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Small animal SPECT imaging systems have multiple potential applications in biomedical research. Whereas SPECT data are commonly interpreted qualitatively in a clinical setting, the ability to accurately quantify measurements will increase the utility of the SPECT data for laboratory measurements involving small animals. In this work, we assess the effect of photon attenuation, scatter and partial volume errors on the quantitative accuracy of small animal SPECT measurements, first with Monte Carlo simulation and then confirmed with experimental measurements. The simulations modeled the imaging geometry of a commercially available small animal SPECT system. We simulated the imaging of a radioactive source within a cylinder of water, and reconstructed the projection data using iterative reconstruction algorithms. The size of the source and the size of the surrounding cylinder were varied to evaluate the effects of photon attenuation and scatter on quantitative accuracy. We found that photon attenuation can reduce the measured concentration of radioactivity in a volume of interest in the center of a rat-sized cylinder of water by up to 50% when imaging with iodine-125, and up to 25% when imaging with technetium-99m. When imaging with iodine-125, the scatter-to-primary ratio can reach up to approximately 30%, and can cause overestimation of the radioactivity concentration when reconstructing data with attenuation correction. We varied the size of the source to evaluate partial volume errors, which we found to be a strong function of the size of the volume of interest and the spatial resolution. These errors can result in large (>50%) changes in the measured amount of radioactivity. The simulation results were compared with and found to agree with experimental measurements. The inclusion of attenuation correction in the reconstruction algorithm improved quantitative accuracy. We also found that an improvement of the spatial resolution through the use of resolution recovery techniques (i.e. modeling the finite collimator spatial resolution in iterative reconstruction algorithms) can significantly reduce the partial volume errors. [ABSTRACT FROM AUTHOR]

Computed tomography (CT) remains a critical diagnostic tool for evaluating patients with cerebrovascular disease, and the advent of specialized systems for imaging rodents has extended these techniques to small animal models of these diseases. We therefore have evaluated in vivo methods of imaging rat models of hemorrhagic stroke using a high resolution compact computed tomography (''microCT'') system (FLEX(tm) X-O(tm), Gamma Medica-Ideas, Northridge, CA). For all in vivo studies, the head of the anesthetized rat was secured in a custom immobilization device for microCT imaging with 512 projections over 2 min at 60 kVp and 0.530 mA (Itube × t/rotation = 63.6 mAs). First, imaging without iodinated contrast was performed (a) to differentiate the effect of contrast agent in contrast-enhanced CT and (b) to examine the effectiveness of the immobilization device between two time points of CT acquisitions. Then, contrast-enhanced CT was performed with continuous administration of iopromide (300 mgI ml[?]1 at 1.2 ml min[?]1) to visualize aneurysms and other vascular formations in the carotid and cerebral arteries that may precede subarachnoid hemorrhage. The accuracy of registration between the noncontrast and contrast-enhanced CT images with the immobilization device was compared against the images aligned with normalized mutual information using FMRIB''s linear image registration tool (FLIRT). Translations and rotations were examined between the FLIRT-aligned noncontrast CT image and the nonaligned noncontrast CT image. These two data sets demonstrated translational and rotational differences of less than 0.5 voxel ([?]85 µm) and 0.5°, respectively. Noncontrast CT demonstrated a very small volume (0.1 ml) of femoral arterial blood introduced surgically into the rodent brain. Continuous administration of iopromide during the CT acquisition produced consistent vascular contrast in the reconstructed CT images. As a result, carotid arteries and major cerebral blood vessels were visible with contrast-enhanced CT, but not with noncontrast CT. In conclusion, the CT-compatible immobilization device was useful for in vivo microCT imaging of intracranial blood and of vascular structures within and immediately adjacent to the rodent brain. The microCT imaging technique is also compatible with continuous administration of a conventional iodinated contrast agent (e.g. iopromide) and therefore does not require specialized small animal specific contrast agent that has comparatively long in vivo residence time. [ABSTRACT FROM AUTHOR]

Avalanche photodiodes (APDs), and in particular position-sensitive avalanche photodiodes (PSAPDs), are an attractive alternative to photomultiplier tubes (PMTs) for reading out scintillators for PET and SPECT. These solid-state devices offer high gain and quantum efficiency, and can potentially lead to more compact and robust imaging systems with improved spatial and energy resolution. In order to evaluate this performance improvement, we have conducted Monte Carlo simulations of gamma cameras based on avalanche photodiodes. Specifically, we investigated the relative merit of discrete and PSAPDs in a simple continuous crystal gamma camera. The simulated camera was composed of either a 4 × 4 array of four channels 8 × 8 mm2PSAPDs or an 8 × 8 array of 4 × 4 mm2discrete APDs. These configurations, requiring 64 channels readout each, were used to read the scintillation light from a 6 mm thick continuous CsI:Tl crystal covering the entire 3.6 × 3.6 cm2photodiode array. The simulations, conducted with GEANT4, accounted for the optical properties of the materials, the noise characteristics of the photodiodes and the nonlinear charge division in PSAPDs. The performance of the simulated camera was evaluated in terms of spatial resolution, energy resolution and spatial uniformity at 99mTc (140 keV) and 125I (30 keV) energies. Intrinsic spatial resolutions of 1.0 and 0.9 mm were obtained for the APD- and PSAPD-based cameras respectively for 99mTc, and corresponding values of 1.2 and 1.3 mm FWHM for 125I. The simulations yielded maximal energy resolutions of 7% and 23% for 99mTc and 125I, respectively. PSAPDs also provided better spatial uniformity than APDs in the simple system studied. These results suggest that APDs constitute an attractive technology especially suitable to build compact, small field of view gamma cameras dedicated, for example, to small animal or organ imaging. [ABSTRACT FROM AUTHOR]

Electron swarm parameters, such as the drift velocity and the ionization coefficient, in water vapour have been measured for relatively wide ranges in reduced electric fields (E/N) at room temperature. The drift velocity (Wm) was obtained based upon the arrival-time spectra of electrons by using a double-shutter drift tube for the E/Nfrom 60 to 1000?Td, while the first and second ionization coefficients (? and ?) were determined by the steady-state Townsend method from 50 to 3000?Td. A comparison between the results and other data in the literature shows that our results for both the drift velocity and the effective ionization coefficient are lower than those of the other data in the above ranges. [ABSTRACT FROM AUTHOR]

The distribution of calcium ion (Ca-ion) was demonstrated in the mantle epithelial cells by means of two-step chemical precipitation of Ca-ion in the pulmonate snail, Euhadra hickonis. K-oxalate/K-antimonate chemical replacement was done using a simultaneous computerized microwave-stimulated fixation method. These precipitates in the mantle epithelial cells were studied by electron-probe X-ray microanalysis (EDX) and electron energy-filtered imaging (EFI). The calculated values of the essential-elemental X-ray pulse ratios, which were obtained by computerized EDX analysis, agreed with those of the standard samples and theoretical values of Ca-antimonate. Typical EFI images and spectra energy of Ca and Sb were obtained from the surface mantle epithelial cells in the same tissue block as that used for EDX analysis where the elemental distribution of Ca and Sb was the same. The Ca-antimonate precipitates were formed in the intercellular space, vesicles and microvilli of mantle cells. In day 13 embryos, the columella and peripheral area were almost calcified, but in the dorsal area, Ca was still in the ionic state; the binding ratio of the former case was Ca:Sb = 1:0, that of the latter was Ca:Sb = 1:2, and that of the small intermediate area was Ca:Sb = 1:1.4. After day 17, the embryonal periostracum was almost calcified. Between days 15 and 20, strong Ca2+-ATPase and carbonic anhydrase (CAHase) enzymatic activities were observed at the sites where Ca-ion was observed; intercellular spaces, vacuoles in the mantle cells, periostracum and homogeneous layer between the periostracum and mantle cell, and in the mitochondria. Ca2+-ATPase may play important roles in the transportation of Ca-ion from the basal cell layer to the surface layer of the mantle cells and CAHase may play important roles in the chemical binding of Ca-ion and carbonate ion to produce calcium carbonate crystals in the newly developing embryonal shell. [ABSTRACT FROM AUTHOR]

Background/Purpose. Radiofrequency ablation (RFA) and microwave coagulation therapy (MCT) have been gaining acceptance as a standard method in the management strategy of liver cancer, for reasons of minimally invasive techniques and effective results. We present our experience of RFA and MCT in patients with liver cancer, and analyze retrospectively the advantages and disadvantages of both of the percutaneous and laparoscopic approaches. Methods. Thirty-two consecutive patients (23 men and 9 women) with 19 hepatocellular carcinomas (HCC), 12 metastatic liver cancers, and recurrent cholangiocellular carcinoma (CCC), were enrolled in this study. Out of these 32 patients, as a prior laparotomy, 19 underwent hepatectomy, colectomy, gastrectomy or cholecystectomy, and 15 were treated with the laparoscopic approach, 17 treated with the percutaneous approach, and 2 treated with the combined approach of those two. All of these procedures were carried out under general anesthesia with ultrasound guidance. Seven and 30 days after these procedures, an assessment helical computed tomography was done. Results. No sign of the residual tissues was noted in all patients except only one case. Conclusions. The percutaneous approach was thought to be a more practical and less invasive method regardless previous laparotomy. For the laparoscopic approach, tumors located at the hepatic surface or margin were preferable candidates. [ABSTRACT FROM AUTHOR]

Eigen-vortical-axis line proposed as a vortical axis is analysed with respect to the characteristics of the passage of the core region of a vortex in isotropic homogeneous turbulence. Comparison with the vorticity line shows that the difference between them is derived from the geometrical features of a vortex especially vorticity components parallel to swirl plane in weak region of a vortex. Eigen-vortical-axis line tends to pass through the core region with strong intensity of swirling (swirlity) and vorticity, and high flow symmetry. [ABSTRACT FROM AUTHOR]

Energy storage systems are necessary for renewable energy sources such as solar power in order to stabilize their output power, which fluctuates widely depending on the weather. Since ‘flywheel energy storage systems’ (FWSSs) do not use chemical reactions, they do not deteriorate due to charge or discharge. This is an advantage of FWSSs in applications for renewable energy plants. A conventional FWSS has capacity limitation because of the mechanical bearings used to support the flywheel. Therefore, we have designed a superconducting magnetic bearing composed of a superconducting coil stator and a superconducting bulk rotor in order to solve this problem, and have experimentally manufactured a large scale FWSS with a capacity of 100 kWh and an output power of 300 kW. The superconducting magnetic bearing can levitate 4 tons and enables the flywheel to rotate smoothly. A performance confirmation test will be started soon. An overview of the superconducting FWSS is presented in this paper. [ABSTRACT FROM AUTHOR]

The behavior of the nuclear shell structure far away from the valley of stability is discussed in this paper with an emphasis on the N = 20 magic number. Two experimental examples, namely g-spectroscopy of 27Ne by 1H(28Ne, 27Ne) reaction and single-particle spectroscopy of 23O by 22O(d, p)23O* - 22O+n process in inverse kinematics, are shown providing indirect indication and a direct evidence for the extreme decrease of the N = 20 shell gap and, consequently, the vanishing N = 20 magicity. [ABSTRACT FROM AUTHOR]