Gilles Beaudoin

Montreal Polytechnic, Montréal, Quebec, Canada

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Publications (41)93.74 Total impact

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    ABSTRACT: Magnetic resonance navigation (MRN), achieved with an upgraded MRI scanner, aims to guide new therapeutic magnetic microcarriers (TMMC) from their release in the hepatic vascular network to liver tumor. In this technical note, in vitro and in vivo MRI properties of TMMC, loaded with iron-cobalt nanoparticles and doxorubicin, are reported by following three objectives: (1) to evaluate the lengthening of echo-time (TE) on nano/microparticle imaging; (2) to characterize by MRI TMMC distribution in the liver; and (3) to confirm the feasibility of monitoring particle distribution in real time. Phantom studies were conducted to analyze nano/microparticle signals on T 2*-weighted gradient-echo (GRE) MR images according to sample weight and TE. Twelve animal experiments were used to determine in vivo MRI parameters. TMMC tracking was evaluated by magnetic resonance imaging (MRI) in four rabbits, which underwent MRN in the hepatic artery, three without steering, two in real-time, and three as blank controls. TMMC distribution in the right and left liver lobes, determined by ex vivo MR image analysis, was compared to the one obtained by cobalt level analysis. TMMC induced a hypointense signal that overran the physical size of the sample on MR images. This signal, due to the nanoparticles embedded into the microparticles, increased significantly with echo-time and sample amount (p < 0.05). In vivo, without steering, contrast-to-noise ratio (CNR) values for the right and left lobes were similar. With MRN, the CNR in the targeted lobe was different from that in the untargeted lobe (p = 0.003). Ex vivo, TMMC distribution, based on MRI signal loss volume measurement, was correlated with that quantified by Co level analysis (r = 0.92). TMMC accumulation was tracked in real time with an 8-s GRE sequence. MRI signal loss induced by TMMC can serve to track particle accumulation and to assess MRN efficiency.
    CardioVascular and Interventional Radiology 11/2013; · 2.09 Impact Factor
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    ABSTRACT: Purpose:To evaluate and compare B(1) homogeneity for breast magnetic resonance (MR) imaging performed at 3 T with dual-source radiofrequency (RF) transmission to 1.5-T MR imaging and 3-T MR imaging with quadrature transmission.Materials and Methods:This prospective study received institutional review board approval and patients provided informed consent. Women (n = 25; mean age, 53 years; range, 30-68 years) suspected of having breast lesions underwent breast MR imaging examinations on comparable 1.5-T and 3-T clinical systems between February and May 2012. B(1) maps were obtained at 1.5 T and at 3 T with quadrature and dual-source RF transmission. Intrabreast differences and differences in mean B(1) values between right and left breasts were investigated by using two-sided multivariate analysis of variance with interaction; t tests were used to compare the differences between measured whole-breast mean B(1) values and requested B(1) values.Results:With quadrature transmission at 1.5 T and 3 T, the mean B(1) values showed a statistically significant difference: left-breast measured B(1) was -8.9% of requested B(1) value at 1.5 T and -13.7% at 3 T (P < .001), whereas right-breast measured B(1) was +5.4% of requested B(1) value at 1.5 T (P < .001) and +2.7% at 3 T (P = .01). With dual-source RF transmission at 3 T, mean B(1) values across the breasts were not statistically different, nor were the measured B(1) values compared with requested B(1) values (left breast, -0.6%; right breast, -0.7%). At 3 T with dual-source transmission, slight intrabreast local variations in B(1) were recorded.Conclusion:MR imaging at 3 T with dual-source RF transmission offered an overall B(1) homogeneity for breast imaging that was better than that obtained at 1.5 T and with quadrature transmission.© RSNA, 2013.
