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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; Ventricular tachycardia (VT) is a life-threatening arrhythmia, which can be treated by catheter intervention. Accurate identification of the underlying reentrant circuit is often challenging, yet it is key to successful ablation of the VT. In practice, the cardiologist often uses electrocardiography (ECG) data provided by various catheter mapping techniques, including parameters acquired during sinus rhythm (voltage maps, presence of fragmented/late potentials) and during controlled pacing from different sites of the ventricle, so-called pace-mapping. A novel method is presented here to automatically extract the key information from pace-mapping data with automated detection of paced heartbeats from the surface ECG signals, using wavelet detection of pacing spikes and combined time/energy criteria, and automated delineation of paced beats, QRS peak, and QRS onset. This allows the generation of correlation gradient maps (indicating QRS morphology changes as the catheter is moved) and stimulus-to-QRS maps (sQRS, indicating the delay between pacing and activation of the healthy myocardium). The delineator is shown to be in good agreement with manual annotations from experts in a retrospective study of 18 VT ablation procedures. Paced-QRS detection had 95.2% sensitivity and 98.4% positive predictive value. Resulting sQRS maps had a mean absolute error of 11.1 ms, which was in the same range as the inter-observer errors (9.7 ms). The automatic processing drastically reduces the need for manual annotations. Therefore it makes it feasible to process and visualize, during the procedure, all the relevant parametric maps, which can be analyzed jointly to identify VT circuits and corresponding ablation targets.

Immer mehr Patienten mit aktiven implantierbaren medizinischen Geraten (AIMDs) benotigen Magnetresonanz(MR)-Untersuchungen. Die Hersteller sind dabei, die MR-Kompatibilitat ihrer AIMDs zu verbessern. Dafur werden verschiedenste Messmethoden und numerische Simulationen durchgefuhrt, um die Risiken in Bezug auf die Magnetresonanztomographie (MRT) zu evaluieren. Dieser Beitrag gibt einen Uberblick uber die verwendeten Testmethoden, welche die Interaktionen zwischen AIMDs mit Hochfrequenzfeldern und zeitveranderlichen magnetischen Feldgradienten untersuchen. Ein Literaturuberblick uber die bekannten Testmethoden fur Feldgradienten- und Hochfrequenzexposition von AIMDs mit Anschlussleitungen, insbesondere bei Neurostimulatoren, Cochlea-Implantaten und implantierten Arzneimittelpumpen, wird prasentiert. Der Stand der Technik und vielversprechende Verfahren werden diskutiert. ISO/TS 10974 beschreibt das Design von Hochfrequenz- und Gradienteninjektionsaufbauten fur konduktive Materialtests. Zur Messung der induzierten Spannungen und Strome durch Hochfrequenz- und Gradientenfelder sowie zur Uberwachung der AIMDs wahrend MR-Untersuchungen bei In-vitro-Tests wurde eine Vielzahl von Sensordesigns publiziert. Die Testmethoden sind so konservativ wie moglich ausgelegt und mussen den ungunstigsten Fall abdecken. Allerdings sind In-vitro-Messungen und Computersimulation weit davon entfernt, jede mogliche Konfiguration in ihrer Komplexitat und Einzigartigkeit zu erfassen. Fur sicherere MR-Untersuchungen werden in der rezentesten Forschung In-vivo-Testung vor der MR-Untersuchung, parallele Hochfrequenzsendetechniken und neue Sequenzen mit reduziertem Energieeintrag in der Anwesenheit von AIMDs vorgeschlagen.

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International audience; Magnetic resonance has become a backbone of medical imaging but suffers from inherently low sensitivity. This can be alleviated by improved radio frequency (RF) coils. Multi-turn multi-gap coaxial coils (MTMG-CCs) introduced in this work are flexible, form-fitting RF coils extending the concept of the single-turn single-gap CC by introducing multiple cable turns and/or gaps. It is demonstrated that this enables free choice of the coil diameter, and thus, optimizing it for the application to a certain anatomical site, while operating at the self-resonance frequency. An equivalent circuit for MTMG-CCs is modeled to predict their resonance frequency. Possible configurations regarding size, number of turns and gaps, and cable types for different B 0 field strengths are calculated. Standard copper wire loop coils (SCs) and flexible CCs made from commercial coaxial cable were fabricated as receive-only coils for 3 T and transmit/receive coils at 7 T with diameters between 4 and 15 cm. Electromagnetic simulations are used to investigate the currents on MTMG-CCs, and demonstrate comparable specific absorption rate of 7 T CCs and SCs. Signal-to-noise ratio (SNR), transmit efficiency, and active detuning performance of CCs were compared in bench tests and MR experiments. For the form-fitted receive-only CCs at 3 T no significant SNR degradation was found as compared to flat SCs on a balloon phantom. Form-fitted transmit/receive CCs at 7 T showed higher transmit efficiency and SNR. MTMG-CCs can be sized to optimize sensitivity, are flexible and lightweight, and could therefore enable the fabrication of wearable coils with improved patient comfort.

International audience; Introduction: T1-based method is considered as the gold standard for extracellular volume fraction (ECV) mapping. This technique requires at least a 10 min delay after injection to acquire the post injection T1 map. Quantitative analysis of Dynamic Contrast Enhancement (DCE) images could lead to an earlier estimation of an ECV like parameter (2 min). The purpose of this study was to design a quantitative pixel-wise DCE analysis workflow to assess the feasibility of an early estimation of ECV.Methods: Fourteen patients with mitral valve prolapse were included in this study. The MR protocol, performed on a 3 T MR scanner, included MOLLI sequences for T1 maps acquisition and a standard SR-turboFlash sequence for dynamic acquisition. DCE data were acquired for at least 120 s. We implemented a full DCE analysis pipeline with a pre-processing step using an innovative motion correction algorithm (RC-REG algorithm) and a post-processing step using the extended Tofts Model (ECVETM). Estimated ECVETM maps were compared to standard T1-based ECV maps (ECVT1) with both a Pearson correlation analysis and a group-wise analysis.Results: Image and map quality assessment showed systematic improvements using the proposed workflow. Strong correlation was found between ECVETM, and ECVT1 values (r-square = 0.87).Conclusion: A DCE analysis workflow based on RC-REG algorithm and ETM analysis can provide good quality parametric maps. Therefore, it is possible to extract ECV values from a 2 min-long DCE acquisition that are strongly correlated with ECV values from the T1 based method.

