The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Simon J Doran - One of the best experts on this subject based on the ideXlab platform.
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characterization of a Parallel Beam ccd optical ct apparatus for 3d radiation dosimetry
Physics in Medicine and Biology, 2007Co-Authors: Nikola Krstajic, Simon J DoranAbstract:3D measurement of optical attenuation is of interest in a variety of fields of biomedical importance, including spectrophotometry, optical projection tomography (OPT) and analysis of 3D radiation dosimeters. Accurate, precise and economical 3D measurements of optical density (OD) are a crucial step in enabling 3D radiation dosimeters to enter wider use in clinics. Polymer gels and Fricke gels, as well as dosimeters not based around gels, have been characterized for 3D dosimetry over the last two decades. A separate problem is the verification of the best readout method. A number of different imaging modalities (magnetic resonance imaging (MRI), optical CT, x-ray CT and ultrasound) have been suggested for the readout of information from 3D dosimeters. To date only MRI and laser-based optical CT have been characterized in detail. This paper describes some initial steps we have taken in establishing charge coupled device (CCD)-based optical CT as a viable alternative to MRI for readout of 3D radiation dosimeters. The main advantage of CCD-based optical CT over traditional laser-based optical CT is a speed increase of at least an order of magnitude, while the simplicity of its architecture would lend itself to cheaper implementation than both MRI and laser-based optical CT if the camera itself were inexpensive enough. Specifically, we study the following aspects of optical metrology, using high quality test targets: (i) calibration and quality of absorbance measurements and the camera requirements for 3D dosimetry; (ii) the modulation transfer function (MTF) of individual projections; (iii) signal-to-noise ratio (SNR) in the projection and reconstruction domains; (iv) distortion in the projection domain, depth-of-field (DOF) and telecentricity. The principal results for our current apparatus are as follows: (i) SNR of optical absorbance in projections is better than 120:1 for uniform phantoms in absorbance range 0.3 to 1.6 (and better than 200:1 for absorbances 1.0 to 3.5 with the test target and a novel absorbance range extension method), (ii) the spatial resolution is shown to be at worst 0.5 mm (and often better than this) with an associated DOF of 8 cm, (iii) the SNR of uniform phantoms in reconstruction domain is above 80:1 (one standard deviation) over an absorbance dynamic range of 0.3 to 1.6, (iv) the apparatus is telecentric and without distortion. Finally, a sample scan and reconstruction of a scan of a PRESAGE™ dosimeter are shown, demonstrating the capabilities of the apparatus. For more information on this article, see medicalphysicsweb.org
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characterization of a Parallel Beam ccd optical ct apparatus for 3d radiation dosimetry
Journal of Physics: Conference Series, 2006Co-Authors: Nikola Krstajic, Simon J DoranAbstract:This paper describes the initial steps we have taken in establishing CCD based optical-CT as a viable alternative for 3-D radiation dosimetry. First, we compare the optical density (OD) measurements from a high quality test target and variable neutral density filter (VNDF). A modulation transfer function (MTF) of individual projections is derived for three positions of the sinusoidal test target within the scanning tank. Our CCD is then characterized in terms of its signal-to-noise ratio (SNR). Finally, a sample reconstruction of a scan of a PRESAGETM (registered trademark of Heuris Pharma, NJ, Skillman, USA.) dosimeter is given, demonstrating the capabilities of the apparatus.
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focusing optics of a Parallel Beam ccd optical tomography apparatus for 3d radiation gel dosimetry
Physics in Medicine and Biology, 2006Co-Authors: Nikola Krstajic, Simon J DoranAbstract:Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow ( approximately 9 min per slice) and poorly suited to measurements that require many slices. Here, we describe a fast, three-dimensional (3D) optical computed tomography (optical-CT) apparatus, based on a broad, collimated Beam, obtained from a high power LED and detected by a charged coupled detector (CCD). The main advantages of such a system are (i) an acquisition speed approximately two orders of magnitude higher than a laser-based system when 3D data are required, and (ii) a greater simplicity of design. This paper advances our previous work by introducing a new design of focusing optics, which take information from a suitably positioned focal plane and project an image onto the CCD. An analysis of the ray optics is presented, which explains the roles of telecentricity, focusing, acceptance angle and depth-of-field (DOF) in the formation of projections. A discussion of the approximation involved in measuring the line integrals required for filtered backprojection reconstruction is given. Experimental results demonstrate (i) the effect on projections of changing the position of the focal plane of the apparatus, (ii) how to measure the acceptance angle of the optics, and (iii) the ability of the new scanner to image both absorbing and scattering gel phantoms. The quality of reconstructed images is very promising and suggests that the new apparatus may be useful in a clinical setting for fast and accurate 3D dosimetry.
