abstract：:The introduction of negative pions into cancer therapy has required the construction of large new proton accelerators together with special magnetic systems to form and direct the pion beam to a patient. A summary is presented of the fundamental properties of pions and of the methods used to study the therapeutic beam...

journal_title：Medical physics

authors： Richman C

更新日期：1981-05-01 00:00:00

abstract：:Transthoracic electrical impedance Z consists of a constant baseline component Z0 and the time variable component delta Z such that Z = Z0 + delta Z. The first time derivative of Z has a negative peak, the magnitude of which is (dZ/dt)min. Measurements of 170 volunteers show that (dZ/dt)min is a function of the consta...

journal_title：Medical physics

authors： Djordjevich L,Sadove MS

更新日期：1981-01-01 00:00:00

abstract：:When an (exposure) calibrated ionization chamber is used for the determination of absorbed dose from a photon beam, the reading of the instrument must be multiplied by a number of factors, one of which is an attenuation correction for phantom material displaced by the chamber. the magnitude of this correction must dep...

journal_title：Medical physics

authors： Cunningham JR,Sontag MR

更新日期：1980-11-01 00:00:00

abstract：:A conceptual design is presented showing that, by judiciously choosing the beryllium target thickness and the backstop material, improvements can be achieved in dose-rate, skin sparing, and penetration of neutron beams generated by the same proton accelerator. ...

journal_title：Medical physics

authors： Awschalom M,Rosenberg I

更新日期：1980-09-01 00:00:00

abstract：:The line spread function (LSF) of an imaging system incorporating a pinhole of 0.275 cm radius and a scintillation camera has been measured and its full width at half maximum (FWHM) compared to the values predicted by an expression based on the resolution index of Anger. In most cases, the actual resolution of the sys...

journal_title：Medical physics

authors： Goulet P,Joy ML

更新日期：1980-09-01 00:00:00

abstract：:Neutron and photon energy spectra were measured in different depths and lateral positions in tissue-equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron-gamma fields. Th...

journal_title：Medical physics

authors： Schmidt R,Magiera E,Scobel W

更新日期：1980-09-01 00:00:00

abstract：:This study concerns the accuracy and precision of the IAEA/WHO LiF TLD system used in intercomparison by mail of absorbed doses from 60Co gamma-radiation and 4-25 MV x rays. The system employs 160 mg LiF powder in polystyrene capsules, which are placed at 5 or 7 cm depth in water and irradiated to doses close to 200 r...

journal_title：Medical physics

authors： Bjärngard BE,Kase KR,Rudén BI,Biggs PJ,Boyer AL,Johansson KA

更新日期：1980-09-01 00:00:00

abstract：:This study compared air exposures during conventional dental and maxillofacial radiography and similar views using free-focus radiography with conventional image receptors. The results show that periapical type surveys on nonscreen film placed extraorally or in the buccal fold may be carried out with an exposure to th...

journal_title：Medical physics

authors： Jensen TW,Randall GJ,Goldberg AJ

更新日期：1980-07-01 00:00:00

abstract：:Extensive information has been made available relative to the physical aspects necessary for calculation of radiation absorbed dose from radiopharmaceuticals. A similar data base for the biological factors involved in these calculations has not been documented as thoroughly. The authors present an extensive literature...

journal_title：Medical physics

authors： Flannery A,Veber J,Greenfield MA,McIntyre AB,Hamilton DR

更新日期：1980-05-01 00:00:00

abstract：:A new factor for shifting isodoes curves for oblique Co-60 photon beams has been deduced. Like the two other known factors, this shift factor depends on the source-to-surface distance (SSD), the depth dose (D) and the derivative of D with depth. A comparison of corrected dose distributions has been made by using the t...

journal_title：Medical physics

authors： Iwasaki A,Ishito T

更新日期：1980-05-01 00:00:00

abstract：:A tomographic attachment was designed and developed that attaches to our existing simulator. The film tomograms obtained with the aid of this device exhibit very low geometrical distortion and good contrast and resolution for the objects used in this investigation. In addition, our results to date show that adjacent a...

journal_title：Medical physics

authors： Kessaris ND,Harisiadis L

更新日期：1980-03-01 00:00:00

abstract：:The effective energy of the x-ray beam from linear accelerators changes as a function of the position in the beam due to nonuniform filtration by the flattening filter. In this work, the transmittance through a water column was measured in good geometry and the beam quality characterized in units of HVL in water. Meas...

journal_title：Medical physics

authors： Hanson WF,Berkley LW,Peterson M

更新日期：1980-03-01 00:00:00

abstract：:Using stable materials capable of mimicking any soft tissues of the human body--quantitatively with respect to speed of sound, density, and attenuation coefficient and semiquantitatively with respect to scatter--we have constructed a torso section phantom containing simulated bowel gas, kidney, kidney fat pad, liver, ...

journal_title：Medical physics

authors： Madsen EL,Zagzebski JA,Ghilardi-Netto T

更新日期：1980-01-01 00:00:00

abstract：:Administration of x-ray contrast agents during heart catheterization examination increases the absorbed radiation dose in tissue. To estimate the dose absorbed by the blood of children undergoing diagnostic heart catheterization and angiocardiography, a number of measurements and calculations were conducted. First, en...

