279 research outputs found
Intervertebral Disc Structure and Mechanical Function Under Physiological Loading Quantified Non-invasively Utilizing MRI and Image Registration
The intervertebral discs (IVD) functions to permit motion, distribute load, and dissipate energy in the spine. It performs these functions through its heterogeneous structural organization and biochemical composition consisting of several tissue substructures: the central gelatinous nucleus pulposus (NP), the surrounding fiber reinforced layered annulus fibrosus (AF), and the cartilaginous endplates (CEP) that are positioned between the NP and vertebral endplates. Each tissue contributes individually to overall disc mechanics and by interacting with adjacent tissues. Disruption of the disc\u27s tissues through aging, degeneration, or tear will not only alter the affected tissue mechanical properties, but also the mechanical behavior of adjacent tissues and, ultimately, overall disc segment function. Thus, there is a need to measure disc tissue and segment mechanics in the intact disc so that interactions between substructures are not disrupted. Such measurements would be valuable to study mechanisms of disc function and degeneration, and develop and evaluate surgical procedures and therapeutic implants. The objectives of this study were to develop, validate, and apply methods to visualize and quantify IVD substructure geometry and track internal deformations for intact human discs under axial compression. The CEP and AF were visualized through MRI parameter mapping and image sequence optimization for ideal contrast. High-resolution images enabled geometric measurements. Axial compression was performed using a custom-built loading device that permitted long relaxation times outside of the MRI, 300 m isotropic resolution images were acquired, and image registration methods applied to measure 3D internal strain. In conclusion, new methods to visualize and quantify CEP thickness, annular tear detection and geometric quantification, and non-invasively measure 3D internal disc strains were established. No correlation was found between CEP thickness and disc level; however the periphery was significantly thicker compared to central locations. Clear distinction of adjacent AF lamellae enabled annular tear detection and detailed geometric quantification. Annular tears demonstrated non-classic geometry through interconnecting radial, circumferential, and perinuclear formations. Regional strain inhomogeneity was observed qualitatively and quantitatively. Variation in strain magnitudes might be explained by geometry in axial and circumferential strain while peak radial strain in the posterior AF may have important implications for disc herniation
Lumbar disk 3D modeling from limited number of MRI axial slices
This paper studies the problem of clinical MRI analysis in the field of lumbar intervertebral disk herniation diagnosis. It discusses the possibility of assisting radiologists in reading the patients MRI images by constructing a 3D model for the region of interest using simple computer vision methods. We use axial MRI slices of the lumbar area. The proposed framework works with a very small number of MRI slices and goes through three main stages. Namely, the region of interest extraction and enhancement, inter-slice interpolation, and 3D model construction. We use the Marching Cubes algorithm to construct the 3D model of the the region of interest. The validation of our 3D models is based on a radiologist’s analysis of the models. We tested the proposed 3D model construction on 83 cases and We have a 95% accuracy according to the radiologist evaluation. This study shows that 3D model construction can greatly ease the task of the radiologist which enhances the working experience. This leads eventually to more accurate and easy diagnosis process
3D Interactive model of lumbar spinal structures of anaesthetic interest
A 3D model of lumbar structures of anesthetic interest was reconstructed from human magnetic resonance (MR) images and embedded in a Portable Document Format (PDF) file, which can be opened by freely available software and used offline. The MR images were analyzed using a specific 3D software platform for biomedical data. Models generated from manually delimited volumes of interest and selected MR images were exported to Virtual Reality Modeling Language format and were presented in a PDF document containing JavaScript-based functions. The 3D file and the corresponding instructions and license files can be downloaded freely at http://diposit.ub.edu/dspace/handle/2445/44844?locale5en. The 3D PDF interactive file includes reconstructions of the L3-L5 vertebrae, intervertebral disks, ligaments, epidural and foraminal fat, dural sac and nerve root cuffs, sensory and motor nerve roots of the cauda equina, and anesthetic approaches (epidural medial, spinal paramedial, and selective nerve root paths); it also includes a predefined sequential educational presentation. Zoom, 360 rotation, selective visualization, and transparency graduation of each structure and clipping functions are available. Familiarization requires no specialized informatics knowledge. The ease with which the document can be used could make it valuable for anatomical and anesthetic teaching and demonstration of patient information
Lien entre les pathologies rachidiennes et l’intensité de signal IRM dans le disque intervertébral
RÉSUMÉ
La scoliose et le spondylolisthésis sont des pathologies rachidiennes qui touchent respectivement
1,5-3% et 13.6% des personnes et possèdent un potentiel d’évolution. Ces pathologies
tridimensionnelles sont principalement étudiées par des indices géométriques bidimensionnels ne
reflétant qu’une partie des modifications morphologiques et biomécaniques/biochimiques du
rachis. L’étude clinique de ces pathologies et de leurs évolutions sont réalisées à partir
d’informations limitées sur les modifications engendrées au rachis. Le disque intervertébral
(DIV) est le tissu mou permettant la mobilité entre les segments vertébraux. Il subit les effets
dégénératifs des pathologies de manière précoce en son sein.
Notre étude se base sur l’hypothèse que l’intensité de signal IRM au sein d’images cliniques
pondérées en T2 est sensible à la pathologie rachidienne et à sa sévérité, permettant ainsi à cette
modalité d’imagerie de fournir des informations sur les propriétés géométriques, biochimiques et
mécaniques du DIV, et donc de réaliser des suivis in-vivo de l’évolution des pathologies
rachidiennes. Ce projet vise à développer des techniques permettant l’étude tridimensionnelle de
la distribution géométrique et gaussienne du signal IRM pondéré en T2 au sein d’images
cliniques de patients présentant des pathologies rachidiennes, et ce dans le disque intervertébral
(DIV) complet, dans l’annulus fibrosus (AF) et dans le nucleus pulposus (NP). Ces outils
permettront de vérifier si les dégénérescences des DIV sont spécifiques aux pathologies les ayant
engendrées ainsi qu’à leurs sévérités.
