Connections of the dorsolateral prefrontal cortex with the thalamus: a probabilistic tractography study.

PURPOSE: The dorsolateral prefrontal cortex (DLPFC) is a cortical area involved in higher cognitive functions, and at the center of the pathophysiology of mental disorders such as depression and schizophrenia. Considering these major roles and the development of deep brain stimulation, the object of this study was to assess the patterns of connectivity of the DLPFC with its main subcortical relay, the thalamus, with the help of probabilistic tractography. METHODS: We used T1-weighted imaging and diffusion data from 18 subjects from the Human Connectome Project. The DLPFC and the thalamic nuclear groups were defined using the combination of atlases, sulcogyral anatomy and cytoarchitectonic data. Probabilistic tractography was performed from the DLPFC to the thalamus. The patterns of connectivity were assessed using two indexes: (1) a connectivity index (CI) which evaluate the strength of connection (2) an asymmetry index (AI) which explores the inter-hemispheric variability. RESULTS: The analysis of CI showed significant connections between the DLPFC and the dorsomedial nuclei (p < 0.05), the anterior nuclear groups (p < 0.05) and the right centromedian nucleus (p < 0.05). No link was found between handedness and AI (p > 0.05). Most of subjects (15/18) had a right predominance of the thalamo cortical connections of the DLPFC. CONCLUSIONS: Probabilistic tractography appears as a valuable non-invasive tool for the exploration of the thalamocortical connections between the dorsolateral prefrontal cortex and thalamic nuclei. It allowed to show different inter-hemispheric patterns of connectivity, and highlighted the centromedian nucleus as a key subcortical relay of executive functions.

Federating distributed and heterogeneous information sources in neuroimaging: the NeuroBase Project.

The NeuroBase project aims at studying the requirements for federating, through the Internet, information sources in neuroimaging. These sources are distributed in different experimental sites, hospitals or research centers in cognitive neurosciences, and contain heterogeneous data and image processing programs. More precisely, this project consists in creating of a shared ontology, suitable for supporting various neuroimaging applications, and a computer architecture for accessing and sharing relevant distributed information. We briefly describe the semantic model and report in more details the architecture we chose, based on a media-tor/wrapper approach. To give a flavor of the future deployment of our architecture, we de-scribe a demonstrator that implements the comparison of distributed image processing tools applied to distributed neuroimaging data.

Does subthalamic nucleus stimulation affect the frontal limbic areas? A single-photon emission computed tomography study using a manual anatomical segmentation method.

Among the basal ganglia nuclei, the subthalamic nucleus (STN) is considered to play a major role in output modulation. The STN represents a relay of the motor cortico-basal ganglia-thalamo-cortical circuit and has become the standard surgical target for treating Parkinson's patients with long-term motor fluctuations and dyskinesia. But chronic bilateral stimulation of the STN produces cognitive effects. According to animal and clinical studies, the STN also appears to have direct or indirect connections with the frontal associative and limbic areas. This prospective study was conducted to analyse regional cerebral blood flow changes in single-photon emission computed tomography imaging of six Parkinson's patients before and after STN stimulation. We particularly focused on the dorsolateral prefrontal cortex and the frontal limbic areas using a manual anatomical MRI segmentation method. We defined nine regions of interest, segmenting each MR slice to quantify the regional cerebral blood flow on pre- and postoperative SPECT images. We normalised the region-of-interest-based measurements to the entire brain volume. The patients showed increased activation during STN stimulation in the dorsolateral prefrontal cortex bilaterally and no change in the anterior cingulate and orbito-frontal cortices. In our study, STN stimulation induced activation of premotor and associative frontal areas. Further studies are needed to underline involvement of the STN with the so-called limbic system.

Numeric and symbolic knowledge representation of cerebral cortex anatomy: methods and preliminary results.

The human cerebral cortex anatomy describes the brain organization at the scale of gyri and sulci. It is used as landmarks for neurosurgery as well as localization support for functional data analysis or inter-subject data comparison. Existing models of the cortex anatomy either rely on image labeling but fail to represent variability and structural properties or rely on a conceptual model but miss the inner 3D nature and relations of anatomical structures. This study was therefore conducted to propose a model of sulco-gyral anatomy for the healthy human brain. We hypothesized that both numeric knowledge (i.e., image-based) and symbolic knowledge (i.e., concept-based) have to be represented and coordinated. In addition, the representation of this knowledge should be application-independent in order to be usable in various contexts. Therefore, we devised a symbolic model describing specialization, composition and spatial organization of cortical anatomical structures. We also collected numeric knowledge such as 3D models of shape and shape variation about cortical anatomical structures. For each numeric piece of knowledge, a companion file describes the concept it refers to and the nature of the relationship. Demonstration software performs a mapping between the numeric and the symbolic aspects for browsing the knowledge base.

