Choice of material for HVL measurements in megavoltage x-ray beams.

abstract：:A method for optimizing MR imaging pulse sequence parameters in a statistical framework is presented. Parameters are defined to be optimal when the resulting scalar images yield optimal image segmentations using Bayesian pixel classification. Thus, Bayes risk is used as the objective function to minimize. Approximatio...

journal_title：Medical physics

authors： Prince JL,Pham D,Tan O

更新日期：1995-10-01 00:00:00

abstract：PURPOSE:Because the small-radius photon beams shaped by cones in stereotactic radiosurgery (SRS) lack lateral electronic equilibrium and a detector's finite cross section, direct experimental measurement of dosimetric data for these beams can be subject to large uncertainties. As the dose calculation accuracy of a trea...

journal_title：Medical physics

authors： Yang JN,Ding X,Du W,Pino R

更新日期：2010-10-01 00:00:00

abstract：:Functional single photon emission computed tomography (SPECT) images of brain activation are based on a comparison of base line and activation images. The correctness of the functional images depends, among other factors, on the accurate spatial registration (alignment) of the base line and activation image data. The ...

journal_title：Medical physics

authors： Sychra JJ,Pavel DG,Chen Y,Jani A

更新日期：1994-12-01 00:00:00

abstract：:We have made a comparative investigation of the estimated spectra obtained by the Laplace transform analysis of the transmitted exposure data measured in an absorption study of a 4-MV x-ray beam. Four transform pair models currently used with this method have been evaluated. It has been determined that the Archer-Wagn...

journal_title：Medical physics

authors： Ahuja SD,Steward PG,Roy TS,Slessinger ED

更新日期：1986-05-01 00:00:00

abstract：:In proton therapy, it is important to evaluate the field irradiated with protons and the deposited dose distribution in a patient's body. Positron emitters generated through fragmentation reactions of target nuclei can be used for this purpose. By detecting the annihilation gamma rays from the positron emitters, the a...

journal_title：Medical physics

authors： Inaniwa T,Kohno T,Yamagata F,Tomitani T,Sato S,Kanazawa M,Kanai T,Urakabe E

更新日期：2007-05-01 00:00:00

abstract：PURPOSE:Dynamic myocardial perfusion computed tomography (DM-PCT) imaging offers benefits over quantitative assessment of myocardial blood flow (MBF) for diagnosis and risk stratification of coronary artery disease. However, one major drawback of DM-PCT imaging is that a high radiation level is imparted by repeated sca...

journal_title：Medical physics

authors： Bian Z,Zeng D,Zhang Z,Gong C,Tian X,Yan G,Huang J,Guo H,Chen B,Zhang J,Feng Q,Chen W,Ma J

更新日期：2017-09-01 00:00:00

abstract：:Weighting of given doses from parallel opposed fields is a widespread practice in radiation therapy of cancer in the tonsillar region. In order to determine when weighting is useful, dose distributions on the central axis were calculated for various energies (60Co, 4-, 8-, 15-, and MVp photons), weighting factors, and...

journal_title：Medical physics

authors： Wollin M,Gilbert HA,Kagan AR

更新日期：1976-03-01 00:00:00

abstract：:Knowledge of the relative intensity distribution at the patient's surface is essential for pencil beam calculations of three-dimensional dose distributions for arbitrarily shaped electron beams. To calculate the relative intensity distribution, the spatial spread resulting from angular spread is convolved with a two-d...

journal_title：Medical physics

authors： Mohan R,Chui CS,Fontenla D,Han K,Ballon D

更新日期：1988-03-01 00:00:00

abstract：PURPOSE:To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each ot...

journal_title：Medical physics

authors： Hagen CK,Roche I Morgó O,Olivo A

更新日期：2020-09-01 00:00:00

abstract：:The purpose of the present study is to characterize electron contamination in photon beams in different clinical situations. Variations with field size, beam modifier (tray, shaping block) and source-surface distance (SSD) were studied. Percentage depth dose measurements with and without a purging magnet and replacing...

journal_title：Medical physics

authors： Lopez Medina A,Teijeiro A,Garcia J,Esperon J,Terron JA,Ruiz DP,Carrion MC

更新日期：2005-05-01 00:00:00

abstract：:The wall of an ionization chamber is commonly assumed to have a negligible effect on chamber response in electron beams. For cylindrical chambers with thin walls this assumption is valid. However, parallel-plate chambers commonly possess large mechanical supports which may affect chamber response in a manner not accou...

journal_title：Medical physics

authors： Hunt MA,Kutcher GJ,Buffa A

更新日期：1988-01-01 00:00:00

abstract：:Intravascular brachytherapy requires that the dose be specified within millimeters of the source. High dose gradients near brachytherapy sources require that the source-detector distance be accurately known for dosimetry purposes. Solid phantoms can be designed to accommodate these stringent requirements. This study r...

journal_title：Medical physics

authors： Buckley LA,Thomadsen BR,DeWerd LA

更新日期：2001-06-01 00:00:00

abstract：PURPOSE:Quantitative SPECT imaging is limited by many factors, including penetration of high energy photons through the collimator. Even small peaks of high energy yield extensive contamination in the photopeak energy window. Rotating slat collimators typically offer a 40- to 50-fold increase in geometric detection eff...

journal_title：Medical physics

authors： Van Holen R,Staelens S,Vandenberghe S

更新日期：2009-09-01 00:00:00

abstract：PURPOSE:Elastography using computer tomography (CT) is a promising methodology that can provide patient-specific regional distributions of lung biomechanical properties. The purpose of this paper is to investigate the feasibility of performing elastography using simulated lower dose CT scans. METHODS:A cohort of eight...

