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[EN] In this contribution, large SiPM arrays (8 x 8 elements of 6 x 6 mm(2) each) are processed with an ASIC-based readout and coupled to a monolithic LYSO crystal to explore their potential use for TOF-PET applications. The aim of this work is to study the integration of this technology in the development of clinical PET systems reaching sub-300 ps coincidence resolving time (CRT). The SiPM and readout electronics have been evaluated first, using a small size 1.6 mm (6 mm height) crystal array (32 x 32 elements). All pixels were well resolved and they exhibited an energy resolution of about 20% (using Time-over-Threshold methods) for the 511 keV photons. Several parameters have been scanned to achieve the optimum readout system performance, obtaining a CRT as good as 330 +/- 5 ps FWHM. When using a black-painted monolithic block, the spatial resolution was measured to be on average 2.6 +/- 0.5 mm, without correcting for the source size. Energy resolution appears to be slightly above 20%. CRT measurements with the monolithic crystal detector were also carried out. Preliminary results as well as calibration methods specifically designed to improve timing performance, are being analyzed in the present manuscript.

[EN] In this contribution, large SiPM arrays (8 x 8 elements of 6 x 6 mm(2) each) are processed with an ASIC-based readout and coupled to a monolithic LYSO crystal to explore their potential use for TOF-PET applications. The aim of this work is to study the integration of this technology in the development of clinical PET systems reaching sub-300 ps coincidence resolving time (CRT). The SiPM and readout electronics have been evaluated first, using a small size 1.6 mm (6 mm height) crystal array (32 x 32 elements). All pixels were well resolved and they exhibited an energy resolution of about 20% (using Time-over-Threshold methods) for the 511 keV photons. Several parameters have been scanned to achieve the optimum readout system performance, obtaining a CRT as good as 330 +/- 5 ps FWHM. When using a black-painted monolithic block, the spatial resolution was measured to be on average 2.6 +/- 0.5 mm, without correcting for the source size. Energy resolution appears to be slightly above 20%. CRT measurements with the monolithic crystal detector were also carried out. Preliminary results as well as calibration methods specifically designed to improve timing performance, are being analyzed in the present manuscript.

We consider the generalized Radon transform (defined in terms of smooth weight functions) on hyperplanes in Rn. We analyze general filtered backprojection type reconstruction methods for limited data with filters given by general pseudodifferential operators. We provide microlocal characterizations of visible and added singularities in Rn and define modified versions of reconstruction operators that do not generate added artifacts. We calculate the symbol of our general reconstruction operators as pseudodifferential operators and provide conditions for the filters under which the reconstruction operators are elliptic for the visible singularities. If the filters are chosen according to those conditions, we show that almost all visible singularities can be recovered reliably. Our work generalizes the results for the classical line transforms in R2 and the classical reconstruction operators (that use specific filters). In our proofs, we employ a general paradigm that is based on the calculus of Fourier integral operators. Since this technique does not rely on explicit expressions of the reconstruction operators, it enables us to analyze more general imaging situations.

Filtered back-projection and weighted back-projection have long been the methods of choice within the electron microscopy com- munity for reconstructing the structure of macromolecular assem- blies from electron tomography data. Here, we describe electron lambda-tomography, a reconstruction method that enjoys the ben- efits of the above mentioned methods, namely speed and ease of implementation, but also addresses some of their shortcomings. In particular, compared to these standard methods, electron lambda- tomography is less sensitive to artifacts that come from structures outside the region that is being reconstructed, and it can sharpen boundaries., QC 20120131

In limited data tomography, with applications such as electron microscopy and medical imaging, the scanning views are within an angular range that is often both limited and sparsely sampled. In these situations, standard algorithms produce reconstructions with notorious artifacts. We show in this paper that a sparsity image representation principle, based on learning dictionaries for sparse representations of image patches, leads to significantly improved reconstructions of the unknown density from its limited angle projections. The presentation of the underlying framework is complemented with illustrative results on artificial and real data., Sponsored in part by the Office of Naval Research, the Defense Advanced Research Projects Agency and the Army Research Office.

We present a componentwise iterated relative entropy regularization method (COMET) where the prior and regularization parameter could be updated in the iterates. Such a reconstruction method could be useful for multicomponent inverse problems, such as the one occurring in electron tomography. The paper also contains a brief introduction to regularization theory with emphasis on variational based regularization methods, and we rigorously prove that the tolerance-based entropy reconstruction method that occurs in the COMET iterates is a regularization method. We conclude by showing examples of COMET applied to electron tomography data., QC 20120207

We present a new local tomographic algorithm applicable to electron microscopy tomography. Our algorithm applies to the standard data acquisition method, single-axis tilting, as well as for more arbitrary acquisition methods. Using microlocal analysis we put the reconstructions in a mathematical context, explaining which singularities are stably visible from the limited data given by the data collection protocol in the electron microscope., QC 20120131

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.