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RISS 인기검색어
- 검색키워드
- 저자 : Haltmeier (검색결과 5 건)
- 무료
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- 유료
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The spherical Radon transform with centers on cylindrical surfaces
Haltmeier, M.,Moon, S. Academic Press 2017 Journal of mathematical analysis and applications Vol.448 No.1
<P>Recovering a function from its spherical Radon transform with centers of spheres of integration restricted to a hypersurface is at the heart of several modern imaging technologies, including SAR, ultrasound imaging, and photo- and thermoacoustic tomography. In this paper we study an inversion of the spherical Radon transform with centers of integration restricted to cylindrical surfaces of the form Gamma x R-m, where r is a hypersurface in R-n. We show that this transform can be decomposed into two lower dimensional spherical Radon transforms, one with centers on r and one with a planar center-set in Rm+1. Together with explicit inversion formulas for the spherical Radon transform with a planar center-set and existing algorithms for inverting the spherical Radon transform with a center-set Gamma, this yields reconstruction procedures for general cylindrical domains. In the special case of spherical or elliptical cylinders we obtain novel explicit inversion formulas. For three spatial dimensions, these inversion formulas can be implemented efficiently by backprojection type algorithms only requiring Omicron(N-4/3) floating point operations, where N is the total number of unknowns to be recovered. We present numerical results demonstrating the efficiency of the derived algorithms. (C) 2016 Elsevier Inc. All rights reserved.</P>
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Inversion of the Attenuated V-Line Transform With Vertices on the Circle
Haltmeier, Markus,Moon, Sunghwan,Schiefeneder, Daniela IEEE 2017 IEEE transactions on computational imaging Vol.3 No.4
<P>The Compton camera is a promising alternative to the Anger camera for imaging gamma radiation, with the potential to significantly increase the sensitivity of SPECT. Two-dimensional Compton camera image reconstruction can be implemented by inversion of the V-line transform, which integrates the emission distribution over V-lines (unions of two half-lines) that have vertices on a surrounding detector array. Inversion of the V-line transform without attenuation has recently been addressed by several authors. However, it is well known from standard SPECT that ignoring attenuation can significantly degrade the quality of the reconstructed image. In this paper, we address this issue and study the attenuated V-line transform accounting for attenuation of photons in SPECT with Compton cameras. Assuming vertices of V-lines on a circle, we derive an analytic inversion approach based on circular harmonics expansion, and show uniqueness of reconstruction for the attenuated V-line transform. We further develop a discrete image reconstruction algorithm based on our analytic studies, and present numerical results that demonstrate the effectiveness of our algorithm.</P>
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Photoacoustic tomography with direction dependent data: an exact series reconstruction approach
Zangerl, Gerhard,Moon, Sunghwan,Haltmeier, Markus Institute of Physics 2019 Inverse problems Vol.35 No.11
<P>Photoacoustic image reconstruction often assumes that the restriction of the acoustic pressure on the detection surface is given. However, commonly used detectors often have a certain directivity and frequency dependence, in which case the measured data are more accurately described as a linear combination of the acoustic pressure and its normal derivative on the detection surface. In this paper, we consider the inverse source problem for data that are a combination of the acoustic pressure and its normal derivative. For the special case of a spherical detection geometry we derive exact frequency domain reconstruction formulas. We present numerical results showing the robustness and validity of the derived formulas. Moreover, we compare several different combinations of the pressure and its normal derivative showing that used measurement model significantly affects the recovered initial pressure.</P>
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Kim, Hekap,Patricia Haltmeier,Judith B. Klotz,Clifford P. Weisel 江原大學校 附設 環境硏究所 1999 環境硏究 Vol.16 No.-
A study wss conducted to determine if DCAA and TCAA urinary excretion rates are valid biomarkers of chronic ingestion exposure to these disinfection by-products of chlorination of drinking water. Entire first morning urine voids, time-of-visit urine samples, and tap water samples were collected from 47 female subjects. In addition, a 48-h recall questionnaire was administered to determine the amounts and types of liquids ingested by each subject as well as other exposures that could lead to DCAA and TCAA urinary excretion. The TCAA excretion rate for the first morning urine samples was significantly correlated with estimated 48-h TCAA ingestion exposure for 25 subjects whose ingestion exposures primarily occurred at home, while the DCAA excretion rate was not correlated with the DCAA ingestion exposure. Thus, urinary TCAA appears to be a valid biomarker of chronic ingestion exposure to TCAA from chlorinated water, while urinary DCAA is not. It is proposed that the difference in the biological half-lives between these two compounds is the rationale for this finding. The bilogical half-life of TCAA is longer than successive exposure intervals; thus TCAA accumulates until it reaches a steady state. The halflife of DCAA is shorter than successive exposure intervalsl; thus DCAA is almost coplectely metabolized following an exposure and is eliminated from the bodly. This study suggests that biological half-life, exposure interval, and sample collection interval should be considered in selecting biomarkers and designing studies to validate them.
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