    Radiology 02/2013; · 6.34 Impact Factor
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    ABSTRACT: BACKGROUND: The treatment planning of spine pathologies requires information on the rigidity and permeability of the intervertebral discs (IVDs). Magnetic resonance imaging (MRI) offers great potential as a sensitive and non-invasive technique for describing the mechanical properties of IVDs. However, the literature reported small correlation coefficients between mechanical properties and MRI parameters. Our hypothesis is that the compressive modulus and the permeability of the IVD can be predicted by a linear combination of MRI parameters. METHODS: Sixty IVDs were harvested from bovine tails, and randomly separated in four groups (in-situ, digested-6h, digested-18h, digested-24h). Multi-parametric MRI acquisitions were used to quantify the relaxation times T1 and T2, the magnetization transfer ratio MTR, the apparent diffusion coefficient ADC and the fractional anisotropy FA. Unconfined compression, confined compression and direct permeability measurements were performed to quantify the compressive moduli and the hydraulic permeabilities. Differences between groups were evaluated from a one way ANOVA. Multi linear regressions were performed between dependent mechanical properties and independent MRI parameters to verify our hypothesis. A principal component analysis was used to convert the set of possibly correlated variables into a set of linearly uncorrelated variables. Agglomerative Hierarchical Clustering was performed on the 3 principal components. RESULTS: Multilinear regressions showed that 45 to 80% of the Young's modulus E, the aggregate modulus in absence of deformation HA0, the radial permeability kr and the axial permeability in absence of deformation k0 can be explained by the MRI parameters within both the nucleus pulposus and the annulus pulposus. The principal component analysis reduced our variables to two principal components with a cumulative variability of 52-65%, which increased to 70-82% when considering the third principal component. The dendograms showed a natural division into four clusters for the nucleus pulposus and into three or four clusters for the annulus fibrosus. CONCLUSIONS: The compressive moduli and the permeabilities of isolated IVDs can be assessed mostly by MT and diffusion sequences. However, the relationships have to be improved with the inclusion of MRI parameters more sensitive to IVD degeneration. Before the use of this technique to quantify the mechanical properties of IVDs in vivo on patients suffering from various diseases, the relationships have to be defined for each degeneration state of the tissue that mimics the pathology. Our MRI protocol associated to principal component analysis and agglomerative hierarchical clustering are promising tools to classify the degenerated intervertebral discs and further find biomarkers and predictive factors of the evolution of the pathologies.
    BMC Musculoskeletal Disorders 10/2012; 13(1):195. · 1.88 Impact Factor
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    ABSTRACT: OBJECTIVE: Magnetic resonance imaging (MRI) offers great potential as a sensitive and noninvasive technique for describing the alterations in mechanical properties, as shown in vitro on intervertebral disc (IVD) or cartilage tissues. However, in vivo, the IVD is submitted to complex loading stimuli. Thus, the present question focuses on the influence of the mechanical loading during an MRI acquisition on the relaxation times, magnetization transfer and diffusion parameters within the IVD. METHODS: An apparatus allowing the compression of isolated IVDs was designed and manufactured in acrylonitrile butadiene styrene. IVDs were dissected from fresh young bovine tail, measured for their thickness and submitted to compression just before the MRI acquisition. Six discs received 0% (platen positioned at the initial disc thickness), 5% (platen positioned at 95% of the initial disc thickness), 10%, 20% and 40% deformation. The MRI parameters were compared between the loading states using mean and standard deviation for T1 and T2, and matrix subtraction for Magnetization Transfer, fractional anisotropy and apparent diffusion coefficient. RESULTS: The compression of the IVD did not lead to any significant change of the MRI parameters, except for the diffusion that decreased in the direction of the compressive stress. DISCUSSION: This experimental in vitro study shows that multi-parametric MRI on isolated discs in vitro is not sensitive to compression or to the partial confined relaxation that followed the compression.
    Magnetic Resonance Imaging 08/2012; · 2.06 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps.
