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124 results on '"Hasegawa B"'

2. Evaluation of a EMCCD detector for emission-transmission computed tomography

Author

Teo, B K, Shestakova, I, Sun, M, Barber, W C, Nagarkar, V V, and Hasegawa, B H

Subjects
charge coupled device, single photon emission computed tomography, X-ray tomography
Abstract

A prototype electron multiplying charged coupled device (EMCCD) based gamma camera is evaluated for emission-transmission computed tomography. The detector has an 8.2 x 8.2 mm(2) active sensor area with a 512 X 512 pixel array, and can be operated with a 3:1 fiber optic taper to expand the effective imaging area to approximately 25 x 25 mm(2) for small animal studies. We demonstrate the possibility of operating the camera in either charge integrating or single photon counting mode for pinhole SPECT with I-125 and Tc-99m sources. In photon counting mode, we show that energy discrimination can be used to distinguish between these two sources for dual isotope imaging. X-ray CT images of phantoms are taken without a collimator to evaluate the quality of the camera for transmission imaging.

Published
2006

3. Investigation of a continuous crystal PSAPD-based gamma camera

Author

Després, P, Barber, W C, Funk, T, McClish, M, Shah, K S, and Hasegawa, B H

Subjects
avalanche photodiodes, biomedical nuclear imaging, position sensitive particle detectors, scintillation detectors
Abstract

Position-sensitive avalanche photodiodes; (PSAPDs) have recently been proposed as optical light detectors in scintillation based gamma cameras. They are compact solid-state devices that provide high quantum efficiency and gain, and they can achieve precise positioning over relatively large surfaces with few readout channels. In previous studies, PSAPDs were coupled to scintillator arrays and the imaging task consisted in identifying the crystal of interaction. In this paper, we investigate the possibility of using a PSAPD to read the light of a single continuous crystal. Such a configuration has the potential to reduce the cost and simplify the construction of a PSAPD-based gamma camera while maintaining good overall performance. The spatial resolution of a small imaging unit having a continuous scintillator coupled to an 8 x 8 mm(2) PSAPD was evaluated at different energies for CsI:TI and LaBr3:Ce crystals. After correcting the images for the distortion and the minification associated with this camera, spatial resolution values of 0.62, 0.72, 0.99, and 1.25 mm (FWHM) were obtained for Tc-99m (140 keV), Co-57 (122 keV), Am-241 (60 keV), and 1251 (30 keV) respectively for an 8 x 8 x 1 mm(3) CsI:TI crystal. Corresponding values of 0.55, 0.64, 0.92 and 1.10 mm (FWHM) were obtained from a 1 mm thick LaBr3:Ce crystal. These results, reproduced by Monte Carlo simulations, suggest that the continuous crystal configuration is an attractive approach to develop a PSAPD-based high-resolution gamma camera and is especially well suited for a small-animal imaging system.

Published
2006

8. High-resolution X-ray imaging using a silicon strip detector

Author

Beuville, E., Cahn, R., Cederstrom, B., Danielsson, M., Hall, A., Hasegawa, B., Luo, L., Lundqvist, M., Nygren, D., Oltman, E., and Walton, J.

Subjects
Imaging systems -- Research, X-rays -- Research, Business, Electronics, Electronics and electrical industries
Abstract

We are presenting the first images and an initial evaluation of a scanned-slot X-ray imaging system based on edge-on silicon strip detectors and high-speed low-noise parallel processing ASICs. We have demonstrated noiseless single photon counting above a minimal threshold of 7.2 keV. Edge scans show negligible cross talk between different channels in the ASIC. The Modulation Transfer Function (MTF) has been measured and found to agree with the ideal MTF for 100 [[micro]meter] pixel size. The first images are obtained at very low exposures and show the high performance of the system. We also present a way of enhancing the X-ray flux to a slot by using a refractive X-ray lens. We believe this focusing device will significantly enhance the potential for scanned-slot X-ray imaging.

