摘要:

The 10.3‐h165Er, decaying by electron capture to stable165Ho, offers an excellent promise for use in diagnostic nuclear medicine, especially in conjuction with multiwire proportional‐counter cameras. Using an ultra‐high‐resolution Si(Li) photon spectrometer,LandKx‐ray photon yields in165Er decay have been measured. The ratioPL/PKof electron‐capture probabilities inLandKshells is determined to be 0.196±0.030, in good agreement with theory. Estimates of Auger electron yields and yields of very‐low‐energy electrons from Coster–Kronig transitions are presented. Levels of169Er and171Er radioactive impurities in the reactor‐produced165Er sample are experimentally determined. Whole‐body dose estimates for165Er are given. These compare favorably with99mTc dose.

ISSN:0094-2405    

DOI:10.1118/1.594363

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A high‐purity germanium spectrometer system was used to determine primary x‐ray spectra over the 45–90‐kVp region. Methods were devised for producing and examining spectra simulating diagnostic conditions without operating the x‐ray generator at high current levels. The techniques used to correct the experimental data and produce a photon fluence spectrum are discussed. The results, presented graphically and in tables, have been normalized to yield the relative number of photons per 2‐keV interval. Methods for converting a normalized spectrum into a photon fluence spectrum that will produce an exposure of 1 R are presented. The analytical model and procedures used to calculate theK‐escape fraction are discussed.

ISSN:0094-2405    

DOI:10.1118/1.594364

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Accurate bolus is needed for extension of Bragg‐peak therapy. Proton beam‐stopping profiles in a lucite–styrofoam–tissue phantom and in a Rando phantom were recorded photographically. Air volumes caused the largest distortions. Lucite bolus was cut to achieve desired beam‐stopping profiles. Verification of bolus effectin situwill be important to control beam penetration within 5 mm.

ISSN:0094-2405    

DOI:10.1118/1.594365

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

This work deals with the introduction of a gas electronic gain factor in high‐pressure ionography (or “electron radiography”). The purpose is to check the possibility of a further reduction of radiation dose per radiograph. It is shown that xenon or krypton can be mixed with special molecular gases in order to achieve charge‐carrier multiplication at comparatively weak electrostatic fields and in an easily controllable manner. Some radiographs are reproduced which have been obtained in the amplifying working modes of the system. Relevant image characteristics and their limits are discussed. The obtainable resolution is limited by electron diffusion and by quantum noise (lowering of the effective quantum‐detection efficiency).

ISSN:0094-2405    

DOI:10.1118/1.594387

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The application of a dual photon beam to the measurement of tissue and tissue‐like substances has generally required the use of a filter to attain the required monochromaticity of the lower‐energy x‐ray photons. In many cases this has the undesirable effect of also severely attenuating the desired low‐energy beam. A method for circumventing the use of the filter is described. The technique relies on a knowledge of the initial intensities of the components of the x‐ray portion of the dual beam and involves an iterative mathematical procedure. Experimental verification of the method using both tissue and nontissue substances has been carried out.Rvalues obtained with the iterative system show good correlation with filtered values.

ISSN:0094-2405    

DOI:10.1118/1.594366

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Large‐area contrast measurements have been made upon a fiber‐optic x‐ray image intensifier with an external input phosphor. Both photometric and photographic techniques were used. For a shadowed area of 10% of the input window area, a contrast ratio in excess of 150 was determined. This is a factor of 5 higher than previously reported for any x‐ray image intensifier. The improved contrast in the device is attributed to (1) reduced effect of x‐ray Compton scattering in the input window; (2) less cross‐chord light at the photocathode; and (3) greatly reduced light scattering and reflecting in output phosphor and window.

ISSN:0094-2405    

DOI:10.1118/1.594367

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The use of a compact, mobile, relatively inexpensive electromechanical patient‐contouring mechanism is described. The system utilizes a Numonics Model 224 graphics digitizer suspended over the patient. The digitalXandYcoordinates of the patient contour in either of multiple, parallel transverse, or sagittal planes are inherently accurate to within ±0.25 mm over a total reading area of 60×90 cm. Display features include the interface to an analog 11‐in.×17‐in.X–Yplotter with a variable scale‐down factor for those contours which would otherwise be larger than the plotting surface. The system is easy to use and may also be readily interfaced for on‐line entry of patient contours to calculator‐ or minicomputer‐based treatment‐planning systems.

ISSN:0094-2405    

DOI:10.1118/1.594368

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Cobalt‐60 γ rays and 4‐ and 10‐MV x rays are compared for moving‐strip therapy in terms of the dose uniformity and the given dose needed to deliver a prescribed tumor dose. Dose distributions in phantoms of 14–32‐cm thickness were calculated for each therapy unit. Individual given doses which would deliver the most uniform dose along the midline of the treatment volume were determined by computer and were verified experimentally by thermoluminescent dosimetry. Using computer optimization techniques, the midplane dose uniformity is improved significantly for the three therapy units considered.

ISSN:0094-2405    

DOI:10.1118/1.594369

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Rotation of a system consisting of a single x‐ray source and a linear detector array allows rapid collection of x‐ray projection data from which transaxial cross sections can be reconstructed. In this paper, we present an algorithm which makes possible rapid computerized reconstruction from such data. We describe some experiments aimed at investigating the optimal choice of some of the parameters associated with the algorithm. We report on reconstructions using our algorithm of the intact thorax of a dog and also of cross sections of the human female breast from x‐ray data obtained by a computerized mammography machine.

ISSN:0094-2405    

DOI:10.1118/1.594370

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A suitable wax phantom was designed for evaluating various film techniques used in subtraction radiography. Holes are drilled in a slab of wax and filled with various concentrations of iodinated wax, producing disk‐shaped regions with diffuse borders. The technical details of construction and a representative application are described.

ISSN:0094-2405    

DOI:10.1118/1.594371

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY