Induction of chromosome aberrations by monochromatic X-rays with resonance energy of phosphorus K-shell absorption edge.

The induction of chromosome aberrations by monochromatic soft X-rays with energies corresponding to the K-shell absorption edge of phosphorus has been studied in density-inhibited mouse m5S cells. The frequency of dicentrics was markedly enhanced when the cells were irradiated with energy at the K-shell resonance peak (2.153 keV) as compared to those at below (2.146 keV) or above (2.160 keV) the peak. The quantum efficiency was calculated to be 2.7 x 10(-3) for the induction of dicentrics per photoelectric absorption of phosphorus atom in DNA, which was comparable to the known efficiencies of X- or gamma-ray-induced DNA double-strand breaks. However, comparison of the efficiencies based on the absorbed dose indicated that the magnitude of the enhancement was not due solely to the selective photoelectric absorption of the phosphorus atoms in DNA, and suggested the combined contributions of Auger electrons from phosphorus atoms within and outside the DNA molecules.     

Influence of gamma emitter source intensity against energy on the image RMS contrast

Gamma energy and intensity are the key components in the reconstructed image, which play an important role in image quality of medical and industrial tomography equipments. In order to investigate and compare the effect of energy and intensity, a computed tomography (CT) system is designed and developed on the base of the first generation CT system. In this article we intended to compare the effect of intensity and energy on reconstructed image quality experimentally. To go through the process, several experiments are performed using ¹⁹²Ir (8 mCi), ⁷⁵Se (30 mCi) sources and mixture of ¹³⁷Cs (30 mCi)–⁷⁵Se (30 mCi) sources. Finally, the quality of different images is analyzed with RMS contrast to compare the effect of intensity and energy on image quality. The results show that energy and intensity have, respectively, inverse and direct relationship with RMS contrast of obtained images.     

高能光源储存环及同步加速器屏蔽计算与探讨

目的 验证和探讨在高能同步辐射光源辐射屏蔽计算中半经验公式和蒙特卡罗模拟方法的一致性和适用性.方法 分别采用半经验公式和蒙特卡罗模拟独立计算单电子打靶时屏蔽体外产生的周围剂量当量.结果 Jenkins半经验公式计算结果与蒙特卡罗模拟结果比值范围为111％～153％,Sakano半经验公式计算结果与蒙特卡罗模拟结果比值为...     

Bicycle shock absorption systems and energy expended by the cyclist

Bicycle suspension systems have been designed to improve bicycle comfort and handling by dissipating terrain-induced energy. However, they may also dissipate the cyclist's energy through small oscillatory movements, often termed 'bobbing', that are generated by the pedalling movements. This phenomenon is a major concern for competitive cyclists engaged in events where most of the time is spent climbing, e.g. off-road cross-country races. An acceptable method to assess the overall efficacy of suspension systems would be to evaluate energy consumed by cyclists using different types of suspension systems. It could be assumed that any system that reduces metabolic expenditure for the cyclist would automatically lead to performance improvement. Unfortunately, only a limited number of studies have been conducted on that subject. Moreover, the conclusions that can be drawn from most of them are limited due to unsatisfactory statistical power, experimental protocols, measuring techniques and equipment. This review presents and discusses the most relevant results of studies that focused on mechanical simulations as well as on energy expenditure in relation to off-road bicycle suspension systems. Evidence in the literature suggests that cyclist-generated power that is dissipated by suspensions is minimal and probably negligible on most terrains. However, the scarce studies on the topic as well as the limitations in the conclusions that can be drawn from most of them indicate that we should remain cautious before supporting the use of dual suspension bicycles on all course types and for all cyclists. For example, it should be kept in mind that most cross-country racers still use front suspension bicycles. This might be explained by excessive cyclist-generated power dissipation at the high mechanical powers developed by elite cross-country cyclists that have not been studied in the literature. Finally, suspended bicycles are more comfortable. Moreover, the fact that suspension systems may significantly reduce physical stress should not be overlooked, especially in very long events and for recreational cyclists.     

