François Destrempes

Université de Montréal, Montréal, Quebec, Canada

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Publications (33)53 Total impact

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    ABSTRACT: Purpose To develop a classification method based on the statistical backscatter properties of tissues that can be used as an ancillary tool to the usual Breast Imaging Reporting and Data System ( BI-RADS Breast Imaging Reporting and Data System ) classification for solid breast lesions identified at ultrasonography (US). Materials and Methods This study received institutional review board approval, and all subjects provided informed consent. Eighty-nine women (mean age, 50 years; age range, 22-82 years) with 96 indeterminate solid breast lesions ( BI-RADS Breast Imaging Reporting and Data System category 4-5; mean size, 13.2 mm; range, 2.6-44.7 mm) were enrolled. Prior to biopsy, additional radiofrequency US images were obtained, and a 3-second cine sequence was used. The research data were analyzed at a later time and were not used to modify patient management decisions. The lesions were segmented manually, and parameters of the homodyned K distribution (α, k, and μn values) were extracted for three regions: the intratumoral zone, a 3-mm supratumoral zone, and a 5-mm infratumoral zone. The Mann-Whitney rank sum test was used to identify parameters with the best discriminating value, yielding intratumoral α, supratumoral k, and infratumoral μn values. Results The 96 lesions were classified as follows: 48 BI-RADS Breast Imaging Reporting and Data System category 4A lesions, 16 BI-RADS Breast Imaging Reporting and Data System category 4B lesions, seven BI-RADS Breast Imaging Reporting and Data System category 4C lesions, and 25 BI-RADS Breast Imaging Reporting and Data System category 5 lesions. There were 24 cancers (25%). The area under the receiver operating characteristic curve was 0.76 (95% confidence interval: 0.65, 0.86). Overall, 24% of biopsies (in 17 of 72 lesions) could have been spared. By limiting analysis to lesions with a lower likelihood of malignancy ( BI-RADS Breast Imaging Reporting and Data System category 4A-4B), this percentage increased to 26% (16 of 62 lesions). Among benign lesions, the model was used to correctly classify 10 of 38 fibroadenomas (26%) and three of seven stromal fibroses (43%). Conclusion The statistical model performs well in the classification of solid breast lesions at US, with the potential of preventing one in four biopsies without missing any malignancy. © RSNA, 2014.
    Radiology 12/2014; · 6.34 Impact Factor
  • Louis Le Tarnec, François Destrempes, Guy Cloutier, Damien Garcia
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    ABSTRACT: The Horn-Schunck (HS) method, which amounts to the Jacobi iterative scheme in the interior of the image, was one of the first optical flow algorithms. In this paper, we prove the convergence of the HS method whenever the problem is well-posed. Our result is shown in the framework of a generalization of the HS method in dimension n≥1, with a broad definition of the discrete Laplacian. In this context, the condition for the convergence is that the intensity gradients not all be contained in the same hyperplane. Two other works ([A. Mitiche and A. Mansouri, IEEE Trans. Image Process. 13, 848–852 (2004)] and [Y. Kameda, A. Imiya and N. Ohnishi, “A convergence proof for the Horn-Schunck optical-flow computation scheme using neighborhood decomposition”, in Combinatorial Image Analysis. Berlin: Springer (2008), p. 262–273]) claimed to solve this problem in the case n=2, but it appears that both of these proofs are erroneous. Moreover, we explain why some standard results about the convergence of the Jacobi method do not apply for the HS problem, unless n=1. It is also shown that the convergence of the HS scheme implies the convergence of the Gauss-Seidel and successive overrelaxation schemes for the HS problem.
