摘要:

The feasibility of using the information contained in the radiative capture gamma ray spectrum of the neutron‐irradiated human body to measure quantitatively total body elemental compositioninvivohas been investigated. Results of time dependent Monte Carlo simulations have shown that spectral interference of nonradiative capture origin can be completely eliminated by pulsing the detector/spectrometer system in anticoincidence with the neutron source. Calculations based on the results of the Monte Carlo simulation and on an experimental measurement of the efficiency versus energy characteristics of a Ge(Li) detector suggest that the primary limitation of the proposed technique would be inter‐element spectral interference rather than inadequate detector sensitivity. Experimental measurements using a pulsed 14‐MeV neutron generator and Ge(Li) gamma‐ray spectrometer have produced results that are consistent with the predictions of the theoretical model. A radiative capture gamma‐ray spectrum of a tissue‐equivalent phantom was measured in pulsed mode and analyzed off‐line using a computerized spectral analysis procedure. The results were scaled to a proposed facility consisting of a 2.5‐MeV pulsed neutron source and a detection system comprising two 50‐cm3Ge(Li) detectors past which the subject would be scanned. It has been shown that in principle the elements hydrogen, chlorine, calcium, and nitrogen [the latter using large NaI (T1) detectors] could be measured with such a facility at an average body dose level of 0.1 rad. At this dose level the coefficients of variation based on counting statistics alone would be ±2%, or better, for these four elements. With an improvement in the detector/spectrometer energy resolution, the elements sulfur and carbon might also be measurable. It is also shown that by modifying the pulsing sequence appropriately and using 14‐MeV neutrons, total body oxygen could also be measured at the 0.1 rad dose level via its inelastic neutron scattering deexcitation gamma activity.

ISSN:0269-3127    

DOI:10.1118/1.594631

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Spectra, yields, average energies, and kerma rates in tissue of neutrons from 21‐MeV deuteron bombardment of deuterium gas targets have been calculated for target thicknesses of 1, 3.5, and 5 MeV. A high pressure gas cell was constructed and was filled with 33 atm of D2gas (equivalent to an energy loss of 3.5 MeV for 21‐MeV deuterons); dose rate, dose buildup, and depth‐dose properties of neutrons produced by the D(d,n) reaction were measured. Dosimetric properties of these neutrons are superior to those of neutrons from a thick Be target bombarded by a deuteron beam of the same energy.

ISSN:0269-3127    

DOI:10.1118/1.594561

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A scanning multiple slit assembly (SMSA) has been constructed for the purpose of reducing scatter in medical radiography. The SMSA consists of a series of long, narrow beam‐defining slits above the patient that are aligned and synchronously moved with scatter‐eliminating slots beneath the patient during an exposure. Evidence, based on measurements of the ratio of scattered‐to‐primary radiation imaged and radiographs of patients, is presented indicating that such a device is a practical and efficient method of reducing scatter and improving contrast compared to conventional grids. The design considerations and trade‐offs associated with the choice of slit width, slit separation distance, and aft slot depth are discussed along with the effect of these parameters on the SMSA's performance. The various problems encountered in obtaining a uniform scan and the manner in which they were handled are also discussed.

ISSN:0269-3127    

DOI:10.1118/1.594562

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Comparisons of different mammography techniques can be significantly altered by assumptions about the relevant measures for carcinogenic effects in mammography at low doses. Using a combination of recent data available from the literature, a study has been made of the significance of various assumptions concerning both the appropriate measures for carcinogenesis in mammography and the shape of the dose–effects relationship. It is found that for techniques typical of current reduced‐dose mammography systems, the comparison of the relative carcinogenic effects of the techniques is significantly affected by both the measures that are used and the shape of the dose–effects relationship.

ISSN:0269-3127    

DOI:10.1118/1.594563

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Angular distributions of photon depth dose produced by 25‐MeV electrons incident on several fully stopping single‐element targets (C, Al, Cu, Mo, Ta, Pb) and two composite layered targets (Ni–Al, W–Al) were studied. Depth‐dose curves were measured using TLD‐700 (thermoluminescent dosimeter) chips embedded in lucite phantoms. Several useful therapy electron accelerator design curves were determined, including relative flattener thickness as a function of target atomic number, “effective” bremsstrahlung endpoint energy or beam “hardness” as a function of target atomic number and photon emission angle, and estimates of shielding thickness as a function of angle required to reduce the radiation outside the treatment cone to required levels.

ISSN:0269-3127    

DOI:10.1118/1.594564

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An instrument is described which can scan radiographs and collect densitometric readings for subsequent computer analysis. A laser beam is focused onto the film. Raster scan of the beam is provided by two orthogonal mirror galvanometers. The light, attenuated by the radiograph, is gathered by a lens in such a way that it is directed onto a small detector regardless of the scan position. Beam position signals and density readings are stored and analyzed in a minicomputer.

ISSN:0269-3127    

DOI:10.1118/1.594565

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

From clinical and biological experience it is oftentimes necessary to administer hyperthermia with a minimum number of temperature monitoring tumor probes. For this reason a digital readout device has been developed to monitor the feedback temperature of a hyperthermia generator. In this way the thermometry used to monitor tumor core temperature during biological or clinical hyperthermia can be minimized. The unit and its capabilities are described.

ISSN:0269-3127    

DOI:10.1118/1.594566

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Absorbed doses were calculated or taken from the literature for various compounds of11C,13N, and15O, and compared to those of presently used gamma‐ray‐emitting nuclear medicine radiopharmaceuticals. As a rule of thumb, the doses per millicurie of the injectable positron‐emitting compounds are of the same order of magnitude as the dose per millicurie of99mTc compounds. The absorbed doses from the injectable positron emitters are nearly one or more orders of magnitude lower on a per millicurie basis than those from the other injectable gamma emitters that were investigated.

ISSN:0269-3127    

DOI:10.1118/1.594567

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Although the gamma camera and multi‐crystal scanner have largely replaced the old dual probe rectilinear scanners in the larger hospitals, a large number of such scanners are still in use today. Modifications to these units can greatly enhance their usefulness. This paper describes the addition of dual SCA windows to each probe of a rectilinear scanner to increase sensitivity to multiple gamma‐ray isotopes such as67Ga. This method allows increased information density and/or decreased scanning time without degrading image quality. NIM electronics are used to keep down capital costs, as these modules can be shared with other counting systems when multiple‐peak isotopes are not being scanned. A simple connection to an Ohio Nuclear Mdl 84 dual probe scanner is described. For other scanners, a slight modification would be necessary.

ISSN:0269-3127    

DOI:10.1118/1.594568

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The improvement in MTF that can be obtained by the reduction of crossover exposures is evaluated using an experimental film supplied by the 3M Company (3M XUD). It was found that image resolution, as measured by the equivalent passband (2<∫∞0[M(f)]2df), of 3M Trimax 8 screens when used with the experimental 3M XUD film was 2.9 c/mm as compared to 1.8 c/mm when used with a conventional double coated film such as Kodak Ortho G or 3M XD. On the other hand, system speed with 3M XUD film was only 1.6 mR−1as compared to 3.2 mR−1with 3M XD film and 2.4 mR−1with Kodak Ortho G film. These findings were substantiated by phantom studies as well.

ISSN:0269-3127    

DOI:10.1118/1.594647

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY