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International audience; installation which might be impossible in some cases (e.g. pregnant women in lateral position, utilization of a tight flexible coil), and allows monitoring of only respiratory and heart activities. Moreover, being designed for clinical use, they offer no control over data acquisition and post-processing, which can be critical for some applications. For example, standard ECG processing can lead to incorrect QRS detection in case of steep gradient waveforms; no control over respiratory belt signal gain and offset (to avoid signal saturation) is available. Thus, often, accessory devices are thirdparty systems, which offer more flexibility, however have no communication interface with the MR system, or limited ones. Dedicated computer and electronics systems, as well as communication interfaces, are needed for use in either realtime/online applications or retrospective/offline applications. In the following we review several exemplary applications with the aim to derive typical requirements for such systems. Example applications that require real-time processing and communication include ECG denoising (7-10) and detection of the QRS complex (11-13), in order to trigger the MR sequence to the heart rate prospectively. The trigger is provided to the MR system by a TTL signal. The delays introduced by the real-time processing system, as defined by the latency (mean delay) and jitter (standard deviation of the delay), should be significantly lower that the temporal resolution of cardiac MR imaging, which is typically above 20 ms. Real-time display of the denoised ECG is also desired during anesthesia, cardiac stress MRI, or interventional MRI. Prospective motion correction (14) using external devices also relies on a real-time setup to modulate the MRI pulses (RF and magnetic field gradient pulses) in order to compensate for the effect of patient motion during spatial encoding. Low latency is also desired, ideally to be equal to the repetition time (TR) of the sequence or lower, i.e. 3 to 5 ms, though in practice it is limited by the time needed to process video images, e.g. 60 to 150 ms in (15). Software communication interfaces need to be defined with the vendor-dependent pulse sequence program in order to provide certain motion parameters (e.g. translations, rotations).

The study of articulatory gestures has a wide spectrum of applications, notably in speech production and recognition. Sets of phonemes, as well as their articulation, are language-specific; however, existing MRI databases mostly include English speakers. In our present work, we introduce a dataset acquired with MRI from 10 healthy native French speakers. A corpus consisting of synthetic sentences was used to ensure a good coverage of the French phonetic context. A real-time MRI technology with temporal resolution of 20 ms was used to acquire vocal tract images of the participants speaking. The sound was recorded simultaneously with MRI, denoised and temporally aligned with the images. The speech was transcribed to obtain phoneme-wise segmentation of sound. We also acquired static 3D MR images for a wide list of French phonemes. In addition, we include annotations of spontaneous swallowing., Measurement(s)Vocal tract images • SpeechTechnology Type(s)Magnetic Resonance Imaging • Microphone DeviceSample Characteristic - OrganismHomo sapiens Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.16404453

International audience; In this work, we address the prediction of speech articulators' temporal geometric position from the sequence of phonemes to be articulated. We start from a set of real-time MRI sequences uttered by a female French speaker. The contours of five articulators were tracked automatically in each of the frames in the MRI video. Then, we explore the capacity of a bidirectional GRU to correctly predict each articulator's shape and position given the sequence of phonemes and their duration. We propose a 5-fold cross-validation experiment to evaluate the generalization capacity of the model. In a second experiment, we evaluate our model's data efficiency by reducing training data. We evaluate the point-to-point Euclidean distance and the Pearson's correlations along time between the predicted and the target shapes. We also evaluate produced shapes of the critical articulators of specific phonemes. We show that our model can achieve good results with minimal data, producing very realistic vocal tract shapes.

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International audience; In this paper we propose an algorithm for estimating vocal tract para sagittal slices in order to have a better overview of the behaviour of the articulators during speech production. The first step is to align the consonant-vowel (CV) data of the sagittal plains between them for the train speaker. Sets of transformations that connect the midsagittal frames with the neighbouring ones is acquired for the train speaker. Another set of transformations is calculated which transforms the midsagittal frames of the train speaker to the corresponding midsagittal frames of the test speaker and is used to adapt to the test speaker domain the previously computed sets of transformations. The newly adapted transformations are applied to the midsagittal frames of the test speaker in order to estimate the neighbouring sagittal frames. Several mono speaker models are combined to produce the final frame estimation. To evaluate the results, image cross-correlation between the original and the estimated frames was used. Results show good agreement between the original and the estimated frames.

International audience; A set of rtMR image transformations across time is computed during the production of CV that is afterwards applied to a new speaker in order to synthesize his/her CV pseudo rtMRI data. Synthesized images are compared with the original ones using image cross-correlation. 2 Purpose To be able to enlarge MRI speech corpus by synthesizing data.

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International audience; Tongue contour extraction from real-time magnetic resonance images is a nontrivial task due to the presence of artifacts manifesting in form of blurring or ghostly contours. In this work, we present results of automatic tongue delineation achieved by means of U-Net auto-encoder convolutional neural network. We present both intra- and inter-subject validation. We used real-time magnetic resonance images and manually annotated 1-pixel wide contours as inputs. Predicted probability maps were post-processed in order to obtain 1-pixel wide tongue contours. The results are very good and slightly outperform published results on automatic tongue segmentation.

Sorti le 3 aout 2016 et applicable au premier janvier 2017, le decret 2016–1074 etablit des regles et recommandations a suivre pour proteger les travailleurs face aux risques dus aux champs electromagnetiques. Transposant la directive europeenne 2013/35/UE, il concerne tout employeur et impose au minimum l'etablissement d'une evaluation des risques. Les unites, clinique ou de recherche, utilisant des dispositifs d'imagerie par resonance magnetique (IRM) sont particulierement concernees. En effet, cette modalite d'imagerie emet des champs electromagnetiques susceptibles d'engendrer des niveaux d'exposition des travailleurs depassant les valeurs declenchant l'action et les valeurs limites d'exposition definies par la directive et le decret. Une section de ce dernier lui est d'ailleurs entierement consacree. Le present document propose, en premier lieu, une analyse detaillee du decret 2016–1074 et des obligations de l'employeur. Il propose, dans un second temps, une analyse concernant la mise en application de cette directive et du decret associe pour le dispositif particulier qu'est l'IRM.

International audience; In this work we present an algorithm for synthesising pseudo rtMRI data of the vocal tract. rtMRI data on the midsagittal plane were used to synthesise target consonant-vowel (CV) using only a silence frame of the target speaker. For this purpose, several single speaker models were created. The input of the algorithm is a silence frame of both train and target speaker and the rtMRI data of the target CV. An image transformation is computed from each CV frame to the next one, creating a set of transformations that describe the dynamics of the CV production. Another image transformation is computed from the silence frame of train speaker to the silence frame of the target speaker and is used to adapt the set of transformations computed previously to the target speaker. The adapted set of transformations is applied to the silence of the target speaker tosynthesise his/her CV pseudo rtMRI data. Synthesised images from multiple single speaker models are frame aligned and then averaged to create the final version of synthesised images. Synthesised images are compared with the original ones using image cross-correlation. Results show good agreement between the synthesised and the original images.

International audience; We present an algorithm for augmenting the shape of the vocal tract using 3D static and 2D dynamic speech MRI data. While static 3D images have better resolution and provide spatial information, 2D dynamic images capture the transitions. The aim of this work is to combine strong points of these two types of data to obtain better image quality of 2D dynamic images and extend the 2D dynamic images to the 3D domain. To produce a 3D dynamic consonant-vowel (CV) sequence, our algorithm takes as input the 2D CV transition and the static 3D targets for C and V. To obtain the enhanced sequence of images , the first step is to find a transformation between the 2D images and the mid-sagittal slice of the acoustically corresponding 3D image stack, and then find a transformation between neighbouring sagittal slices in the 3D static image stack. Combination of these transformations allows producing the final set of images. In the present study we first examined the transformation from the 3D mid-sagittal frame to the 2D video in order to improve image quality and then we examined the extension of the 2D video to the 3rd dimension with the aim to enrich spatial information.

International audience; In this work we describe the creation of ArtSpeechMRIfr: a real-time as well as static magnetic resonance imaging (rtMRI, 3D MRI) database of the vocal tract. The database contains also processed data: denoised audio, its phonetically aligned annotation, articulatory contours, and vocal tract volume information , which provides a rich resource for speech research. The database is built on data from two male speakers of French. It covers a number of phonetic contexts in the controlled part, as well as spontaneous speech, 3D MRI scans of sustained vocalic articulations, and of the dental casts of the subjects. The corpus for rtMRI consists of 79 synthetic sentences constructed from a phonetized dictionary that makes possible to shorten the duration of acquisitions while keeping a very good coverage of the phonetic contexts which exist in French. The 3D MRI includes acquisitions for 12 French vowels and 10 consonants, each of which was pronounced in several vocalic contexts. Ar-ticulatory contours (tongue, jaw, epiglottis, larynx, velum, lips) as well as 3D volumes were manually drawn for a part of the images.

International audience; Purpose: To quantitatively evaluate a superresolution technique for 3D, one-millimeter isotropic diffusion-weighted imaging (DWI) of the whole breasts.Methods: Isotropic 3D DWI datasets are obtained using a combination of (i) a readout-segmented diffusion-weighted-echo-planar imaging (DW-EPI) sequence (rs-EPI), providing high in-plane resolution, and (ii) a superresolution (SR) strategy, which consists of acquiring 3 datasets with thick slices (3 mm) and 1-mm shifts in the slice direction, and combining them into a 1 × 1 × 1-mm3 dataset using a dedicated reconstruction. Two SR reconstruction schemes were investigated, based on different regularization schemes: conventional Tikhonov or Beltrami (an edge-preserving constraint). The proposed SR strategy was compared to native 1 × 1 × 1-mm3 acquisitions (i.e. with 1-mm slice thickness) in 8 healthy subjects, in terms of signal-to-noise ratio (SNR) efficiency, using a theoretical framework, Monte Carlo simulations and region-of-interest (ROI) measurements, and image sharpness metrics. Apparent diffusion coefficient (ADC) values in normal breast tissue were also compared.Results: The SR images resulted in an SNR gain above 3 compared to native 1 × 1 × 1-mm3 using the same acquisition duration (acquisition gain 3 and reconstruction gain >1). Beltrami-SR provided the best results in terms of SNR and image sharpness. The ADC values in normal breast measured from Beltrami-SR were preserved compared to low-resolution images (1.91 versus 1.97 ×10-3 mm2 /s, P = .1).Conclusion: A combination of rs-EPI and SR allows 3D, 1-mm isotropic breast DWI data to be obtained with better SNR than a native 1-mm isotropic acquisition. The proposed DWI protocol might be of interest for breast cancer monitoring/screening without injection.

Exploiting redundancies between multiple images of an MRI examination can be formalized as the joint reconstruction of these images. The anatomy is preserved indeed so that specific constraints can be implemented (e.g. most of the features or spatial gradients should be in the same place in all these images) and only the contrast changes from one image to another need to be encoded. The application of this concept is particularly challenging in cardiovascular and body imaging due to the complex organ deformations, especially with the patient breathing. In this study a joint optimization framework is proposed for reconstructing multiple MR images together with a nonrigid motion model. The motion model takes into account both intra-image and inter-image motion and therefore can correct for most ghosting/blurring artifacts and misregistration between images. The framework was validated with free-breathing myocardial ${\rm T}_{2}$ mapping experiments from nine heart transplant patients at 1.5 T. Results showed improved image quality and excellent image alignment with the multi-image reconstruction compared to the independent reconstruction of each image. Segment-wise myocardial ${\rm T}_{2}$ values were in good agreement with the reference values obtained from multiple breath-holds (62.5 $\pm$ 11.1 ms against 62.2 $\pm$ 11.2 ms which was not significant with ${\rm p}=0.49$ ).

International audience; This work concerns the construction of articulatory models for synthesis of speech, and more specifically the velum and epiglottis. The direct application of principal component analysis to the contours of these articulators extracted from MRI images results in unrealistic factors due to delineation errors. The approach described in this paper relies on the application of PCA to the centerline of the articulator and a simple reconstruction algorithm to obtain the global articulator contour. The complete articulatory model was constructed from static Magnetic Resonance (MR) images because their quality is much better than that of dynamic MR images. We thus assessed the extent to which the model constructed from static images is capable of approaching the vocal tract shape in MR images recorded at 55 Hz for continuous speech. The analysis of reconstruction errors shows that it is necessary to add dynamic images to the database of static images, in particular to approach the tongue shape for the /l/ sound.

International audience; Purpose: Segmentation of cardiac cine MRI data is routinely used for the volumetric analysis of cardiac function. Conventionally, 2D contours are drawn on short-axis (SAX) image stacks with relatively thick slices (typically 8 mm). Here, an acquisition/reconstruction strategy is used for obtaining isotropic 3D cine datasets; reformatted slices are then used to optimize the manual segmentation workflow.Methods: Isotropic 3D cine datasets were obtained from multiple 2D cine stacks (acquired during free-breathing in SAX and long-axis (LAX) orientations) using nonrigid motion correction (cine-GRICS method) and super-resolution. Several manual segmentation strategies were then compared, including conventional SAX segmentation, LAX segmentation in three views only, and combinations of SAX and LAX slices. An implicit B-spline surface reconstruction algorithm is proposed to reconstruct the left ventricular cavity surface from the sparse set of 2D contours.Results: All tested sparse segmentation strategies were in good agreement, with Dice scores above 0.9 despite using fewer slices (3-6 sparse slices instead of 8-10 contiguous SAX slices). When compared to independent phase-contrast flow measurements, stroke volumes computed from four or six sparse slices had slightly higher precision than conventional SAX segmentation (error standard deviation of 5.4 mL against 6.1 mL) at the cost of slightly lower accuracy (bias of -1.2 mL against 0.2 mL). Functional parameters also showed a trend to improved precision, including end-diastolic volumes, end-systolic volumes, and ejection fractions).Conclusion: The postprocessing workflow of 3D isotropic cardiac imaging strategies can be optimized using sparse segmentation and 3D surface reconstruction. Magn Reson Med 79:2665-2675, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Object: To demonstrate the possibility to model the power deposited at the electrode of an insulated cable in gel at 64MHz with a transmission line model with a strictly passive electrode model. This offers a more related to physics alternative to the transfer function model. The equivalence between both models is shown.Materials and Methods: In a first step, the possibility of modeling an insulated cable with a transmission line model was analyzed through full-wave numerical simulations. An electrode model that has a physical meaning was proposed. The transmission line model predictions were confronted to experimental and simulated data of the transfer function of a cable and of the resonant behavior as a function of length of cables with different termination conditions.Results: The assumption of a transmission line model which underlies the transfer function model is right for a simple cable embedded in tissue imitating gel. A transmission line model extracted from a transfer function allows to predict the resonant behavior of two cables with different termination conditions.Conclusion: A transmission line model of an insulated cable embedded in tissue imitating gel offers a more directly related to physics alternative to the transfer function model.

International audience; The paper presents a method to acquire articulatory data from a sequence of MRI images at a high framerate. The acquisition rate is enhanced by partially collecting data in the kt-space. The combination of compressed sensing technique, along with homodyne reconstruction, enables the missing data to be recovered. The good reconstruction is guaranteed by an appropriate design of the sampling pattern. It is based on a pseudo-random Cartesian scheme, where each line is partially acquired for use of the homodyne reconstruction, and where the lines are pseudo-randomly sampled: central lines are constantly acquired and the sampling density decreases as the lines are far from the center. Application on real speech data show that the framework enables dynamic sequences of vocal tract images to be recovered at a framerate higher than 30 frames per second and with a spatial resolution of 1 mm. A method to extract articulatory data from contour identification is presented. It is intended, in fine, to be used for the creation of a large database of articulatory data.

Purpose: To assess cardiac function by means of a novel free-breathing cardiac magnetic resonance imaging (MRI) strategy. Materials and Methods: A stack of ungated 2D steady-state free precession (SSFP) slices was acquired during free breathing and reconstructed as cardiac cine imaging based on the generalized reconstruction by inversion of coupled systems (GRICS). A motion-compensated sliding window approach allows reconstructing cine movies with most motion artifacts cancelled. The proposed reconstruction uses prior knowledge from respiratory belts and electrocardiogram recordings and features a piecewise linear model that relates the electrocardiogram signal to cardiac displacements. The free-breathing protocol was validated in six subjects against a standard breath-held protocol. Results: Image sharpness, as assessed by the image gradient entropy, was comparable to that of breath-held images and significantly better than in uncorrected images. Volumetric parameters of cardiac function in the left ventricle (LV) and right ventricle (RV) were similar, including end-systolic volumes, end-diastolic volumes and mass, stroke volumes, and ejection fractions (with differences of 3% ± 2.4 in the LV and 2.9% ± 4.4 in the RV). The duration of the free-breathing protocol was nearly the same as the breath-held protocol. Conclusion: Free-breathing cine-GRICS enables accurate assessment of volumetric parameters of cardiac function with efficient correction of motion. J. Magn. Reson. Imaging 2012;340-351. © 2011 Wiley Periodicals, Inc.

Black Blood Fast Spin Echo imaging of the heart is usually performed during mid-diastolic rest. This is a direct consequence of the long inversion time required to suppress the blood signal, which is constrained by the T(1) of the blood, and of the heart rate. To overcome these constraints, and to acquire black blood images in the end-systolic rest period, a new approach is introduced aiming at adaptively predicting the best time to prepare and acquire MR signals. It is based on a RR interval prediction algorithm and on a cardiac cycle model. The proposed method was applied to 14 healthy volunteers and is compared to a simple alternative method using a fixed delay and to the standard black blood imaging method for imaging in the mid-diastolic rest period. Results show that the proposed method offers an increased robustness in terms of trigger delay error and image quality compared to the tested simple alternative. Also, it has been shown by qualitative analysis done by an experienced observer that the right ventricle, especially the thin right ventricle free wall, is better depicted with our method than with the standard mid-diastolic rest acquisition.

This paper describes a rigorous framework for reconstructing MR images of the heart, acquired continuously over the cardiac and respiratory cycle. The framework generalizes existing techniques, commonly referred to as retrospective gating, and is based on the properties of reproducing kernel Hilbert spaces. The reconstruction problem is formulated as a moment problem in a multidimensional reproducing kernel Hilbert spaces (a two-dimensional space for cardiac and respiratory resolved imaging). Several reproducing kernel Hilbert spaces were tested and compared, including those corresponding to commonly used interpolation techniques (sinc-based and splines kernels) and a more specific kernel allowed by the framework (based on a first-order Sobolev RKHS). The Sobolev reproducing kernel Hilbert spaces was shown to allow improved reconstructions in both simulated and real data from healthy volunteers, acquired in free breathing.

Background During pediatric cardiac Cine-MRI, data acquired during cycles of different lengths must be combined. Feinstein’s model is used to project multiple cardiac cycles of variable lengths into a mean cycle. Methods 1/The temporal errors during Feinstein’s projection were computed in 306 cardiac cycles fully characterized by tissue Doppler imaging with 6-phase analysis (from a population of 7 children and young adults). 2/The effects of these temporal errors on tissue velocities were assessed by simulating a typical tissue phase mapping acquisition and reconstruction. 3/Myocardial velocities curves, extracted from high-resolution phase-contrast cine images, were compared for the 6 volunteers with lowest and highest heart rate variability, within a population of 36young adults. Results 1/The mean of temporal misalignments was 30ms over the cardiac cycle but reached 60ms during early diastole. 2/During phase contrast MRI simulation, early diastole velocity peaks were diminished by 5cm/s leading to virtual disappearance of isovolumic relaxation peaks. 3/The smoothing and erasing of isovolumic relaxation peaks was confirmed on tissue phase mapping velocity curves, between subjects with low and high heart rate variability (p=0.05). Conclusions Feinstein cardiac model creates temporal misalignments that impair high temporal resolution (notably for phase contrast cine imaging) in a population of high heart rate variations such as in paediatry (figure next page). Download : Download high-res image (187KB) Download : Download full-size image Abstract 0217 – Figure: Velocity curves with/without heart rate variation

Exploiting redundancies between multiple images of an MRI examination can be formalized as the joint reconstruction of these images. The anatomy is preserved indeed so that specific constraints can be implemented (e.g. most of the features or spatial gradients should be in the same place in all these images) and only the contrast changes from one image to another need to be encoded. The application of this concept is particularly challenging in cardiovascular and body imaging due to the complex organ deformations, especially with the patient breathing. In this study a joint optimization framework is proposed for reconstructing multiple MR images together with a nonrigid motion model. The motion model takes into account both intra-image and inter-image motion and therefore can correct for most ghosting/blurring artifacts and misregistration between images. The framework was validated with free-breathing myocardial T2 mapping experiments from nine heart transplant patients at 1.5 T. Results showed improved image quality and excellent image alignment with the multi-image reconstruction compared to the independent reconstruction of each image. Segment-wise myocardial T2 values were in good agreement with the reference values obtained from multiple breath-holds (62.5 ± 11.1 ms against 62.2 ± 11.2 ms which was not significant with p=0.49).

International audience; Cardiac cine MRI with 3D isotropic resolution is challenging as it requires efficient data acquisition and motion management. It is proposed to use a 2D balanced SSFP (steady-state free precession) sequence rather than its 3D version as it provides better contrast between blood and tissue. In order to obtain 3D isotropic images, 2D multi-slice datasets are acquired in different orientations (short axis, horizontal long axis and vertical long axis) while the patient is breathing freely. Image reconstruction is performed in two steps: (i) a motion-compensated reconstruction of each image stack corrects for nonrigid cardiac and respiratory motion; (ii) a super-resolution (SR) algorithm combines the three motion-corrected volumes (with low resolution in the slice direction) into a single volume with isotropic resolution. The SR reconstruction was implemented with two regularization schemes including a conventional one (Tikhonov) and a feature-preserving one (Beltrami). The method was validated in 8 volunteers and 10 patients with breathing difficulties. Image sharpness, as assessed by intensity profiles and by objective metrics based on the structure tensor, was improved with both SR techniques. The Beltrami constraint provided efficient denoising without altering the effective resolution.

International audience; Non-invasive quantitative assessment of articular cartilage integrity is essential for early detection and evaluation of osteoarthritis (OA) and for the follow-up of stem-cell-driven cartilage engineering. In this study, we investigated the feasibility of exploiting diffusion tensor imaging (DTI) on porcine knee joints with a clinical magnetic resonance (MR) scanner to extract micro-structural information in order to complement biochemical information quantified by T2 maps. We propose an MR protocol for quantifying T2 and cartilage microstructure with diffusion MR on a clinical scanner. Preliminary results were obtained on four pig knee joints using a 3 T GE clinical MRI scanner and an 8-channel knee coil array. The measured cartilage volume, T2 values, apparent diffusion coefficient and fractional anisotropy (FA) of femoral and tibial cartilage were respectively 9.8/2.3 mm2, 67.0/56.1 ms, 1.3/1.3×10-3 mm2/s and 0.4/0.3. This new protocol has the potential to be combined in vivo with quantitative assessment of both cartilage degradation and restoration in osteoarthritis.

Summary This study demonstrates the feasibility of free-breathing phase-contrast CINE MRI without averaging. A new version of the CINE GRICS algorithm[1] was used to correct for motion. Background Phase-contrast MRI encodes speed and direction of moving spins by means of toggling a bipolar gradient. It is a valuable tool for assessing conditions affecting the vascular system by measuring the velocity of flowing blood[2]. Clinically, this sequence is performed in breath-hold or in free breathing but, in the latter case, using signal averaging. We propose to demonstrate the feasibility of free-breathing phase-contrast CINE MRI without averaging exploiting the acquisition redundancy by applying a new version of the CINE GRICS algorithm[1] to correct for motion. Methods Cardiac examination (approved by our local ethics committee) was performed on one normal volunteer during which three 2D phase-contrast CINE MRI sequences (common parameters: 256x128 acquisition matrix, 6 views per segment (vps), 32 reconstructed cardiac phases, 150 cm/sec VENC, slice direction velocity encoding, 5 mm slice thickness, 44 cm FOV, 62.5 kHz bandwidth, 3.05/8.08 ms TE/TR, 15° flip angle) were acquired on a 3T scanner (Signa HDxt, GE Healthcare, Milwaukee, WI) with a 8-element cardiac coil : (1) breath-held (2) averaged (3 NEX) in free breathing (3) in free breathing storing the raw data of 3 NEX to an external computer for offline processing. Signals from a respiratory belt were carried by a custom Maglife patient monitoring system (Schiller Medical, France) and recorded with a dedicated home-made hardware. Offline processing consisted of splitting the raw data from the 2 velocity encoding steps thus giving 2 sets of

Magnetic resonance images are affected by motion artefacts due to breathing and cardiac beating that occur during the acquisition. Methods for joint reconstruction of image and motion have been proposed recently. Such optimization problems are ill-conditioned, therefore regularization methods are required such as motion smoothness constraints using the Tikhonov method. However with Tikhonov methods the solution often relies on a good choice of the regularization parameter μ, especially in large parameter search spaces (e.g. in 3D reconstructions). In this paper, we propose an adaptive, implicit regularization method which results in subject-specific, spatially varying smoothness constraints on the motion model. It is based on the idea of solving for motion only in certain key points that form a mesh. A practical algorithm is proposed for generating this mesh automatically. The proposed method is shown to have a better convergence rate than the Tikhonov method, both in silico and in vivo. The accuracy of the reconstructed image and motion is also improved.

The analysis of abdominal and thoracic dynamic contrast-enhanced MRI is often impaired by artifacts and misregistration caused by physiological motion. Breath-hold is too short to cover long acquisitions. A novel multipurpose reconstruction technique, entitled dynamic contrast-enhanced generalized reconstruction by inversion of coupled systems, is presented. It performs respiratory motion compensation in terms of both motion artefact correction and registration. It comprises motion modeling and contrast-change modeling. The method feeds on physiological signals and x-f space properties of dynamic series to invert a coupled system of linear equations. The unknowns solved for represent the parameters for a linear nonrigid motion model and the parameters for a linear contrast-change model based on B-splines. Performance is demonstrated on myocardial perfusion imaging, on six simulated data sets and six clinical exams. The main purpose consists in removing motion-induced errors from time–intensity curves, thus improving curve analysis and postprocessing in general. This method alleviates postprocessing difficulties in dynamic contrast-enhanced MRI and opens new possibilities for dynamic contrast-enhanced MRI analysis. Magn Reson Med, 2011. © 2010 Wiley-Liss, Inc.

International audience; This article describes a general framework for multiple coil MRI reconstruction in the presence of elastic physiological motion. On the assumption that motion is known or can be predicted, it is shown that the reconstruction problem is equivalent to solving an integral equation--known in the literature as a Fredholm equation of the first kind--with a generalized kernel comprising Fourier and coil sensitivity encoding, modified by physiological motion information. Numerical solutions are found using an iterative linear system solver. The different steps in the numerical resolution are discussed, in particular it is shown how over-determination can be used to improve the conditioning of the generalized encoding operator. Practical implementation requires prior knowledge of displacement fields, so a model of patient motion is described which allows elastic displacements to be predicted from various input signals (e.g., respiratory belts, ECG, navigator echoes), after a free-breathing calibration scan. Practical implementation was demonstrated with a moving phantom setup and in two free-breathing healthy subjects, with images from the thoracic-abdominal region. Results show that the method effectively suppresses the motion blurring/ghosting artifacts, and that scan repetitions can be used as a source of over-determination to improve the reconstruction.

International audience; A system was developed for real-time electrocardiogram (ECG) analysis and artifact correction during magnetic resonance (MR) scanning, to improve patient monitoring and triggering of MR data acquisitions. Based on the assumption that artifact production by magnetic field gradient switching represents a linear time invariant process, a noise cancellation (NC) method is applied to ECG artifact linear prediction. This linear prediction is performed using a digital finite impulse response (FIR) matrix, that is computed employing ECG and gradient waveforms recorded during a training scan. The FIR filters are used during further scanning to predict artifacts by convolution of the gradient waveforms. Subtracting the artifacts from the raw ECG signal produces the correction with minimal delay. Validation of the system was performed both off-line, using prerecorded signals, and under actual examination conditions. The method is implemented using a specially designed Signal Analyzer and Event Controller (SAEC) computer and electronics. Real-time operation was demonstrated at 1 kHz with a delay of only 1 ms introduced by the processing. The system opens the possibility of automatic monitoring algorithms for electrophysiological signals in the MR environment.

Myocardial T2 mapping is a valuable tool for tissue characterization and oedema visualization. For instance, it is used to detect early rejection of heart transplant [1]. T2 values are usually estimated by performing several black blood Fast Spin Echo (FSE) sequences with different Echo Times (TE), what requires multiple breath holds. Successive apneas could lead to misregistration between images and to patient discomfort. A method allowing free breathing myocardial T2 measurements has been recently proposed and evaluated at 3T [2]. Results at 1.5T are presented here.

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Methods Eighteen healthy volunteers underwent cardiac MRI examination on a Signa HDxt 3T scanner (General Electric, Waukesha). A phase contrast sequence modified to acquire only the central k-space line was used in a midventricular small axis scan plane with through-plane velocity encoding during 128 heartbeats. The frequency encoding direction was angulated to encompass the projection of the left ventricular outflow tract plane (Figure 1). Relevant parameters were: 256-point frequency k-space size, 35 cm FOV, 1 view per segment, 150 cm/s velocity encoding and 7 ms TR. Data were Fourier transformed into 1D+t image space, subjected to SVD decomposition for automatic spatial segmentation and finally automatic temporal domain peak detection. This process lead to the measurement of four durations for each heartbeat (RR): IsoVolumic Contraction (IVC), Systolic Ejection (SE), IsoVolumic Relaxation (IVR), and Diastolic Diastasis (DD). For every cardiac cycle, the results of the automatic detection were quality controlled by a physician who could either discard the data, correct or accept it. Myocardiac Performance Index (MPI) [4] was computed as (IVC+IVR)/SE as well as normalized systole duration (IVC+SE)/RR and normalized diastasis duration DD/RR. These values were checked

In this thesis we used MRI (Magnetic Resonance Imaging) data of the vocal tract to study speech production. The first part consist of the study of the impact that the velum, the epiglottis and the head position has on the phonation of five french vowels. Acoustic simulations were used to compare the formants of the studied cases with the reference in order to measure their impact. For this part of the work, we used 3D static MR (Magnetic Resonance) images. As speech is usually a dynamic phenomenon, a question arose, whether it would be possible to process the 3D data in order to incorporate dynamic information of continuous speech. Therefore the second part presents some algorithms that one can use in order to enhance speech production data. Several image transformations were combined in order to generate estimations of vocal tract shapes which are more informative than the original ones. At this point, we envisaged apart from enhancing speech production data, to create a generic speaker model that could provide enhanced information not for a specific subject, but globally for speech. As a result, we devoted the third part in the investigation of an algorithm that one can use to create a spatiotemporal atlas of the vocal tract which can be used as a reference or standard speaker for speech studies as it is speaker independent. Finally, the last part of the thesis, refers to a selection of open questions of the field that are still left unanswered, some interesting directions that one can expand this thesis and some potential approaches that could help someone move forward towards these directions., Dans cette thèse, nous avons utilisé les données de l’IRM du conduit vocal pour étudier la production de la parole. La première partie consiste en l’étude de l’impact que le vélum, l’épiglotte et la position de la tête a sur la phonation de cinq voyelles françaises. Des simulations acoustiques ont été utilisées pour comparer les formants des cas étudiés avec la référence afin de mesurer leur impact. Pour cette partie du travail, nous avons utilisé des IRM statiques en 3D. Comme la parole est généralement une phénomène dynamique une question s’est posée, à savoir s’il serait possible de traiter les données 3D afin d’incorporer des informations temporelles de la parole continue. Par conséquent, la deuxième partie présente quelques algorithmes que l’on peut utiliser pour améliorer les données de production de la parole. Plusieurs transformations d’images ont été combinées afin de générer des estimations des formes du conduit vocal qui sont plus informatives que les originales. À ce stade, nous avons envisagé, outre l’amélioration des données de production de la parole, de créer un modèle de référence générique qui pourrait fournir des informations améliorées non pas pour un sujet spécifique, mais globalement pour la parole. C’est pourquoi nous avons consacré la troisième partie l’étude d’un algorithme permettant de créer un atlas spatio-temporel de l’appareil vocal qui peut être utilisé comme référence ou standard pour l’étude de la parole car il est indépendant du locuteur. Enfin, la dernière partie de la thèse, fait référence à une sélection de questions ouvertes du domaine qui restent encore sans réponse, quelques pistes intéressantes que l’on peut développer à partir de cette thèse et quelques approches potentielles qui pourraient être envisager afin de répondre à ces questions.