International audience; PurposeMultiple medical‐device leads implanted next to each other are often encountered in clinical practice. The aim of this work is to study a coupled transfer function model to evaluate the safety of these coupled leads submitted to the RF field of a 1.5T MRI scanner for a constant distance between both leads.MethodsThe effect of coupling on the heating of 2 cables with different termination conditions is evaluated experimentally. The coupled and single transfer functions are determined experimentally and used to predict the relative temperature increases of both cables alone and coupled. Two different coupled models, an additive model and a global model, are proposed. The coupled transfer functions are also simulated.ResultsThe coupling between cables has a strong influence on the resulting heating at the electrodes. The coupled additive transfer function model is a relevant tool to evaluate the heating of coupled leads separated by a constant distance. The global model underestimates the heating in one of the coupled cases by about 30%. The measured coupled transfer functions coincide with the simulated models.ConclusionIt is necessary to take into account the coupling effect between leads to evaluate the safety of implanted devices. This work shows that, in the case of 2 cables separated by a constant distance, that an experimentally determined coupled transfer function allows estimation of the heating of the 2 electrodes for a given incident field. Further work should take into account the in vivo varying distance between the 2 cables.

This paper tackles the problem of estimating exposure to static magnetic field (SMF) in magnetic resonance imaging (MRI) sites using a non-invasive approach. The proposed approach relies on a vision-based system to detect people's body parts and on a mathematical model to compute SMF exposure. A multi-view camera system was used to capture the MRI room, and a vision-based system was applied to detect body parts. The detected localization was then fed into a mathematical model to compute SMF exposure. In this study, we focused on exposure at the neck due to two main reasons. First, according to regulations, the limit of exposure at head and trunk for MR workers is higher than that for the general public. Second, it was easier to attach a dosimeter at the neck to perform measurements, which allowed a quantitative evaluation of our approach. This approach was applied to two scenarios simulating the daily movements of medical workers for which dosimeter measurements were also recorded. The results indicated that the proposed approach predicted occupational SMF exposure with reasonable accuracy compared with the dosimeter measurements. The proposed approach is a simple safe working procedure to estimate the exposure of MR workers at different parts of the body without wearing any marker detection. It can be applied to reduce occupational SMF exposure, without changes in workers' performances. For that reason, our non-invasive proposed method can be used as a simple safety tool to estimate occupational SMF exposure in MR sites. Bioelectromagnetics. 39:503-515, 2018.© 2018 Wiley Periodicals, Inc.

Background The relative modification of the myocardial volume between end-systole and end-diastole ([Formula: see text]) has already been assessed with different methods and falls in a range of 0.9–0.97 (mean value = 0.93). Purpose To estimate [Formula: see text] from the three longitudinal ([Formula: see text], circumferential ([Formula: see text]), and radial ([Formula: see text]) strains of the left ventricle using the formula: [Formula: see text] and to test whether this estimate of [Formula: see text] can be used as a marker of the echocardiography quality. Material and Methods Two hundred manuscripts, including a total of 34,690 patients or healthy volunteers, were identified in the Medline database containing values of [Formula: see text], [Formula: see text], and [Formula: see text] measured from echocardiography. Results The median value of was 0.93, in accordance with the literature, with no significant difference between patients or healthy volunteers ( P = 0.38). The proportion of studies with [Formula: see text] was 79%. When only considering groups of healthy volunteers, the studies failing this test had higher standard deviations for the three individual strains: 0.038 vs. 0.029 ( P = 0.02) for [Formula: see text]; 0.060 vs. 0.034 ( P –6) for [Formula: see text], and 0.243 vs. 0.101 ( P –14) for [Formula: see text]. Conclusion The median ratio of the left ventricular myocardial volumes between end-systole and end-diastole in the investigated studies was [Formula: see text]. The formula [Formula: see text] could be used to detect studies with inaccurate strain measurements.

A Magnetic Resonance Imaging (MRI) scanner uses three different electromagnetic fields (EMF) to produce body images: a static permanent magnetic field (MF), several pulsed magnetic gradients, and a radiofrequency pulse. As a result, any occupation that includes an MRI exposes workers to a strong MF. The World Health Organization has now given the monitoring of occupational EMF exposure a high priority. One design for a low-cost, compact MF exposure monitor (« MR exposimeter ») uses a set of three orthogonally assembled Hall sensors. However, at such a strong EMF exposure intensity, the non-linearity and non-orthogonality (misalignment between the three Hall sensors) have an impact on the accuracy of EMF measurement. Therefore, a sensor characterization was performed in order to link Hall-effect output voltage to MF intensity. The sensor was then calibrated using an orthogonalization matrix and an offset vector. For each sensor configuration, the matrix and vector parameters were optimized with a calibration set generated by the movement of a three-axis sensor inside homogeneous MF areas. Once calibrated, the sensor was tested at different MF intensities and returned accuracy improvements. This calibration procedure was tested on synthetic data and performed on experimental data. The calibration parameters can be easily reused by the user, and their stability could be used as a quality control sensor. Finally, real-time monitoring test for static MF exposure was completed and validated on an MRI worker during a typical working day. Bioelectromagnetics. 39:108-119, 2018. © 2018 Wiley Periodicals, Inc.

OBJECTIVE We aimed to characterize the association between pretreatment lesional volume measured on diffusion-weighted images and functional outcome, and estimate the impact on thrombectomy efficacy for ischemic stroke with anterior proximal intracranial arterial occlusion. METHODS Anterior circulation ischemic stroke patients who had pretreatment diffusion-weighted imaging in the THRACE study were included. Lesional volume was semiautomatically segmented. Logistic regression was applied to model clinical outcome as a function of lesional volume. Outcomes included functional independence (modified Rankin Scale [mRS] 0-2), degree of disability (ordinal mRS 0-6), and mortality at 3 months. RESULTS Of 298 included patients, with median lesional volume 17.2ml (interquartile range [IQR], 9.2-51.8) and median mRS 2 (IQR, 1-4), 51.0% achieved functional independence. Increased lesional volume was an independent predictor for a lower probability of functional independence (odds ratio [OR], 0.90 [95% confidence interval {CI}, 0.81-0.99] per 10ml; p