    Magnetic Resonance Imaging 03/2012; 30(5):722-30. · 2.06 Impact Factor
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    Year: 06/2011
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    ABSTRACT: An iterative edge-preserving CT reconstruction algorithm for high-resolution imaging of small regions of the field of view is investigated. It belongs to a family of region-of-interest reconstruction techniques in which a low-cost pilot reconstruction of the whole field of view is first performed and then used to deduce the contribution of the region of interest to the projection data. These projections are used for a high-resolution reconstruction of the region of interest (ROI) using a regularized iterative algorithm, resulting in significant computational savings. This paper examines how the technique by which the pilot reconstruction of the full field of view is obtained affects the total runtime and the image quality in the region of interest. Previous contributions to the literature have each focused on a single approach for the pilot reconstruction. In this paper, two such approaches are compared: the filtered backprojection and a low-resolution regularized iterative reconstruction method. ROI reconstructions are compared in terms of image quality and computational cost over simulated and physical phantom (Catphan600) studies, in order to assess the compromises that most impact the quality of the ROI reconstruction. With the simulated phantom, new artifacts that appear in the ROI images are caused by significant errors in the pilot reconstruction. These errors include excessive coarseness of the pilot image grid and beam-hardening artifacts. With the Catphan600 phantom, differences in the imaging model of the scanner and that of the iterative reconstruction algorithm cause dark border artifacts in the ROI images. Inexpensive pilot reconstruction techniques (analytical algorithms, very-coarse-grid penalized likelihood) are practical choices in many common cases. However, they may yield background images altered by edge degradation or beam hardening, inducing projection inconsistency in the data used for ROI reconstruction. The ROI images thus have significant streak and speckle artifacts, which adversely affect the resolution-to-noise compromise. In these cases, edge-preserving penalized-likelihood methods on not-too-coarse image grids prove to be more robust and provide the best ROI image quality.
    Medical Physics 09/2010; 37(9):4577-89. · 2.91 Impact Factor
  • N Olamaei, F Cheriet, G Beaudoin, S Martel
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    ABSTRACT: In magnetic resonance imaging (MRI), the susceptibility-based contrast provides a way to amplify the effects of a magnetic microparticle, whereas its volume is largely inferior to the spatial resolution of the system. This concept presents an approach to visualization by means of susceptibility artifact using ferromagnetic microparticles. In this work, the amount of the susceptibility artifact was investigated using a simulation model and in vitro experiments on stainless steel microspheres measuring 40, 20 and 15 microm in diameter. The results showed that using a clinical MRI system, a single 15 microm microsphere is detectable in gradient-echo scans. The extent of the susceptibility artifact was found to be related to the scan parameters and the particles' sizes. Since the same ferromagnetic microparticle can be used for MRI-based propulsion, these results suggest several potential applications for navigable agents and microrobots involved in therapy, diagnostics, and imaging inside the microvascular network of the human body.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:4355-8.
  • Guillaume Gilbert, Gilles Soulez, Gilles Beaudoin
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    ABSTRACT: To investigate the ability of an intravascular magnetic resonance (MR) loopless antenna to reduce the radiofrequency shielding of a vascular stent during signal reception as a way to improve the visualization of the in-stent lumen. Using a balanced steady-state free-precession (bSSFP) sequence and a dedicated vascular phantom, the signal-to-noise ratio (SNR) inside the lumen of a stent is evaluated as a function of the nominal flip angle and compared with the results obtained for a reference vessel without a stent. All experiments are performed using successively an intravascular loopless antenna and surface arrays coils. Using an optimized protocol, in vitro in-stent restenosis visualization and quantification experiments are performed to evaluate the validity of an approach using an intravascular antenna and cross-sectional images to depict a vascular lesion inside a stent. The use of a loopless antenna effectively eliminates the radiofrequency shielding effect of the stent during signal reception. Furthermore, using a bSSFP sequence with a carefully chosen nominal flip angle, an equally good blood SNR can be obtained inside and outside the stent. Results of in vitro in-stent restenosis quantification measurements using the proposed method illustrate the benefits arising from the use of the intravascular antenna. In the perspective of MR-guided vascular interventions, the presented results illustrate that the use of an intravascular antenna can significantly facilitate imaging inside a vascular stent. Potential applications include the monitoring of stent deployment as well as visualization and quantification of in-stent restenosis during an intervention.