Diffusion-weighted imaging (DWI) is a promising tool to increase the specificity of MRI for breast cancer screening. However, the field of view covering the breasts makes the DWI at high resolution difficult and the images obtained have low signal-to-noise ratios (SNR). The current DWI techniques are limited by the spatial resolution, mainly a slice thickness greater than or equal to 3 mm. In this work, an isotropic DWI method was developed to obtain high resolution isotropic images (1x1x1 mm3) covering the entire breast. These images are obtained by combining: (i) a readout-segmented DW-EPI sequence (rs-EPI), with several segments of k-space and echo navigator providing high in-plane resolution, (ii) a super-resolution (SR) strategy, which consists of acquiring three datasets with thick slices (3 mm) and 1mm-shifts in the slice direction, (iii) and combining them into a 1x1x1 mm3 dataset using a dedicated reconstruction. Several SR reconstruction schemes were investigated, based on different regularizations. The proposed SR strategy was compared to native 1x1x1 mm3 acquisitions (i.e. with 1 mm slice thickness) on eight healthy subjects, and synthetics phantoms. To validate the SR method, we used several methods: Monte Carlo simulations, SNR measurements and sharpness metrics, the apparent diffusion coefficient (ADC) values in normal breast tissue and breast diffusion/resolution phantom were also compared. A new clinical research protocol is proposed to evaluate the effectiveness of the high resolution diffusion sequence on breast cancer screening. The aim of this protocol is to replace the contrast-enhanced perfusion by the diffusion sequence for screening., L’imagerie pondérée en diffusion (DWI) représente un outil prometteur pour augmenter la spécificité de l’IRM mammaire en vue du dépistage du cancer du sein. L’épaisseur de coupe pour une acquisition ayant un rapport signal sur bruit suffisant et couvrant les seins dans un temps compatible avec un examen clinique, reste égale ou supérieur à 3 mm, limitant la possibilité de dépistage. Dans ce travail, une méthode DWI isotrope a été développée pour obtenir des images haute résolution isotropes (1x1x1 mm3) couvrant entièrement les seins. Ces images sont obtenues en combinant : (i) une séquence à train de lecture segmenté (rs-EPI) qui correspond à plusieurs segments de lecture EPI avec écho navigation, permettant d’obtenir de hautes résolutions dans le plan, (ii) une stratégie de super-résolution (SR) consistant à acquérir trois jeux de données avec des coupes épaisses (3 mm) et des décalages de 1 mm dans le sens de coupe entre chaque acquisition et (iii) une méthode de reconstruction dédiée pour obtenir des données isotropes 1x1x1 mm3. Plusieurs schémas de reconstruction basés sur différentes régularisations ont été étudiés. La SR proposée a été comparée aux acquisitions natives de 1x1x1 mm3 sans algorithme SR sur huit sujets sains et des fantômes synthétiques. Pour valider la méthode SR, nous avons utilisé plusieurs méthodes : des simulations Monte-Carlo, des mesures de SNR et des métriques de netteté et enfin le coefficient de diffusion apparent (ADC). Ces validations ont aussi été confirmées par des mesures expérimentales sur fantômes contenant des objets de dimensions et diffusion calibrées. Un nouveau protocole de recherche clinique est proposé pour évaluer l’efficacité de la séquence de diffusion à haute résolution sur le dépistage d’un cancer mammaire, dans le but de remplacer la séquence de perfusion avec injection de produit de contraste utilisée en IRM mammaire.

With an aging population worldwide, more and more persons are at risk of suffering from pathologies which are best diagnosed or monitored with Magnetic Resonance Imaging (MRI): thus, the number of MRI exams is constantly increasing. Moreover, elderly patients being likely to undergo a medical device implantation (such as a pacemaker or a hip prosthesis) the safety of implanted patient in MRI is crucial. The medical imaging technique involves indeed different electromagnetic fields which can interact with a metallic implant and lead to potential hazard for the patient. Even though compatibility guidelines exist today to subject individually medical devices to standardized tests and ensure their harmlessness in an MRI environment, the interactions between multiple medical devices with respect to radiofrequency electromagnetic waves (and to the hazards that may follow) are a complex research area that has to be understood. The aim of this thesis is to study these interactions on different levels: intra-device interactions, inter-devices interactions and interactions between a device and several antennas. A prediction method has been proposed to simplify the study of large range of implants, according to the variations of parameters characterizing the different parts of a prosthesis. Electromagnetic and thermal simulations, associated with experimental measurements in a clinical MRI environment, allowed to highlight a coupling phenomenon between two simplified implants and to introduce a new metric to quantify them. Finally, a multi-antenna study led to some insights to answer the question of the safety of an implanted patient with several antennas, in a configuration similar to a clinical routine exam. Thus, the research work presented in this thesis allowed to assess the interactions with respect to MRI radiofrequency in presence of one or several medical devices and antennas, opening new prospects towards a safe MRI for everyone, Avec une population mondiale vieillissante, de plus en plus de personnes sont à risque de présenter des pathologies pour lesquelles l’Imagerie par Résonance Magnétique (IRM) est une modalité de choix : ainsi, le nombre d’examens IRM est en constante augmentation. Les patients âgés étant par ailleurs une population davantage susceptible de recevoir une implantation de dispositifs médicaux (tels qu’un pacemaker ou une prothèse de hanche), la sécurité des patients implantés en IRM est primordiale. En effet, cet appareil d’imagerie médicale fait intervenir différents champs électromagnétiques pouvant interagir avec un implant métallique et donner lieu à des risques potentiels pour le patient. Si des normes de compatibilité existent aujourd’hui pour soumettre individuellement les dispositifs médicaux à des tests standardisés et assurer leur innocuité en environnement IRM, les interactions entre multiples dispositifs médicaux vis-à-vis des ondes électromagnétiques radiofréquence (et des dangers qui peuvent en résulter) sont un domaine complexe qu’il est nécessaire de comprendre. L’objet de cette thèse est d’étudier ces interactions sur plusieurs niveaux : interactions intra-dispositif, interactions inter-dispositifs et interactions entre dispositif et plusieurs antennes. Une méthode de prédiction d’échauffement a été proposée pour simplifier l’étude de larges gammes d’implants, suivant les variations de paramètres caractérisant les différentes parties au sein d’une prothèse. Des simulations électromagnétiques et thermiques, associées à des mesures expérimentales dans un environnement IRM clinique, ont permis de mettre en évidence des phénomènes de couplages entre deux implants simplifiés et d’introduire une nouvelle métrique pour les quantifier. Enfin, une étude multi-antennes a fourni des éléments de réponse à la question de la sécurité d’un patient implanté en présence de plusieurs antennes, dans une configuration semblable à celle des examens en routine clinique. Les travaux présentés dans cette thèse ont ainsi permis d’évaluer les interactions vis-à-vis de la radiofréquence de l’IRM en présence d’un ou plusieurs dispositifs médicaux et antennes, ouvrant plusieurs perspectives pour aller vers une IRM sûre pour tous

