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Dominguez J.B.,Université de Sherbrooke | Berube-Lauziere Y.,Université de Sherbrooke | Berube-Lauziere Y.,Center Dimagerie Moleculaire Of Sherbrooke Cims
Applied Optics | Year: 2011

We noticed a few errors in the mathematical notations in the text. In addition, an exponent was missing in the denominator of the definition of the Henyey-Greenstein phase function. Besides, the normalization factor of the phase function was presented for the three-dimensional case only.We present the correct expression in this erratum for the two- and three-dimensional cases. These corrections do not alter the results nor the conclusions of the paper. © 2011 Optical Society of America.


Ait-Mohand S.,Université de Sherbrooke | Denis C.,Université de Sherbrooke | Tremblay G.,Université de Sherbrooke | Paquette M.,Université de Sherbrooke | And 2 more authors.
Organic Letters | Year: 2014

Convenient approaches for the synthesis of DOTHA2 and NOTHA2, two cyclic bifunctional chelates (BFCs) bearing hydroxamate arms, have been developed. These novel BFCs coordinate 64Cu with fast kinetics at room temperature in a wide range of concentrations and pH. The corresponding radiochemical complexes showed high stability, low residual activity in various tissues, and fast clearance in normal mice. The ability to conjugate DOTHA2 to both a small peptide and a large protein is also reported. © 2014 American Chemical Society.


Bouza Dominguez J.,Université de Sherbrooke | Berube-Lauziere Y.,Center Dimagerie Moleculaire Of Sherbrooke Cims
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2013

In this work, synthetic time-domain data are generated as if it were collected with a state-of-the-art multi-view experimental optical scanner developed in our group for small animal imaging, and used in a tomographic image reconstruction algorithm. The collected data comprises full time-dependent optical signals leaving the biological medium and acquired all around the medium. The diffuse optical tomography (DOT) algorithm relies on the time dependent parabolic simplified spherical harmonics (TD-pSPN) equations as the forward model to recover the 3D absorption and diffusion coefficient maps of the medium. The inverse problem is casted and solved as an iterative constrained optimization problem where an objective function determines the accuracy of the forward model predictions at each iteration. Time-dependent adjoint variables are introduced to accelerate the calculation of the gradient of the objective function. A three-dimensional case involving an absorption heterogeneity in a homogeneous medium is presented, reproducing practical situations encountered in our lab. The results support our hypothesis that accurate quantitative 3D maps of optical properties of biological tissues can be retrieved using intrinsic measurements obtained with our experimental scanner along with our DOT algorithm. © 2013 Copyright SPIE.


Renauld E.,Université de Sherbrooke | Descoteaux M.,Université de Sherbrooke | Descoteaux M.,Center Dimagerie Moleculaire Of Sherbrooke Cims | Bernier M.,Université de Sherbrooke | And 3 more authors.
PLoS ONE | Year: 2016

At rest, healthy human brain activity is characterized by large electroencephalography (EEG) fluctuations in the 8-13 Hz range, commonly referred to as the alpha band. Although it is well known that EEG alpha activity varies across individuals, few studies have investigated how this may be related to underlying morphological variations in brain structure. Specifically, it is generally believed that the lateral geniculate nucleus (LGN) and its efferent fibres (optic radiation, OR) play a key role in alpha activity, yet it is unclear whether their shape or size variations contribute to its inter-subject variability. Given the widespread use of EEG alpha in basic and clinical research, addressing this is important, though difficult given the problems associated with reliably segmenting the LGN and OR. For this, we employed a multi-modal approach and combined diffusion magnetic resonance imaging (dMRI), functional magnetic resonance imaging (fMRI) and EEG in 20 healthy subjects to measure structure and function, respectively. For the former, we developed a new, semi-automated approach for segmenting the OR and LGN, from which we extracted several structural metrics such as volume, position and diffusivity. Although these measures corresponded well with known morphology based on previous post-mortem studies, we nonetheless found that their inter-subject variability was not significantly correlated to alpha power or peak frequency (p >0.05). Our results therefore suggest that alpha variability may be mediated by an alternative structural source and our proposed methodology may in general help in better understanding the influence of anatomy on function such as measured by EEG or fMRI. © 2016 Renauld et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Dominguez J.B.,Université de Sherbrooke | Berube-Lauziere Y.,Université de Sherbrooke | Berube-Lauziere Y.,Center Dimagerie Moleculaire Of Sherbrooke Cims
Biomedical Optics Express | Year: 2011

An exponent was missing in the denominator of the definition of the Henyey-Greenstein phase function. Besides, the normalization constant of the phase function was presented for the three dimensional case only. We give the correct expression in this erratum for the two- and three-dimensional cases. In addition, we correct for a forgotten scalar product operator in Eq. (15). Those corrections do not alter the results or the conclusions of the paper. © 2011 Optical Society of America.