    Academic radiology 12/2009; 16(12):1466-74. · 2.09 Impact Factor
  • Guillaume Gilbert, Gilles Soulez, Gilles Beaudoin
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    ABSTRACT: To evaluate and compare the accuracy of cross-sectional imaging using an intravascular antenna in the context of vascular morphological measurements performed during a magnetic resonance imaging (MRI)-guided vascular intervention. Cross-sectional imaging of a multimodality vascular phantom was performed using intravascular and surface MRI, multidetector computed tomography, and intravascular ultrasound (IVUS). Using a balanced steady-state free-precession sequence, 18 sequences parameters sets were investigated (12 for intravascular MRI and 6 for surface MRI). Vessel diameters for all images and modalities were computed using an automated vessel segmentation algorithm. Using IVUS as a gold standard, imaging using an intravascular antenna leads to an increase in geometrical accuracy in comparison to traditional surface MRI. This level of accuracy appears to follow a significant inverse proportionality relation in respect to vessel wall signal-to-noise ratio (SNR). Taking into account the rapid decrease in SNR as a function of the distance to the intravascular antenna, these results imply that, for a given level of geometrical accuracy, faster sequences can be used for the imaging of smaller vessels. Imaging using an intravascular antenna appears as a valuable assistance to increase the accuracy of vascular morphological measurements. This increase in geometrical accuracy would be beneficial during the realization of an MRI-guided intervention, either to perform pretreatment measurements or to assess the outcome of the procedure. Acquisition parameters should be tailored to vessel size and procedural time constraints.
    Academic radiology 05/2009; 16(8):988-96. · 2.09 Impact Factor
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    ABSTRACT: This paper aims at developing a quantitative system for measuring human hip cartilage thickness and volume using magnetic resonance imaging (MRI). A new MRI-acquisition technique, named axial rotation, where the acquisition planes are organized around a virtual axis, was used. The MRI protocol consists of a 2-D multiple-echo data image combination (MEDIC) using water excitation. Inner and outer interface contours of acetabulum and femoral head cartilage are obtained using a semiautomated 3-D segmentation method and combined to form 3-D surfaces. A local spherical coordinate system computed from the original contours enables cartilage thickness and volume computation. An anatomical labeling is performed automatically for thickness and volume measurements in predefined subregions: inferior, anterior, superior, and posterior. A registration module is introduced allowing the assessment of cartilage changes over time. Validation of the system was conducted with three protocols each involving data obtained from nine subjects: 1) registration process accuracy; 2) intrareader reproducibility; and 3) intervisit coefficient of variation. Data showed excellent correlation coefficients for either the intrareader (r>or=0.0942, p<0.0001 ) or intervisit (r>or=0.0837, p<0.005) protocols. This noninvasive system, which enables the quantification of cartilage thickness and volume in the human hip joint using MRI, is the first to discriminate the acetabular and femoral head cartilage throughout the entire hip without the use of an external device, and to implement hip registration for follow-up studies on the same subject.