The Magnetic Resonance Imaging (MRI) is a medical imaging modality using electromagnetic fields (EMF) in order to perform human body tomodensitometric images. Even if these fields are Non-Ionizing Radiations (NIR), some transitory effects can be felt by the staff working in the vicinity of the MRI. Such workers are qualified as “exposed” to EMF, even if all expert comities agree to say that no accumulative or long term effects have been identified yet. Short term effects are known and identified, from metallic taste in the mouth, nerve and muscle stimulation, to biologic tissue heating, which can be troublesome or dangerous. The main exposure concern comes from the MRI permanent static magnetic field (ranging from 1.5 T to 7 T). An expert comity, mandated by the World Health Organization (WHO), has therefore defined the evaluation of the exposure of the MRI workers to the static magnetic field as a priority. This was the focus of this PhD thesis. A light and autonomous static magnetic field monitor (called "exposimeter") has been developed. It allows the recording of the three-dimensional magnetic fields as well as workers’ movements. Its magnetic induction measurement accuracy has been ensured by a specific calibration, which takes into account non-linearity and non-orthogonality of the magnetic sensors. Based on exposimeter data, a magnetic induction extrapolation method has then been developed. This method allows the estimation of the EMF exposure at the head with sensors placed on the torso. Finally, a practical validation of the device has been performed in multiple MRI clinical and research centers, included clinical MRIs (1.5 T and 3 T), an interventional MRI (1.5 T) and an ultra-high field MRI (7 T). Metrics have been defined in order to precisely analyze and compare workers exposure. All the works presented in this PhD thesis open new perspectives such as long term static magnetic field exposure follow-up. Moreover, industrial transfer of the device has been performed and is currently being validated, L'Imagerie par Résonance Magnétique (IRM) est une modalité d'imagerie médicale reposant sur l'utilisation de champs électromagnétiques pour acquérir des images tomodensitométriques du corps humain. Bien qu'appartenant à la catégorie des rayonnements non-ionisants (RNI), des effets transitoires peuvent être ressentis par les personnels travaillant à proximité d'une IRM. Ces travailleurs sont dits exposés aux champs électromagnétiques, même si les différents comités d’experts s’accordent pour dire qu’aucun effet d’accumulation de dose ou d’effet à long terme n’a été trouvé. Ces effets à court terme, allant d’un goût métallique au niveau de la bouche à la stimulation nerveuse et à l'échauffement, sont connus et identifiés. Ils peuvent néanmoins provoquer une gêne, voire un danger, pour le travailleur. Ces préoccupations concernent spécifiquement le champ magnétique permanent (de 1,5 T à 7 T) utilisé par l'IRM. Un groupement d'experts mandatés par l'Organisation Mondiale de la Santé (OMS) a ainsi déterminé l'évaluation de l'exposition des travailleurs au champ magnétique statique comme une priorité importante. Les travaux de cette thèse ont permis de répondre à cette demande en définissant et en implémentant un dispositif de mesure autonome et léger permettant la mesure de cette exposition ainsi que la caractérisation des mouvements du travailleur. La justesse de la mesure d'induction magnétique réalisée par le dispositif est garantie par une méthode de correction numérique prenant en compte les défauts de linéarité et d'orthogonalité du capteur. Basée sur les données du capteur, une méthode d'ajustement de la mesure d'induction magnétique a ensuite été définie. Cette méthode permet, à partir d'une mesure réalisée au niveau du torse du travailleur, d'extrapoler la valeur d'induction magnétique au niveau de la tête de celui-ci. Enfin, une validation pratique du dispositif de mesure a été effectuée à travers un suivi de l'exposition des travailleurs IRM de trois centres d'imagerie médicale : imagerie clinique, imagerie interventionnelle et IRM ultra hauts champs (7~T). Des méthodes d'extraction de métriques permettant l'analyse précise et la comparaison de l'exposition des travailleurs au champ magnétique statique ont été proposées. Les travaux présentés dans cette thèse ont ouvert des perspectives intéressantes, permettant de réaliser le suivi à long terme de l'exposition des travailleurs au champ magnétique statique de façon quasi autonome. De plus, une industrialisation des outils et méthodes définis a pu être réalisée et est actuellement en cours de validation

Especially in cardiac and thoracic magnetic resonance imaging, respiratory motion and heart movement need to be registered using sensors like electrocardiogram or respiratory belts, in order to trigger the image acquisition or perform retrospective corrections. The placement of the sensors extends the patient preparation time, is critical for signal quality and, hence, image quality, and expects patients to tolerate additional sensors besides the imaging coil and space restrictions. In this work, the imaging coil itself was investigated for sensor-less motion registration. Motion-related variations of the electromagnetic properties of tissue have a direct effect on the coil impedance. Lung motion, myocardial-related motion, and vascular blood flow were registered with this method. The experimental findings were compared to electromagnetic simulations and the data gathered by state-of-the-art sensors, and retrospective motion correction with the GRICS algorithm was executed, En imagerie par résonance magnétique cardiaque et thoracique, les mouvements cardiaques et respiratoires sont enregistrés avec des capteurs tels que les capteurs ECG et les ceintures respiratoires pour synchroniser les acquisitions et pour pratiquer des corrections rétrospectives des images. Le positionnement de ces capteurs augmente le temps de préparation des patients. Il présuppose également la tolérance des patients à être placés dans un espace restreint et déjà contraint par l'antenne radio-fréquence (RF) nécessaire à l'imagerie. Enfin, ces capteurs peuvent diminuer la qualité du signal et donc celle des images. Dans ces travaux, l'antenne RF déjà présente pour la réalisation de l'examen d'imagerie a été elle-même étudiée en tant que capteur de mouvements. Les variations des propriétés électromagnétiques des tissus dues aux mouvements se répercutent de manière directe sur l'impédance de l'antenne. Les variations d'impédance induites par les mouvements ont été étudiées dans des dispositifs utilisant soit des antennes RF volumiques ou des antennes RF surfaciques sur des objets-test animés et sur des sujets sains. Les mouvements respiratoires, cardiaques et les taux sanguins ont été enregistrés avec cette méthode. Puis, les résultats expérimentaux ont été comparés à des simulations électromagnétiques et aux données de la littérature. Une correction de mouvements rétrospective avec l'algorithme GRICS a été appliquée à ces données démontrant la faisabilité de l'utilisation des antennes d'imagerie comme capteurs de mouvements

Cine MRI of cardiac contraction is a relatively slow imaging technique. Comparatively, patient motion, especially cardiac beating and breathing, are fast and can lead to imaging artefacts. Cardiac contraction velocity provides clinically useful information. Firstly, we have shown that making this measurement was possible using phase contrast Cine MRI, and that getting similar values as those obtained in clinical routine using cardiac echography. The condition is to reach high temporal resolution, but to do so, the acquisition duration must be longer than a breathhold. Free-breathing motion management was done by two approaches: by averaging then by motion compensation using Cine-GRICS. Secondly, in order to achieve high temporal resolution Cine reconstruction, we proposed a way to deal with changing heart rate during Cine MRI acquisition, by the construction of a patient adapted cardiac model using realtime phase contrast MRI. Finally, cardio-respiratory motion management was adapted to small animal Cine MRI thanks to IntraGate echo navigators, L'Imagerie par Résonance Magnétique de la cinématique de la contraction cardiaque est une technique d'imagerie relativement lente. En comparaison, les mouvements du patient, en particulier cardiaque et respiratoire, sont rapides et peuvent provoquer des artéfacts sur les images. La vitesse de contraction cardiaque apporte justement des informations cliniquement utiles. Premièrement, nous avons montré qu'il était possible d'effectuer cette mesure en IRM Cine à contraste de phase, et d'obtenir des valeurs similaires à celles obtenues de façon clinique en échographie cardiaque. La condition est d'obtenir une haute résolution temporelle, or, pour ce faire, la durée d'acquisition doit être plus longue qu'une apnée. La gestion du mouvement respiratoire en respiration libre a été réalisée de deux façons : avec moyennage puis avec correction de mouvement à l'aide de Cine-GRICS. Deuxièmement, pour atteindre une bonne reconstruction de la résolution temporelle en Cine, nous avons proposé une gestion temps réel de la variation du rythme cardiaque pendant l'acquisition IRM Cine, avec la construction d'un modèle cardiaque adapté au patient à l'aide de l'IRM à contraste de phase temps réel. Enfin, la gestion du mouvement cardio-respiratoire en IRM Cine est appliquée chez le petit animal à l'aide d'écho navigateurs IntraGate