Retrospective evaluation of intersubject brain registration.

Although numerous methods to register brains of different individuals have been proposed, no work has been done, as far as we know, to evaluate and objectively compare the performances of different nonrigid (or elastic) registration methods on the same database of subjects. In this paper, we propose an evaluation framework, based on global and local measures of the relevance of the registration. We have chosen to focus more particularly on the matching of cortical areas, since intersubject registration methods are dedicated to anatomical and functional normalization, and also because other groups have shown the relevance of such registration methods for deep brain structures. Experiments were conducted using 6 methods on a database of 18 subjects. The global measures used show that the quality of the registration is directly related to the transformation's degrees of freedom. More surprisingly, local measures based on the matching of cortical sulci did not show significant differences between rigid and non rigid methods.

Interindividual functional mapping: a nonlinear local approach.

Within the scope of three-dimensional brain imaging, we propose an interindividual fusion scheme to register functional activations according to anatomical cortical structures, the sulci. This paper is based on the assumption that an important part of functional intersubject variability is encoded in anatomical variability. The aim of this paper is therefore to propose a generic framework to register functional activations according to the relevant anatomical landmarks. Compared to "classical" interindividual fusion schemes, this approach is local. It relies on a statistical sulci shape model accounting for the interindividual variability of a population of subjects and providing deformation modes relative to a reference shape (a mean sulcus). The deformation field obtained between a given sulcus and the reference sulcus is extended to a neighborhood of the given sulcus by using the thin-plate spline interpolation. It is then applied to functional activations located in the vicinity of this sulcus. This approach is compared with rigid and nonrigid registration methods. In this paper, we present results on MEG somatosensory data acquired on 18 subjects. We show that the nonlinear local fusion scheme significantly reduces the observed functional variability.

Detection of inter-hemispheric asymmetries of brain perfusion in SPECT.

Technetium-99m HMPAO and technetium-99m ECD single photon emission computed tomography (SPECT) imaging is commonly used to highlight brain regions with altered perfusion. It is particularly useful in the investigation of intractable partial epilepsy. However, SPECT suffers from poor spatial resolution that makes interpretation difficult. In this context, we propose an unsupervised voxel neighbourhood based method to assist the detection of significant functional inter-hemispheric asymmetries in brain SPECT, using anatomical information from MRI. For each MRI voxel, the anatomically homologous voxel in the contralateral hemisphere is identified. Both homologous voxel coordinates are then mapped into the SPECT volume using SPECT-MRI registration. Neighbourhoods are then defined around each SPECT voxel and compared to obtain a volume of inter-hemispheric differences. A volume including only the statistically significant inter-hemispheric differences is deduced from this volume using a non-parametric approach. The method was validated using realistic analytical simulated SPECT data including known asymmetries (in size and amplitude) as ground truth (gold standard). Detection performance was assessed using an ROC (receiver operating characteristic) approach based on the measures of the overlap between known and detected asymmetries. Validation with computer-simulated data demonstrates the ability to detect asymmetric zones with relatively small extension and amplitude. The registration of these detected functional asymmetries on the MRI enables good anatomical localization to be achieved.

[Electronic imaging with photo-realistic rendering for neuroanatomy teaching. Methods and preliminary results]. / Imagerie électronique en rendu photo-réaliste pour l'enseignement de la Neuro-anatomie. Méthodes et résultats.

Advances in software, networking, and imaging technology provide a unique opportunity for developing information systems in anatomy that can deliver relevant knowledge to the clinicians, researchers, educators, and students. Recent software tools initially produced for graphic imaging are now available in the medical graphic design field. The authors describe an original method they used to create electronic images of the central nervous system and its coverings with photo-realistic rendering. They present preliminary results and discuss the potential of this new technique as a teaching tool for neuroanatomy.

A methodology for generating normal and pathological brain perfusion SPECT images for evaluation of MRI/SPECT fusion methods: application in epilepsy.