    SIAM Journal on Imaging Sciences 01/2014; 7(1). · 2.97 Impact Factor
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    ABSTRACT: The goal of this study was to show the feasibility of a 2D segmentation fast-marching method (FMM) in the context of intravascular ultrasound (IVUS) imaging of coronary arteries. The original FMM speed function combines gradient-based contour information and region information, that is the gray level probability density functions of the vessel structures, that takes into account the variability in appearance of the tissues and the lumen in IVUS images acquired at 40MHz. Experimental results on 38 in vivo IVUS sequences yielded mean point-to-point distances between detected vessel wall boundaries and manual validation contours below 0.11mm, and Hausdorff distances below 0.33mm, as evaluated on 3207 images. The proposed method proved to be robust in taking into account various artifacts in ultrasound images: partial shadowing due to calcium inclusions within the plaque, side branches adjacent to the main artery to segment, the presence of a stent, injection of contrast agent or dissection, as tested on 209 images presenting such artifacts.
    Computerized medical imaging and graphics: the official journal of the Computerized Medical Imaging Society 09/2013; · 1.04 Impact Factor
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    ABSTRACT: This paper describes an evaluation framework that allows a standardized and quantitative comparison of IVUS lumen and media segmentation algorithms. This framework has been introduced at the MICCAI 2011 Computing and Visualization for (Intra)Vascular Imaging (CVII) workshop, comparing the results of eight teams that participated. We describe the available data-base comprising of multi-center, multi-vendor and multi-frequency IVUS datasets, their acquisition, the creation of the reference standard and the evaluation measures. The approaches address segmentation of the lumen, the media, or both borders; semi- or fully-automatic operation; and 2-D vs. 3-D methodology. Three performance measures for quantitative analysis have been proposed. The results of the evaluation indicate that segmentation of the vessel lumen and media is possible with an accuracy that is comparable to manual annotation when semi-automatic methods are used, as well as encouraging results can be obtained also in case of fully-automatic segmentation. The analysis performed in this paper also highlights the challenges in IVUS segmentation that remains to be solved.
    Computerized medical imaging and graphics: the official journal of the Computerized Medical Imaging Society 09/2013; · 1.04 Impact Factor
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    ABSTRACT: Non invasive vascular elastography (NIVE) was developed to highlight atherosclerotic plaque constituents. However, NIVE motion estimates are affected by artifacts, such as an underestimation of deformations due to projected movement angles with respect to the ultrasound beam, movements of the operator or of the patient during image acquisition. The main objective of this work was to propose a local angle compensation method within small measurement windows for the axial strain based on kinematics constraints, and to introduce a filtering process on the strain time-varying curve to reduce as much as possible the impact of motion artifacts. With such preprocessing, we successfully quantified the strain behavior of near and far walls in longitudinal images of internal carotid arteries without (n=30) and with (n=21) significant atherosclerotic disease (greater than 50% stenosis). Maximum strain rates of 4.49%s(-1) for the healthy group and of 2.29%s(-1) for the atherosclerotic group were calculated on the far wall of internal carotid arteries; significant differences were found between these values (p=0.001). The minimum strain rates, also on the far wall of internal carotid arteries, of -3.68%s(-1) for the healthy group and of -1.89%s(-1) for the atherosclerotic group were significantly different as well (p=8×10(-4)). The mean systolic, diastolic and cumulated axial strains could also distinguish the two groups after normalization by the pressure gradient between acquired images. To conclude, the proposed techniques allowed to differentiate healthy and atherosclerotic carotid arteries and may help to diagnose vulnerable plaques.
    Computerized medical imaging and graphics: the official journal of the Computerized Medical Imaging Society 08/2013; · 1.04 Impact Factor
  • François Destrempes, Jonathan Porée, Guy Cloutier
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    ABSTRACT: The homodyned K-distribution appears naturally in the context of random walks and provides a useful model for the distribution of the received intensity in a wide range of non-Gaussian scattering configurations, including medical ultrasonics. An estimation method for the homodyned K-distribution based on the first moment of the intensity and two log-moments (XU method), namely the X and U-statistics previously studied in the special case of the K-distribution, is proposed as an alternative to a method based on the first three moments of the intensity (MI method) or the amplitude (MA method), and a method based on the signal-to-noise ratio (SNR), the skewness and the kurtosis of two fractional orders of the amplitude (labeled RSK method). Properties of the X and U statistics for the homodyned K-distribution are proved, except for one conjecture. Using those properties, an algorithm based on the bisection method for monotonous functions was developed. The algorithm has a geometric rate of convergence. Various tests were performed to study the behavior of the estimators. It was shown with simulated data samples that the estimations of the parameters 1/α and 1/(κ + 1) of the homodyned K-distribution are preferable to the direct estimations of the clustering parameter α and the structure parameter κ (with respective relative root mean squared errors (RMSEs) of 0.63 and 0.13 as opposed to 1.04 and 4.37, when N = 1000). Tests on simulated ultrasound images with only diffuse scatterers (up to 10 per resolution cell) indicated that the XU estimator is overall more reliable than the other three estimators for the estimation of 1/α, with relative RMSEs of 0.79 (MI), 0.61 (MA), 0.53 (XU) and 0.67 (RSK). For the parameter 1/(κ + 1), the relative RMSEs were equal to 0.074 (MI), 0.075 (MA), 0.069 (XU) and 0.100 (RSK). In the case of a large number of scatterers (11 to 20 per resolution cell), the relative RMSEs of 1/α were equal to 1.43 (MI), 1.27 (MA), 1.25 (XU) and 1.33 (RSK), and the relative RMSEs of 1/(κ + 1) were equal to 0.14 (MI), 0.16 (MA), 0.17 (XU) and 0.20 (RSK). The four methods were also tested on simulated ultrasound images with a variable density of periodic scatterers to test images with a coherent component. The addition of noise on ultrasound images was also studied. Results showed that the XU estimator was overall better than the three other ones. Finally, on the simulated ultrasound images, the average computation times per image were equal to 6.0 ms (MI), 8.0 ms (MA), 6.8 ms (XU) and 500 ms (RSK). Thus, a fast, reliable, and novel algorithm for the estimation of the homodyned K-distribution was proposed.
    SIAM Journal on Imaging Sciences 08/2013; 6(3):1499-1530. · 2.97 Impact Factor
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    ABSTRACT: The main motivation in this study was to increase the accuracy of the breast tissue characterization by combining quantitative ultrasound (QUS) with ultrasound (US) dynamic elastography. To demonstrate that, an agar-gelatin breast mimicking phantom with two inclusions containing the same density of agar (US scatterers) but different proportions of gelatin corresponding to different mechanical properties was made. Transient plane shear waves (SW) at 200 Hz were transmitted through the phantom while the displacement of scatterers was imaged at 5 MHz with an ultrafast imaging technique. With segmented inclusions, the reciprocal (beta parameter) of the effective density of scatterers of a general distribution model of the echo envelope and its normalized range (normalized by the mean of beta during SW propagation) were estimated for each inclusion. The results showed that the relative difference of beta between the surrounding medium and both inclusions A and B were 55.6% (A) and 0.9% (B), respectively, whereas differences (in %) of the beta normalized range were 46.2% (A) and 52.6% (B), respectively. The static value beta failed to distinguish inclusion B from the surrounding; however, the dynamic range of beta succeeded in that task for the two inclusions. Thus, dynamic QUS might add information to QUS in a static framework.
