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In this paper, we provide polynomial coefficients and a semi-empirical relation using which one can derive photon mass energy
absorption coefficient of any H-, C-, N-, O-based sample of biological interest containing any other elements in the atomic
number range 2–40 and energy range 200–1500 keV. More interestingly, it has been observed in the present work that in this
energy range, both the mass attenuation coefficients and the mass energy absorption coefficients for such samples vary only
with respect to energy. Hence it was possible to represent the photon interaction properties of such samples by a mean value
of these coefficients. By an independent study of the variation of the mean mass attenuation coefficient as well as mass energy
absorption coefficient with energy, two simple semi-empirical relations for the photon mass energy absorption coefficients
and one relation for the mass attenuation coefficient have been obtained in the energy range 200–1500 keV. It is felt that
these semi-empirical relations can be very handy and convenient in biomedical and other applications. One possible significant
conclusion based on the results of the present work is that in the energy region 200–1500 keV, the photon interaction characteristics
of any H-, C-, N-, O-based sample of biological interest which may or may not contain any other elements in the atomic number
range 2–40 can be represented by a sample-independent (single) but energy-dependent mass attenuation coefficient and mass
energy absorption coefficient.
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A generalized method of converting CT image to PET linear attenuation coefficient distribution in PET/CT imaging 下载免费PDF全文
The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenu- ation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for con- verting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently. 相似文献
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In this study, mass attenuation coefficients of the undoped and 2% boron nitride–doped magnesium diboride superconductor samples were investigated. Mass attenuation coefficients were measured at 8.04–59.5?keV x-ray energies by using a high-purity germanium detector with a resolution of 182?eV at 5.9?keV. It is observed that mass attenuation coefficients in undoped and doped magnesium diboride samples decrease with increasing photon energy, and doping with the boron nitride leads to increase the absorption of the electromagnetic radiation. 相似文献
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本文从理论和实验上分析了水的衰减系数及有效增益长度对受激布里渊散射(SBS)输出能量的影响。实验结果表明,衰减系数越小,SBS输出能量越高。由于脉宽压缩效应,当入射光能量足够高并且有效增益长度相对较长时,SBS易获得高能量而形成极高的峰值功率。一旦这种峰值功率超过受激拉曼散射(SRS)或者二阶SBS阈值,SBS就会作为一个新的激发源去激发SRS或者二阶SBS,从而消耗掉部分SBS的能量,所以会出现后向有效增益长度越长,SBS的输出能量越低的现象。
关键词:
受激布里渊散射
衰减系数
有效增益长度
脉宽压缩 相似文献