Influence of source composition and particle energy on the determination of gross alpha activity

The influence of different source compositions and α-particle energies on the detection efficiency of a gas-flow proportional counter was examined using experimental measurements and Monte Carlo simulations. Efficiency variation with alpha-particle energy was very marked, being less significant with the substrate composition. These results show that the determination of gross alpha activity in an unknown sample must be carried out very carefully in order to give a correct estimation of its activity.     

Response to and control of destructive energy by magnetic resonance

Magnetic resonance imaging techniques can be used to control and monitor the deposition of destructive energy. The authors evaluated the feasibility of phosphorus-31 magnetic resonance spectroscopy for the control, monitoring, and prediction of the three-dimensional extent of tissue destruction during interstitial laser surgery. Characteristic metabolic changes were demonstrated within the lesion and in the adjacent normal tissue during the deposition of thermal energy.     

Measurement of energy absorption coefficients at 662 keV in soil samples

The sphere transmission method is employed for the direct measurement of the energy absorption coefficients of different soil samples by placing a point source of Cs-137 inside a spherical shell. The transmitted and scattered gamma-rays are detected using a proportional response NaI detector. The measured values are compared with the theoretical values.     

双源CT双能量及其融合技术的临床应用

双源CT(DSCT)双能量扫描是通过2套相互垂直的球管发出2种不同能量的射线进行同步螺旋扫描,经探测器接受后对不同能量下所采集的多种不同密度物质的衰减信息进行分析的一种新的 CT 成像方法。融合技术作为双能量扫描后处理的一种新技术,在不增加扫描期相的情况下,能够明显提高图像的对比度,同时降低图像的噪声,从而提高小病变的检出及图像质量,本文旨在对双能量及其融合技术进行综述。     

微波暴露下实验用鼠体重与电磁能量吸收关系研究

探讨实验用鼠暴露于3GHz微波时,其体重与全身平均比吸收率以及电磁能量吸收之间的关系。方法 首先基于鼠核磁共振三维解剖图像,建立了包含45种生物组织的鼠电磁模型,再通过改变模型的单元尺寸来改变模型的大小与体重,得到长度9～24cm,相应体重16～334g共16个鼠电磁模型;然后采用时域有限差分法计算3GHz微波照射下各个鼠模型体内的感生电场分布,进而得到鼠模型吸收的电磁能量与比吸收率。结果 在3 GHz微波照射下,鼠体重与全身平均比吸收率的关系可分为3个区域,每个区域均可拟合成一条直线;其中,小鼠区域全身平均比吸收率变化剧烈,中等鼠区域变化趋于平缓,大鼠区域变化更为平缓。鼠体重与电磁能量吸收的关系可以拟合成一条二次曲线,当鼠模型较小时,吸收的电磁能量大致相同,当鼠模型逐渐增大时,鼠吸收的电磁功率也逐渐增大,但增大的幅度小于体重增加的幅度。结论 动物越大,其在电磁场中吸收的电磁功率也越大,但其全身平均比吸收率却越小。在相同的照射条件下,大鼠因体重变化而产生的受照剂量差异比小鼠小很多,因此建议使用大鼠作为电磁生物效应实验用鼠。     

Electron beam effective source surface distances for a high energy linear accelerator

The design of the Varian Clinac 1800 linear accelerator electron applicator system does not allow clearance for all head and neck patients to be treated at the standard calibration distance of 100 cm. Discrepancies have been found between dose calculations using the inverse square law for extended distances and their measured data. A 4 X 4 cm2 applicator at an energy of 9 MeV, for example, had dose differences of 13 and 23% at distances of 105 and 110 cm SSD. Because of these discrepancies, effective source surface distances (SSDeff) were determined for all the standard electron energies and applicators of a Clinac 1800. These effective source surface distances ranged from 41.6 cm to 92.6 cm for the 4 X 4 cm2 cone/6 MeV electron beam through the 25 X 25 cm2 cone/20 MeV electron beam. A summary of these distances and an analysis of the clinical use of both a best fit SSDeff and a common SSDeff for patient dosimetry calculations is presented.     

