85 steradians. Each LYSO element has a cross-section of 0.44 × 0.44 mm ² and the pitch size of the LYSO arrays are all 0.5 mm. The four scanners can be divided into two groups: (1) H ² RS110-C10 and H ² RS110-C20 with 40 × 40 LYSO arrays, a ring diameter of 110 mm and axial length of 167 mm, and (2) H ² RS160-C10 and H ² RS160-C20 with 60 × 60 LYSO arrays, a diameter of 160 mm and axial length of 254 mm. C10 and C20 denote the crystal thickness of 10 and 20 mm, respectively. The simulation results show that all scanners have a spatial resolution better than 0.5 mm at the center of the field-of-view (FOV). The radial resolution strongly depends on the DOI resolution and radial offset, but not the axial resolution and tangential resolution. Comparing the C10 and C20 designs, the former provides better resolution, especially at positions away from the center of the FOV, whereas the latter has 2× higher sensitivity (∼10% versus ∼20%). This simulation study provides evidence that the 110 mm systems are a good choice for total-body mouse studies at a lower cost, whereas the 160 mm systems are suited for both total-body mouse and rat studies.

Monte Carlo (MC) simulation method plays an essential role in the refinement and development of positron emission tomography (PET) systems. However, most existing MC simulation packages suffer from long execution time for practical PET simulations. To fully address this issue, we developed and validated gPET, a graphics processing unit (GPU)-based MC simulation tool for PET. gPET was built on the NVidia CUDA platform. The simulation process was modularized into three functional parts and carried out by the GPU parallel threads: (1) source management, including positron decay, transport and annihilation; (2) gamma transport inside the phantom; and (3) signal detection and processing inside the detector. A hybrid of voxelized (for patient phantoms) and parametrized (for detectors) geometries were employed to sufficiently support particle navigations. Multiple inputs and outputs were available. Hence, a user can flexibly examine different aspects of a PET simulation. We evaluated the performance of gPET in three test cases with benchmark work from GATE8.0, in terms of the testing of the functional modules, the physics models used for gamma transport inside the detector, and the geometric configuration of an irregularly shaped PET detector. Both accuracy and efficiency were quantified. In all test cases, the differences between gPET and GATE for the coincidences with respect to the energy and crystal index distributions are below 3.18% and 2.54%, respectively. The speedup factor is 500 for gPET on a single Titan Xp GPU (1.58 GHz) over GATE8.0 on a single core of Intel i7-6850K CPU (3.6 GHz) for all test cases. In summary, gPET is an accurate and efficient MC simulation tool for PET.

Computational reproductions of medical imaging tests, a form of virtual clinical trials (VCTs), are increasingly being used, particularly in breast imaging research. The accuracy of the computational platform that is used for the imaging and dosimetry simulation processes is a fundamental requirement. Moreover, for practical usage, the imaging simulation computation time should be compatible with the clinical workflow. We compared three different platforms for in-silico X-ray 3D breast imaging: the Agata (University & INFN Napoli) that was based on the Geant4 toolkit and running on a CPU-based server architecture; the XRMC Monte Carlo (University of Cagliari) that was based on the use of variance reduction techniques, running on a CPU hardware; and the Monte Carlo code gCTD (University of Texas Southwestern Medical Center) running on a single GPU platform with CUDA environment. The tests simulated the irradiation of cylindrical objects as well as anthropomorphic breast phantoms and produced 2D and 3D images and 3D maps of absorbed dose. All the codes showed compatible results in terms of simulated dose maps and imaging values within a maximum discrepancy of 3%. The GPU-based code produced a reduction of the computation time up to factor 10⁴, and so permits real-time VCT studies for X-ray breast imaging.

Non-$D\overline{D}$ decay $\psi (3770)\to \rho \pi$ is searched for using a data sample of $(17.3\pm 0.5)\mathrm{p}{\mathrm{b}}^{-1}$ taken at the center-of-mass energy of 3.773 GeV by the BESII detector at the BEPC. No $\rho \pi$ signal is observed, and the upper limit of the cross section is measured to be $\sigma (e^{+}{e}^{-}\to \rho \pi )<6.0\mathrm{pb}$ at 90% C. L. Considering the interference between the continuum amplitude and the $\psi (3770)$ resonance amplitude, the branching fraction of $\psi (3770)$ decays to $\rho \pi$ is determined to be $\mathcal{B}(\psi (3770)\to \rho \pi )\in (6.0\times {10}^{-6},2.4\times {10}^{-3})$ at 90% C. L. This is in agreement with the prediction of the $S$- and $D$-wave mixing scheme of the charmonium states for solving the “$\rho \pi$ puzzle” between $J/\psi$ and $\psi (2S)$ decays.