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Biomedical subjects

W R Hendee

Publications and source records attributed to W R Hendee.

176 records · Page 10Linked to original sources
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An instrument with digital readout for indirect determination of kVp.

An electronic instrument with digital readout has been designed and constructed for indirect determination of the kVp applied to diagnostic x-ray tubes. The signals from two detectors exposed simultaneously to a differentially filtered x-ray beam are processed by analog computing circuitry to yield an output signal directly proportional to the applied peak kilovoltage. Theory and preliminary results are presented and discussed.

Electricity↗
PubMedDate not supplied

Thermal conductivity and diffusivity of neuroblastoma tumor.

In the application of hyperthermia to cancer management, it would be useful to know the temperature/tim 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 degrees, 37 degrees, and 44 degrees 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.

Animals↗
PubMedDate not supplied

Computerized patient contours using the scanning arm of compound B-scanner.

Full utilization of the precision of newer radiation therapy devices requires patient contours drawn with greater accuracy than is possible with the conventional lead wire technique. Polaroid photographs can introduce large errors due to distortion and small image size. Techniques including electromechanical or optical devices and CT scans offer improved accuracy, but often at added expense. A method for obtaining contours has been developed which utilizes a treatment planning minicomputer (equipped with an analog-to-digital converter and plotter) and a commercially available ultrasound B-scanning arm. Voltages corresponding to the X-Y position of the tip of the scanning arm are fed from the scanner to the A/D interface, smoothed, scaled, and plotted. The resulting drawing is a full scale external patient contour. The accuracy of this method is compared to alternative techniques.

Analog-Digital Conversion↗
PubMedDate not supplied

Millimeter wavelength thermographic scanner.

Two new types of thermographic instruments sensitive to millimeter-wave electromagnetic radiation have been designed, constructed, and tested. These instruments utilize wavelengths that are three orders of magnitude longer and much more penetrating than those used in conventional infrared thermography. The instruments are capable of detecting apparent thermal variations as small as a fraction of a degree existing at tissue depths of several millimeters below the skin. By comparison, conventional IR thermographic units are limited to sampling radiation emitted only from the surface. The millimeter wave thermographic units are designed to contribute to the clinical detection of breast abnormalities with the specific aim of accurately and noninvasively detecting breast cancer.

Adult↗
PubMedDate not supplied

Multisegmented ion chamber for CT scanner dosimetry.

A multisegmented, ionization chamber capable of determining dosimetric profiles from a CT scanner has been developed and tested. The chamber consists of a number of 2 mm wide electrically isolated segments from which ionization currents may be measured. Presented here are the performance characteristics of the chamber including energy response, dose linearity, and corrections for "cross talk" between segments. Sample dosimetric profiles are depicted for 3 and 6 mm nominal beam widths at two locations in a dosimetric phantom positioned in the x-ray beam of a fourth generation CT scanner. The results agree well with the conventional method of obtaining dosimetry measurements with TLD chips.

Radiation Dosage↗
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Ionization produced by electron beams beneath curved surfaces.

Ionization produced by high-energy (6-18 MeV) electrons beneath cylindrical surfaces has been measured and compared to ionization at corresponding locations under a flat surface. Results are reported as ionization ratios over a range of depths, off-axis distances, radii of curvature, and electron energies. Phantoms with cylindrical entrance surfaces (radii 6-15 cm) were utilized to simulate patient contours. Measurements reveal that ionization ratios may depart from unity by as much as 50% and that a simple shifting of isodose curves may be insufficient to compensate for perturbation in electron dose distribution introduced by curved surfaces.

Electrons↗
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History, current status, and trends of radiation protection standards.