双源双能CT在尿路结石成分分析中的应用

目的:探讨双源CT双能量技术应用于尿路结石成分分析中的临床价值。方法:226例尿路结石患者行双源CT双能量扫描,对其结石成分进行分析,将结果与用红外光谱法分析结石成分的结果作对比,计算双源CT在体分析草酸钙结石、磷酸盐结石、胱氨酸结石及尿酸结石的灵敏度与特异度。结果:双源CT能够准确的区分尿酸结石和非尿酸结石(灵敏度和特异度均为100%),较准确的区分草酸钙结石(灵敏度为89.03%、特异度为85.62%),磷酸盐结石(灵敏度为67.28%、特异度为90.71%)及胱氨酸结石(灵敏度为73.56%、特异度为93.43%)。结论:双源CT双能量技术能在治疗前对尿路结石的成分进行初步分析,对了解结石成因,预防结石形成及指导治疗具有重要的意义。     

Dual source dual energy CT in the analysis of urinary calculi composition

目的:探讨双源CT双能量技术应用于尿路结石成分分析中的临床价值.方法:226例尿路结石患者行双源CT双能量扫描,对其结石成分进行分析,将结果与用红外光谱法分析结石成分的结果作对比,计算双源CT在体分析草酸钙结石、磷酸盐结石、胱氨酸结石及尿酸结石的灵敏度与特异度.结果:双源CT能够准确的区分尿酸结石和非尿酸结石(灵敏度和特异度均为100％),较准确的区分草酸钙结石(灵敏度为89.03％、特异度为85.62％),磷酸盐结石(灵敏度为67.28％、特异度为90.71％)及胱氨酸结石(灵敏度为73.56％、特异度为93.43％).结论:双源CT双能量技术能在治疗前对尿路结石的成分进行初步分析,对了解结石成因,预防结石形成及指导治疗具有重要的意义.     

Microscopic energy absorption of the DNA molecules from auger electrons of iodine-125

The microscopic energy distribution along the DNA duplex due to local absorption of Auger electrons of iodine-125 incorporated into the DNA molecule, has been theoretically calculated. Our calculation method [Ünak T. Nucl. Instrum. Methods A255, 274 (1987); Ünak T. Ibid. A255, 281 (1987)]^(12,13) recently presented for spatial energy distribution from low-energy electrons in different chemical systems, has also been used for these calculations. As a result, it has been determined that the maximum range of the highest energy ¹²⁵I Auger electrons in a linear DNA duplex is about 38 μm, and the total energy absorbed by DNA molecule per decay is about 10.3 keV, which is approximately half of the total energy released by electrons (19.8 keV per decay). This absorbed energy is not uniformly distributed along the DNA duplex. Consequently, it has also been determined that the microscopic energy absorption per DNA base or sugar-phosphate group rapidly decreased with the distance from the ¹²⁵I nuclide, and reached about 5 eV per DNA base or sugar-phosphate group at a distance of about 2 nm. On the other hand, the results also demonstrated that the local absorption of ¹²⁵I Auger electrons is able to produce alone at least one double strand break (DSB) on the DNA duplex without the support of the neutralization effects of highly charged tellurium ions.     

脑神经元移行异常的CT诊断

报道10例脑神经元移行异常。其中巨脑回畸形1例,脑裂畸形8例,孤立性灰质移位1例。并存其他畸形5例。脑裂畸形8例中1例两侧大脑外侧裂联合,为一种特殊型,2例裂隙仅达白质,属轻型。减薄扫描有助显示裂隙全貌。构成裂隙壁的内折灰质直径在1.5cm 以上,呈团块状者,尽管未伸达室管膜,也应视为脑裂畸形并存灰质移位。