Analytic image concept combined to SENSE reconstruction

Object: Two approaches of reconstructing undersampled partial k-space data, acquired with multiple coils are compared: homodyne detection combined with SENSE (HM_SENSE) and analytic image reconstruction combined with SENSE (AI_SENSE). The latter overcomes limitations of HM_ SENSE by considering aliased images as analytic thus avoiding the need for phase correction required for HM_SENSE. Materials and methods: In vivo imaging experiments were carried out in male Lewis rats using both gradient echo and spin echo sequences. Accelerated images obtained by using the various reconstruction algorithms were compared to fully sampled reference images both qualitatively and quantitatively. Results: For the various sampling patterns evaluated, both HM_SENSE and AI_SENSE were found to yield robust image reconstruction with small deviations from the reference image. Even for high acceleration factors AI_SENSE still provided useful results and was found superior compared to HM_SENSE. Conclusion: Combination of partial k-space sampling and parallel image acquisition allows for further acceleration of data acquisition as compared to each method alone. Image reconstruction from undersampled data sets using the AI_SENSE algorithm was found to considerably reduce reconstruction errors and artifacts observed for HM_SENSE reconstruction caused by errors in phase estimatio

Increasing temporal resolution of DSC perfusion MRI using the analytic image concept

Object: Dynamic susceptibility contrast MRI (DSC-MRI) is increasingly being used to evaluate cerebral microcirculation. In this study, the use of the analytic image reconstruction (AIR), with the aim to increase the temporal resolution, is evaluated for DSC-MRI in small animals. Materials and methods: Imaging was performed using a T 2*- weighted sequence to acquire male Lewis rats raw data. Results show that AIR satisfactory reconstructs DSC-MRI while preserving a good reconstruction quality and the image characteristics compared to the full k-space and keyhole reconstructed images. The combination of the choice of the baseline image and the proposed asymmetric acquisition schema enables an increase in temporal resolution, by a factor of four, thus having more sample points for better estimating perfusion parameters. Results: Computer simulations result in a mean cerebral blood volume of 1.22 that deviates from the full k-space value by −3% and a mean cerebral blood flow of 1.97 deviating from the full k-space value by −3% when the mean transit time did not change. Even if these deviations increase when achieving real acquisitions, AIR still better computes quantitative values than keyhole. Conclusion: AIR allows a good reconstruction of the dynamic stage of the image series thus leading to better dynamic effects analysi

Reconstruction d\u27images de résonance magnétique à partir de l\u27espace k partiel

Dans le souci d\u27éviter les artéfacts que pourrait provoquer le mouvement sur la qualité des images, l\u27obtention de temps d\u27acquisition de données courts est essentiel en imagerie par résonance magnétique (IRM). En particulier, comme des sujets malades ont la plus part du temps des difficultés à retenir leur respiration pendant l\u27examen, il devient par conséquent impératif de recueillir l\u27information nécessaire le plus rapidement possible dans certaines études, telles que celles réalisées en imagerie cardiaque. L\u27acquisition partielle des données de l\u27espace k est une pratique couramment utilisée dans le but de diminuer le temps d\u27acquisition des données en IRM. La nécessité d\u27accélérer ce temps d\u27acquisition et/ou d\u27augmenter la résolution spatiale des images en résonance magnétique nucléaire (RMN), a conduit à la proposition de plusieurs méthodes de reconstruction qui acquièrent les données de l\u27espace k de façon partielle, tant pour des objets statiques que pour des objets ou études dynamiques. Ces méthodes utilisent des informations a priori (données acquises) pour retrouver celles manquantes. Ce manuscrit présente trois méthodes de reconstruction IRM utilisant les données de l\u27espace k acquises partiellement. La première méthode proposée est dédiée à la reconstruction d\u27objets ou d\u27organes statiques, tandis que les deux autres sont consacrées à la reconstruction d\u27organes dynamiques (application à l\u27imagerie cardiaque). Ces trois méthodes sont basées sur l\u27utilisation, dans l\u27algorithme de reconstruction, du concept d\u27image analytique, combinée, dans le cas des images statiques, à l\u27exploitation des redondances dans les données de l\u27espace k, et à l\u27utilisation des r

Reconstruction d'images de résonance magnétique à partir de l'espace k partiel

Dans le souci d'éviter les artéfacts que pourrait provoquer le mouvement sur la qualité des images, l'obtention de temps d'acquisition de données courts est essentielle en imagerie par résonance magnétique (IRM). En particulier, comme des sujets malades ont la plus part du temps des difficultés à retenir leur respiration pendant l'examen, il devient par conséquent impératif de recueillir l'information nécessaire le plus rapidement possible dans certaines études, telles que celles réalisées en imagerie cardiaque. L'acquisition partielle des données de l'espace k est une pratique couramment utilisée dans le but de diminuer le temps d'acquisition des données en IRM. La nécessité d'accélérer ce temps d'acquisition et/ou d'augmenter la résolution spatiale des images en résonance magnétique nucléaire (RMN), a conduit à la proposition de plusieurs méthodes de reconstruction qui acquièrent les données de l'espace k de façon partielle, tant pour des objets statiques que pour des objets ou études dynamiques. Ces méthodes utilisent des informations à priori (données acquises) pour retrouver celles manquantes. Ce manuscrit présente trois méthodes de reconstruction IRM utilisant les données de l'espace k acquises partiellement. La première méthode proposée est dédiée à la reconstruction d'objets ou d'organes statiques, tandis que les deux autres sont consacrées à la reconstruction d'organes dynamiques (application à l'imagerie cardiaque). Ces trois méthodes sont basées sur l'utilisation, dans l'algorithme de reconstruction, du concept d'image analytique, combinée, dans le cas des images statiques, à l'exploitation des redondances dans les données de l'espace k, et à l'utilisation des redondances temporelles associées à la substitution des données, pour les organes en mouvement. Ces méthodes ont été évaluées, dans le cadre de la reconstruction d'images statiques, par des expériences sur des images simulées auxquelles ont été rajouté un terme de phase pour la destruction de la symétrie hermitienne. On a utilisé également des fantômes physiques et de vraies images de cerveaux humains. Les deux autres méthodes ont été évaluées par des expériences sur de vraies séquences ciné cardiaques humaines. Le schéma de reconstruction proposé pour la reconstruction d'images statiques permet la réalisation d'une réduction du temps d'acquisition d'un facteur de 2. En ce qui concerne les images dynamiques, une réduction du temps d'acquisition d'un facteur de 4 a été réalisée, tout en maintenant une bonne qualité de reconstruction, tant sur le plan visuel que quantitatif (bon rapport signal sur bruit, faibles valeurs d'erreurs).With the aim of avoiding the bad influence which the movement could have on the quality of the images, short acquisition time is mandatory in magnetic resonance imaging (MRI). Especially for sick patients who have problems holding their breath during examination, it becomes consequently imperative to collect necessary information as faster as possible in certain studies, such as those carried out in cardiac imaging. Partial k-space acquisition is a common way used to shorten the data acquisition time in MRI applications. For the sake of short acquisition time and/or increased spatial resolution of the reconstructed images, several methods have already been proposed, which partially acquired the k-space data. These methods use a priori information to recover the missing data. This manuscript presents three MRI reconstruction methods using partial k-space data. The first proposed method is dedicated to the reconstruction of static objects or organs, while the two others are devoted to the reconstruction of dynamic organs (application to cardiac imaging). These three methods are based on the use, in the reconstruction algorithm, of the analytic image concept, combined in the case of the static images with the exploitation of the redundancies in the k-space data, and with the use of the temporal redundancies associated to the data substitution, for the moving organs. These methods were evaluated, within the framework of static images reconstruction, by experiments on simulated images to which were added a slowly varying phase term to destroy the Hermitian symmetry, and also on physical phantoms and true human brain images. The two other methods were evaluated by experiments.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Increasing temporal resolution of DSC perfusion MRI using the analytic image concept

ISSN:0968-5243ISSN:1352-866

Cardiac Cine MR Reconstruction From Partial k-Space Using the Notion of Analytic Image.

noneInternational audienceIn the concern of speeding the acquisition time and to increase the spatial resolution of magnetic resonance (MR) images, several methods have already been proposed that acquire partial k-space data and use this known information about the imaged object to deal the problem. This work presents a new approach of reconstructing cardiac cine images by using k-space redundancies. The proposed method is based on the use of the analytic image concept. It is evaluated by experiments on real human heart images and compared with the Homodyne detection (HM) and the Projection onto convex set (POCS) reconstruction techniques

Periventricular [11C]flumazenil binding for predicting postoperative outcome in individual patients with temporal lobe epilepsy and hippocampal sclerosis

AbstractA third of patients with intractable temporal lobe epilepsy and hippocampal sclerosis (HS) are not seizure free (NSF) after surgery. Increased periventricular [11C]flumazenil (FMZ) binding, reflecting heterotopic neuron concentration, has been described as one predictor of NSF outcome at the group level. We aimed to replicate this finding in an independent larger cohort and investigated whether NSF outcome can be predicted in individuals.Preoperative [11C]FMZ summed radioactivity images were available for 16 patients with HS and 41 controls. Images were analyzed using SPM8, explicitly including the white matter, and correction for global radioactivity via group-specific ANCOVA. Periventricular increases were assessed with a mask and different cutoffs for distinguishing NSF and seizure free (SF) patients.NSF patients had increased [11C]FMZ binding around the posterior horn of the ventricles ipsilaterally (z=2.53) and contralaterally (z=4.44) to the seizure focus compared with SF patients. Compared with controls, SF patients had fewer periventricular increases (two clusters, total volume 0.87cm3, zmax=3.8) than NSF patients (two ipsilateral and three contralateral clusters, 6.15cm3, zmax=4.8). In individuals and at optimized cutoffs, five (63%) of eight NSF patients and one (13%) of eight SF patients showed periventricular increases compared with controls (accuracy 75%). Only one (2%) of the 41 controls had increases at the same cutoff.The association between periventricular [11C]FMZ increases and NSF outcome after temporal lobe resection for HS has been confirmed in an independent cohort on simple summed activity images. [11C]FMZ-PET may be useful for individual preoperative counseling with clinically relevant accuracy

Analytic image concept combined to SENSE reconstruction

Two approaches of reconstructing undersampled partial k-space data, acquired with multiple coils are compared: homodyne detection combined with SENSE (HM_SENSE) and analytic image reconstruction combined with SENSE (AI_SENSE). The latter overcomes limitations of HM_ SENSE by considering aliased images as analytic thus avoiding the need for phase correction required for HM_SENSE. MATERIALS AND METHODS: In vivo imaging experiments were carried out in male Lewis rats using both gradient echo and spin echo sequences. Accelerated images obtained by using the various reconstruction algorithms were compared to fully sampled reference images both qualitatively and quantitatively. RESULTS: For the various sampling patterns evaluated, both HM_SENSE and AI_SENSE were found to yield robust image reconstruction with small deviations from the reference image. Even for high acceleration factors AI_SENSE still provided useful results and was found superior compared to HM_SENSE. CONCLUSION: Combination of partial k-space sampling and parallel image acquisition allows for further acceleration of data acquisition as compared to each method alone. Image reconstruction from undersampled data sets using the AI_SENSE algorithm was found to considerably reduce reconstruction errors and artifacts observed for HM_SENSE reconstruction caused by errors in phase estimation