Abstract:
:Geometric and penetration responses of a multihole focusing collimator to a point source have been determined using a digital computer and a ray tracing technique. Results are presented as point and line spread functions for collimated rays and penetrating rays, and as plane sensitivities and modulation transfer functions derived from the line spread functions. Responses to a 141Ce line source have been measured for a lead collimator and for a cadium collimator of practically identical dimensions. A comparison of measured and computed responses shows that while computed penetration approximates measured penetration reasonably well, there is a measurable contribution from scattered rays. Plane sensitivities and the modulation transfer function derived from the computed responses are shown. The effects of penetration are compared with predictions made by other investigators. This analysis of collimator performance provides information not previously available and should be useful for evaluating collimators of existing or proposed design.
journal_name
Phys Med Bioljournal_title
Physics in medicine and biologyauthors
Jahns MJdoi
10.1088/0031-9155/26/1/011subject
Has Abstractpub_date
1981-01-01 00:00:00pages
113-24issue
1eissn
0031-9155issn
1361-6560journal_volume
26pub_type
杂志文章abstract::Radiochromic films are useful as dosimeters in high-precision radiotherapy owing to their high spatial resolution. However, when a particle beam is measured using a radiochromic film, the dose cannot be estimated accurately because the film darkness varies with variations in linear energy transfer (LET). This paper pr...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/ab8bf3
更新日期:2020-06-15 00:00:00
abstract::The lipid disordering effect of aspirin on the liposomal membrane of dipalmitoyl phosphatidyl choline has recently been studied using the fluorescence polarization method. From the anisotropy-temperature curve, we have calculated here the associated change in van't Hoff enthalpy. Since the fluorescence technique requi...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/41/3/003
更新日期:1996-03-01 00:00:00
abstract::Respiratory motion can blur the tomographic reconstruction of positron emission tomography or single-photon emission computed tomography (SPECT) images, which subsequently impair quantitative measurements, e.g. in the upper abdomen area. Respiratory signal phase-based gated reconstruction addresses this problem, but d...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/58/8/2657
更新日期:2013-04-21 00:00:00
abstract::A novel approach to read out radiochromic film was introduced recently by the manufacturer of GafChromic film. In this study, the performance of this triple-channel film dosimetry method was compared against the conventional single-red-channel film dosimetry procedure, with and without inclusion of a pre-irradiation (...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/57/13/4353
更新日期:2012-07-07 00:00:00
abstract::A Monte Carlo model of a novel electronic portal imaging device (EPID) has been developed using Geant4 and its performance for imaging and dosimetry applications in radiotherapy has been characterised. The EPID geometry is based on a physical prototype under ongoing investigation and comprises an array of plastic scin...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/59/22/6827
更新日期:2014-11-21 00:00:00
abstract::We investigated the physical characteristics of two complementary metal oxide semiconductor (CMOS) mammography detectors. The detectors featured 14-bit image acquisition, 50 microm detector element (del) size and an active area of 5 cm x 5 cm. One detector was a passive-pixel sensor (PPS) with signal amplification per...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/54/6/022
更新日期:2009-03-21 00:00:00
abstract::In recent years, the Monte Carlo method has been used in a large number of research studies in radiation therapy. For applications such as treatment planning, it is essential to validate the dosimetric accuracy of the Monte Carlo simulations in heterogeneous media. The AAPM Report no 105 addresses issues concerning cl...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/53/16/016
更新日期:2008-08-21 00:00:00
abstract::A phantom study for dosimetry in the urethra using alanine/ESR during (192)Ir HDR brachytherapy of prostate cancer is presented. The measurement method of the secondary standard of the Physikalisch-Technische Bundesanstalt had to be slightly modified in order to be able to measure inside a Foley catheter. The absorbed...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/54/9/022
更新日期:2009-05-07 00:00:00
abstract::Our newly developed method using spatially and time-resolved reflectances can easily estimate the absorption coefficients of each layer in a two-layered medium if the thickness of the upper layer and the reduced scattering coefficients of the two layers are known a priori. We experimentally validated this method using...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/54/16/014
更新日期:2009-08-21 00:00:00
abstract::The ion recombination is examined in parallel-plate ionization chambers in scanning proton beams at the Danish Centre for Particle Therapy and the Skandion Clinic. The recombination correction factor k s is investigated for clinically relevant energies between 70 MeV and 244 MeV for dose rates below 400 Gy min-1 in ai...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/ab8579
更新日期:2020-06-05 00:00:00
abstract::We propose bilinear models for capturing and effectively decoupling the expected shape variations of an organ both across the patient population and within a specific patient. Bilinear models have been successfully introduced in other areas of computer vision, but they have rarely been used in medical imaging applicat...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/55/13/010
更新日期:2010-07-07 00:00:00
abstract::Dose calculations for radiation arc therapy are traditionally performed by approximating continuous delivery arcs with multiple static beams. For 3D conformal arc treatments, the shape and weight variation per degree is usually small enough to allow arcs to be approximated by static beams separated by 5 degrees -10 de...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/53/17/018
更新日期:2008-09-07 00:00:00
abstract::This paper presents calculated specific absorption rate (SAR) dosimetry in 4 and 8 week Japanese pregnant-woman models exposed to plane waves over the frequency range of 10 MHz-1.5 GHz. Two types of 2 mm spatial-resolution pregnant-woman models comprised a woman model, which is similar to the average-sized Japanese ad...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/55/1/N01
更新日期:2010-01-07 00:00:00