Ge Wang - One of the best experts on this subject based on the ideXlab platform.
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inverse fourier transform in the gamma coordinate system
International Journal of Biomedical Imaging, 2011Co-Authors: Yuchuan Wei, Ge WangAbstract:This paper provides auxiliary results for our general scheme of computed tomography. In 3D Parallel-Beam geometry, we first demonstrate that the inverse Fourier transform in different coordinate systems leads to different reconstruction formulas and explain why the Radon formula cannot directly work with truncated projection data. Also, we introduce a gamma coordinate system, analyze its properties, compute the Jacobian of the coordinate transform, and define weight functions for the inverse Fourier transform assuming a simple scanning model. Then, we generate Orlov's theorem and a weighted Radon formula from the inverse Fourier transform in the new system. Furthermore, we present the motion equation of the frequency plane and the conditions for sharp points of the instantaneous rotation axis. Our analysis on the motion of the frequency plane is related to the Frenet-Serret theorem in the differential geometry.
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a general exact method for synthesizing Parallel Beam projections from cone Beam projections via filtered backprojection
Physics in Medicine and Biology, 2006Co-Authors: Zhiqiang Chen, Yuxiang Xing, Li Zhang, Kejun Kang, Ge WangAbstract:In recent years, image reconstruction methods for cone-Beam computed tomography (CT) have been extensively studied. However, few of these studies discussed computing Parallel-Beam projections from cone-Beam projections. In this paper, we focus on the exact synthesis of complete or incomplete Parallel-Beam projections from cone-Beam projections. First, an extended central slice theorem is described to establish a relationship between the Radon space and the Fourier space. Then, data sufficiency conditions are proposed for computing Parallel-Beam projection data from cone-Beam data. Using these results, a general filtered backprojection algorithm is formulated that can exactly synthesize Parallel-Beam projection data from cone-Beam projection data. As an example, we prove that Parallel-Beam projections can be exactly synthesized in an angular range in the case of circular cone-Beam scanning. Interestingly, this angular range is larger than that derived in the Feldkamp reconstruction framework. Numerical experiments are performed in the circular scanning case to verify our method.
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data consistency based translational motion artifact reduction in fan Beam ct
IEEE Transactions on Medical Imaging, 2006Co-Authors: Yuchuan Wei, Jiang Hsieh, Ge WangAbstract:A basic assumption in the classic computed tomography (CT) theory is that an object remains stationary in an entire scan. In biomedical CT/micro-CT, this assumption is often violated. To produce high-resolution images, such as for our recently proposed clinical micro-CT (CMCT) prototype, it is desirable to develop a precise motion estimation and image reconstruction scheme. In this paper, we first extend the Helgason-Ludwig consistency condition (HLCC) from Parallel-Beam to fan-Beam geometry when an object is subject to a translation. Then, we propose a novel method to estimate the motion parameters only from sinograms based on the HLCC. To reconstruct the moving object, we formulate two generalized fan-Beam reconstruction methods, which are in filtered backprojection and backprojection filtering formats, respectively. Furthermore, we present numerical simulation results to show that our approach is accurate and robust
Kenneth R Morris - One of the best experts on this subject based on the ideXlab platform.
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quantitative determination of polymorphic composition in intact compacts by Parallel Beam x ray powder diffractometry ii data correction for analysis of phase transformations as a function of pressure
Journal of Pharmaceutical and Biomedical Analysis, 2005Co-Authors: Peter L D Wildfong, Nicole A Morley, Michael D Moore, Kenneth R MorrisAbstract:An analytical, non-destructive method using Parallel-Beam transmission powder X-ray diffractometry (PXRD) is presented for in situ whole compact detection and quantification of solid-state phase transformations in powder compacts. Accurate quantification of analyte in intact compacts using PXRD requires a mathematical correction prior to interpolation of calibration data to account for sample differences that result as a function of pressure; namely, compact thickness and solid fraction. Chlorpropamide is examined as a model system, selected because of its susceptibility to polymorphic transformations when consolidated using moderately low pressures. The results indicate that quantification of the transformed phase of chlorpropamide without corrections for solid fraction and thickness, underestimates the extent of transformation by 2.4%. Although the magnitude of the correction for this particular system of polymorphs is small, more significant values are expected for other compounds, particularly those with sufficient compactibility to allow the formation of low solid fraction calibration samples.
