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The IBIS telescope onboard INTEGRAL, the ESA gamma-ray space mission to be launched in 2002, is a soft gamma-ray (20 keV - 10 MeV) device based on a coded aperture imaging system. We describe here basic concepts of coded masks, the imaging system of the IBIS telescope, and the standard data analysis procedures to reconstruct sky images. This analys...
Context in source publication
Context 1
... IBIS coded mask imaging system is composed by a replicated Modified URA (MURA) mask of tungsten elements ( Fig. 2) and 2 pixellated detector planes of the same size, ISGRI for the low energy band (20-1000 keV) and PICSIT for the higher band (150 keV - 10 MeV) disposed about 10 cm below (Ubertini et al. 1998). The MURA (Gottesman & Fenimore 1989) are nearly-optimum masks and previous discussion for such system is valid for the IBIS telescope. The detector planes can be divided in a regular grid of square pixels where each detector element occupies a pixel of the array. Essential imaging characteristics and performances are reported in Table 1, including value of efficiency for fitting procedure and ...
Similar publications
IBIS is the imaging telescope onboard the ESA satellite INTEGRAL. IBIS will produce images of the gamma-ray sky in the region between 15 keV and 10 MeV by means of a position sensitive detection plane coupled with a coded aperture mask. The detection plane comprises two position sensitive layers: ISGRI and PICsIT. PICsIT is a 64 X 64 unit array of...
Citations
... Coded aperture imaging (CAI) is an imaging technique originally developed for and commonly used in the fields of x-ray and gamma-ray astronomy. [20][21][22] Coded apertures are a physical collection (mask) of pinholes (collimators), arranged in a specific pattern which when placed in front of a detector, collectively embed directional information of point sources. For example, a single point source will produce a shadow of the mask pattern on the detector. ...
Purpose
Real‐time visualization of target motion using fiducial markers during radiation therapy treatment will allow for more accurate dose delivery. The purpose of this study was to optimize techniques for online fiducial marker tracking by detecting the scattered treatment beam through coded aperture imaging (CAI). Coded aperture imaging is a novel imaging technique that can allow target tracking in real time during treatment, and do so without adding any additional radiation dose, by making use of the scattered treatment beam radiation.
Methods
Radiotherapy beams of various energies, incident on phantoms containing gold fiducial markers were modeled using MCNP6.2 Monte Carlo transport code. Orthogonal scatter radiographs were collected through a CAI geometry. After decoding the simulated radiograph data, the centroid location and FWHM/SNR of the fiducial signals were analyzed. The effects of properties related to the CA (rank, pattern, and physical dimensions), detector (dimensions and pixel count), position (CA and phantom), and the incident beam (spectrum and direction) were investigated. These variables were evaluated by quantifying the positional accuracy, resolution, and SNR of the fiducials' signal. The effects of phantom scatter and decoding artifacts were reduced via Fourier filtering to avoid treatment interruption and physical interaction with the coded mask.
Results
The method was able to accurately localize the markers to within 1 pixel of a simulated radiograph. A 10 × 10 × 2 cm tungsten mask was chosen to attenuate >99 % of incident scatter through opaque elements, while minimizing collimation artifacts which arise from vignetting of the coded radiograph. Clear separation of centroids from fiducial signals with 2.5 mm separation was maintained, and initial optimization of parameters has produced an aperture which decodes the location of multiple fiducial markers inside a human phantom properly with a high SNR in the final radiograph image.
Conclusion
Current results show a proof of concept for a novel real‐time imaging method. Coded aperture imaging is a promising technique for extracting the fiducial scatter signal from a broader Compton‐scatter background. These results can be used to further optimize the CAI parameter space and guide fabrication and testing of a clinical device.
... To overcome this, the background shape is first modeled by fitting a 2D 2 nd degree polynomial function to the shadowgram. The sky reconstruction is performed on the background corrected count and variance shadowgrams, using a FFT-based balanced mask pattern deconvolution [6], which produces sky images in counts, variance and SNR (Fig. 4). Those sky images are put into a sky image history (Fig. 5), which constructs subsequent sky images on 7 time-scales ranging from 20.48 s to 1310.72 s (about 20 min), by summation of the count and variance sky images obtained at previous time-scale. ...
The on-board Scientific Trigger Unit (UTS) is designed to detect Gamma Ray
Bursts (GRBs) in real-time, using the data produced by the ECLAIRs camera,
foreseen to equip the future French-Chinese satellite mission SVOM (Space-based
Variable Objects Monitor). The UTS produces GRB alerts, sent to the ground for
GRB follow-up observations, and requests the spacecraft slew to repoint its
narrow field instruments onto the GRB afterglow. Because of the diversity of
GRBs in duration and variability, two simultaneously running GRB trigger
algorithms are implemented in the UTS, the so called Image Trigger performing
systematic sky image reconstruction on time scales above 20 s, and the
Count-Rate Trigger, selecting a time scale from 10 ms to 20 s showing an excess
in count-rate over background estimate, prior to imaging the excess for
localization on the sky. This paper describes both trigger algorithms and their
implementation in a library, compiled for the Scientific Software Model (SSM)
running on standard Linux machines, and which can also be cross-compiled for
the Data Processing Model (DPM), in order to have the same algorithms running
on both platforms. While the DPM permits to validate the hardware concept and
benchmark the algorithms (see paper II), the SSM allows to optimize the
algorithms and estimate the GRB trigger-rate of ECLAIRs/UTS. The result of
running on the SSM a dynamic photon by photon simulation based on the BATSE GRB
catalog is presented.
Astronomy in the ultraviolet, X-ray, and gamma-ray parts of the spectrum can only be carried out from above the Earth’s atmosphere using satellites or rockets. In the UV and X-ray regimes we again come across the CCD, but other important electronic imaging technologies are also used for reasons that will be explained. High-energy photons with extremely small (sub-atomic) wavelengths require different kinds of detectors, and even the telescope design must change. Within the scope of this text, we can only illustrate some of the most important innovations and advances that have made imaging possible in these exciting fields.
Fast decoding algorithms are described for a number of established coded aperture systems. The fast decoding algorithms for all these systems offer significant reductions in the number of calculations required when reconstructing images formed by a coded aperture system and hence require less computation time to produce the images. The algorithms may therefore be of use in applications that require fast image reconstruction, such as near real-time nuclear medicine and location of hazardous radioactive spillage. Experimental tests confirm the efficacy of the fast decoding techniques.