Dominguezl J.B.,Université de Sherbrooke | Berube-Lauziere Y.,Université de Sherbrooke | Berube-Lauziere Y.,Center Dimagerie Moleculaire Of Sherbrooke Cims
Biomedical Optics Express | Year: 2011

We introduce a system of coupled time-dependent parabolic simplified spherical harmonic equations to model the propagation of both excitation and fluorescence light in biological tissues. We resort to a finite element approach to obtain the time-dependent profile of the excitation and the fluorescence light fields in the medium. We present results for cases involving two geometries in three-dimensions: a homogeneous cylinder with an embedded fluorescent inclusion and a realistically-shaped rodent with an embedded inclusion alike an organ filled with a fluorescent probe. For the cylindrical geometry, we show the differences in the time-dependent fluorescence response for a point-like, a spherical, and a spherically Gaussian distributed fluorescent inclusion. From our results, we conclude that the model is able to describe the time-dependent excitation and fluorescent light transfer in small geometries with high absorption coefficients and in nondiffusive domains, as may be found in small animal diffuse optical tomography (DOT) and fluorescence DOT imaging. © 2011 Optical Society of America.


Presseau C.,Université de Sherbrooke | Presseau C.,Center Dimagerie Moleculaire Of Sherbrooke Cims | Jodoin P.-M.,Université de Sherbrooke | Jodoin P.-M.,Center Dimagerie Moleculaire Of Sherbrooke Cims | And 4 more authors.
NeuroImage | Year: 2015

A single diffusion MRI streamline fiber tracking dataset may contain hundreds of thousands, and often millions of streamlines and can take up to several gigabytes of memory. This amount of data is not only heavy to compute, but also difficult to visualize and hard to store on disk (especially when dealing with a collection of brains). These problems call for a fiber-specific compression format that simplifies its manipulation. As of today, no fiber compression format has yet been adopted and the need for it is now becoming an issue for future connectomics research. In this work, we propose a new compression format,zfib, for streamline tractography datasets reconstructed from diffusion magnetic resonance imaging (dMRI). Tracts contain a large amount of redundant information and are relatively smooth. Hence, they are highly compressible. The proposed method is a processing pipeline containing a linearization, a quantization and an encoding step. Our pipeline is tested and validated under a wide range of DTI and HARDI tractography configurations (step size, streamline number, deterministic and probabilistic tracking) and compression options. Similar to JPEG, the user has one parameter to select: a worst-case maximum tolerance error in millimeter (mm). Overall, we find a compression factor of more than 96% for a maximum error of 0.1. mm without any perceptual change or change of diffusion statistics (mean fractional anisotropy and mean diffusivity) along bundles. This opens new opportunities for connectomics and tractometry applications. © 2015 Elsevier Inc.


Dominguez J.B.,Université de Sherbrooke | Berube-Lauziere Y.,Université de Sherbrooke | Berube-Lauziere Y.,Center Dimagerie Moleculaire Of Sherbrooke Cims
Journal of Biomedical Optics | Year: 2012

We investigate the problem of retrieving the optical properties (absorption and scattering) of biological tissue from a set of optical measurements. A diffuse optical tomography (DOT) algorithm that incorporates constrained optimization methods is implemented. To improve image quality, the DOT algorithm exploits full timedomain data. The time-dependent parabolic simplified spherical harmonics equations (TD-pSPN) are used as the forward model. Time-dependent adjoint variables are resorted to in the calculation of the gradient of the objective function. Several numerical experiments for small geometric media with embedded inclusions that mimic small animal imaging are performed. In the experiments, optical coefficient values are varied in the range of realistic values for the near-infrared spectrum, including high absorption values. Single and multiparameter reconstructions are performed with the diffusion equation and higher orders of the TD-pSPN equations. The results suggest the DOT algorithm based on the TD-pSPN model outperforms the DE, and accurately reconstructs optical parameter distributions of biological media both spatially and quantitatively. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE).

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