    The Journal of the Acoustical Society of America 05/2013; 133(5):3357. · 1.65 Impact Factor
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    ABSTRACT: OBJECTIVES: To evaluate the ability of ultrasound non-invasive vascular elastography (NIVE) strain analysis to characterise carotid plaque composition and vulnerability as determined by high-resolution magnetic resonance imaging (MRI). METHODS: Thirty-one subjects with 50 % or greater carotid stenosis underwent NIVE and high-resolution MRI of internal carotid arteries. Time-varying strain images (elastograms) of segmented plaques were generated from ultrasonic raw radiofrequency sequences. On MRI, corresponding plaques and components were segmented and quantified. Associations between strain parameters, plaque composition and symptomatology were estimated with curve-fitting regressions and Mann-Whitney tests. RESULTS: Mean stenosis and age were 72.7 % and 69.3 years, respectively. Of 31 plaques, 9 were symptomatic, 17 contained lipid and 7 were vulnerable on MRI. Strains were significantly lower in plaques containing a lipid core compared with those without lipid, with 77-100 % sensitivity and 57-79 % specificity (P < 0.032). A statistically significant quadratic fit was found between strain and lipid content (P < 0.03). Strains did not discriminate symptomatic patients or vulnerable plaques. CONCLUSIONS: Ultrasound NIVE is feasible in patients with significant carotid stenosis and can detect the presence of a lipid core with high sensitivity and moderate specificity. Studies of plaque progression with NIVE are required to identify vulnerable plaques. KEY POINTS : • Non-invasive vascular elastography (NIVE) provides additional information in vascular ultrasound • Ultrasound NIVE is feasible in patients with significant carotid stenosis • Ultrasound NIVE detects a lipid core with high sensitivity and moderate specificity • Studies on plaque progression with NIVE are required to identify vulnerable plaques.
    European Radiology 02/2013; · 4.34 Impact Factor
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    ABSTRACT: This paper describes an evaluation framework that allows a standardized and quantitative comparison of IVUS lumen and media segmentation algorithms. This framework has been introduced at the MICCAI 2011 Computing and Visualization for (Intra)Vascular Imaging (CVII) workshop, comparing the results of eight teams that participated. We describe the available data-base comprising of multi-center, multi-vendor and multi-frequency IVUS datasets, their acquisition, the creation of the reference standard and the evaluation measures. The approaches address segmentation of the lumen, the media, or both borders; semi-or fully-automatic operation; and 2-D vs. 3-D methodology. Three perfor-mance measures for quantitative analysis have been proposed. The results of the evaluation indicate that segmentation of the vessel lumen and media is possible with an accuracy that is comparable to manual annotation when semi-automatic methods are used, as well as encouraging results can be obtained also in case of fully-automatic segmentation. The analysis performed in this paper also highlights the challenges in IVUS segmentation that remains to be solved.
    Computerized Medical Imaging and Graphics 01/2013; · 1.50 Impact Factor
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    ABSTRACT: In the context of tissue characterization, one may wonder what does the consideration of a quantitative ultrasound (QUS) feature of a medium under the propagation of a shear wave (SW) add to its discriminant power. This study presents the time-varying behavior of the K-distribution beta parameter - the reciprocal of the effective density of scatterers - under SW propagation and its relation with the viscoelasticity of the medium. Transient plane SW at 300 Hz central frequency was transmitted to three agar-gelatin phantoms at different concentrations. The amplitude of the B-mode backscatter echoes acquired with an 8 MHz probe was modeled with the K-distribution. The normalized range of beta (i.e., its range normalized by its mean value as the SW propagates) was determined by considering the B-mode images during SW propagation. Also, the storage (G') and loss (G") moduli of each phantom were measured on samples with the RheoSpectris hyper-frequency instrument (Rheolution, Montreal, Canada). The time-evolution of the beta parameter and displacements (using cross-correlation) within tissue-mimicking phantoms under SW vibration suggest that the beta parameter can be used to track SW propagation. In-vitro results showed that the normalized range of beta is related to the viscoelasticity of phantoms. By increasing G' and G", the normalized range of beta decreased. Thus, the consideration of the behavior of beta under SW propagation modifies the effective density of scatterers with respect to static conditions (i.e., without SW). This is new observation and a new step towards understanding statistical QUS behavior.
