摘要:

A method for the analysis of metallic foreign bodies (and, in particular, for the determination of the concentration of dissolved copper) in the vitreous body of the eye is discussed. The method is based on the x‐ray fluorescence of the foreign metal. The limit of detection of the system for a given dose is thoroughly investigated. Experiments on test animals indicate a natural content of copper in the wall of the eye which is equal for both eyes. Analyses of metallic foreign bodies in the eyes of patients are reported.

ISSN:0269-3127    

DOI:10.1118/1.1637303

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

From the computer simulation study of blood vessel imaging in cerebral angiography it is found that, with proper choice of the focal‐spot size and magnification ratio, radiographic magnification in conjunction with fast screens can give blood vessel images “equivalent” to or better than those from slower screens without magnification. However, this result is highly dependent on blood vessel diameter. If a sufficiently small focal spot is not available so that the proper choice of focal‐spot size and magnification cannot be made, then the vessel image from slower screens without magnification can be better than that from fast screens with magnification.

ISSN:0269-3127    

DOI:10.1118/1.1637304

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

In liquid ionography the x‐ray photons are absorbed in a liquid containing a high‐atomic‐number atom, such as tetra‐methyl‐tin. The liquid is contained between two parallel electrodes separated by a few millimeters. Most of the ions produced in the liquid recombine. Those that escape recombination are collected on an insulating foil covering one of the electrodes. The resulting charge pattern is rendered visible using powder‐cloud development. For a 4‐mm electrode separation and using 45‐kVp x rays, about 98% of the radiation is absorbed; for 105‐kVp x rays, about 88% of the radiation is absorbed. We studied the sensitivity of a 4‐mm chamber as a function of the applied electric field and found that, for 65‐kVp x rays and an electric field of 70 kV/cm, the sensitivity is 1 nC/cm2‐mR. We present an image of a test pattern with a resolution of better than 10 1p/mm produced by this system.

ISSN:0269-3127    

DOI:10.1118/1.1637305

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

The physical properties of the concepts frequently used in radiation dosimetry to compute dose are studied for high‐energy x‐ray beams. The dose in tissue is divided into total incident and phantom‐scatter components. The incident beam includes the primary photons as well as the collimator scattering contribution. The phantom scattering is composed of back‐ and front‐scatter functions. The former function is shown to have essentially zero effect on dose at 33‐ and 45‐MV energy x rays. Characteristics of tissue‐maximum‐ratio (TMR) at high energies are investigated and TMR tables are provided. Contrary to the definition of TMR, this function is observed to depend on SSD. TMR curves are fitted with a semi‐empirical function with a maximum deviation of 1%. Mathematical equations are derived for the computation of dose from TMR. The applicability of the equivalent square technique to high energy photons is examined and found to be adequate. Properties of percent depth dose are studied and a number of related phenomena are discussed.

ISSN:0269-3127    

DOI:10.1118/1.1637306

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

Energy dependences (thermoluminescent response to 30–130 keVeffx rays compared to that from60Co gammas) were measured for normal LiF dosimeters and for ones which had been sensitized by pre‐irradiation (103–106R) followed by annealing near 300°C. Unsensitized LiF (Harshaw's TLD‐100 and TLD‐700) responds slightly higher (5–10%) to the x rays than expected from changes in dose. When LiF is radiation sensitized, the relative response decreases in the 30–135 keVeffrange as much as 40% for pre‐exposures ≳ 105R. A commercial dosimeter (Radiation Detection Co. “throwaway powder”) displays this altered energy dependence because the LiF is pre‐exposed by the manufacturer. To emphasize the major point: Sensitization alters the energy dependence of LiF without any change in atomic number. Possible uses for this effect are discussed.

ISSN:0269-3127    

DOI:10.1118/1.1637307

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

Water has long been used to develop depth‐dose data for clinical use. Biological material differs from water physically and chemically. Using tissue‐equivalent liquids for phantom materials, central‐axis depth‐dose values are found which are lower for60Co gamma rays than the corresponding values using water, perhaps significantly.

ISSN:0269-3127    

DOI:10.1118/1.1637308

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

A direct measurement of the photon yield of the 148.9‐keV gamma of123Xe has been made. The value obtained: 48.0±1.0 photons of 148.9‐keV emitted per 100 decays of123Xe. The advantage of the present method is that it is a direct measurement and does not rely upon conversion coefficient measurements in123Xe and the summing of many gamma intensities. The half life of123Xe was measured and found to be 2.23±0.02 h.

ISSN:0269-3127    

DOI:10.1118/1.1637309

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1118/1.1637310

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1974.tb36051.x

出版商:Wiley    

年代:2003

数据来源: WILEY