abstract::Although field area and object thickness are important parameters in comparisons of techniques for optimal reduction of scattered radiation to the image, they are in practice seldom varied. For this reason, we suggest that contrast degradation (CDF) and contrast improvement (CIF) factors be more frequently used and ap...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/31/7/004
更新日期:1986-07-01 00:00:00
abstract::In positron emission tomography (PET) with pixelated detectors, a significant number of annihilation photons interact with scintillation crystals through single or multiple Compton scattering events. When these partial energy depositions occur across multiple crystal elements, we call them inter-crystal scatter (ICS) ...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aba8b4
更新日期:2020-10-21 00:00:00
abstract::The dose-response of LiF:Mg,Ti (TLD-100) exposed to 15 and 35 kVp (8.0 +/- 0.1 and 8.1 +/- 0.1 keV effective energy respectively) x-rays and 60Co gamma-rays has been measured in the dose interval from (1.2-5.4) x 10(3) Gy for x-rays, and from 0.14 to 850 Gy for gamma-rays. In both cases the total TL signal and glow cu...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/43/8/006
更新日期:1998-08-01 00:00:00
abstract::The extent to which occupational radiation exposure contributes to cancer mortality is an influence on future world energy policy. It is also a factor in deciding the level of expenditure to reduce radiation levels experienced by workers. Here we discuss some of the difficulties in analysing the situation and presen...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/21/6/001
更新日期:1976-11-01 00:00:00
abstract::Dynamic positron emission tomography (PET) imaging can provide information about metabolic changes over time, used for kinetic analysis and auxiliary diagnosis. Existing deep learning-based reconstruction methods have too many trainable parameters and poor generalization, and require mass data to train the neural netw...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/abc09d
更新日期:2020-10-13 00:00:00
abstract::Dose reconstruction is a process that re-creates the treatment-time dose deposited in a patient provided there is knowledge of the delivered energy fluence and the patient's anatomy at the time of treatment. A method for reconstructing dose is presented. The process starts with delivery verification, in which the inci...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/46/4/303
更新日期:2001-04-01 00:00:00
abstract::Imaging technologies that allow non-radiative visualization and quantification of apoptosis have a great potential for assessing therapy response, early diagnosis, and disease monitoring. Magnetic particle imaging (MPI), the direct imaging of magnetic nanoparticles as positive contrast agent and sole signal source, en...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/abad7c
更新日期:2020-09-24 00:00:00
abstract::Many of the inadequacies of the system presently used for surveying environments containing penetrating radiation stem from the impossibility of defining a radiation parameter which is additive, measurable and closely related to peak dose equivalent in the body. Many of the present conceptual difficulties would be eli...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/20/6/012
更新日期:1975-11-01 00:00:00
abstract::In electron beam dosimetry using parallel-plate chambers solid phantoms are sometimes necessary. To obtain the dose to water from the ionization obtained in the solid phantom, fluence correction factors and perturbation factors have to be applied. In this study fluence factors in a perturbation free geometry have been...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/42/11/007
更新日期:1997-11-01 00:00:00
abstract::The dosimetrical characteristics of a new miniature multileaf collimator (ModuLeaf MLC, MRC Systems GmbH, Heidelberg, Germany) attached to the accessory holder of a Siemens accelerator with 6 MV x-rays (PRIMUS, Siemens OCS, Concord, California, USA) have been investigated. In particular, those parameters which are imp...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/47/12/402
更新日期:2002-06-21 00:00:00
abstract::An iterative algorithm has been developed to reduce blur artefacts in images obtained from the Pho/Con multiplane tomographic scanner. In this technique estimates of the activity distribution are convolved with the detector response function and compared with the original blurred image planes. Successive estimates of ...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/30/7/004
更新日期:1985-07-01 00:00:00
abstract::In order to measure in vivo resistivity of tissues in the thorax, the possibility of combining anatomical data extracted from high-resolution images with multiple-electrode impedance measurements, a priori knowledge of the range of tissue resistivities, and a priori data on the instrumentation noise is assessed in thi...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/39/1/001
更新日期:1994-01-01 00:00:00
abstract::Recently, the Task Group 103 of the International Commission on Radiological Protection (ICRP) has developed new mesh-type reference computational phantoms (MRCPs) for adult male and female. When compared to the current voxel-type reference computational phantoms in ICRP Publication 110, the MRCPs have several advanta...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aafcdb
更新日期:2019-02-05 00:00:00
abstract::A system is described in which large superficial areas of tissue may be heated using a single plane ultrasonic transducer scanned in a raster fashion. The shape of the heated area is determined by the movement of a microswitch which is activated when it strikes the rigid edge of a hole of the required shape cut in a p...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/30/12/006
更新日期:1985-12-01 00:00:00
abstract::In magnetic particle imaging (MPI), the relation between the particle distribution and the measurement signal can be described by a linear system of equations. For 1D imaging, it can be shown that the system matrix can be expressed as a product of a convolution matrix and a Chebyshev transformation matrix. For multidi...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/60/10/4033
更新日期:2015-05-21 00:00:00
abstract::Respiratory motion in emission tomography leads to reduced image quality. Developed correction methodology has been concentrating on the use of respiratory synchronized acquisitions leading to gated frames. Such frames, however, are of low signal-to-noise ratio as a result of containing reduced statistics. In this wor...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/52/17/006
更新日期:2007-09-07 00:00:00
abstract::Recent studies of the minute morphology of the skin by optical coherence tomography revealed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. This, together with the fact that the dielectric permittivity of the dermis is higher than that of the epidermis, brings...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/54/11/005
更新日期:2009-06-07 00:00:00