The right ventricle (RV) has been neglected for a long time by cardiologists. Only recently, it has been pointed out as yielding pronostic or diagnostic value in numerous clinical situations. This thesis, after a review of the different methods used to assess the right ventricular function, stresses the limitations of the two most used methods to assess RV function: 1) Long-axis contraction indices fail to predict ejection fraction in a volumetric overload situation. 2) Short-axis MRI relies upon a rather difficult manual contouring of the endocardium. The main variation in this contouring occurs in the infundibulum (40%) and in the basal part around the tricuspid valve (40%). Then, we propose a novel geometric indice, easy to compute during a MRI examination and aimed to select the patients needing an accurate RV study. This index was validated within 340 patients and reduced the operator time of 35% without inducing any diagnostic error. The last part of this thesis concerns tissue phase-mapping. High temporal resolution is the key point for the accuracy of myocardial velocities and can be achieved by a simple averaging during free-breathing at the expense of longer acquisitions., Le ventricule droit (VD) fut longtemps oublié par les cardiologues mais l'expérience a montré qu'il conditionne le pronostic des patients dans de nombreuses situations cliniques et que l'évaluation de sa fonction est un élément diagnostique majeur lorsqu'une pathologie du VD est suspectée. Après une revue des différentes méthodes d'évaluation de la fonction ventriculaire droite, cette thèse explore tout d'abord les limites des deux méthodes d'évaluation du VD les plus répandues (IRM et échographie) : Premièrement, les indices de contraction longitudinale en échographie ne permettent pas de dépister correctement les altérations de la fraction d'éjection dans la situation d'une surcharge volumétrique notamment. Deuxièmement, l'IRM en coupes petit-axe présente des difficultés importantes de délinéation de l'endocarde. Les principaux écarts de contours entre deux observateurs concernent l'infundibulum pour 40% et la valve tricuspide pour 40% également. Dans une troisième partie, nous proposons un indice géométrique simple à calculer lors d'un examen IRM et permettant de pré-sélectionner les patients nécessitant une étude précise du VD. Cet indice validé sur 340 patients réduit le temps opérateur de 35% sans entrainer d'erreur diagnostique. La dernière partie de cette thèse s'intéresse 'a la mesure de la vitesse tissulaire du myocarde et aux indices fonctionnels qui en dérivent. Cette mesure nécessite une haute résolution temporelle qui peut être atteinte en IRM en respiration libre au prix d'une augmentation de la durée d'acquisition.

Magnetic resonance imaging (MRI) is a valuable tool for the clinical diagnosis for brain imaging as well as cardiac and abdominal imaging. For instance, MRI is the only modality that enables the visualization and characterization myocardial edema. However, motion remains a challenging problem for cardiac MRI. Breathing as well as cardiac beating have to be carefully handled during patient examination. Moreover they limit the achievable temporal and spatial resolution of the images. In this work an approach that takes these physiological motions into account during image reconstruction process has been proposed. It allows performing cardiac examination while breathing freely. First, an iterative reconstruction algorithm, that compensates motion estimated from a motion model constrained by physiological signals, is applied to morphological cardiac imaging. A semi-automatic method for edema detection has been tested on reconstructed images. It has also been associated with an adaptive acquisition strategy which enables free-breathing end-systolic imaging. This reconstruction has then been extended to the assessment of transverse relaxation times T2, which is used for myocardial edema characterization. The proposed method, ARTEMIS, enables free-breathing T2 mapping without additional acquisition time. The proposed free breathing approaches take advantage of physiological signals to estimate the motion that occurs during MR acquisitions. Several solutions have been tested to measure this information. Among them, accelerometer-based external sensors allow local measurements at several locations. Another approach consists in the use of k-space based measurements, which are "embedded" inside the MRI pulse sequence (navigator) and prevent from the requirement of additional recording hardware. Hence, several adaptive reconstruction algorithms were developed to obtain diagnostic information from free breathing acquisitions. These works allow performing efficient and accurate free breathing cardiac MRI, L'imagerie par résonance magnétique (IRM) est un outil remarquable pour le diagnostic clinique, aussi bien pour l'imagerie cérébrale que pour l'imagerie cardiaque et abdominale. C'est notamment la seule modalité d'imagerie qui permet de visualiser et de caractériser l'oedème myocardique. Cependant, la gestion du mouvement reste un problème récurrent en IRM cardiaque. Tant le battement cardiaque que la respiration nécessitent une prise en compte attentive lors de l'acquisition des images et limitent la résolution temporelle et spatiale accessible en pratique clinique courante. L'approche adoptée dans ce travail propose d'intégrer ces mouvements physiologiques dans le processus de reconstruction des images et permet ainsi de réaliser des explorations cardiaques en respiration libre. Un algorithme de reconstruction itératif, corrigeant les mouvements estimés par un modèle contraint par les signaux physiologiques, est dans un premier temps appliqué à l'imagerie cardiaque morphologique. Ses performances vis-à-vis d'une méthode semi-automatique de détection de l'oedème sont évaluées. Il a également été utilisé en association avec une méthode d'acquisition adaptative, afin de permettre l'acquisition d'images en télésystole et en respiration libre. Dans un deuxième temps, cette méthode a été étendue à la quantification du temps de relaxation transversale T2. La cartographie T2 du coeur fournit en effet une caractérisation de l'oedème myocardique. La méthode de reconstruction présentée, ARTEMIS, permet de réaliser cette cartographie en respiration libre et sans allongement du temps d'examen. Ces méthodes exploitent des signaux physiologiques afin d'estimer le mouvement ayant eu lieu pendant l'acquisition. Différentes solutions pour obtenir ces informations physiologiques ont donc également été explorées. Parmi elles, les capteurs à base d'accéléromètres permettent de multiplier les points de mesure alors que les informations "embarquées" dans la séquence d'acquisition IRM ("navigateur") facilitent le déploiement de ces techniques puisqu'elles évitent de recourir à des équipements supplémentaires. Ainsi pendant ces travaux, des méthodes de reconstruction adaptatives ont été développées afin de corriger le mouvement et de prendre en compte les spécificités de chaque patient. Ces travaux ouvrent la voie de l'imagerie par résonance magnétique cardiaque en respiration libre dans un contexte clinique