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quantitative determination of polymorphic composition in intact compacts by Parallel Beam x ray powder diffractometry
Journal of Pharmaceutical and Biomedical Analysis, 2002Co-Authors: Simon Bates, Garnet E Peck, Peter L D Wildfong, Kenneth R MorrisAbstract:This paper details the development of a method using Parallel-Beam X-ray powder diffractometry as a novel means of determining polymorphic composition in intact compacts. Two polymorphic systems, chlorpropamide and glycine, were selected. The polymorphic components were weighed, mixed, and compressed using a Carver press with 3/8-in. concave tooling. The compacts were then analyzed using Parallel-Beam X-ray powder diffractometry in transmission geometry. The data were processed using the profile-fitting module in the Shimadzu XRD-6000 software V 4.1 (for NT 4.0/98). The integrated intensity ratio of a selected peak for each crystal form was used for quantitation of each polymorph. Excellent linear correlation was observed for both polymorphic systems. The convex shape of the compact surface had no effect on the XRD patterns. Since Parallel-Beam X-ray diffractometry is not sensitive to the shape of the sample surface, it provides a simple method for quantifying polymorphs in intact compacts. Further work to extend this to formulated tablets is ongoing. The relatively larger variation in one of the peaks in the chlorpropamide study was found to be consistent with the computational analysis of the slip behavior of the stable polymorph. This method provides the first reported non-invasive X-ray diffraction pattern quantitation of crystal forms in intact compacts.
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quantifying amorphous content of lactose using Parallel Beam x ray powder diffraction and whole pattern fitting
Journal of Pharmaceutical and Biomedical Analysis, 2001Co-Authors: Xiaoming Chen, Simon Bates, Kenneth R MorrisAbstract:Abstract The objective of this study was to demonstrate the applicability of Parallel Beam X-ray powder diffraction (XRPD) and a new method for whole pattern fitting to the quantification of the residual amount of amorphous content in a pharmaceutical solid using lactose as a model system. Lactose monohydrate, prepared by slurry conversion of anhydrous lactose, was mixed with different amounts of amorphous lactose produced by lyophilization. X-ray powder diffractograms of each mixture were recorded and analyzed by whole pattern fitting using Percentage Crystallinity Determination Software from Kratos Analytical Inc. The polycapillary X-ray optic, which provides a Parallel Beam of X-radiation, has advantages over Bragg–Brentano Optics with respect to sample height artifacts. Significant shifts in peak position with changes in sample height of lactose monohydrate were observed using Bragg–Brentano Optics while no change was detected for the polycapillary X-ray optic. A technique to normalize all diffractograms to have the same total integrated intensity was necessary to eliminate tube fluctuation effects. After normalization, the amorphous content of lactose in the range of 1–10% was reproducibly predicted (small standard deviation between samplings) using whole pattern fitting. The limit of detection was calculated to be 0.37% amorphous content. The results indicated that Parallel Beam XRPD and whole pattern fitting can provide accurate analysis of relatively small amounts of amorphous content in pharmaceuticals compared to typical XRPD analysis.
Nikola Krstajic - One of the best experts on this subject based on the ideXlab platform.
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characterization of a Parallel Beam ccd optical ct apparatus for 3d radiation dosimetry
Physics in Medicine and Biology, 2007Co-Authors: Nikola Krstajic, Simon J DoranAbstract:3D measurement of optical attenuation is of interest in a variety of fields of biomedical importance, including spectrophotometry, optical projection tomography (OPT) and analysis of 3D radiation dosimeters. Accurate, precise and economical 3D measurements of optical density (OD) are a crucial step in enabling 3D radiation dosimeters to enter wider use in clinics. Polymer gels and Fricke gels, as well as dosimeters not based around gels, have been characterized for 3D dosimetry over the last two decades. A separate problem is the verification of the best readout method. A number of different imaging modalities (magnetic resonance imaging (MRI), optical CT, x-ray CT and ultrasound) have been suggested for the readout of information from 3D dosimeters. To date only MRI and laser-based optical CT have been characterized in detail. This paper describes some initial steps we have taken in establishing charge coupled device (CCD)-based optical CT as a viable alternative to MRI for readout of 3D radiation dosimeters. The main advantage of CCD-based optical CT over traditional laser-based optical CT is a speed increase of at least an order of magnitude, while the simplicity of its architecture would lend itself to cheaper implementation than both MRI and laser-based optical CT if the camera itself were inexpensive enough. Specifically, we study the following aspects of optical metrology, using high quality test targets: (i) calibration and quality of absorbance measurements and the camera requirements for 3D dosimetry; (ii) the modulation transfer function (MTF) of individual projections; (iii) signal-to-noise ratio (SNR) in the projection and reconstruction domains; (iv) distortion in the projection domain, depth-of-field (DOF) and telecentricity. The principal results for our current apparatus are as follows: (i) SNR of optical absorbance in projections is better than 120:1 for uniform phantoms in absorbance range 0.3 to 1.6 (and better than 200:1 for absorbances 1.0 to 3.5 with the test target and a novel absorbance range extension method), (ii) the spatial resolution is shown to be at worst 0.5 mm (and often better than this) with an associated DOF of 8 cm, (iii) the SNR of uniform phantoms in reconstruction domain is above 80:1 (one standard deviation) over an absorbance dynamic range of 0.3 to 1.6, (iv) the apparatus is telecentric and without distortion. Finally, a sample scan and reconstruction of a scan of a PRESAGE™ dosimeter are shown, demonstrating the capabilities of the apparatus. For more information on this article, see medicalphysicsweb.org
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characterization of a Parallel Beam ccd optical ct apparatus for 3d radiation dosimetry
Journal of Physics: Conference Series, 2006Co-Authors: Nikola Krstajic, Simon J DoranAbstract:This paper describes the initial steps we have taken in establishing CCD based optical-CT as a viable alternative for 3-D radiation dosimetry. First, we compare the optical density (OD) measurements from a high quality test target and variable neutral density filter (VNDF). A modulation transfer function (MTF) of individual projections is derived for three positions of the sinusoidal test target within the scanning tank. Our CCD is then characterized in terms of its signal-to-noise ratio (SNR). Finally, a sample reconstruction of a scan of a PRESAGETM (registered trademark of Heuris Pharma, NJ, Skillman, USA.) dosimeter is given, demonstrating the capabilities of the apparatus.