journal_title：Medical physics

authors： Callisen HH,Norman A,Adams FH

更新日期：1979-11-01 00:00:00

abstract：:A direct data link between a CT scanner and a radiation treatment planning system has been developed. The link transmits the data serially over a coaxial cable using the pseudo-paper-tape punch and reader (serial PIO) interfaces. The data transmission rate with error-check is approximately 25,000 8-bit bytes/s. This t...

journal_title：Medical physics

authors： Abel RN,Buhler LA,Chu WT,Slater JM,Neilsen IR,Zimmerman DC

更新日期：1979-09-01 00:00:00

abstract：: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 D2 gas (equivalent to an energy loss of 3.5 MeV for...

journal_title：Medical physics

authors： Weaver KA,Eenmaa J,Bichsel H,Wootton P

更新日期：1979-05-01 00:00:00

abstract：:The gamma-ray dose component of a d(80) + Be neutron beam was measured with a 6Li-shielded Geiger-Mueller counter in a tissue-equivalent liquid phantom. The proportion of gamma-ray dose to total dose increased from 0.07 near the surface to 0.09 at 25 cm depth. Due to thermal neutron sensitivity, the G-M count rate inc...

journal_title：Medical physics

authors： Harrison GH,Cox CR

更新日期：1979-05-01 00:00:00

abstract：:Variations in the atomic composition, and mass and electron densities of polystyrene and polymethylmethacrylate (PMM) plastics were assessed from experimentally determined mass attenuation coefficients for 125I and 137Cs gamma rays. The means and standard deviations in the mass densities of 16 samples of PMM and 10 sa...

journal_title：Medical physics

authors： Schulz RJ,Nath R

更新日期：1979-03-01 00:00:00

abstract：:A systems analysis of reduced dose mammography with scatter removal has quantitatively specified the relationships between the several parameters in mammography systems. While the results are only preliminary in the sense that they need to be proven experimentally, they do seem to provide a good feel for the nature of...

journal_title：Medical physics

authors： Muntz EP

更新日期：1979-03-01 00:00:00

abstract：:A commercial optical system developed by Solid Photography, Inc., has been used to generate precise paraffin--polyethylene tissue compensators. A program with the objective of constructing a medical facility has been undertaken to access patient topology for treatment planning, tissue-compensator fabrication, and pati...

journal_title：Medical physics

authors： Lerch IA,Barish RJ,Stern H

更新日期：1978-11-01 00:00:00

abstract：:Computed tomography is sensitive to changes in the imaged distribution during acquisition of the projection data. Previous investigations have emphasized discrete or discontinuous changes in the imaged object. Recent advances have motivated our investigation of object time-dependence characterized by a continuous func...

journal_title：Medical physics

authors： Holden JE,Ip WR

更新日期：1978-11-01 00:00:00

abstract：:We have recently installed a linear accelerator, modified to allow computer control of several machine parameters during irradiation of the patient. As an initial feasibility study of computer-controlled radiation therapy, its application to produce wedge-shaped dose distributions by moving the collimator jaws has bee...

journal_title：Medical physics

authors： Kijewski PK,Chin LM,Bjärngard BE

更新日期：1978-09-01 00:00:00

abstract：:A proton beam is extracted from the 200-MeV linear accelerator at the Fermi National Accelerator Laboratory to investigate the efficacy of proton radiography in medical diagnosis. Fluence rates from 2 X 10(3) to 2 X 10(5) protons/cm2s over a 28-cm diameter field are obtained with a full width at half-maximum beam-ener...

journal_title：Medical physics

authors： Curry J,Steward VW

更新日期：1978-05-01 00:00:00

abstract：:An automated data-acquisition and analysis system has been developed for dosimetry measurements on the pion therapy beam at the Clinton P. Anderson Meson Physics Facility Biomedical Channel in Los Alamos using a PDP-11/45 computer and CAMAC interface. Initialization, test, and monitor programs allow the user to set th...

journal_title：Medical physics

authors： Rosen I,Smith A,Lane R,Kelsey C,Lake D,Hogstrom K,Somers J,Helland J,Kittell R,Amols H,Bradbury J,Richman C

更新日期：1978-03-01 00:00:00

abstract：:The resolution has been evaluated for an experimental x-ray image intensifier employing three microchannel plates (MCPs) as the photon absorber and electron multipliers. The line spread function (LSF) was measured and used for determination of the modulation transfer function (MTF). The MTF was found to be independent...

journal_title：Medical physics

authors： Gould RG

更新日期：1978-01-01 00:00:00

abstract：:The photon response of silicon-diode neutron detectors is analyzed theoretically and measured in the 15-25-MeV region. The main mechanism for producing a response in the diode is shown to be the displacement of silicon atoms by scattering of electrons. If the photon source is an electron accelerator target, the respon...

