ISSN:0094-2405    

DOI:10.1002/j.2473-4209.1978.tb36108.x

出版商:Wiley    

年代:1998

数据来源: WILEY

摘要:

This paper presents methods for evaluating the effects of technical factors on observers’ detection of small blood vessels in angiographic images. A fixed set of physical parameters was used to generate computer‐simulated angiographs that contained blood vessels of various diameters. Observers’ judgments about each set of images permitted estimation of the receiver operating characateristic (ROC) curves for vessel detection and of the probability of correctly locating the vessels. Both parametric and nonparametric methods were used to characerize the ROC curves. Three different, but theoretically related, measures of vessel detectability varied systematically with changes in the blood vessel's diameter, reflecting changes in observer performance.

ISSN:0094-2405    

DOI:10.1118/1.594510

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A system based upon the16O(n,p)16N reaction has been developed for monitoring 14‐MeV neutron production. The system has proven to be quite applicable for monitoring the output of a disk‐shaped neutron source and computer analysis has shown it equally suitable for monitoring the ouput of cone‐shaped neutron sources from gas targets presently being considered for cancer therapy.

ISSN:0094-2405    

DOI:10.1118/1.594435

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Up until now, no material has been found whose attenuation and speed of sound properties not only mimic those of human soft tissue, but are controllable in magnitude. We have discovered such a material in the form of water‐based pharmaceutical gels containing uniform distributions of graphite powder and known concentrations of alcohol. The magnitude of the attenuation coefficient can be controlled easily between 0.2 and 1.5 dB/cm at 1 MHz, by varying the concentration of graphite. These attenuation coefficients are nearly proportional to the frequency. The speed of sound varies between 1520 and 1650 m/s at room temperature, depending primarily upon the concentration of alcohol. Bacterial invasion has been prevented by sterilization procedures and the introduction of appropriate preservatives. The ultrasonic properties exhibit temporal stability and change little over the range of room temperatures.

ISSN:0094-2405    

DOI:10.1118/1.594483

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

There is much interest in visualizing dynamic physiological function using nuclear‐medicine techniques. In particular, these methods are used in cardiac studies, but it is likely that many other functions will be better visualized with cinematographic‐type displays. A new instrument is described which takes a sequence of images, records on a single sheet of film by standard formatting devices and, by means of digitally controlled mirrors, projects them in rapid sequence onto a screen to produce the dynamic movie display.

ISSN:0094-2405    

DOI:10.1118/1.594436

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The determining factors of a good analysis by x‐ray fluorescence are discussed, emphasizing the importance of the geometrical arrangement, especially the excitation‐source to analysis‐material distance. The variation of the peak area of theKαx‐ray of Fe is evaluated as a function of the distance. Precautions are given for the analysis of low concentration samples as well as for obtaining the relative concentration of an element in a specific material or organ.

ISSN:0094-2405    

DOI:10.1118/1.594437

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Modern curative radiotherapy requires higher doses to the tumor volume and, necessarily, minimal doses to the surrounding normal tissues. Attempts to use heavy charged particles to achieve such optimization are currently under investigation in many centers. Our data indicate that a static, superimposed magnetic field on a clinical electron‐therapy beam also offers the capability of some ’'tailoring” of isodose distributions. Furthermore, avariable, superimposed magnetic field minimizes those tissue‐generated dose heterogeneities which are inherent with all charged‐particle beams. We suggest that magnetically modified, clinically available electron beams also offer a practical and less expensive means of achieving tailored, heterogeneity‐corrected isodose distributions.

ISSN:0094-2405    

DOI:10.1118/1.594438

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Moderately strong transverse‐magnetic fields were used to modify conventional electron‐dose distributions in tissue‐ and lung‐equivalent phantoms. Magnetically modified symmetrical‐isodose contours and central‐axis depth‐dose curves were measured for central fields in the range of 9–18 kG, field gradients of ≈5 kG/cm, and accelerator energies of 10–45 MeV. To the extent that our experimental field strengths and gradients can be reproduced clinically, the measurements showed that magnetic distributions can be generated (in tissue) which are superior to conventional distributions for the treatment of tumors lying at depths ≲ 7 cm provided that the tumor cross‐section dimensions are equal to or greater than tumor depth. The surface dose in tissue is typically reduced by ≈40% compared to the conventional surface dose for treating the same tumor volume. For the lung phantom data, a significant reduction (≳50%) in the integrated central‐axis dose to healthy tissue was achieved for tumor depths of 10–14 cm. The possibility of reproducing our experimental magnetic fields and gradients inside a patient under realistic clinical conditions is discussed.

ISSN:0094-2405    

DOI:10.1118/1.594484

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In the application of hyperthermia to cancer management, it would be useful to know the temperature/time profile of heated tissues, including the tumor and surrounding normal structures. To obtain this information, knowledge of thermal conductivity and diffusivity of the tissues is required. The thermal conductivity of neuroblastoma was determined by a transient technique to be 89% of the thermal conductivity of water at 25°, 37°, and 44°C. From the latter measurements, the thermal diffusivity of neuroblastoma cells was estimated as 93% of the thermal diffusivity for water. Further, in this study of neuroblastoma cells, the water content was measured as 87.4 g/100 ml of cells, a rather high value not atypical of tumor cells. From literature values of density, specific heat, and thermal conductivity, values for the thermal diffusivity of a variety of normal tissues were estimated. The thermal diffusivity values of normal tissues and neuroblastoma cells exhibit an excellent correlation with water content.

ISSN:0094-2405    

DOI:10.1118/1.594434

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The application of cavity‐ionizaion chambers to the standadization of60Co γ‐ray beams, in terms of exposure, requires that the specific ionization of airJg, be corrected for the attenuation and scatter of the incident rays by the wall, central electrode, and suporting stem of the chamber. A Monte Carlo photon–electron transport code has been developed for the purpose of calculating this correction for spherical and cylindrical chambers. The code has been applied to a spherical graphite chamber having dimensions typical of the chambers used by the NBS, the calculated wall‐correction factor is in close agreement with the average of the NBS factors which were determined experimentally. The code was also used to calculateAeq, which is central to the determination of tissue‐air ratios. The calculated value, 0.989±0.003, is very close to the generally accepted value, 0.985.

ISSN:0094-2405    

DOI:10.1118/1.594439

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY