Vol.20,

Based on the femtosecond accelerator facility at Shanghai Institute of Applied Physics (SINAP), a conventional far-infrared Michelson interferometer was built to measure the bunch length by means of optical autocorrelation. However, according to the preliminary experiment result, the resolution of interferometer is not good enough, because the mirror-driving mechanism makes the moving mirror tend to tilt or wobble as it retards. Considering of the allowable errors, we calculate the maximum allowable titling angle of the moving mirror, and discuss the alignment plan in this paper.

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This work was to investigate the pharmacologic characteristics of ¹⁸F-FECNT (2β-carbomethoxy-3β- (4-chlorophenyl)-8-(2-[¹⁸F]fluoroethyl)nortropane) as a dopamine transporter (DAT) PET imaging agent. Its partition coefficients were determined in n-octanol and phosphate buffer (PB) (pH 7.0 and pH 7.4). 6-Hydroxydopamine (6-OHDA) left-sided lesioned Parkinsonian rats were established and validated by rotational behavior tests. Biodistribution in vivo in mice, autoradiography in normal and hemi-Parkinsonian rat brains, and toxicity test were performed. The results showed that partition coefficients were 34.14 (pH 7.0) and 56.41 (pH 7.4), respectively. Biodistribution exhibited rapid uptake and favorable retention in the mice brains. The major radioactivity was metabolized by the hepatic system. The autoradiography showed that ¹⁸F-FECNT was highly concentrated in striatum, and that the left and the right striatal uptake were symmetrical in normal SD rat brains. In left-sided lesioned PD rat brains, the striatal uptake of ¹⁸F-FECNT bilaterally decreased in comparison with normal rats. No significant uptake was visible in the 6-OHDA lesioned-sided striatal areas. The results demonstrated that ¹⁸F-FECNT binds to DAT was specific. Toxicity trial displayed that the acceptable dose per kilogram to mice was 625 times greater than that to human. These indicate that 18F-FECNT is a potentially safe and useful DAT PET imaging agent in the brain.

442

Aimed at comparing diagnostic accuracy of ¹⁸F-FDG PET with PET/CT for pulmonary neoplasm, a study based on multi-center clinical trial of the diagnoses, in randomized and semi-blind ways, was executed from January 2006 to June 2007. It included 55 patients, i.e. 16 with histopathologically proved lung tumors, 16 with tuberculosis and 23 with benign lesions (inflammation, pseudotumor, granuloma, fibrosis and others). The histopathologic and clinic results were served as reference standard. Statistical significances in pulmonary nodule diagnosis between ¹⁸F-FDG PET and PET/CT were determined with 95% confidence interval obtained by ROC analysis. The ¹⁸F-FDG PET detected lung neoplasm with a sensitivity of 87.5% (14/16), a specificity of 59.0% (23/39), an accuracy of 67.3% (37/55) and a positive-likelihood ratio of 2.13. The ¹⁸F-FDG PET/CT detected lung neoplasm with a sensitivity of 93.8% (15/16), a specificity of 61.5% (24/39), an accuracy of 70.9% (39/55) and a positive-likelihood ratio of 2.43. The area under curves (AUC) of ¹⁸F-FDG PET and PET/CT were 0.803±0.068 and 0.799±0.063, respectively. It can be concluded that the diagnostic accuracy for malignant pulmonary nodules between ¹⁸F-FDG PET and PET/CT was not statistically different.

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Computed radiography (CR) imaging has high irradiation tolerance and it is easy to archive CR images along with other image information by Digital Imaging and Communications in Medicine (DICOM) format, and to process them. CR can be used in radiation Quality Control (QC) task and verification of treatment setting-up. In this paper, the role of high-energy CR in radiation oncology is studied. The patients were imaged by CR system and EPID before radiotherapy. All verification images were acquired with 1-2 MU (Monitor Unit) using 6 MV X-rays. QC for a linac was done with film and high-energy CR to collect the data on daily, weekly and monthly basis. The QC included Multileaf Collimators (MLC) calibration and mechanical iso-centre check. CR was also adapted to verify patient position, the film was used to compare with digitally reconstructed radiographs (DRR) and portal image from EPID. Treatment setting-up was verified based on the result of comparison. High quality verification images could be acquired by the CR system. Comparing to EPID, the results showed that the system was suitable for practical use to acquire daily verification images, and it was useful to fulfill part of quality assurance (QA) in radiation oncology. The quality of image acquired by the high-energy CR system is comparable or even better than DRRs and portal images. The final treatment set-up for the patients could be verified more accurately with the CR system.

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Needs in scintimammography applications, especially for small animal cardiac imaging, lead to develop a small field of view, high spatial resolution gamma camera with a pinhole collimator. However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity. In order to design a pinhole collimator with an optimized sensitivity and spatial resolution, the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters. The results show that the camera with pinhole of 1 mm, 1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm, 2.25 mm and 3 mm and geometric sensitivity of 0.016%, 0.022% and 0.036%, while the source to collimator distance is 3 cm. We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the trade-off between sensitivity and resolution.

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Due to their low cost, big reaction cross-section with neutrons, flexibility, and convenience for long distance data transfer, plastic scintillation fibers (PSF) have been increasingly used as detectors or sensors for high-energy neutron radiography. In this paper, Geant4 Monte Carlo simulation tool was used to obtain some characteristics of energy and angular distributions of recoil protons in plastic scintillation fibers irradiated by fast neutrons. The plastic fiber with BCF-20 as the core and an acrylic outer cladding was used in the simulation. The results show that there is a big range of energy and angular distribution of recoil protons in energies varying inversely with the recoil angle.

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CdZnTe (CZT) capacitive Frisch grid detectors can achieve a higher detecting resolution. The anode structure might have an important role in improving the weighting potential distribution of the detectors. In this paper, four anode structures of capacitive Frisch grid structures have been analyzed with FE simulation, based on a 3-dimensional weighting potential analysis. The weighting potential distributions in modified anode devices (Model B, C and D) are optimized compared with a square device (Model A). In model C and D, the abrupt weighting potential can be well modified. However, with increased radius of the circular electrode in Model C the weighting potential platform away from the anode becomes higher and higher and in Model D, the weighting potential does not vary too much.

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Based on calculating the influence of RF-field with various physical parameters on the dynamics of the spin 1/2 system, it was found that the spin state could be changed up and down by choosing appropriate RF pulses, and the coherent control of the RF pulses could substantially modify the behavior of spin dynamics: quicker change of two states could be produced even for small pulse duration. In addition, the oscillatory structures around the resonant frequency and the propagation features of the pulses depend on the relative phase of the bichromatic RF pulses.

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A multi-group pin power reconstruction method that fully exploits nodal information obtained from global coarse mesh solution has been developed. It expands the intra-nodal flux distributions into nonseparable semi-analytic basis functions, and a colorset based form function generating method is proposed, which can accurately model the spectral interaction occurring at assembly interface. To demonstrate its accuracy and applicability to realistic problems, the new method is tested against two benchmark problems, including a mixed-oxide fuel problem. The results show that the new method is comparable in accuracy to fine-mesh methods.

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