Modulation patterns of astronomical imaging systems based on rotating grids

Dadurkevičius, Virginijus; Ralys, D. A.

doi:10.1007/bf00650959

Cited by 8 publications

(6 citation statements)

References 8 publications

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“…The ideal modulation function I m (θ ) means the probability of detecting counts from a point source located at position m, when the collimator is at angle θ 5,6) :…”

Section: Principle Of Image Reconstructionmentioning

confidence: 99%

Gamma-ray Imaging System with a Rotation Collimator

Kim

2011

Progress in Nuclear Science and Technology

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The performance of a gamma-ray imaging system consisting of a gridded collimator and coaxial NaI(Tl) detector was investigated. A gamma-ray imaging system with rotation collimators does not require a position-sensitive detector so as to find the location of gamma-ray sources and therefore this feature allows for significant amount of flexibility not only detector selection but also the geometry of the system. A reconstructed image from the 137 Cs gamma-ray source have been obtained by using the simple flat-fielded back-projection algorithm. The background events are jumbled together in the correct modulation-patterns. Therefore a possibility may be caused by those events that the image is reconstructed at random on the image plane. The theoretical image resolution for the current proof-of-principle gamma-ray imager is ∼ 1 o with a FOV ∼ 53.6 o . The image resolution with FWHM shows about 11.2 o . Therefore our gamma-ray imaging system is required the more collimators, because the reconstructed image was significantly affected by the modulation patterns. Future research will be to focus on the improvement of the image resolution with two or more collimators.

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“…The ideal modulation function I m (θ ) means the probability of detecting counts from a point source located at position m, when the collimator is at angle θ 5,6) :…”

Section: Principle Of Image Reconstructionmentioning

confidence: 99%

Gamma-ray Imaging System with a Rotation Collimator

Kim

2011

Progress in Nuclear Science and Technology

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“…Sensitivity may be increased by utilizing a single mask design, which increases the transmission to 50%. A rotating modulator (RM) (Durouchoux et al 1983;Dadurkevicius & Ralys 1985) is one such instrument developed to image hard x-ray and gamma-ray photons (tens of keV to MeV). As we have shown previously (Budden et al 2010b), the RM may have some significant sensitivity advantages over the commonly-used coded aperture, particularly at high energies.…”

Section: Figmentioning

confidence: 99%

“…Brute force Monte Carlo simulations are able to accomplish these tasks, but the computation is time-consuming. Durouchoux et al (1983) and Dadurkevicius & Ralys (1985) have presented a standard characteristic profile that can be calculated analytically, as described in Sec. 2.…”

Section: Figmentioning

confidence: 99%

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Characteristic count rate profiles for a rotating modulator gamma-ray imager

Budden

Case

et al. 2011

Astrophys Space Sci

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Rotating modulation is a technique for indirect imaging in the hard x-ray and soft gamma-ray energy bands, which may offer an advantage over coded aperture imaging at high energies. A rotating modulator (RM) consists of a single mask of co-planar parallel slats typically spaced equidistance apart, suspended above an array of circular non-imaging detectors. The mask rotates, temporally modulating the transmitted image of the object scene. The measured count rate profiles of each detector are folded modulo the mask rotational period, and the object scene is reconstructed using pre-determined characteristic modulation profiles. The use of Monte Carlo simulation to derive the characteristic count rate profiles is accurate but computationally expensive; an analytic approach is preferred for its speed of computation. We present both the standard and a new advanced characteristic formula describing the modulation pattern of the RM; the latter is a more robust description of the instrument response developed as part of the design of a wide-field highresolution telescope for gamma-ray astronomy. We examine an approximation to the advanced formula to simplify reconstruction software and increase computational speed, and comment on both the inherent limitations and usefulness of the approach. Finally, we show comparisons to the standard formula and demonstrate image reconstructions from Monte Carlo simulations.

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“…A Rotational Modulator (Fig. 1, right) [6,7] is another temporal modulation imager, but consists of only a single grid of opaque slats suspended above a small array of detectors. For a large-area gamma-ray detector, where the grid must be thick and correspondingly massive, the use of one rather than two grids can potentially be a significant advantage.…”

Section: Introductionmentioning

confidence: 99%

Image reconstruction with a LaBr3-based rotational modulator

Budden

Case

Cherry

2011

Nuclear Instruments and Methods in Physics Research Section A:

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A rotational modulator (RM) gamma-ray imager is capable of obtaining significantly better angular resolution than the fundamental geometric resolution defined by the ratio of detector diameter to mask-detector separation. An RM imager consisting of a single grid of absorbing slats rotating ahead of an array of a small number of position-insensitive detectors has the advantage of fewer detector elements (i.e., detector plane pixels) than required by a coded aperture imaging system with comparable angular resolution. The RM therefore offers the possibility of a major reduction in instrument complexity, cost, and power. A novel image reconstruction technique makes it possible to deconvolve the raw images, remove sidelobes, reduce the effects of noise, and provide resolving power a factor of 6 -8 times better than the geometric resolution. A 19-channel prototype RM developed in our laboratory at Louisiana State University features 13.8• full-angle field of view, 1.9• geometric angular resolution, and the capability of resolving sources to within 35 ′ separation. We describe the technique, demonstrate the measured performance of the prototype instrument, and describe the prospects for applying the technique to either a high-sensitivity standoff gamma-ray imaging detector or a satelliteor balloon-borne gamma-ray astronomy telescope.

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Modulation patterns of astronomical imaging systems based on rotating grids

Cited by 8 publications

References 8 publications

Gamma-ray Imaging System with a Rotation Collimator

Gamma-ray Imaging System with a Rotation Collimator

Characteristic count rate profiles for a rotating modulator gamma-ray imager

Image reconstruction with a LaBr3-based rotational modulator

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