journal_title：Medical physics

authors： McCall RC,Jenkins TM,Oliver GD Jr

更新日期：1978-01-01 00:00:00

abstract：:The radiation dose to the lungs from 133Xe in lung air is directly proportional to the time integral of 133Xe concentration; i.e., the cumulated concentration in the lungs. Using kinetic models developed to fit clinical observations, we have studied the effect of retention on cumulated concentration in lung air. The m...

journal_title：Medical physics

authors： Watson EE,Cloutier RJ

更新日期：1977-11-01 00:00:00

abstract：:The proper evaluation of the accuracy of a new computer program for radiation-therapy dosimetry requires consideration of both the mathematical algorithm used in the program and the performance required in clinical applications. As an example, our evaluation of the irregular-fields dosimetry program currently marketed...

journal_title：Medical physics

authors： Hallberg JR,Ibbott GS,Carson PL,Hendee WR

更新日期：1977-11-01 00:00:00

abstract：:In order to use negative pions for the treatment of large deep-seated tumors in radiotherapy, it is necessary to produce depth-dose distributions tailored to specific shapes. We present here a method of beam shaping which utilizes a fluid-filled piston having a programmable, computer-controlled, time-dependent thickne...

journal_title：Medical physics

authors： Amols HI,Liska DJ,Halbig J

更新日期：1977-09-01 00:00:00

abstract：:Backscatter factors for kVps and half-value layers typical of mammographic beams have been determined as a function of beam diameter and half-value layer. The method utilized thin TLD-100 chips with the scattering medium alternately present and absent. Results indicate that the field-size dependence of the backscatter...

journal_title：Medical physics

authors： Dubuque GL,Cacak RK,Hendee WR

更新日期：1977-09-01 00:00:00

abstract：:A suitable was 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 applicat...

journal_title：Medical physics

authors： Ort MG,Gregg EC

更新日期：1977-05-01 00:00:00

abstract：:Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques an...

journal_title：Medical physics

authors： Heintz PH,Johnsen SW,Peek NF

更新日期：1977-05-01 00:00:00

abstract：:The immediate goal of clinically based x-ray-transmission computed tomography (CT) is to provide a measurement of the x-ray linear attenuation coefficient in cross section with the ultimate goal of impacting on patient management and care. To do this with the accuracy needed for clinical goals requires the careful int...

journal_title：Medical physics

authors： McCullough EC,Payne JT

更新日期：1977-03-01 00:00:00

abstract：:An overall practical dosimetric study of a 10-MV photon beam produced by a Varian Clinac-18 linear accelerator is presented. In particular measurements were made to provide data which could be utilized in computerized dosage calculations using the concept of dividing the radiation beam into primary and scatter compone...

journal_title：Medical physics

authors： Van Dyk J

更新日期：1977-03-01 00:00:00

abstract：:The calibration (in rad/nC) of an air-filled tissue-equivalent ionization chamber for neutrons of 15-MeV average energy was determined by measuring absolute fluences and calculating the kerma per unit fluence. The neutron calibration determined from the gamma-ray calibration and application of the Bragg-Gray relation ...

journal_title：Medical physics

authors： Barschall HH,Goldberg E

更新日期：1977-03-01 00:00:00

abstract：:The use of the stable isotope 48Ca as a tracer in biological systems has been studied. Determination of 48Ca concentrations in samples was accomplished by proton activation via the (p,n) reaction with subsequent measurement of gamma-ray spectra from 44-h 48Sc and 4-h 44Sc. With protons of about 5.5 MeV and a Ge(Li) ga...

journal_title：Medical physics

authors： Edwards FM,Kraushaar JJ,Ristinen RA,Rudolph H

更新日期：1977-01-01 00:00:00

abstract：:An integrating solid-state dosimeter has been developed to detect ultraviolet radiation using the process of "direct" ultraviolet stimulation. This process yields a thermoluminescent signal after an exposure to ultraviolet radiation, without prior exposure to ionizing radiation. Magnesium oxide crystals were found to ...

journal_title：Medical physics

authors： Dhar A,DeWerd LA,Stoebe TG

更新日期：1976-11-01 00:00:00

abstract：:Attention is given to means of sensing ultrasonic energy distributions over an area. Under the restraints appropiate to real-time imaging of deep body organs, piezoelectric arrays offer the most promising method. Adaptation of integrated circuit techniques to array assembly permits very large arrays of small elements ...

journal_title：Medical physics

authors： Maginness MG,Plummer JD,Beaver WL,Meindl JD

更新日期：1976-09-01 00:00:00

abstract：:Tumor cells can be killed by heating to 42.5 degrees C. It is convenient to localize heating by passing electric current at 500 kHz through tissue between a pair of electrodes. It is desirable to determine, for a given electrode-tissue configuration, what the resulting field and, therefore, current distribution will b...

journal_title：Medical physics

authors： Hutson RL

更新日期：1976-07-01 00:00:00

abstract：:A simple method to measure the line spread function of computed tomographic scanners has been developed. The line spread function of the EMI-Scanner was measured and the MTF of the scanner was calculated. The reproducibility of the method indicated this technique could be utilized to compare the spatial resolution of ...

journal_title：Medical physics

authors： Judy PF

更新日期：1976-07-01 00:00:00