Published
1998

9. Medical Imaging

Author

Degrado, T, primary, Zagzebski, J, additional, Hasegawa, B, additional, Frayne, R, additional, Hames, S, additional, and Dobbins, J, additional

Published
1999
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10. Gamma-Ray Focusing Optics for Small Animal Imaging

Author

Pivovaroff, M. J, Barber, W. C, Craig, W. W, Hasegawa, B. H, Ramsey, B. D, and Taylor, C

Subjects
Optics
Abstract

There is a well-established need for high-resolution radionuclide imaging techniques that provide non-invasive measurement of physiological function in small animals. We, therefore, have begun developing a small animal radionuclide imaging system using grazing incidence mirrors to focus low-energy gamma-rays emitted by I-125, and other radionuclides. Our initial prototype optic, fabricated from thermally-formed glass, demonstrated a resolution of 1500 microns, consistent with the performance predicted by detailed simulations. More recently, we have begun constructing mirrors using a replication technique that reduces low spatial frequency errors in the mirror surface, greatly improving the resolution. Each technique offers particular advantages: e.g., multilayer coatings are easily deposited on glass, while superior resolution is possible with replicated optics. Scaling the results from our prototype optics, which only have a few nested shells, to system where the lens has a full complement of several tens of nested shells, a sensitivity of approx. 1 cps/micro Ci is possible, with the exact number dependent on system magnification and radionuclide species. (Higher levels of efficiency can be obtained with multi-optic imaging systems.) The gamma-ray lens will achieve a resolution as good as 100 microns, independent of the final sensitivity. The combination of high spatial resolution and modest sensitivity will enable in vivo single photon emission imaging studies in small animals.

Published
2004

11. Description of a prototype emission-transmission computed tomography imaging system

Author

Lang, T. F, Hasegawa, B. H, Liew, S. C, Brown, J. K, Blankespoor, S. C, Reilly, S. M, Gingold, E. L, and Cann, C. E

Subjects
Life Sciences (General)
Abstract

We have developed a prototype imaging system that can perform simultaneous x-ray transmission CT and SPECT phantom studies. This system employs a 23-element high-purity-germanium detector array. The detector array is coupled to a collimator with septa angled toward the focal spot of an x-ray tube. During image acquisition, the x-ray fan beam and the detector array move synchronously along an arc pivoted at the x-ray source. Multiple projections are obtained by rotating the object, which is mounted at the center of rotation of the system. The detector array and electronics can count up to 10(6) cps/element with sufficient energy-resolution to discriminate between x-rays at 100-120 kVp and gamma rays from 99mTc. We have used this device to acquire x-ray CT and SPECT images of a three-dimensional Hoffman brain phantom. The emission and transmission images may be superimposed in order to localize the emission image on the transmission map.

Published
1992

18. Determination of the attenuation map in emission tomography

Author

Habib Zaidi and Hasegawa, B.

Subjects
Health Physics and Radiation Effects
Abstract

Reliable attenuation correction methods for quantitative emission computed tomography (ECT) require accurate delineation of the body contour and often necessitate knowledge of internal anatomical structure. Two broad classes of methods have been used to calculate the attenuation map referred to as "transmissionless" and transmission-based attenuation correction techniques. While calculated attenuation correction belonging to the first class of methods is appropriate for brain studies, more adequate methods must be performed in clinical applications where the attenuation coefficient distribution is not known a priori, and for areas of inhomogeneous attenuation such as the chest. Measured attenuation correction overcomes this problem and utilizes different approaches to determine this map including transmission scanning, segmented magnetic resonance images or appropriately scaled X-ray CT scans acquired either independently on separate or simultaneously on multimodality imaging systems. Combination of data acquired from different imagers suffers from the usual problems of working with multimodality images, namely, accurate coregistration from the different modalities and assignment of attenuation coefficients. A current trend in ECT is to employ transmission scanning to reconstruct the attenuation map. Combined ECT/CT imaging is an interesting approach; however, it considerably complicates both the scanner design and the data acquisition and processing protocols. Moreover, the cost of such systems may be prohibitive for small nuclear medicine departments. A dramatic simplification could be made if the attenuation map could be obtained directly from the emission projections, without the use of a transmission scan. This is being investigated either using a statistical model of emission data or by applying the consistency conditions that allow to identify the operator of the problem and, thus, to reconstruct the attenuation map. This paper presents the physical and methodological basis of attenuation correction and summarizes recent developments in algorithms used to compute the attenuation map in ECT. Other potential applications are also discussed.

