SPECT均匀衰减投影数据的反演公式

依据近年来公开发表的有关单光子发射断层成像(SPECT)成像技术的文献,探索SPECT均匀衰减投影数据的反投影问题.主要采用指数型拉动变换的性质和构造特殊函数—–δ函数的方法,进而应用δ函数的特殊性得到了一个精确的反演公式.结果表明,由这种方法得到的反演公式能够更加有效和精确地实现图像的重建.     

Strict topologies on measure spaces

Let X be a measurable space, let be a family of measurable subsets of it, and let be a subspace of complex measures on X that is also closed under restrictions of measures. In this paper we introduce the ‐convergence topology and the ‐strict topology on . Among other results, we find necessary and sufficient conditions for Hausdorff‐ness and coincide‐ness of these topologies. Applications to Lebesgue spaces, and also examples in Hausdorff topological spaces and locally compact groups are given.     

A preliminary study of post-seismic effects of radon following the Ms 8.0 Wenchuan earthquake

The observation data for radon from national geochemical observation points have been collected and analyzed following the Ms 8.0 Wenchuan earthquake on 12th May, 2008 and a post-seismic effect of radon was observed. It has provided the most abundant record since the radon observation network had been set up in china. In this paper, the behaviour of the post-seismic effects of radon gas and water radon is reported. The results were obtained that observation points recording post-seismic effects of radon release were distributed mainly along the extended line of Longmenshan faults, and located on the boundary faults of regional tectonic blocks (Category II) and inside some tectonic blocks (Category II). The pattern of variation in radon emission observed was largely in the form of rising steps. A comparison was made with the variation of water level and flow observed simultaneously with radon measurement, to investigate a dynamic link with post-seismic radon with underground water conditions. This study confirmed a response of radon concentration to the seismic wave, and also raised other scientific issues, such as the dynamic association between geochemical composition of underground water and medium parameter variation of aquifers under dynamic loading, which may support the study of the mechanism of earthquake precursors of radon.     

Development of cataract and corneal opacity in mice due to radon exposure

This work investigates the radiation damage on the eye of albino mice exposed to effective radon doses ranging from 20.92 to 83.68 mSv. These doses were taken over 2–8 weeks using a radon chamber constructed by the National Institute for Standard (Egypt). The guidance on the quality assurance program for radon measurements was followed. Therefore, the estimated doses received by the laboratory animals meet the requirements of national standard. The refractive index(RI) and protein concentration were measured for soluble proteins of both corneas and lenses. In addition, the sodium dodecyle sulfate polyacrylamide gel electrophoresis (SDSPAGE) technique was used. The results show increasing of the RI of both cornea and lens proteins and decreasing in total protein concentration of exposed animals. These results were accompanied with changes in the SDSPAGE profile for both cornea and lens. Therefore, radon exposure produces substantial hazards to the cornea and lens of experimental animals and has a crucial role in the development of cataract and corneal opacity.     

Seasonal variation of radon-222 concentrations in specific locations in Jordan

Previously calibrated passive detectors (CR-39) and an active radon device (Radon Monitor RM3) were used to study seasonal variation of radon-222 concentration levels inside and outside specific locations in Jordan. The study sites were located in an area that used to be an old phosphate mine. We found that the maximum value of radon concentration in air inside the dwellings, as measured by the passive dosimeters, was 1532.9 Bq/m³ during the winter season, and the minimum one was 46.3 Bq/m³ during fall season. While the highest and lowest readings of the active monitor were 892 and 4 Bq/m³ during fall and summer seasons, respectively. The radon concentration in soil ranges from 0.2 kBq/m³ in spring to 37.8 kBq/m³ in fall.     

Ra in geothermal and bottled mineral waters of Hungary

Geothermal waters have been used on a large scale for bathing, drinking and medical purposes, while the consumption of bottled mineral waters is increasing. In this work, radon and radium activity concentrations of thermal and bottled mineral waters, originating from different regions of Hungary, were studied by different radioanalytical methods. It was found that the thermal springs, which supply the world famous baths of Budapest along the right riverside of the Danube, have high ²²²Rn and ²²⁶Ra activity concentration: up to about 100 and 1 kBqm⁻³, respectively. The radium content of some investigated geothermal waters found in the NE region of the Great Hungarian Plain is even higher: up to several kBqm⁻³. The ²²⁶Ra content of bottled mineral waters, commercially available in Hungary, was determined by gamma-spectrometric method, applying radiochemical separation. The highest value exceeded 2 kBqm⁻³ in the case of the Apenta mineral water, which is a popular brand in Hungary, as well as in Europe and North America.     

Indoor radon survey in Eastern Sicily

Inhalation of radon (Rn-222) and its progeny is one of the most significant sources of natural radiation exposure of the population. Nowadays, high radon exposures have been shown to cause lung cancer and many governments all over the world have therefore recommended that radon exposures in dwellings and indoor workplaces should be limited. Radon levels in buildings vary widely from area to area depending on local geology. This paper presents the results of a long-term survey of radon concentrations carried out from 2005 till 2010 in schools and dwellings of Eastern Sicily, using the solid-state nuclear track detector (SSNTD) technique. The investigated area shows medium-high indoor radon concentrations, higher than the Italian average of about 70 Bq/m³, with peaks of 500 Bq/m³ or more in buildings near active faults. Fortunately, only a small fraction of the measurements, about 1.5% of total, was found greater than EU and Italian action limits for indoor and workplaces.     

ACCURATE ATTENUATION CORRECTION FOR ALGEBRAIC RECONSTRUCTION TECHNIQUE IN SPECT

We present a new iterative reconstruction algorithm to improve the algebraic reconstruction technique （ART） for the Single-Photon Emission Computed Tomography. Our method is a generalization of the Kaczmarz iterative algorithm for solving linear systems of equations and introduces exact and implicit attenuation correction derived from the attenuated Radon transform operator at each step of the algorithm. The performances of the presented algorithm have been tested upon various numerical experiments in presence of both strongly non-uniform attenuation and incomplete measurements data. We also tested the ability of our algorithm to handle moderate noisy data. Simulation studies demonstrate that the proposed method has a significant improvement in the quality of reconstructed images over ART. Moreover, convergence speed was improved and stability was established, facing noisy data, once we incorporate filtration procedure in our algorithm.     

Abel transform on PSL(2, ℝ) and some of its applications

We shall investigate the use of Abel transform on PSL₂(ℝ) as a tool beyond K-biinvariant setup, discuss its properties and show some applications.     

Measurements of the size distribution of unattached radon progeny by using the imaging plate

The size distribution of unattached radon progeny is an important parameter for an accurate estimation of the internal dose of radon exposure. In this study, a new measuring system was developed to evaluate the size distribution of unattached radon progeny in air. In the system, airborne radon progeny were collected with a newly designed graded screen array (GSA), the activity concentrations were measured by using the imaging plate technique, and the size distribution of unattached fraction was retrieved by using an iterative nonlinear algorithm. The simulation results indicated that the collection characteristics of the new GSA system were well agreed with other systems. Test experiments showed that the activity-weighted median diameters (AMD) for unattached ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi were 0.89 ± 0.11 nm, 0.96 ± 0.13 nm and 1.01 ± 0.25 nm in a particle-free radon chamber, and the distribution changed with different concentrations of particles. As multiple measurements can be simultaneously carried out with a single IP, the new technique is considered as an optional and useful way to measure the size distribution measurement of unattached radon progeny.