Purpose To evaluate by cardiac magnetic resonance imaging (MRI) the impact of microvascular obstruction (MVO) on regional left ventricular (LV) wall characteristics and local remodeling after acute myocardial infarction (AMI). Materials and Methods In all, 114 AMI patients underwent cardiac MRI at 3T within 2–4 days (baseline) and at 6 months (follow-up) after reperfusion. Late gadolinium enhancement and cine sequences were performed. The impact of MVO (ie, presence and extent) on regional wall thickening (WT, %), end-diastolic wall thickness (EDWT, mm), and local cavity change (mm) of LV were quantitatively analyzed. Local cavity change, calculated as surface-to-surface distance from registered endocardial surface meshes of cine imaging datasets acquired initially and at follow-up, was used to assess local remodeling. Results MVO was detected in 69 patients (60.5%). WT was significantly lower when MVO was present (P 75% with further thinning by MVO presence; and EDWT decreased with increasing MVO transmural extent (P < 0.0001). LV cavity shrank in patients without MVO, whereas it dilated in those with MVO. Local cavity changes were not significantly different by a region-to-region analysis throughout the LV within each group (P = 0.57 and 0.74, respectively). Conclusion MVO has a significant adverse effect on LV wall characteristics and LV remodeling. Postinfarct remodeling seems to be globally mediated rather than locally mediated during the first 6 months. Level of Evidence: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017.

International audience; Worker exposure to electromagnetic fields (EMF) is a growing concern of international commissions. A European directive from 2013 (2013/35/EU) recommend to estimate or measure EMF exposure of all exposed workers. Magnetic resonance imaging (MRI) workers are specially concerned by this point because they work all day long in the vicinity of a very strong magnet (generally 1.5 or 3 T), which cannot be turned off. Setting up a magnetic field monitoring device on these workers would therefore be a good way to ensure their security. European directive threshold adequacy could then be verified. But this verification does not ensure a complete analysis of the worker exposure. Such an analysis based on quality control charts and exposure time's metrics has been described in this paper. The proposed magnetic field exposure analysis has additionally been tested on a long-term exposure follow-up of 18 MRI workers during 2 months.

Purpose To evaluate the impact of a novel postprocessing denoising technique on accuracy and precision in myocardial T1 mapping. Materials and Methods This study introduces a fast and robust denoising method developed for magnetic resonance T1 mapping. The technique imposes edge-preserving regularity and exploits the co-occurence of spatial gradients in the acquired T1-weighted images. The proposed approach was assessed in simulations, ex vivo data and in vivo imaging on a cohort of 16 healthy volunteers (12 males, average age 39 ± 8 years, 62 ± 9 bpm) both in pre- and postcontrast injection. The method was evaluated in myocardial T1 mapping at 3T with a saturation-recovery technique that is accurate but sensitive to noise. ROIs in the myocardium and left-ventricle blood pool were analyzed by an experienced reader. Mean T1 values and standard deviation were extracted and compared in all studies. Results Simulations on synthetic phantom showed signal-to-noise ratio and sharpness improvement with the proposed method in comparison with conventional denoising. In vivo results demonstrated that our method preserves accuracy, as no difference in mean T1 values was observed in the myocardium (precontrast: 1433/1426 msec, 95%CI: [−40.7, 55.9], p = 0.75, postcontrast: 766/759 msec, 95%CI: [−60.7, 77.2], p = 0.8). Meanwhile, precision was improved with standard deviations of T1 values being significantly decreased (precontrast: 223/151 msec, 95%CI: [27.3, 116.5], p = 0.003, postcontrast: 176/135 msec, 95%CI: [5.5, 77.1], p = 0.03). Conclusion The proposed denoising method preserves accuracy and improves precision in myocardial T1 mapping, with the potential to offer better map visualization and analysis. Level of Evidence: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1377–1388.

Aims Our study assesses the value of electrograms (EGMs) characteristics to identify a ventricular tachycardia (VT) isthmus entrance in patients with post-infarct VT. Post-infarct VTs are mostly due to a re-entrant circuit. A pacemapping (PM) approach is able to localize the VT isthmus during sinus rhythm. Limited data are available about the role of local EGMs in defining VT isthmus location. Methods and results Twenty consecutive patients (70% male) referred for post-infarct VT catheter ablation were included in the present study. The VT isthmus was defined according to the PM method. At each recording site, 10 characteristics of the local EGM were assessed to predict the location of the VT isthmus entrance. In total, 924 EGMs were acquired, of which 127 were located in the VT isthmus entrance. Logistic regression analysis showed that bipolar voltage, number of EGM positive peaks, and sQRS interval were independently associated with VT isthmus entrance location. The ROC curve best fitted the model at the cut-off 0.1641 (sensitivity 72%, specificity 75.2%, positive predictive value 31.3%, negative predictive value 94.4%, area under the curve 0.78, P Conclusion Our study suggests that three EGM characteristics: bipolar voltage, number of positive peaks, and sQRS interval can successfully identify a VT isthmus entrance in post-infarct patients.

International audience; Purpose: Current electrocardiography (ECG) devices in MRI use non-conventional electrode placement, have a narrow bandwidth, and suffer from signal distortions including magnetohydrodynamic (MHD) effects and gradient-induced artifacts. In this work a system is proposed to obtain a high-quality 12-lead ECG.Methods: A network of N electrically independent MR-compatible ECG sensors was developed (N = 4 in this study). Each sensor uses a safe technology - short cables, preamplification/digitization close to the patient, and optical transmission - and provides three bipolar voltage leads. A matrix combination is applied to reconstruct a 12-lead ECG from the raw network signals. A subject-specific calibration is performed to identify the matrix coefficients, maximizing the similarity with a true 12-lead ECG, acquired with a conventional 12-lead device outside the scan room. The sensor network was subjected to radiofrequency heating phantom tests at 3T. It was then tested in four subjects, both at 1.5T and 3T.Results: Radiofrequency heating at 3T was within the MR-compatibility standards. The reconstructed 12-lead ECG showed minimal MHD artifacts and its morphology compared well with that of the true 12-lead ECG, as measured by correlation coefficients above 93% (respectively, 84%) for the QRS complex shape during steady-state free precession (SSFP) imaging at 1.5T (respectively, 3T).Conclusion: High-quality 12-lead ECG can be reconstructed by the proposed sensor network at 1.5T and 3T with reduced MHD artifacts compared to previous systems. The system might help improve patient monitoring and triggering and might also be of interest for interventional MRI and advanced cardiac MR applications.

Increasing numbers of patients with active implantable medical devices (AIMDs) require magnetic resonance (MR) examinations. The manufacturers are continuing to improve the MR compatibility of their AIMDs. To this end, a variety of measurement methods and numerical simulations are used to evaluate the risks associated with magnetic resonance imaging (MRI). In this article, test methods used to investigate interactions between AIMDs with radio frequency fields and time-varying magnetic gradient fields are reviewed. A literature review of known test methods for radio frequency and gradient field exposure of AIMDs with leads, in particular for neurostimulators, cochlear implants, and implanted infusion pumps, is presented. The state of the art and promising methods are discussed. ISO/TS 10974 describes the design of high frequency and gradient injection setups to test conductive materials. A large number of sensor designs have been published to measure the induced voltages and currents through radio frequency and gradient fields and for monitoring AIMDs during MR examinations in in vitro tests. The test methods should be planned to be as conservative as possible to cover the worst case scenario. However, in vitro measurements and computer simulation are far from being able to cover all possible configurations in their complexity and uniqueness. For safer MR examinations, current research recommends in vivo testing prior to MR, parallel radiofrequency transmission techniques, and new sequences with reduced energy input in the presence of AIMDs.

Background With ablation, the follow-up of preexcitation syndrome now is difficult to assess. The purpose was to collect data of children with a preexcitation syndrome studied on two separate occasions within a minimal interval of 1 year. Methods This is a retrospective chart review of 47 children initially aged 12 ± 4 years, who underwent two or more invasive electrophysiological studies (EPS) within 1–25 years of one another (6.3 ± 4.8) for occurrence of symptoms or new evaluation. Results Among initially symptomatic children (n = 25), four (19%) became asymptomatic and one presented life-threatening arrhythmia. Among asymptomatic children (n = 22), five became symptomatic (22.7%). Anterograde conduction disappeared in seven of 23 children with initially long accessory pathway-effective refractory period, but four of six had still induced atrioventricular reentrant tachycardia (AVRT). AVRT was induced at second EPS in three of 13 asymptomatic preexcitation syndrome with negative initial EPS. There were no spontaneous adverse events in the five children with criteria of malignancy at initial EPS; signs of malignancy disappeared in two. At multivariate analysis, AVRT at initial EPS was the only independent factor of symptomatic AVRT during follow-up. Absence of induced AVRT at initial EPS was the only factor of absence of symptoms and a negative study at the second EPS. Conclusions There were no significant changes of data in children after 6.3 ± 4.8 years of follow-up. Most children with spontaneous/inducible AVRTs at initial EPS had still inducible AVRT at second EPS. Induced AF conducted with high rate has a relatively low prognostic value for the prediction of adverse events.

Purpose: To compare three widely used methods for myocardial infarct (MI) sizing on late gadolinium-enhanced (LGE) magnetic resonance (MR) images: manual delineation and two semiautomated techniques (full-width at half-maximum [FWHM] and n-standard deviation [SD]). Materials and methods: 3T phase-sensitive inversion-recovery (PSIR) LGE images of 114 patients after an acute MI (2-4 days and 6 months) were analyzed by two independent observers to determine both total and core infarct sizes (TIS/CIS). Manual delineation served as the reference for determination of optimal thresholds for semiautomated methods after thresholding at multiple values. Reproducibility and accuracy were expressed as overall bias ± 95% limits of agreement. Results: Mean infarct sizes by manual methods were 39.0%/24.4% for the acute MI group (TIS/CIS) and 29.7%/17.3% for the chronic MI group. The optimal thresholds (ie, providing the closest mean value to the manual method) were FWHM30% and 3SD for the TIS measurement and FWHM45% and 6SD for the CIS measurement (paired t-test; all P > 0.05). The best reproducibility was obtained using FWHM. For TIS measurement in the acute MI group, intra-/interobserver agreements, from Bland-Altman analysis, with FWHM30%, 3SD, and manual were -0.02 ± 7.74%/-0.74 ± 5.52%, 0.31 ± 9.78%/2.96 ± 16.62% and -2.12 ± 8.86%/0.18 ± 16.12, respectively; in the chronic MI group, the corresponding values were 0.23 ± 3.5%/-2.28 ± 15.06, -0.29 ± 10.46%/3.12 ± 13.06% and 1.68 ± 6.52%/-2.88 ± 9.62%, respectively. A similar trend for reproducibility was obtained for CIS measurement. However, semiautomated methods produced inconsistent results (variabilities of 24-46%) compared to manual delineation. Conclusion: The FWHM technique was the most reproducible method for infarct sizing both in acute and chronic MI. However, both FWHM and n-SD methods showed limited accuracy compared to manual delineation. J. Magn. Reson. Imaging 2016;44:1206-1217.

International audience; Objective: Despite being routinely acquired during MRI examinations for triggering or monitoring purposes, electrocardiogram (ECG) signal recording and analysis remain challenging due to the inherent magnetic environment of an MRI scanner. The ECG signals are particularly distorted by the induction of electrical fields in the body by the MRI gradients. In this study, we propose a new hardware and software solution for the acquisition of ECG signal during MRI up to 3 T.Approach: Instead of restricting the sensor bandwidth to limit these gradient artifacts, the new sensor architecture has a higher bandwidth, higher sampling frequency and larger input dynamics, in order to acquire the ECG signals and the gradient artifacts more precisely. Signal processing based on a novel detection algorithm and blanking are then applied for improved artifact suppression.Main results: The proposed sensor allows the gradient artifacts to be acquired more precisely, and these artifacts are recorded with peak-to-peak amplitudes two orders of magnitude larger than for QRS complexes. The proposed method outperforms a state-of-the-art approach both in terms of signal quality (+9% 'SNR') and accuracy of QRS detection (+11%).Significance: The proposed hardware and software solutions open the way for the acquisition of high-quality of ECG gating in MRI, and improved diagnostic quality of ECG signals in MRI.

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.