    Ultrasonics Symposium (IUS), 2012 IEEE International; 01/2012
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    ABSTRACT: The goal of this paper is to perform a segmentation of atherosclerotic plaques in view of evaluating their burden and to provide boundaries for computing properties such as the plaque deformation and elasticity distribution (elastogram and modulogram). The echogenicity of a region of interest comprising the plaque, the vessel lumen, and the adventitia of the artery wall in an ultrasonic B-mode image was modeled by mixtures of three Nakagami distributions, which yielded the likelihood of a Bayesian segmentation model. The main contribution of this paper is the estimation of the motion field and its integration into the prior of the Bayesian model that included a local geometrical smoothness constraint, as well as an original spatiotemporal cohesion constraint. The Maximum A Posteriori of the proposed model was computed with a variant of the exploration/selection algorithm. The starting point is a manual segmentation of the first frame. The proposed method was quantitatively compared with manual segmentations of all frames by an expert technician. Various measures were used for this evaluation, including the mean point-to-point distance and the Hausdorff distance. Results were evaluated on 94 sequences of 33 patients (for a total of 8988 images). We report a mean point-to-point distance of 0.24 ± 0.08 mm and a Hausdorff distance of 1.24 ± 0.40 mm. Our tests showed that the algorithm was not sensitive to the degree of stenosis or calcification.
    IEEE Transactions on Biomedical Engineering 09/2011; · 2.35 Impact Factor
  • Guy Cloutier, François Destrempes
    Ultrasound in medicine & biology 03/2011; · 2.46 Impact Factor
  • J. Poree, F. Destrempes, G. Soulez, G. Cloutier
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    ABSTRACT: Partitioning an atheromatous carotid plaque into its main biological components can be a valuable tool to assess its vulnerability. One could compute textural or elasticity features on each component to describe them. In this paper, we propose a fully automated segmentation method, based on statistical properties of the ultrasound backscattered envelope signals, to classify plaque pixels into a fixed number of components. The echogenicity of each plaque was modeled as a mixture of 2 Nakagami distributions leading to 2 main components. The mixture parameters were at first estimated with an Expectation Maximization algorithm (EM). Each class of the partition was then initialized using the Maximum Likelihood segmentation (ML). The optimal partition of the plaque area was then found using a level-set formulation of the Maximum A Posteriori (MAP) estimator with a spatial cohesion prior. Nakagami mixture parameters were extracted from those components. Uncompressed B-mode sequences of 8 symptomatic and 13 asymptomatic subjects were analyzed for a total of 42 plaque sequences. We found that the Nakagami parameters were able to distinguish symptomatic from asymptomatic patients with a significant p-value. Further works including elasticity mapping on each component are in progress and might lead to new indexes of vulnerability.
    Ultrasonics Symposium (IUS), 2011 IEEE International; 01/2011
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    François Destrempes, Guy Cloutier
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    ABSTRACT: In ultrasound imaging, various statistical distributions have been proposed to model the first-order statistics of the amplitude of the echo envelope. We present an overview of these distributions based on their compound representation, which comprises three aspects: the modulated distribution (Rice or Nakagami); the modulating distribution (gamma, inverse Gaussian or even generalized inverse Gaussian); and the modulated parameters (the diffuse signal power with or without the coherent signal component or the coherent signal power). This unifying point of view makes the comparison of the various models conceptually easier. In particular, we discuss the implications of the modulated parameters on the mean intensity and the signal-to-noise ratio of the intensity in the case of a vanishing diffuse signal. We conclude that the homodyned K-distribution is the only model among the literature for which the parameters have a physical meaning that is consistent with the limiting case, although the other distributions may fit real data.