Quantitative evaluation of brain MRI/SPECT fusion methods for normal and in particular pathological datasets is difficult, due to the frequent lack of relevant ground truth. We propose a methodology to generate MRI and SPECT datasets dedicated to the evaluation of MRI/SPECT fusion methods and illustrate the method when dealing with ictal SPECT. The method consists in generating normal or pathological SPECT data perfectly aligned with a high-resolution 3D T1-weighted MRI using realistic Monte Carlo simulations that closely reproduce the response of a SPECT imaging system. Anatomical input data for the SPECT simulations are obtained from this 3D T1-weighted MRI, while functional input data result from an inter-individual analysis of anatomically standardized SPECT data. The method makes it possible to control the 'brain perfusion' function by proposing a theoretical model of brain perfusion from measurements performed on real SPECT images. Our method provides an absolute gold standard for assessing MRI/SPECT registration method accuracy since, by construction, the SPECT data are perfectly registered with the MRI data. The proposed methodology has been applied to create a theoretical model of normal brain perfusion and ictal brain perfusion characteristic of mesial temporal lobe epilepsy. To approach realistic and unbiased perfusion models, real SPECT data were corrected for uniform attenuation, scatter and partial volume effect. An anatomic standardization was used to account for anatomic variability between subjects. Realistic simulations of normal and ictal SPECT deduced from these perfusion models are presented. The comparison of real and simulated SPECT images showed relative differences in regional activity concentration of less than 20% in most anatomical structures, for both normal and ictal data, suggesting realistic models of perfusion distributions for evaluation purposes. Inter-hemispheric asymmetry coefficients measured on simulated data were found within the range of asymmetry coefficients measured on corresponding real data. The features of the proposed approach are compared with those of other methods previously described to obtain datasets appropriate for the assessment of fusion methods.

Model of surgical procedures for multimodal image-guided neurosurgery.

OBJECTIVE: Improvement of the planning stage of image-guided surgery requires a better anticipation of the surgical procedure and its anatomical and functional environment. This anticipation should be provided by acquisition of multimodal medical images of the patient and by a better understanding of surgical procedures. In this paper, we propose improvements to the planning and performance of multimodal image-guided neurosurgery through the use of information models related to neurosurgical procedures. MATERIALS AND METHODS: A new generic model of surgical procedures is introduced in the context of multimodal image-guided craniotomies. The basic principle of the model is to break down the surgical procedure into a sequence of steps defining the surgical script. In the model, a step is defined by an action. The model assigns to each surgical step a list of image entities extracted from multimodal preoperative images (i.e., anatomical and/or functional images) which are relevant to the performance of that particular step. A semantic validation of the model was performed by instantiating the model entities for 29 surgical procedures. RESULTS: The resulting generic model is described by a UML class diagram and a textual description. The validation showed the relevance of the model, confirming the main underlying assumptions. It also provided some leads to improve the model. CONCLUSION: While further validation is needed, the initial benefits of this approach can already be outlined. It should add real value to the different levels of image-guided surgery, from preprocessing to planning, as well as during surgery. Models of surgical procedures can manage image data according to the surgical script, which should lead to better anticipation of surgery through the development of simulation tools. Furthermore, the models may improve the performance of surgery using microscope-based neuronavigation systems by making it possible to adapt both visualization and interaction features of multimodal preoperative images according to the model.

The RETAIN project: DICOM teleradiology over an ATM-based network. Radiological Examinations Transfer on an ATM Integrated Network.

The RETAIN project (Radiological Examinations Transfer on an ATM Integrated Network) has aimed at testing videoconferencing and DICOM image transfers to get advice about difficult radiological cases over an asynchronous transfer mode (ATM)-based network, which affords a more comfortable interface than narrow-band networks and allows exchange of complete image series using the DICOM format of studies. For this purpose, an experimental ATM network was applied between six university hospitals in four different countries. An assessment of the functionalities of the system was performed by means of log-file analysis, video recording of the sessions and forms filled out by the participants at the end of each session. Questionnaires were answered by the users at the end of the project to bring out perspectives of utilisation and added value. We discussed 43 cases during 20 sessions. For technical or organisational problems, only 20 of the 36 planned sessions took place. The throughput over ATM (10.5 Mbit/s, 20 times faster than six ISDN B-channels) was adequate. Despite the experimental configuration of the network, the system was considered as satisfactory by all the physicians. In 72 % of the sessions, the expected result (answer to the question) was gained. By common consent, videoconferencing was unanimously regarded as a prominent tool in improving the interaction quality. Asynchronous transfer mode is an efficient method for fast transferring of radiologic examinations in DICOM format and for discussing them through high-quality videoconferencing.