International audience; This paper demonstrates that one can model the power deposited at the electrode of an implanted insulated cable submitted to the radiofrequency field of a 1.5 T magnetic resonance imaging modality (64 MHz) with a transmission line model. This offers an alternative that is more related to physics to the usually used transfer function model. The equivalence between the models is shown through a finite difference model and a new analytical formula for the transfer function as a function of transmission line parameters. First, the possibility of modeling an insulated cable with a transmission line model was analyzed through full-wave numerical simulations. The assumption of a transmission line model underlying the transfer function model was shown to be right for a simple cable embedded in tissue imitating gel, and the transmission line parameters extracted from this analysis were consistent with analytical formulas derived from the laws of physics. The transmission line model predictions were first compared to experimental and simulated data of the cable transfer function and then to experimental and simulated data of the resonant behavior as a function of length of cables with different termination conditions. The measured and simulated transfer functions fit perfectly a transmission line model with an analytical expression of the propagating constant. The transmission line model extracted from the transfer function allows us to predict the resonant behavior of two cables with different termination conditions.

International audience; Isotropic three-dimensional (3D) acquisition is a challenging task in magnetic resonance imaging (MRI). Particularly in cardiac MRI, due to hardware and time limitations, current 3D acquisitions are limited by low-resolution, especially in the through-plane direction, leading to poor image quality in that dimension. To overcome this problem, super-resolution (SR) techniques have been proposed to reconstruct a single isotropic 3D volume from multiple anisotropic acquisitions. Previously, local regularization techniques such as total variation have been applied to limit noise amplification while preserving sharp edges and small features in the images. In this paper, inspired by the recent progress in patch-based reconstruction, we propose a novel isotropic 3D reconstruction scheme that integrates non-local and self-similarity information from 3D patch neighborhoods. By grouping 3D patches with similar structures, we enforce the natural sparsity of MR images, which can be expressed by a low-rank structure, leading to robust image reconstruction with high signal-to-noise ratio efficiency. An Augmented Lagrangian formulation of the problem is proposed to efficiently decompose the optimization into a low-rank volume denoising and a SR reconstruction. Experimental results in simulations, brain imaging and clinical cardiac MRI, demonstrate that the proposed joint SR and self-similarity learning framework outperforms current state-of-the-art methods. The proposed reconstruction of isotropic 3D volumes may be particularly useful for cardiac applications, such as myocardial infarction scar assessment by late gadolinium enhancement MRI.

Background The da Vinci robot provides a sitting position and an armrest to decrease workload and increase dexterity. We investigated the surgeon's ergonomic behaviour by installing force sensors on the dV-Trainer® simulator's armrest to measure the 'armrest load' during the performance of simulated exercises. Methods Five experts and 48 novices performed two robotic simulation exercises on the dV-Trainer. We calculated the armrest load and evaluated their armrest-using habits. Overall score and workspace range were evaluated automatically by the simulator and compared with armrest load. Results Statistically significant differences exist for overall score, workspace range and armrest load between novices and experts. Conclusion The armrest load score is a direct, sensitive measure for the ergonomic evaluation of a simulator's armrest use. This experience-dependent ergonomic difference between experts and novices (p = 0.007) highlights the importance of ergonomic training for novice robot users. Copyright © 2016 John Wiley & Sons, Ltd.

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; Respiratory motion is a source of artifacts in multimodality imaging such as PET/MR. Solutions include retrospective or prospective gating. They have however found limited use in clinical practice, since their increased overall acquisition duration to maintain overall image quality. More elaborate methods consist of using 4D MR datasets to extract spatial deformations in order to correct for the respiratory motion in PET. The main drawbacks of such approaches is the relatively long acquisition times associated with 4D MR imaging which is often incompatible with clinical PET/MR protocols. The objective of this work was to overcome these limitations by exploiting a generalized reconstruction by inversion of coupled systems (GRICS) approach. The methodology is based on a joint estimation of motion during the MR image reconstruction process, providing internal structure motion and associated deformation matrices for retrospective use in PET respiratory motion correction. This method was first validated on four MR volunteers and two PET/MR patient datasets by comparing GRICS generated MR images to 4D MR series obtained by retrospective gating. In a second step 4D PET datasets corresponding to acquired 4D MR images were simulated using the GATE Monte Carlo simulation platform. GRICS generated deformation matrices were subsequently used to correct respiratory motion in comparison to the 4D MR image based deformations both for the simulated and the two 4D PET/MR patient datasets. Results confirm that GRICS synchronized MR images correlate well with the acquired 4D MR series. Similarly, the use of GRICS for respiratory motion correction allows an equivalent percentage improvement on lesion contrast, position and size, considering the PET simulated tumors as well as PET real tumors. This work demonstrates the potential interest of using GRICS for PET respiratory motion correction in combined PET/MR using shorter duration acquisitions without the need for 4D MRI and associated specific MR sequences.

To evaluate the function of an active implantable medical device (AIMD) during magnetic resonance imaging (MRI) scans. The induced voltages caused by the switching of magnetic field gradients and rectified radio frequency (RF) pulse were measured, along with the AIMD stimulations. An MRI-compatible voltage probe with a bandwidth of 0–40 kHz was designed. Measurements were carried out both on the bench with an overvoltage protection circuit commonly used for AIMD and with a pacemaker during MRI scans on a 1.5 T (64 MHz) MR scanner. The sensor exhibits a measurement range of ± 15 V with an amplitude resolution of 7 mV and a temporal resolution of 10 µs. Rectification was measured on the bench with the overvoltage protection circuit. Linear proportionality was confirmed between the induced voltage and the magnetic field gradient slew rate. The pacemaker pacing was recorded successfully during MRI scans. The characteristics of this low-frequency voltage probe allow its use with extreme RF transmission power and magnetic field gradient positioning for MR safety test of AIMD during MRI scans.

International audience; Objective: We describe a new real-time filter to reduce artefacts on electrocardiogram (ECG) due to magnetic field gradients during MRI. The proposed filter is a least mean square (LMS) filter able to continuously adapt its step size according to the gradient signal of the ongoing MRI acquisition.Materials and methods: We implemented this filter and compared it, within two databases (at 1.5 and 3 T) with over 6000 QRS complexes, to five real-time filtering strategies (no filter, low pass filter, standard LMS, and two other filters optimized within the databases: optimized LMS, and optimized Kalman filter).Results: The energy of the remaining noise was significantly reduced (26 vs. 68%, p < 0.001) with the new filter vs. standard LMS. The detection error of our ventricular complex (QRS) detector was: 11% with our method vs. 25% with raw ECG, 35% with low pass filter, 17% with standard LMS, 12% with optimized Kalman filter, and 11% with optimized LMS filter.Conclusion: The adaptive step size LMS improves ECG denoising during MRI. QRS detection has the same F1 score with this filter than with filters optimized within the database.