    IEEE transactions on bio-medical engineering 12/2008; 55(12):2731-40. · 2.15 Impact Factor
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    ABSTRACT: The possibility of automatically navigating untethered microdevices or future nanorobots to conduct target endovascular interventions has been demonstrated by our group with the computer-controlled displacement of a magnetic sphere along a pre-planned path inside the carotid artery of a living swine. However, although the feasibility of propelling, tracking and performing real-time closed-loop control of an untethered ferromagnetic object inside a living animal model with a relatively close similarity to human anatomical conditions has been validated using a standard clinical Magnetic Resonance Imaging (MRI) system, little information has been published so far concerning the medical and technical protocol used. In fact, such a protocol developed within technological and physiological constraints was a key element in the success of the experiment. More precisely, special software modules were developed within the MRI software environment to offer an effective tool for experimenters interested in conducting such novel interventions. These additional software modules were also designed to assist an interventional radiologist in all critical real-time aspects that are executed at a speed beyond human capability, and include tracking, propulsion, event timing and closed-loop position control. These real-time tasks were necessary to avoid a loss of navigation control that could result in serious injury to the patient. Here, additional simulation and experimental results for microdevices designed to be targeted more towards the microvasculature have also been considered in the identification, validation and description of a specific sequence of events defining a new computer-assisted interventional protocol that provides the framework for future target interventions conducted in humans.
    Computer Aided Surgery 12/2008; 13(6):340-52. · 0.78 Impact Factor
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    ABSTRACT: A dedicated software architecture for a novel interventional method allowing the navigation of ferromagnetic endovascular devices using a standard real-time clinical MRI system is shown. Through a specially developed software environment integrating a tracking method and a real-time controller algorithm, a clinical 1.5T Siemens Avanto MRI system is adapted to provide new functionality for potential automated interventional applications. The proposed software architecture was successfully validated through in vivo controlled navigation inside the carotid artery of a swine. Here we present how this MRI-upgraded software environment could also be used in more complex vasculature models through the real-time navigation of a 1.5 mm diameter chrome steel bead in two different MR-compatible phantoms with flowless and quiescent flow conditions. The developed platform and software modules needed for such navigation are also presented. Real-time tracking achieved through a dedicated positioning method based on an off-resonance excitation technique has also been successfully integrated in the software platform while maintaining adequate real-time performance. These preliminary feasibility experiments suggest that navigation of such devices can be achieved using a similar software architecture on other conventional clinical MRI systems at an operational closed-loop control frequency of 32 Hz.
    Magnetic Resonance in Medicine 07/2008; 59(6):1287-97. · 3.27 Impact Factor
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    ABSTRACT: We present an iterative tomographic reconstruction procedure suitable for processing of real projection datasets. This method is based on a polychromatic sinogram formation model that takes the beam hardening effect into account and thus reduces the incidence of streak artifacts due to metal inserts in the imaged body. It involves an optimized implementation and a novel measurement uncertainty model aimed at improving the conditioning of the problem and reducing the runtime of each iteration. Reconstruction of realistic-size images was performed on both synthetic and actual projection data. Comparison with results provided by existing techniques indicates that a significant reduction of the runtime is achieved, with no loss in image quality.
    Biomedical Imaging: From Nano to Macro, 2008. ISBI 2008. 5th IEEE International Symposium on; 06/2008
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    ABSTRACT: We propose an algebraic image reconstruction method that can cope with the size and features of datasets produced by actual scanners, such as angular flying focal spot and detector offset. Image reconstruction is performed by minimizing a penalized least squares objective function by means of a preconditioned conjugate gradient (PCG) algorithm. Efficient implementation of the matrix-vector products that represent projection and backprojection operations is crucial to reconstruction speed, as such operations are performed at least once per iteration. For this purpose, we developed an efficient storage scheme for the projection matrix that allowed fast matrix-vector products. These features, along with an appropriate choice of the preconditioning matrix, yielded a numerically efficient method which produces results with better quality than those provided by usual filtered backprojection techniques.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2008; 2008:2717-20.