Influence of the teleradiology technology (N-ISDN and ATM) on the inter-hospital management of neurosurgical patients.

We set out to assess the influence of a teleradiology network on the relations between a general hospital and a 100 km distant university hospital in the context of neurosurgical emergencies, and compared a commercially available technology, N-ISDN (Narrowband Integrated Service/Digital Network), to an emerging technology, ATM (Asynchronous Transfer Mode). The evaluation was conducted using records of advice request calls and patient transfers. Three phases were considered: without teleradiology, with transfer of digitized images over N-ISDN at 64 kbps, and with an experimental ATM network at 10.5 Mbps with DICOM image transfers and videoconferencing. Additionally, staff meetings over ATM videoconferencing were set up. To assess the ATM service, we used log files and questionnaires, 108 advice requests were studied over a 18 month period. The average transmission time for one examination was 38 s with full DICOM image resolution over ATM, versus 150 s with 10:1 JPEG (Joint Photographic Expert Group) compression over N-ISDN. Up to 50% unnecessary patient transfers were avoided. Advice requests increased fourfold, and non-urgent advice requests increased from 0 to 21%. Despite the experimental configuration of the ATM network, the service gave satisfaction to all the physicians. Videoconferencing was unanimously regarded as a prominent tool to improve the quality of interaction. It was particularly useful for non-urgent cases and distant staff meetings. Teleradiology can improve the relations between hospitals through an increase of urgent and non-urgent advice requests. Asynchronous transfer mode is an efficient way for fast transfer of radiological examinations in DICOM format and for discussing them through high-quality videoconferencing.

Computerized brain atlases as decision support systems: a methodological approach.

This paper deals with the development of computerized brain atlases addressing both research and clinical needs. The authors analyze in detail the potential of these systems and discuss the capabilities and limitations of the digital atlases currently being developed around the world. The authors propose to reconsider the concept of a brain atlas, regarding both its content, and the way it has to be used and managed in order to set up more effective cooperation between the user and the system. Particular emphasis is placed on extensibility and reuse issues. which are critical in this rapidly evolving field. These orientations result from both the authors' experience and the analysis of current trends in the field of neuroimaging. The general methodology is illustrated with examples related to computer aided surgical planning.

Standardization in the field of medical image management: the contribution of the MIMOSA model.

This paper deals with the development of standards in the field of medical imaging and picture archiving and communication systems (PACS's), and notably concerning the interworking between PACS's and hospital information systems (HIS). It explains, in detail, how a conceptual model of the management of medical images, such as the medical image management in an open system architecture (MIMOSA) model, can contribute to the development of standards for medical image management and PACS's. This contribution is twofold: 1) Since the model lists and structures the concepts and resources involved to make the images available to the users when and where they are required, and describes the interactions between PACS components and HIS, the MIMOSA work helps by defining a reference architecture which includes an external description of the various components of a PACS, and a logical structure for assembling them. 2) The model and the implementation of a demonstrator based on this model allow the relevance of the Digital Imaging and Communications in Medicine (DICOM) standard with respect to image management issues to be assessed, highlighting some current limitations of this standard and proposing extensions. Such a twofold action is necessary in order both to bring solutions, even partial, in the short term, and to allow for the convergence, in the long term, of the standards developed by independent standardization groups in medical informatics (e.g., those within Technical Committee 251 of CEN: Comité Européen de Normalisation).

Image management in PACS: how should they be decomposed into well-defined and interoperable industrial products?

We consider that no consensus currently exists on how PACS should be decomposed into well-defined and interoperable industrial products. We believe that this lack of consensus hampers the development of multi-vendor PACS and makes the standardization process slower. This paper tries to understand the ins and outs of these choices. To realize this we have used the MIMOSA functional model (EurIPACS project) as a reference model. We have then delineated the borders between several possible industrial products in the fields of work flow management and management of image availability. We have compared these solutions from several perspectives, including the manufacturers' strategy, the users' strategy and the standardization.

MIMOSA: a functional model of the management of medical images.