journal_title：Medical physics

authors： Hasse K,Hsieh SS,O'Connell D,Stiehl B,Min Y,Neylon J,Low DA,Santhanam AP

更新日期：2020-08-01 00:00:00

abstract：PURPOSE:To assess current education, practices, attitudes, and perceptions pertaining to ethics and professionalism in medical physics. METHODS:A link to a web-based survey was distributed to the American Association of Physicists in Medicine (AAPM) e-mail membership list, with a follow-up e-mail sent two weeks later....

journal_title：Medical physics

authors： Ozturk N,Armato SG 3rd,Giger ML,Serago CF,Ross LF

更新日期：2013-04-01 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 American Association of Physicists in Medicine recommends that the reference dose-rate distribution, used for treatment planning for low-energy photon brachytherapy sources in routine clinical use, must be based on at least two independent determinations: one using experimentally measured dose rates and one using ...

journal_title：Medical physics

authors： Chan GH,Nath R,Williamson JF,American Association of Physicists in Medicine.

更新日期：2004-05-01 00:00:00

abstract：:This paper examines the distributions of the SAR (specific absorption rate) ratio and temperature elevation when an ultrasound beam propagates through the interface of muscle and bone. This interface is regarded as a flat boundary to partition the energy of the ultrasound beam, and the analytical solution of temperatu...

journal_title：Medical physics

authors： Lin WL,Liauh CT,Chen YY,Liu HC,Shieh MJ

更新日期：2000-05-01 00:00:00

abstract：:A simple approach was developed that calculates the output factors and tissue maximum ratio of an asymmetric field at any point within the open field, and specifically both at the central axis (when the jaws do not shadow it) and at the effective center of the open field, using the existing tables for symmetric fields...

journal_title：Medical physics

authors： Rosenberg I,Chu JC,Saxena V

更新日期：1995-01-01 00:00:00

abstract：:Photoelectric-enhanced radiation therapy is a bimodal therapy, consisting of the administration of highly radiation-absorbing substances into the tumor area and localized regional irradiation with orthovoltage x-rays. Irradiation can be performed by a modified computed tomography (CT) unit equipped with an additional ...

journal_title：Medical physics

authors： Jost G,Mensing T,Golfier S,Lawaczeck R,Pietsch H,Hütter J,Cibik L,Gerlach M,Krumrey M,Fratzscher D,Arkadiev V,Wedell R,Haschke M,Langhoff N,Wust P,Lüdemann L

更新日期：2009-06-01 00:00:00

abstract：PURPOSE:The aim of this study was to investigate the effect of scatter and its correction on kinetic parameters in dynamic brain positron emission tomography (PET) tumor imaging. The 2-tissue compartment model was used, and two different reconstruction methods and two scatter correction (SC) schemes were investigated. ...

journal_title：Medical physics

authors： Häggström I,Schmidtlein CR,Karlsson M,Larsson A

更新日期：2014-11-01 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：PURPOSE:When designing a collimation system for pencil beam spot scanning proton therapy, a decision must be made whether or not to rotate, or focus, the collimator to match beamlet deflection as a function of off-axis distance. If the collimator is not focused, the beamlet shape and fluence will vary as a function of ...

journal_title：Medical physics

authors： Geoghegan TJ,Nelson NP,Flynn RT,Hill PM,Rana S,Hyer DE

更新日期：2020-07-01 00:00:00

abstract：:Numerical reconstruction of x-ray spectra from narrow-beam transmission data was tested with published spectra in the range from 45 to 100 kVp. Transmission curves were calculated from the spectra to simulate measured data. Spectra were reconstructed from these transmission curves with use of an iterative numerical an...

journal_title：Medical physics

authors： Huang PH,Chen TS,Kase KR

更新日期：1986-09-01 00:00:00

abstract：:Effective radioimmunotherapy may depend on a priori knowledge of the radiation absorbed dose distribution obtained by trace imaging activities administered to a patient before treatment. A new, fast, and effective treatment planning approach is developed to deal with a heterogeneous activity distribution. Calculation ...

journal_title：Medical physics

authors： Erdi AK,Yorke ED,Loew MH,Erdi YE,Sarfaraz M,Wessels BW

更新日期：1998-11-01 00:00:00

abstract：PURPOSE:Identification of calcifications and hemorrhages is essential for the etiological diagnosis of cerebral lesions. The purpose of this work was to develop a robust method for characterization of para- and diamagnetic intracerebral lesions based on clinical gradient-echo magnetic resonance phase data acquired at 1...

journal_title：Medical physics

authors： Schweser F,Deistung A,Lehr BW,Reichenbach JR

更新日期：2010-10-01 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：:To account for clinical divergent and polychromatic photon beams, we have developed kernel tilting and kernel hardening correction methods for convolution dose calculation algorithms. The new correction methods were validated by Monte Carlo simulation. The accuracy and computation time of the our kernel tilting and ke...

journal_title：Medical physics

authors： Liu HH,Mackie TR,McCullough EC

更新日期：1997-11-01 00:00:00

abstract：PURPOSE:Incorporating training into image segmentation is a good approach to achieve additional robustness. This work aims to develop an effective strategy to utilize shape prior knowledge, so that the segmentation label evolution can be driven toward the desired global optimum. METHODS:In the variational image segmen...

journal_title：Medical physics

authors： Zhao T,Ruan D

更新日期：2016-05-01 00:00:00

abstract：:We are evaluating the usefulness of stereomammography in improving breast cancer diagnosis. One area that we are investigating is whether the improved depth perception associated with stereomammography might be significantly enhanced with the use of a virtual 3D cursor. A study was performed to evaluate the accuracy o...

journal_title：Medical physics

authors： Goodsitt MM,Chan HP,Hadjiiski L

更新日期：2000-06-01 00:00:00