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focusing optics of a Parallel Beam ccd optical tomography apparatus for 3d radiation gel dosimetry
Physics in Medicine and Biology, 2006Co-Authors: Nikola Krstajic, Simon J DoranAbstract:Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow ( approximately 9 min per slice) and poorly suited to measurements that require many slices. Here, we describe a fast, three-dimensional (3D) optical computed tomography (optical-CT) apparatus, based on a broad, collimated Beam, obtained from a high power LED and detected by a charged coupled detector (CCD). The main advantages of such a system are (i) an acquisition speed approximately two orders of magnitude higher than a laser-based system when 3D data are required, and (ii) a greater simplicity of design. This paper advances our previous work by introducing a new design of focusing optics, which take information from a suitably positioned focal plane and project an image onto the CCD. An analysis of the ray optics is presented, which explains the roles of telecentricity, focusing, acceptance angle and depth-of-field (DOF) in the formation of projections. A discussion of the approximation involved in measuring the line integrals required for filtered backprojection reconstruction is given. Experimental results demonstrate (i) the effect on projections of changing the position of the focal plane of the apparatus, (ii) how to measure the acceptance angle of the optics, and (iii) the ability of the new scanner to image both absorbing and scattering gel phantoms. The quality of reconstructed images is very promising and suggests that the new apparatus may be useful in a clinical setting for fast and accurate 3D dosimetry.
Ritabrata Sarkar - One of the best experts on this subject based on the ideXlab platform.
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fresnel zone plate telescopes for x ray imaging i experiments with a quasi Parallel Beam
arXiv: Instrumentation and Methods for Astrophysics, 2009Co-Authors: Sandip K. Chakrabarti, S. Palit, D. Debnath, A. Nandi, Vipin K Yadav, Ritabrata SarkarAbstract:Combination of Fresnel Zone Plates (FZP) can make an excellent telescope for imaging in X-rays. We present here the results of our experiments with several pairs of tungsten made Fresnel Zone plates in presence of an X-ray source kept at a distance of about 45 feet. The quasi-Parallel Beam allowed us to study sources placed on the axis as well as off the axis of the telescope. We present theoretical study of the fringe patterns produced by the zone plates in presence of a quasi-Parallel source. We compare the patterns obtained from experiments with those obtained by our Monte-Carlo simulations. The images are also reconstructed by deconvolution from both the patterns. We compare the performance of such a telescope with other X-ray imaging devices used in space-astronomy.
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Fresnel zone plate telescopes for X-ray imaging I: experiments with a quasi-Parallel Beam
Experimental Astronomy, 2009Co-Authors: Sandip K. Chakrabarti, S. Palit, D. Debnath, A. Nandi, V. Yadav, Ritabrata SarkarAbstract:Combination of Fresnel Zone Plates (FZP) can make an excellent telescope for imaging in X-rays. We present here the results of our experiments with several pairs of tungsten made Fresnel Zone plates in presence of an X-ray source kept at a distance of about 45 ft. The quasi-Parallel Beam allowed us to study sources placed on the axis as well as off the axis of the telescope. We present theoretical study of the fringe patterns produced by the zone plates in presence of a quasi-Parallel source. We compare the patterns obtained from experiments with those obtained by our Monte-Carlo simulations. The images are also reconstructed by deconvolution from both the patterns. We compare the performance of such a telescope with other X-ray imaging devices used in space-astronomy.