The concept of picture archiving and communication system (PACS) appeared in 1982. Twelve years later most PACS prototypes still do not satisfy the medical community requirements: too much emphasis has been put on technical solutions and little effort devoted to the management of images itself. A common approach to this problem is needed more than ever to allow cost-effective systems to be developed. Modelling is a way to reach this objective, and the MIMOSA topic within the AIM/EurlPACS project aims at defining such a model of medical image management. This paper presents the MIMOSA approach with the three underlying constraints, i.e. genericity, implementation independence and performance. The MIMOSA group is building three interrelated models: a data model, a functional model and a dynamic model. However, in this report we focus only on the functional model, and explain how it was abstracted from various clinical scenarios in the first phase of the project. The availability level concept is introduced as a customizable and implementation independent solution to the problem of managing the delay of access to the information. The so-called contextual diagram and the acquisition of a new examination which are two representative parts of the model are detailed. The validation aspects and the relationships to projects working on the management of patient records are addressed as a conclusion.

Data fusion in medical imaging: merging multimodal and multipatient images, identification of structures and 3D display aspects.

Data fusion in medical imaging can be seen into two ways (i) multisensors fusion of anatomical and functional information and (ii) interpatient data fusion by means of warping models. These two aspects set the methodological framework necessary to perform anatomical modelling especially when concerning the modelling of brain structures. The major relevance of the work presented here concerns the interpretation of multimodal 3D neuro-anatomical data bases. Three types of data fusion problems are considered in this paper. The first one concerns the problem of data combination which includes multimodal registration (multisensor fusion applied to CT, MRI, DSA, PET, SPECT, or MEG). In particular, the problem of warping patient data to an anatomical atlas is reviewed and a solution is proposed. The second problem of data fusion addressed in this paper is the identification of anatomical structures by means of image analysis methods. Two techniques have been developed. The first one deals with the analysis of image geometrical features to end up with the determination of a fuzzy mask to label the structure of interest. The second technique consists of labelling major cerebral structures by means of statistical image features associated with relaxation techniques. Finally, the paper presents a review of up to date 3D display techniques with a special emphasis on volume rendering and 3D display of combined data.

[Image archiving and communication systems: review of ten years' experiences and perspectives]. / Les systèmes de communication et d'archivage d'images: bilan de dix années d'expérimentations et perspectives.

The paper starts by presenting the major PACS (Picture Archiving and Communication Systems) related concepts and highlights the medical motivations which resulted in PACS developments. The authors review some PACS experiments carried out during the last decade and draw the conclusions of these experiments; the experience of the University Hospital of Rennes is also briefly presented. Finally a discussion is engaged about the future of PACS and their position within the Hospital Information System. According to the authors, this process should not be confined within the small community of PACS specialists but should concern all actors of the hospital, namely medical staff involved in the production or utilisation of medical images, technical staff in charge of equipment and the Hospital Information System, and hospital administrators. Three major lines are proposed: the first one deals with the functional capacities of PACS and their adaptation to actual user needs; the second concerns the methodology required to set up such systems to ensure adequate integration within the HIS and the third concerns economic issues.

Computer graphics in medicine: a survey.

Increased interest is presently given to three-dimensional (3-D) medical applications due to simultaneous emergence of high-resolution imaging systems and computer graphics techniques. This paper intends to present a survey of this field together with discussion and prospective views. The general framework is composed of six parts: data acquisition and preprocessing, polygonal object representation, voxel description, system architecture, medical applications, and prospects. Data base acquisition includes characterization of imaging modalities and medical specificity. Preprocessing schemes are directed to improvements (filtering), windowing, and spatial anisotropy (linear or spline interpolation). The two following sections are devoted to descriptions of the main object representations. Particular emphasis is given to optimal contour approximation, surface triangulation, mathematical surfaces on one hand, and cuberille and voxel representations on the other. Display capabilities--hidden surface removal, surface normal shading, structure enhancement--and data base structuration--hierarchical and nonhierarchical (graph and tree encoding)--are, respectively, described. An overview of 3-D systems is further given (Section V), and features of medical applications are reviewed and gathered in basic functionalities, surgery, and radiotherapy specifications (Section VI). The last section provides some prospective views on reconstruction from a few projections, model-guided labeling, multimodality image overlay, and local image network. Some of these issues are illustrated by examples of 3-D images.