Published
2002

19. Evaluation of a photon-counting X-ray imaging system

Author

Lundqvist, M., Cederström, Björn, Chmill, V., Danielsson, Mats, Hasegawa, B., Lundqvist, M., Cederström, Björn, Chmill, V., Danielsson, Mats, and Hasegawa, B.

Abstract

A digital imaging system has been developed for mammography using silicon strip detectors operated in a pulse-counting mode and configured in a scanned slit geometry. More than 90% of the photons are absorbed in the sensor. The scatter rejection is very efficient and the image formation is nearly optimal since each X ray is processed individually. The result is a very dose-efficient system. In this paper, we present measurements that verify that the performance of the readout electronics is sufficient to count photons at high rates with high quantum efficiency and a charge collection efficiency that does not limit the dose efficiency. The spatial resolution of the system was measured to provide a modulation transfer function of approximately 0.5 at a spatial frequency of 10 lp/mm. Images of a mammography phantom were recorded experimentally to test overall system performance., QC 20100525

Published
2001
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33. Technical exhibits.

Author

McCollough, C H, primary, Cunningham, I A, additional, Hangiandreou, N J, additional, Hasegawa, B H, additional, Huda, W, additional, Kofler, J M, additional, Korosec, F R, additional, Morin, R L, additional, Peppler, W W, additional, and Schueler, B A, additional

Published
1996
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36. Technical exhibits.

Author

McCollough, C H, primary, Cunningham, I A, additional, Felmlee, J P, additional, Hangiandreou, N J, additional, Hasegawa, B H, additional, Kofler, J M, additional, Peppler, W W, additional, and Thomadsen, B R, additional

Published
1994
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43. Effect of acyclovir on bronchoconstriction and urinary leukotriene E"4 excretion in aspirin-induced asthma

Author

Yoshida, S., Sakamoto, H., Yamawaki, Y., Shoji, T., Akahori, K., Onuma, K., Nakagawa, H., Hasegawa ^b, H., and Amayasu, H.

Abstract

Background: Acyclovir (9-[2-hydroxyethoxymethyl] guanine), an inhibitor of the DNA polymerase of the herpes virus, has been reported to exhibit pharmacologic activity other than antiviral activity, including antiasthmatic effects. Objective: This study was designed to investigate the protective effect of acyclovir on airway responsiveness to the sulpyrine provocation test and to investigate whether this protective activity is associated with a reduction in aspirin-induced excretion of urinary leukotriene E"4 (u-LTE"4 ), a marker of cysteinyl leukotriene (LT) overproduction that participates in the pathogenesis of aspirin-induced asthma. Methods: We assessed the effects of pretreatment with acyclovir on bronchoconstriction precipitated by inhalation of sulpyrine in 16 adult patients with mild or moderate aspirin-induced asthma; those who were in stable clinical condition and were hyperresponsive to the sulpyrine provocation test were allocated to this study. A double-blind, randomized, cross-over design was used. u-LTE"4 was measured by a combined reverse-phase HPLC enzyme immunoassay. Results: Acyclovir protects against aspirin-induced attacks of asthma through mechanisms unrelated to its bronchodilator property but related to the improvement of bronchial hypersensitivity to sulpyrine; protection was nearly complete in all patients (P < .0001). By contrast, after acyclovir, the maximum level of u-LTE"4 in patients was significantly lower than that in control subjects (P < .01). Conclusion: Our results suggest that acyclovir is not only an antiviral drug but also an inhibitor of analgesic-induced bronchoconstriction, probably acting by inhibiting the release of cysteinyl LTs. (J Allergy Clin Immunol 1998;102:909-14.)

Published
1998
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