The orientation of the heart in the chest impacts the shape and amplitude of surface ECG signals. It is also key information in electrocardiographic imaging (ECGI), where a model of the heart and torso is required. In this study we seek to analyze statistical relations between heart orientation and several easily available patient characteristics. Heart orientation data were obtained from an MRI database of 185 healthy adults. Relations with sex, height, weight (collected from case reports forms) and chest circumference (extracted from the images) were analyzed using univariate and multivariate linear regression. Chest circumference was found to be the best single predictor of heart orientation, and simple formulas were determined for its estimation. The proposed heart orientation statistical model might be used for selecting a torso/heart model from an existing database; this approach might allow ECGI techniques to be integrated into an ECG device.

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.

International audience; Objective: The objective of our study was to evaluate the diagnostic performance of qualitative 3-T proton MR spectroscopy (1H-MRS) for the characterization of musculoskeletal neoplasms.Subjects and methods: Proton MRS studies of 74 patients (76 lesions) with a histologically confirmed musculoskeletal neoplasm or neoplasms were prospectively included in this study. All studies were performed using a 3-T MRI scanner. Spectra were analyzed with conventional MRI software provided by the fabricant and with dedicated independent MRS software. Spectra were evaluated visually for the presence or absence of a choline peak at 3.2 ppm. The presence of a choline peak was considered indicative of malignancy. The influences of tumor origin and spectral quality on diagnostic performance were considered.Results: Diagnostic performance was similar with both software used (κ = 0.97). Qualitative 1H-MRS failed to differentiate benign from malignant bone tumors regardless of the application of quality criteria (best sensitivity and specificity, 50.0% and 61.5%, respectively). Diagnostic performance was better with soft-tissue lesions, but the specificity remained low (best sensitivity and specificity, 82.4% and 64.3%, respectively). The application of spectral quality criteria for the evaluation of soft-tissue tumors led to the exclusion of 35.4% of the evaluated spectra.Conclusion: Qualitative 3-T 1H-MRS cannot be used to characterize bone tumors. This technique has good sensitivity but poor specificity for the characterization of soft-tissue lesions.

International audience; To evaluate the added value of ULTRAFAST-MR sequence to an abbreviated FAST protocol in comparison with FULL protocol to distinguish benign from malignant lesions in a population of women, regardless of breast MR imaging indication. Materials and methods: From March 10th to September 22th, 2014, we retrospectively included a total of 70 consecutive patients with 106 histologically proven lesions (58 malignant and 48 benign) who underwent breast MR imaging for preoperative breast staging (n = 38), high-risk screening (n = 7), problem solving (n = 18), and nipple discharge (n = 4) with 12 time resolved imaging of contrast kinetics (TRICKS) acquisitions during contrast inflow interleaved in a regular high-resolution dynamic MRI protocol (FULL protocol). Two readers scored MR exams as either positive or negative and described significant lesions according to Bi-RADS lexicon with a TRICKS images (ULTRAFAST), an abbreviated protocol (FAST) and all images (FULL protocol). Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated for each protocol and compared with McNemar's test. Results: For all readers, the combined FAST-ULTRAFAST protocol significantly improved the reading with a specificity of 83.3% and 70.8% in comparison with FAST protocol or FULL protocol, respectively, without change in sensitivity. By adding ULTRAFAST protocol to FAST protocol, readers 1 and 2 were able to correctly change the diagnosis in 22.9% (11/48) and 10.4% (5/48) of benign lesions, without missing any malignancy, respectively. Both interpretation and image acquisition times for combined FAST-ULTRAFAST protocol and FAST protocol were shorter compared to FULL protocol (p < 0.001). Conclusion: Compared to FULL protocol, adding ULTRAFAST to FAST protocol improves specificity, mainly in correctly reclassifying benign masses and reducing interpretation and acquisition time, without decreasing sensitivity.

Background The effect of telesurgical training was evaluated at two latency levels. Methods Eleven subjects were randomly assigned to two delay groups (400 and 600 ms). Each group trained with latency on a simple task of dV-Trainer® and performed a difficult task before (pre-test) and after (post-test) the training. The follow-up was conducted 1 week after the training. Results The difficulty decreased gradually during training for both groups, while the task completion time and the instrument motion improved only in the 600 ms group. Both groups made progress from pre- to post-test, but statistical significance was not achieved. In the follow-up, subjects maintained their highest level achieved during training. Conclusions Latency training is effective and this effect lasts at least 1 week. Latency training on a simple task may improve results in complex procedures. However, attention should be paid to avoiding carelessness due to confidence from training. Copyright © 2014 John Wiley & Sons, Ltd.

International audience; This study was designed retrospectively to assess the value of myocardial T2 to detect or predict ongoing acute heart rejection, in heart transplant patients, with a 1.5-T MRI magnet. One hundred and ninety-six myocardial T2 quantifications were performed on sixty consecutive heart transplant patients during routine follow- up. T2 values were assessed (i) with regard to the results of concomitant biopsies and (ii) with a Cox multivariate model for the prediction of subsequent rejections, defined by a ≥ grade 2 at biopsy or highly suspected in the absence of biopsy (>10% drop in ejection fraction with subsequent reversibility under treatment). T2 values were proposed as main covariate, after logit transformation andadjustment for other confounding parameters such as delay since graft surgery and delay before biopsy. T2 values were strongly linked (i) to the presence of rejection on concomitant biopsy (P < 0.0001) and (ii) to the risk of subsequent rejection on Cox multivariate model (P < 0.001). T2 values above 60 ms were associated with relative risk of rejection higher than 2.0 and rapidly increasing. In conclusion, myocardial T2 yields a high diagnostic and prognostic value for graft rejection in heart transplant patients.