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    ABSTRACT: A novel magnetic resonance (MR)-tracking method specifically developed to locate the ferromagnetic core of an untethered microdevice, microrobot, or nanorobot for navigation or closed-loop control purpose is described. The tracking method relies on the application of radio-frequency (RF) excitation signals tuned to the equipotential magnetic curves generated by the magnetic signature of the object being tracked. Positive contrast projections are obtained with reference to the position of the magnetic source. A correlation function performed on only one k-space line for each of the three axes and corresponding to three projections, is necessary to obtain a 3-D location of the device. In this study, the effects of the sphere size and the RF frequency offset were investigated in order to find the best contrast noise ratio (CNR) for tracking. Resolution and precision were also investigated by proper measurement of the position of a ferromagnetic sphere by magnetic resonance imaging (MRI) acquisition and by comparing them with the real position. This method is also tested for a moving marker where the positions found by MRI projections were compared with the ones taken with a camera. In vitro and in vivo experiments show the operation of the technique in tortuous phantom and in animal models. Although the method was developed in the prospect of new interventional MR-guided endovascular operations based on miniature untethered devices, it could also be used as a passive tracking method using tools such as catheters or guide wires.
    IEEE Transactions on Medical Imaging 01/2008; 27:28-35. · 4.03 Impact Factor
  • Journal of Vascular and Interventional Radiology - J VASC INTERVEN RADIOL. 01/2008; 19(2).
  • Guillaume Gilbert, Dany Simard, Gilles Beaudoin
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    ABSTRACT: An improved method for the combination of signals from array coils is presented as a way to reduce the influence of the noise floor on the estimation of diffusion tensor imaging (DTI) parameters. By an optimized combination of signals from the array channels and complex averaging of measurements, this method leads to a significant reduction of the noise bias. This combination algorithm allows computation of accurate tensors by using the simple two point method and is shown to provide results similar to the ones obtained using the standard signal combination and a nonlinear regression method with noise parameter estimation. In many applications, the use of this combination method would result in a scan time reduction in comparison to the current standard. The effects of the improved combination on diffusion decay curves, fractional anisotropy maps, and apparent diffusion coefficient (ADC) profiles are demonstrated.
    IEEE Transactions on Medical Imaging 12/2007; 26(11):1428-36. · 4.03 Impact Factor
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    ABSTRACT: The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5 mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging (MRI) platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.
    Applied Physics Letters 03/2007; 90(11):114105-114105-3. · 3.79 Impact Factor
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    ABSTRACT: A 1.5 mm magnetic sphere was navigated automatically inside the carotid artery of a living swine. The propulsion force, tracking and real-time capabilities of a Magnetic Resonance Imaging (MRI) system were integrated into a closed loop control platform. The sphere was released using an endovascular catheter approach. Specially developed software is responsible for the tracking, propulsion, event timing and closed loop position control in order to follow a 10 roundtrips preplanned trajectory on a distance of 5 cm inside the right carotid artery of the animal. Experimental protocol linking the technical aspects of this in vivo assay is presented. In the context of this demonstration, many challenges which provide insights about concrete issues of future nanomedical interventions and interventional platforms have been identified and addressed.
    Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention. 02/2007; 10(Pt 1):144-52.

Publication Stats

1k Citations
93.74 Total Impact Points

Institutions

  • 2005–2013
    • Montreal Polytechnic
      • • Department of Computer and Software Engineering
      • • Institut de génie biomédical
      Montréal, Quebec, Canada
  • 2012
    • Government of Quebec
      Québec, Quebec, Canada
  • 2005–2012
    • Université de Montréal
      • • Department of Radiology, Radiation Oncology and Nuclear Medicine
      • • Institute of Biomedical Engineering
      Montréal, Quebec, Canada
  • 2005–2008
    • Hôpital Notre-Dame
      Montréal, Quebec, Canada
  • 2006–2007
    • Centre hospitalier de l'Université de Montréal (CHUM)
      • Département Radiologie
      Montréal, Quebec, Canada
  • 2004–2006
    • École de Technologie Supérieure
      • Imaging and Orthopaedics Research Laboratory (LIO)
      Montréal, Quebec, Canada
  • 2003
    • Université du Québec à Montréal
      Montréal, Quebec, Canada