Quantitative standards for protection against exposure to ionizing radiation were first formulated in the 1930s. Since that time, standards have been restated periodically in different radiation units and conceptual frameworks that reflect improved understanding of the biological effects of radiation interactions and their consequences for human health. In the 1970s the expression of protection standards shifted from a dose- to a risk-based approach, with dose limits established to yield risks to radiation workers comparable with those for workers in other "safe" industries. Over the years, radiation protection standards have exhibited a downward trend to more rigorous limits that require increased commitments of personnel and resources for their enforcement. There are several reasons for this trend, including increased recognition of the long-term health effects of radiation, improved protection measures that permit radiation use at lower levels of exposure, growing numbers of persons exposed occupationally to radiation, and probably a greater intolerance to involuntary risks in society, with radiation targeted as a highly visible source of involuntary risks in the form of nuclear power plants and radioactive waste sites. In the past few years, reports of the Radiation Effects Research Foundation, United Nations Scientific Committee on the Effects of Atomic Radiation, and the National Research Council of the U.S. National Academy of Sciences have presented increased risk estimates for radiation exposure as a consequence of ongoing epidemiological analyses of human populations exposed to ionizing radiation. These risk estimates have enhanced public concern about radiation exposure and set the stage for discussions about the desirability of further reductions in exposure standards for radiation workers and members of the public. Such reductions would directly affect the professional activities, educational responsibilities, and administrative burdens of most medical and health physicists. These persons should understand the process of deriving risk estimates from epidemiological data, the factors that influence the risk estimates, how risk estimates are integrated into radiation protection standards, and the possible impact of more rigorous standards on the use of radiation in medicine.

Biophysics↗
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Informatics at the National Institutes of Health: a call to action.

Biomedical informatics, imaging, and engineering are major forces driving the knowledge revolutions that are shaping the agendas for biomedical research and clinical medicine in the 21st century. These disciplines produce the tools and techniques to advance biomedical research, and continually feed new technologies and procedures into clinical medicine. To sustain this force, an increased investment is needed in the physics, biomedical science, engineering, mathematics, information science, and computer science undergirding biomedical informatics, engineering, and imaging. This investment should be made primarily through the National Institutes of Health (NIH). However, the NIH is not structured to support such disciplines as biomedical informatics, engineering, and imaging that cross boundaries between disease- and organ-oriented institutes. The solution to this dilemma is the creation of a new institute or center at the NIH devoted to biomedical imaging, engineering, and informatics. Bills are being introduced into the 106th Congress to authorize such an entity. The pathway is long and arduous, from the introduction of bills in the House and Senate to the realization of new opportunities for biomedical informatics, engineering, and imaging at the NIH. There are many opportunities for medical informaticians to contribute to this realization.

Academies and Institutes↗
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Overview of radiation effects and control.

The controversy over the effects of low-level exposure to radiation enhances the perception of radiation as a particularly insidious phenomenon of nature. Yet radiation has many useful purposes, including applications for medical diagnosis and therapy, industrial quality control, and the generation of electrical power. Attainment of such societal benefits without compromising the health and safety of potentially exposed persons requires imposition of rigorous measures to control radiation exposures.

Animals↗
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Adolescents and their music. Insights into the health of adolescents.

During adolescence, teenagers are expected to develop standards of behavior and reconcile them with their perceptions of adult standards. In this context, music, a powerful medium in the lives of adolescents, offers conflicting values. The explicit sexual and violent lyrics of some forms of music often clash with the themes of abstinence and rational behavior promoted by adult society. Identification with rock music, particularly those styles that are rejected by adults, functions to separate adolescents from adult society. Some forms of rock music extend well beyond respectability in fulfilling this definitional role. Total immersion into a rock subculture, such as heavy metal, may be both a portrait of adolescent alienation and an unflattering reflection of an adolescent's perception of the moral and ethical duplicity of adult society. Physicians should be aware of the role of music in the lives of adolescents and use music preferences as clues to the emotional and mental health of adolescents.

Adolescent↗
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Federal support of radiological research.

Pervading the plans and objective outlined herein for continued and enhanced federal support of research in radiology is a challenge of unparalleled magnitude, for the economic foundation on which this support is based has rarely been more precarious. The new administration in Washington may well be the most fiscally constrained in half a century, and its stated interest in reducing federal expenditures could have disastrous consequences for the scientific research effort in this country, including that in radiology and the radiological sciences. The circumvention of these consequences may well require the dedicated effort of the entire scientific community over the next few months and years, including that part representing radiology and the radiological sciences.

Centers for Disease Control and Prevention, U.S.↗