نتایج جستجو برای: optical collimator

تعداد نتایج: 269265  

Journal: :IEEE transactions on medical imaging 1994
Gengsheng Lawrence Zeng Grant T. Gullberg

Fan-beam collimators are used in single photon emission computed tomography to improve the sensitivity for imaging of small organs. The disadvantage of fan-beam collimation is the truncation of projection data surrounding the organ of interest or, in those cases of imaging large patients, of the organ itself producing reconstruction artifacts. A spatially varying focal length fan-beam collimato...

2011
J. M. Warwick S. Rubow M. du Toit E. Beetge P. Carey P. Dupont

Purpose. Striatal single photon emission computed tomography (SPECT) imaging of the dopaminergic system is becoming increasingly used for clinical and research studies. The question about the value of nonuniform attenuation correction has become more relevant with the increasing availability of hybrid SPECT-CT scanners. In this study, the value of nonuniform attenuation correction and correctio...

1995
A. W. Chao

A collimator is often used to clean a beam of its excessive tail particles. If the beam intensity is high enough or if the beam is brought too close to the collimator, however, the wakefields generated by the beam-collimator interaction can cause additional beam tails to grow, thus defeating, or even worsening, the beam-tail cleaning process. The wakefield generated by a sheet beam moving past ...

Journal: :Physics in medicine and biology 2013
R J Havelin B W Miller H H Barrett L R Furenlid J M Murphy R M Dwyer M J Foley

This work outlines the design and construction of a single-photon emission computed tomography imaging system based on the concept of synthetic collimation. A focused multi-pinhole collimator is constructed using rapid-prototyping and casting techniques. The collimator projects the centre of the field of view (FOV) through 46 pinholes when the detector is adjacent to the collimator, with the nu...

ژورنال: کومش 2020

Introduction: Most beta and gamma radiation radioisotopes used for treatment are not suitable for imaging. The bremsstrahlung images on a conventional gamma camera helped to localize the radionuclide within and outside of the lesion. Secondary scattering of gamma rays of higher energy and bremsstrahlung causes contamination in the energy window and reducing the contrast and resolution of the im...

Journal: :RADIOISOTOPES 1970

Journal: :Physics in medicine and biology 2009
G G Echner W Kilby M Lee E Earnst S Sayeh A Schlaefer B Rhein J R Dooley C Lang O Blanck E Lessard C R Maurer W Schlegel

Robotic radiosurgery using more than one circular collimator can improve treatment plan quality and reduce total monitor units (MU). The rationale for an iris collimator that allows the field size to be varied during treatment delivery is to enable the benefits of multiple-field-size treatments to be realized with no increase in treatment time due to collimator exchange or multiple traversals o...

2014
Amine Samoudi Karen Van Audenhaege Günter Vermeeren Micahel Poole Luc Martens Roel Van Holen Wout Joseph

INTEC, Ghent University/iMinds, Ghent, Belgium Combining Single Photon Emission Computed Tomography (SPECT) with Magnetic Resonance Imaging (MRI) results in an interaction of the time-varying magnetic field gradients with the highly conducting tungsten collimator, which generates a secondary magnetic field causing spatial distortions in reconstructed MR images. Accurate simulations are importan...

Journal: :EPJ Web of Conferences 2015

Parvaneh Darkhor Samira Abbaspour جلیل پیرایش اسلامیان,

Introduction: We have investigated cardiac SPECT with slant hole collimator in which the holes are slanted towards the target organ, to provide greater sensitivity over the parallel hole collimator. In addition, parallel hole collimator was used to obtain a comparison in FWHM, sensitivity, Compton and photoelectric area values in the simulations. Materials and Methods...

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