Introduction Evaluate the capability of different Computed Tomography scanners to determine urinary stone compositions based on CT attenuation values and to evaluate potential differences between each model. Methods 241 human urinary stones were obtained and their biochemical composition determined. Four different CT scanners (Siemens, Philips, GEMS and Toshiba) were evaluated. Mean CT-attenuation values and the standard deviation were recorded separately and compared with a t-paired test. Results For all tested CT scanners, when the classification of the various types of stones was arranged according to the mean CT-attenuation values and to the confidence interval, large overlappings between stone types were highlighted. The t-paired test showed that most stone types could not be identified. Some types of stones presented mean CT attenuation values significantly different from one CT scanner to another. At 80 kV, the mean CT attenuation values obtained with the Toshiba Aquilion were significantly different from those obtained with the Siemens Sensation. On the other hand, mean values obtained with the Philips Brilliance were all significantly equal to those obtained with the Siemens Sensation and with the Toshiba Aquilion. At 120 kV mean CT attenuation values of uric acid, cystine and struvite stones obtained with the Philips model are significantly different from those obtained with the Siemens and the Toshiba but equal to those obtained with the GE 64. Conclusions According to our study, there is a great variability when different brands and models of scanners are compared directly. Furthermore, the CT scan analysis and HU evaluation appears to gather insufficient information in order to characterize and identify the composition of renal stones.

Summary background data Robotic surgery has witnessed a huge expansion. Robotic simulators have proved to be of major interest in training. Some authors have suggested that prior experience in micro-surgery could improve robotic surgery training. Objective To test micro-surgery as a new approach in training, we proposed a prospective study comparing the surgical performance of micro-surgeons with that of general surgeons on a robotic simulator. Methods 49 surgeons were enrolled; 11 in the micro-surgery group (MSG); 38 n the control group (CG). Performance was evaluated based on five dV-Trainer® exercises. Results MSG achieved better results for all exercises including exercises requiring visual evaluation of force feed-back, economy of motion, instrument force and position. Conclusions These results show that experience in micro-surgery could significantly improve surgeons' abilities and their performance in robotic training. So, as micro-surgery practice is relatively cheap, it could be easily included in basic robotic surgery training. Copyright © 2013 John Wiley & Sons, Ltd.

Background Standard laparoscopy is responsible for musculoskeletal problems because of surgeons anti-ergonomic positions. Robot-assisted laparoscopy seems to reduce these musculoskeletal disorders thanks to the surgeons seated position. The objective of this study is to evaluate the muscular strain and cognitive stress induced by these two techniques during real operations conducted on the pig. Methods Electromyographic activities, heart rate, physical and mental workloads (NASA Tlx and Borg CR-10) were recorded. Results Physical workload and perception of the effort invested was significantly greater during the standard laparoscopies (p

To develop an efficient motion-compensated reconstruction technique for free-breathing cardiac magnetic resonance imaging (MRI) that allows high-quality images to be reconstructed from multiple undersampled single-shot acquisitions. The proposed method is a joint image reconstruction and motion correction method consisting of several steps, including a non-rigid motion extraction and a motion-compensated reconstruction. The reconstruction includes a denoising with the Beltrami regularization, which offers an ideal compromise between feature preservation and staircasing reduction. Results were assessed in simulation, phantom and volunteer experiments. The proposed joint image reconstruction and motion correction method exhibits visible quality improvement over previous methods while reconstructing sharper edges. Moreover, when the acceleration factor increases, standard methods show blurry results while the proposed method preserves image quality. The method was applied to free-breathing single-shot cardiac MRI, successfully achieving high image quality and higher spatial resolution than conventional segmented methods, with the potential to offer high-quality delayed enhancement scans in challenging patients., Comment: 12 pages, 6 figures, accepted at MICCAI 2016

International audience; Age estimation of living individuals aged less than 13, 18 or 21 years, which are some relevant legal ages in most European countries, is currently problematic in the forensic context. Thus, numerous methods are available for legal authorities, although their efficiency can be discussed. For those reasons, we aimed to propose a new method, based on the biometric analysis of hand bones. 451 hand radiographs of French individuals under the age of 21 were retrospectively analyzed. This total sample was divided into three subgroups bounded by the relevant legal ages previously mentioned: 0–13, 13–18 and 18–21 years. On these radiographs, we numerically applied the osteometric board method used in anthropology, by including each metacarpal and proximal phalange of the five hand rays in the smallest rectangle possible. In that we can access their length and width information thanks to a measurement protocol developed precisely for our treatment with the ORS Visual 1 software. Then, a statistical analysis was performed from these biometric data: a Linear Discriminant Analysis (LDA) evaluated the probability for an individual to belong to one of the age group (0–13, 13–18 or 18–21); and several multivariate regression models were tested for the establishment of age estimation formulas for each of these age groups. The mean Correlation Coefficient between chronological age and both lengths and widths of hand bones is equal to 0.90 for the total sample. Repeatability and reproducibility were assessed. The LDA could more easily predict the belonging to the 0–13 age group. Age can be estimated with a mean standard error which never exceeds 1 year for the 95% confidence interval. Finally, compared to the literature, we can conclude that estimating an age from the biometric information of metacarpals and proximal phalanges is promising.

International audience; Objectives: To assess cardiac and vascular adaptations in long-distance male triathletes and the influence of an increased training volume on these parameters. Design: Case-control study using long-distance male triathletes (Tri) (n = 12) and an age-matched cohort of sedentary volunteers (Ctrl). Methods: All participants gave an informed consent and underwent a Cardiovascular Magnetic Resonance imaging (CMR) exam to measure left and right ventricle functional parameters, and aortic parameters (surface, strain, compliance, pulse wave velocity). This exam was repeated in the triathletes' group after an increased training volume of at least 2 h/week for six weeks. Results: Compared to control volunteers, triathletes presented at baseline a typical pattern of athlete's heart (higher end-diastolic, end-systolic and stroke volumes index, p ≤ 0.009, and lower cardiac rate, p = 0.015) but similar vascular characteristics except a trend towards an enlarged ascending aorta (surface 942 ± 106 vs 812 ± 127 mm 2 , p = 0.058). Between the two visits, the triathletes increased their weekly training time from 9.67 ± 2.43 (Tri1) to 12.15 ± 3.01 h (Tri2): no modifications were found regarding cardiac parameters, but compliance and distensibility of the ascending aorta increased, from 2.60 to 3.34 mm 2 /mmHg (p = 0.028) and from 3.36 to 4.40 × 10 −3 mmHg −1 (p = 0.048) respectively. Conclusions: Using CMR, we showed that vascular characteristics of the ascending aorta may vary along the sport season in endurance athletes. This remodelling could be considered as a physiological adaptation, but could eventually lead to an adverse vascular remodelling.

International audience

International audience; Goal: A novel magnetic resonance (MR) compatible accelerometer for respiratory motion sensing (MARMOT) is developed as a surrogate of the vendors' pneumatic belts. We aim to model and correct respiratory motion for free-breathing thoracic-abdominal MR imaging and to simplify patient installation.Methods: MR compatibility of MARMOT sensors was assessed in phantoms and its motion modeling/correction efficacy was demonstrated on 21 subjects at 3 T. Respiration was modeled and predicted from MARMOT sensors and pneumatic belts, based on real-time images and a regression method. The sensor accuracy was validated by comparing motion errors in the liver/kidney. Sensor data were also exploited as inputs for motion-compensated reconstruction of free-breathing cardiac cine MR images. Multiple and single sensor placement strategies were compared.Results: The new sensor is compatible with the MR environment. The average motion modeling and prediction errors with MARMOT sensors and with pneumatic belts were comparable (liver and kidney) and were below 2 mm with all tested configurations (belts, multiple/single MARMOT sensor). Motion corrected cardiac cine images were of improved image quality, as assessed by an entropy metric (p < 10-6), with all tested configurations. Expert readings revealed multiple MARMOT sensors were the best (p < 0.03) and the single MARMOT sensor was similar to the belts (nonsignificant in two of the three readers).Conclusion: The proposed sensor can model and predict respiratory motion with sufficient accuracy to allow free-breathing MR imaging strategy.Significance: It provides an alternative sensor solution for the respiratory motion problem during MR imaging and may improve the convenience of patient setup.

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.

A reconstruction strategy is proposed for physiological motion correction, which overcomes many limitations of existing techniques. The method is based on a general framework allowing correction for arbitrary motion–nonrigid or affine, making it suitable for cardiac or abdominal imaging, in the context of multiple coil, arbitrarily sampled acquisition. A model is required to predict motion in the field of view at each sample time point, based on prior knowledge provided by external sensors. A theoretical study is carried out to analyze the influence of motion prediction errors. Small errors are shown to propagate linearly in that reconstruction algorithm, and thus induce a reconstruction residue that is bounded (stability). Furthermore, optimization of the motion model is proposed in order to minimize this residue. This leads to reformulating reconstruction as two inverse problems which are coupled: motion-compensated reconstruction (known motion) and model optimization (known image). A fixed-point multiresolution scheme is described for inverting these two coupled systems. This framework is shown to allow fully autocalibrated reconstructions, as coil sensitivities and motion model coefficients are determined directly from the corrupted raw data. The theory is validated with real cardiac and abdominal data from healthy volunteers, acquired in free-breathing. Magn Reson Med 60:146–157, 2008. © 2008 Wiley-Liss, Inc.

International audience; OBJECTIVE:To evaluate the performance of quantitative diffusion-weighted imaging (DWI) correlated with T2 signal in differentiating non-fatty benign from malignant tumors.MATERIAL AND METHODS:A total of 76 patients with a histologically confirmed non-fatty soft tissue tumors (46 benign and 30 malignant) were prospectively included in this ethics committee approved study. All patients signed an informed consent and underwent MRI with DWI with two b values (0 and 600). ADC values from the solid components of these tumors were obtained and were correlated with the lesion's signal intensity on T2-weighted fat-saturated sequences. ADC values were obtained from adjacent normal muscle to allow calculation of tumor/muscle ADC ratios.RESULTS:There were 58 hyperintense and 18 iso or hypointense lesions. All hypointense lesions were benign. The mean ADC values for benign and malignant tumors were 1.47 ± 0.54 × 10(-3) and 1.17 ± 0.38 × 10(-3) mm(2)/s respectively (p

International audience; OBJECTIVES:Blood pressure (BP) and its changes with antihypertensive therapy are key parameters when monitoring left ventricular (LV) remodeling. This dual cross-sectional and longitudinal MRI study aimed to determine whether this monitoring is enhanced by aortic stroke volume (SV) values provided by a phase-contrast sequence.METHODS:The study involved 334 MRI examinations from 247 study participants who had no significant cardiac disease (18-85 years old, 40% with hypertension) and among whom 48 had a 2-4-year MRI follow-up. Left ventricular hypertrophy and concentric geometry were: respectively assessed according to LV mass indexed to body surface area (g/m) and mass/end-diastolic volume ratio (concentric remodeling index); and correlated with vascular parameters involving BP and the indexed SV (ml/m) determined in the ascending aorta with a phase-contrast sequence.RESULTS:Stroke volume was highly variable, ranging from 22 to 74 ml/m. The best cross-sectional correlates were: mean BP × SV product, reflecting cardiac work, for LV mass (r = 0.21); and mean BP/SV ratio, reflecting arterial load, for concentric geometry (r = 0.29). These two SV-derived parameters led to more than two-fold enhancements in cross-sectional predictions compared with BP parameters alone, whereas their longitudinal changes over time paralleled those of concentric geometry (P = 0.003 for mean BP/SV) and LV mass (P = 0.006 for mean BP × SV), suggesting direct links with cardiac remodeling.CONCLUSION:The determination of aortic SV with a phase-contrast sequence leads to a significant enhancement in the characterization and monitoring of cardiac remodeling.

Summary Objectives: To review past and present challenges and ongoing trends in numerical simulation for MRI (Magnetic Resonance Imaging) safety evaluation of medical devices. Methods: A wide literature review on numerical and analytical simulation on simple or complex medical devices in MRI electromagnetic fields shows the evolutions through time and a growing concern for MRI safety over the years. Major issues and achievements are described, as well as current trends and perspectives in this research field. Results: Numerical simulation of medical devices is constantly evolving, supported by calculation methods now well-established. Implants with simple geometry can often be simulated in a computational human model, but one issue remaining today is the experimental validation of these human models. A great concern is to assess RF heating on implants too complex to be traditionally simulated, like pacemaker leads. Thus, ongoing researches focus on alternative hybrids methods, both numerical and experimental, with for example a transfer function method. For the static field and gradient fields, analytical models can be used for dimensioning simple implants shapes, but limited for complex geometries that cannot be studied with simplifying assumptions. Conclusions: Numerical simulation is an essential tool for MRI safety testing of medical devices. The main issues remain the accuracy of simulations compared to real life and the studies of complex devices; but as the research field is constantly evolving, some promising ideas are now under investigation to take up the challenges.