摘要:

A method has been devised to enable users of half‐ and full‐wave rectified x‐ray sets to match the revised National Bureau of Standards (NBS) x‐ray beam qualities obtained with a constant potential generator. The method provides a rapid technique for determining the added filter necessary to attain the same first half‐value layers and nearly the same homogeneity coefficients as NBS. Beam qualities from 100 to 250 kVcp have been duplicated and used to perform blind calibrations at four beam qualities on each of two ion chambers owned by the National Bureau of Standards.

ISSN:0269-3127    

DOI:10.1118/1.595714

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Ready availability has prompted the use of computed tomography (CT) data in various applications in radiation therapy. For example, some radiation treatment planning systems now utilize CT data in heterogeneous dose calculation algorithms. In radiotherapy imaging applications, CT data are projected onto specified planes, thus producing “radiographs,” which are compared with simulator radiographs to assist in proper patient positioning and delineation of target volumes. All these applications share the common geometric problem of evaluating the radiological path through the CT array. Due to the complexity of the three‐dimensional geometry and the enormous amount of CT data, the exact evaluation of the radiological path has proven to be a time consuming and difficult problem. This paper identifies the inefficient aspect of the traditional exact evaluation of the radiological path as that of treating the CT data as individual voxels. Rather than individual voxels, a new exact algorithm is presented that considers the CT data as consisting of the intersection volumes of three orthogonal sets of equally spaced, parallel planes. For a three‐dimensional CT array ofN3voxels, the new exact algorithm scales with 3N, the number of planes, rather thanN3, the number of voxels. Coded infortran‐77on a VAX 11/780 with a floating point option, the algorithm requires approximately 5 ms to calculate an average radiological path in a 1003voxel array.

ISSN:0269-3127    

DOI:10.1118/1.595715

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In vivo31‐P nuclear magnetic resonance (NMR) spectroscopy was performed on cat brains injected with hematoporphyrin derivative (HpD). A 2‐cm‐diam region of the right parietal lobe was photoactivated with red light. The 31‐P NMR spectra of the photoactivated hemisphere revealed increased inorganic phosphate and decreased phosphocreatine and adenosine triphosphate (ATP) levels, compared to spectra obtained from the control hemisphere. In the absence of drug, no difference in spectra was observed between the photoradiated and control lobes. Our studies suggest thatin vivo31‐P NMR spectroscopy may be used to monitor the effects of phototherapy on tissue high‐energy phosphate metabolism.

ISSN:0269-3127    

DOI:10.1118/1.595765

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In this report we describe an improvement upon the design by Stanton and Lightfoot for a simple photographic null method to determine the kVp of a diagnostic region x‐ray source. The new version has two primary advantages over the Ardran and Crooks design in that it is both simpler and less expensive to produce.

ISSN:0269-3127    

DOI:10.1118/1.595716

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Routine weekly calibration of a Siemens Mevatron 20 linear accelerator with 3‐, 5‐, 7‐, 10‐, 12‐, 15‐, and 18‐MeV electron energies demonstrated fluctuations in dose/monitor unit for the electron beam on the order of 3%–6%. Evaluations and study of the problem demonstrated that the electron chamber, which is open to atmosphere, was undergoing significant temperature changes during the course of a treatment day. The inability of the chamber to compensate for these changes in temperature and pressure led to the addition of a compensating circuit by the manufacturer. The results of the addition of this circuit were evaluated for several extended periods throughout the year, and it was found that the changes in dose/monitor were reduced to approximately ±0.5%.

ISSN:0269-3127    

DOI:10.1118/1.595717

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1118/1.595718

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1985.tb36220.x

出版商:Wiley    

年代:1998

数据来源: WILEY