[Nondestructive imaging of elements distribution in biomedical samples by X-ray fluorescence computed tomography].

X-ray fluorescence computed tomography is a stimulated emission tomography that allows nondestructive reconstruction of the elements distribution in the sample, which is important for biomedical investigations. Owing to the high flux density and easy energy tunability of highly collimated synchrotron X-rays, it is possible to apply X-ray fluorescence CT to biomedical samples. Reported in the present paper, an X-ray fluorescence CT system was established at Shanghai Synchrotron Radiation Facility for the investigations of trace elements distribution inside biomedical samples. By optimizing the experiment setup, the spatial resolution was improved and the data acquisition process was obviously speeded up. The maximum-likelihood expectation-maximization algorithm was introduced for the image reconstruction, which remarkably improved the imaging accuracy of element distributions. The developed system was verified by the test sample and medical sample respectively. The results showed that the distribution of interested elements could be imaged correctly, and the spatial resolution of 150 m was achieved. In conclusion, the developed system could be applied to the research on large-size biomedical samples, concerning imaging accuracy, spatial resolution and data collection time.

[Quantitative analysis of nucleotide mixtures with terahertz time domain spectroscopy].

Adenosine, thymidine, guanosine, cytidine and uridine form the building blocks of ribose nucleic acid (RNA) and deoxyribose nucleic acid (DNA). Nucleosides and their derivants are all have biological activities. Some of them can be used as medicine directly or as materials to synthesize other medicines. It is meaningful to detect the component and content in nucleosides mixtures. In the present paper, components and contents of the mixtures of adenosine, thymidine, guanosine, cytidine and uridine were analyzed. THz absorption spectra of pure nucleosides were set as standard spectra. The mixture's absorption spectra were analyzed by linear regression with non-negative constraint to identify the components and their relative content in the mixtures. The experimental and analyzing results show that it is simple and effective to get the components and their relative percentage in the mixtures by terahertz time domain spectroscopy with a relative error less than 10%. Component which is absent could be excluded exactly by this method, and the error sources were also analyzed. All the experiments and analysis confirms that this method is of no damage or contamination to the sample. This means that it will be a simple, effective and new method in biochemical materials analysis, which extends the application field of THz-TDS.

[Influence of polarization maintaining fibers and polarizer on the lightwave spectrum].

The parameters of polarization maintaining fibers and polarizer, and the splicing angles between them have important influence on the spectral characteristics of lightwave propagating in them. The transmission model of lightwave was established using Jones matrix. For the first time, the effect of degree of polarization, fiber lengths, splicing angles between fibers and between fiber and component on the output spectrum was discussed. It was indicated that the shape of output spectrum of the unpolarized lightwave will not change when the splicing angles between fibers and between fiber and component were not zero, while there were periodical functions added to the output spectrum of polarized of partially polarized lightwave. The result that when the angles were constants, the longer the fibers were, the smaller the periods of periodical functions, and that when the fiber lengths were constants, in a certain range the bigger the angles, the larger the amplitudes of periodical functions, was achieved. The conclusions were verified by experiments and they could supply theoretical guidance for the systems using polarization maintaining fibers and polarizer.

[Levels of transition on maternal transferred measles antibody in infants in 3 cities in China].

OBJECTIVE: To understand the epidemiological characteristics of age distribution of measles and related policies on measles vaccines (live; MV) in infants through analyzing the antibody levels of comparison in maternal-infant pairs. Transition of immunity in infants was also studied to provide theoretic basis for measles immunization strategy and to reduce the incidence of month-old infants. METHODS: In cities of Ningbo, Harbin, and Jinan from Zhejiang, Heilongjiang and Shandong provinces, data was collected from 2004 to 2007 and analyzed regarding the epidemic situation of measles. Studies on maternal-transferred measles antibody were carried our sero-epidemiologically. RESULTS: Most of the measles cases were found among babies younger than 12 months, and the incidence of < 1 year olds had been increasing. The distribution was dominated by 5 - 8 month olds in infant measles cases. The positive rate and GRMT of measles antibody in newborns were 89.3 percent and 738.93. The positive rate of the measles antibody and GMRT of the 6-month infant were 6.9% and 6.89, while 6.7% and 3.69 in 8-month infant. There was a declining trend of the positive rate of the measles antibody during the newborns to 8-month infant. The positive rate and GRMT of measles antibody in mothers were 84.3 percent and 516.94. Mother's measles antibodies mainly to be at low and moderate level, which accounted for 50.4 percent and 30.3 percent respectively, the correlation coefficient between mother and infant was 0.840. CONCLUSION: Maternal-transferred measles antibody decreased as the growth of infants. The positive rates of measles antibody were quite low in 6-month and 8-month olds which were the age range that needs most attention.

Application of x-ray phase contrast imaging to microscopic identification of Chinese medicines.

In the last decade, x-ray phase contrast imaging (XPCI) has received considerable attention as a novel imaging technique, which has proved to be suitable for weakly absorbing materials such as biomedical samples and polymers. In this paper, the microstructures of traditional Chinese medicines (TCMs), which are used as judging criteria in the identification of TCMs, were investigated by XPCI based on a nano-focus x-ray tube. The results demonstrated that XPCI is a promising new method for the identification of TCMs, with advantages such as nondestructivity, no special sample preparation and suitability for thick samples.

Structural evidence for alpha-synuclein fibrils using in situ atomic force microscopy.

Human alpha-synuclein is a presynaptic terminal protein and can form insoluble fibrils that are believed to play an important role in the pathogenesis of several neurodegenerative diseases such as Parkinson's disease, dementia with Lewy bodies and Lewy body variant of Alzheimer's disease. In this paper, in situ atomic force microscopy has been used to study the structural properties of alpha-synuclein fibrils in solution using two different atomic force microscopy imaging modes: tapping mode and contact mode. In the in situ contact mode atomic force microscopy experiments alpha-synuclein fibrils quickly broke into fragments, and a similar phenomenon was found using tapping mode atomic force microscopy in which alpha-synuclein fibrils were incubated with guanidine hydrochloride (0.6 M). The alpha-synuclein fibrils kept their original filamentous topography for over 1 h in the in situ tapping mode atomic force microscopy experiments. The present results provide indirect evidence on how beta-sheets assemble into alpha-synuclein fibrils on a nanometer scale.