    Ultrasound in medicine & biology 07/2010; 36(7):1037-51. · 2.46 Impact Factor
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    ABSTRACT: The analysis of the ultrasonic frequency-dependent backscatter coefficient of aggregating red blood cells reveals information about blood structural properties. The difficulty in applying this technique in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of signals backscattered by blood. An optimization method is proposed to simultaneously estimate tissue attenuation and blood structure properties, and was termed the structure factor size and attenuation estimator (SFSAE). An ultrasound scanner equipped with a wide-band 25 MHz probe was used to insonify porcine blood sheared in both Couette and tubular flow devices. Since skin is one of the most attenuating tissue layers during in vivo scanning, four skin-mimicking phantoms with different attenuation coefficients were introduced between the transducer and the blood flow. The SFSAE gave estimates with relative errors below 25% for attenuations between 0.115 and 0.411 dBMHz and kR<2.08 (k being the wave number and R the aggregate radius). The SFSAE can be useful to examine in vivo and in situ abnormal blood conditions suspected to promote pathophysiological cardiovascular consequences.
    The Journal of the Acoustical Society of America 02/2010; 127(2):1104-15. · 1.65 Impact Factor
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    ABSTRACT: The goal of this work was to perform a segmentation of atherosclerotic plaques in view of evaluating its burden and to provide boundaries for computing properties such as the plaque elasticity distribution (elastogram). The echogenicity of a region of interest comprising the plaque, the lumen, and the adventitia in an ultrasonic B-mode image was modeled by a mixture of three Nakagami distributions. To each of these three tissues corresponds a specific weighted sum of these three distributions, which yields the likelihood of a Bayesian model. The prior of that model includes a geometrical smoothness constraint, as well as an original spatio-temporal cohesion constraint, based on the estimation of the motion field of the plaque in the video sequence. The Maximum A Posteriori (MAP) of the proposed model was computed with a variant of the Exploration/Selection (ES) algorithm. The starting point is a manual segmentation of the first frame. The main contribution of this paper is the estimation of the motion field and its integration into the prior of the Bayesian model. The proposed method was quantitatively compared with manual segmentations of all frames by an expert technician. Various measures were used for this evaluation, including the sensitivity and specificity of the receiver operating characteristic (ROC) analysis, and the error of area of the plaque. Results were evaluated on 21 sequences of 18 symptomatic patients (for a total of 2078 images). We report a sensitivity of 87.7 ± 5.9%, a specificity of 94.6 ± 3.2%, a kappa index of 88.1 ± 4.7%, an error of the plaque area of -0.79 ± 8.0%, and an absolute error of the plaque area of 6.61 ± 4.8%, which compare favorably with previous studies.
    Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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    ABSTRACT: The ultrasound characterization of red blood cell (RBC) aggregation is an attractive tool to determine rheological blood flow disorders in vivo and in situ. The backscattered signals from blood can be spectrally analyzed to deduce the size and spatial distribution of RBC aggregates. One difficulty to apply this analysis in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of backscattered echoes from blood microstructures. An optimization method was recently proposed to simultaneously estimate tissue attenuation and blood structure properties, and was termed the Structure Factor Size and Attenuation Estimator (SFSAE). With in vitro experiments, the method gave satisfactory estimates with relative errors below 25% for attenuations between 0.115 and 0.411 dB/MHz and kR <2.08 (k being the wave number and R the aggregate radius). The current work presents in vivo results to demonstrate the feasibility of the method. Measurements were performed on an arm's vein of a normal subject using an ultrasound scanner equipped with a 25 MHz center frequency probe. The probe was positioned in longitudinal view to examine three blood flow conditions: normal blood flow, stop flow with a proximal and distal constrictions of the ROI, and finally complex flow in the vinicity of two closed venous valves. For each case, the aggregate diameter D, expressed in number of RBCs, the packing factor W and the total attenuation ?<sub>0</sub> were estimated by using the SFSAE, i.e. by comparing the spectrum of the backscattered radio-frequency echoes with newly developed models of RBC aggregate scattering. Quantitative ultrasound parametric images of D, W and ?<sub>0</sub> estimates were constructed. For the two structural parameters D and W, statistically significant differences were observed between normal and stopped flow conditions, as well as between blood stagnation and circulation zones in the case of the two close- d venous valves. To conclude, this work shows the SFSAE ability to estimate blood backscattering properties in vivo and in situ, and opens the way to parametric imaging for clinical studies in abnormal blood conditions.
    Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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    ABSTRACT: Objectifs Evaluer la faisabilité de l’élastographie ultrasonore non invasive par ultrason pour caractériser les plaques carotidiennes vulnérables. Matériels et méthodes Trente-huit patients porteurs d’une sténose carotidienne de plus de 50% ont été enrôlés prospectivement. Des acquisitions RF cumulées sur au moins 5 cycles cardiaques ont été acquises sur les bifurcations carotidiennes. Les déformations induites par la pulsation cardiaque (élastogrammes) ont été calculées à l’aide de l’estimateur Lagrangien. Après appariement pour le degré de sténose, le déformations ont été comparées entre les sténoses sympto-matiques (n = 18) et asymptomatiques (n = 20). Résultats L’âge, les valeurs de pression systolique et diastolique étaient similaires dans les deux groupes. Les valeurs moyennes de déformation élastique étaient comparables entre les 2 groupes (1,30 ± 0,98 versus 1,27 ± 0,84%). Cependant les valeurs d’élasticité étaient plus hétérogènes chez les patients symptomatiques (DS = 2,03 ± 0,57 versus 2,84 ± 1,39%) (p = 0,03). Conclusion La caractérisation de la plaque carotidienne par élastographie ultrasonore non invasive est faisable. Les plaques vulnérables présentent des déformations plus hétérogènes que les plaques stables.
    Journal de Radiologie 10/2009; 90(10):1200-1200. · 0.35 Impact Factor
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    ABSTRACT: The goal of this work is to perform a segmentation of the intimamedia thickness (IMT) of carotid arteries in view of computing various dynamical properties of that tissue, such as the elasticity distribution (elastogram). The echogenicity of a region of interest comprising the intima-media layers, the lumen, and the adventitia in an ultrasonic B-mode image is modeled by a mixture of three Nakagami distributions. In a first step, we compute the maximum a posteriori estimator of the proposed model, using the expectation maximization (EM) algorithm. We then compute the optimal segmentation based on the estimated distributions as well as a statistical prior for disease-free IMT using a variant of the exploration/selection (ES) algorithm. Convergence of the ES algorithm to the optimal solution is assured asymptotically and is independent of the initial solution. In particular, our method is well suited to a semi-automatic context that requires minimal manual initialization. Tests of the proposed method on 30 sequences of ultrasonic B-mode images of presumably disease-free control subjects are reported. They suggest that the semi-automatic segmentations obtained by the proposed method are within the variability of the manual segmentations of two experts.
    IEEE transactions on medical imaging. 09/2008; 28(2):215-29.
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    Francois Destrempes, Max Mignotte, Jean-Francois Angers
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    ABSTRACT: In this paper, we present a new model for deformations of shapes. A pseudo-likelihood is based on the statistical distribution of the gradient vector field of the gray level. The prior distribution is based on the Probabilistic Principal Component Analysis (PPCA). We also propose a new model based on mixtures of PPCA that is useful in the case of greater variability in the shape. A criterion of global or local object specificity based on a preliminary color segmentation of the image, is included into the model. The localization of a shape in an image is then viewed as minimizing the corresponding Gibbs field. We use the Exploration/Selection (E/S) stochastic algorithm in order to find the optimal deformation. This yields a new unsupervised statistical method for localization of shapes. In order to estimate the statistical parameters for the gradient vector field of the gray level, we use an Iterative Conditional Estimation (ICE) procedure. The color segmentation of the image can be computed with an Exploration/Selection/Estimation (ESE) procedure.
    IEEE Transactions on Pattern Analysis and Machine Intelligence 10/2007; 29(9):1603-15. · 4.80 Impact Factor