Afin d’analyser le signal IRM tridimensionnel du DIV de manière automatisée, il est nécessaire
de segmenter les images cliniques. Une méthode semi-automatisée a été utilisée dans ce projet et
sa reproductibilité a été testée. Cette méthode permet un gain de temps par rapport aux méthodes
manuelles utilisées dans la littérature.
Des outils d’analyse de signal IRM au sein du DIV ont été développés afin de détecter la
sensibilité de celui-ci aux pathologies rachidiennes et à leurs sévérités. Ces outils ont permis de
refléter les variations de distribution du signal IRM de manière géométrique en 3D et de manière
gaussienne.
Dans ce but, une cohorte de 79 sujets (32 scolioses, 32 spondylolithésis, 15 contrôles) a été
étudiée. Une normalisation de l’intensité de signal a été nécessaire à la comparaison des signaux----------ABSTRACT
Scoliosis and spondylolisthesis are spine pathologies affecting 1.5-3% and 13.6% of the
population, respectively. These diseases have the potential to further progress. These
tridimensional pathologies are mainly studied using two-dimensional geometric indices, which
reflect only a fraction of the morphological, biomechanical and biochemical variations of the
spine. Clinical interpretations of these pathologies and of their evolution are based on the limited
information of spine modifications. The intervertebral disc (IVD) is the soft tissue between
adjacent vertebrae that allow the mobility of the spine between the rigid segments. Spine
pathologies lead to premature degeneration of the IVD.
In our study, we hypothesize that the MRI signal intensity within clinical T2-weighted images is
sensitive to the spine pathology and to its severity. Thus this imaging technique could provide
information on the geometrical, biochemical and mechanical properties of the IVD, and facilitate
in-vivo follow-up of the evolution of these spine pathologies. This project aims to develop
techniques to analyse the tridimensional geometry as well as the Gaussian distribution of the T2-
weighted MRI signal within clinical images of the IVD, the annulus fibrosus (AF) and the
nucleus pulposus (NP) of patients affected with various spine pathologies. These tools will assess
whether or not a specific degeneration of the IVD is caused by the spine pathologies depending
on their severity.
In order to analyse automatically the tridimensional MRI signal within the IVD, it is necessary to
segment clinical images. A semi-automated method was used in this project and its
reproducibility was tested. This method is less time-consuming compared to the commonly used
manual methods that are reported in the literature.
MRI signal analysis tools were developed to detect its sensitivity within the IVD to spine
pathologies and their severities. These tools allowed a Gaussian and geometric distribution
analysis of the MRI signal intensity within the IVD.
A cohort of 79 subjects (32 scoliosis, 32 spondylolisthesis, 15 controls) was studied. A
normalization of the signal intensity was done in order to compare images from patients with
variable parameters such as the acquisition gain. This study tested two normalizations of the
intensity of the signal. The first one was based on the intensity within the cerebrospinal flui
The value of magnetic resonance imaging and computed tomography in the study of spinal disorders
Computed tomography (CT) and magnetic resonance imaging (MRI) have replaced conventional
radiography in the study of many spinal conditions, it is essential to know when these techniques are indicated
instead of or as complementary tests to radiography, which findings can be expected in different clinical
settings, and their significance in the diagnosis of different spinal conditions. Proper use of CT and MRI in
spinal disorders may facilitate diagnosis and management of spinal conditions. An adequate clinical approach,
a good understanding of the pathological manifestations demonstrated by these imaging techniques and a
comprehensive report based on a universally accepted nomenclature represent the indispensable tools to improve
the diagnostic approach and the decision-making process in patients with spinal pain. Several guidelines are
available to assist clinicians in ordering appropriate imaging techniques to achieve an accurate diagnosis and
to ensure appropriate medical care that meets the efficacy and safety needs of patients. This article reviews the
clinical indications of CT and MRI in different pathologic conditions affecting the spine, including congenital,
traumatic, degenerative, inflammatory, infectious and tumor disorders, as well as their main imaging features. It
is intended to be a pictorial guide to clinicians involved in the diagnosis and treatment of spinal disorders
Interobserver and Test-Retest Reproducibility of T1ρ and T2 Measurements of Lumbar Intervertebral Discs by 3T Magnetic Resonance Imaging
OBJECTIVE: To investigate the interobserver and test-retest reproducibility of T1ρ and T2 measurements of lumbar intervertebral discs using 3T magnetic resonance imaging (MRI).
MATERIALS AND METHODS: This study included a total of 51 volunteers (female, 26; male, 25; mean age, 54 ± 16.3 years) who underwent lumbar spine MRI with a 3.0 T scanner. Amongst these subjects, 40 underwent repeat T1ρ and T2 measurement acquisitions with identical image protocol. Two observers independently performed the region of interest measurements in the nuclei pulposi of the discs from L1-2 through L5-S1 levels. Statistical analysis was performed using intraclass correlation coefficient (ICC) with a two-way random model of absolute agreement. Comparison of the ICC values was done after acquisition of ICC values using Z test. Statistical significance was defined as p value < 0.05.
RESULTS: The ICCs of interobserver reproducibility were 0.951 and 0.672 for T1ρ and T2 mapping, respectively. The ICCs of test-retest reproducibility (40 subjects) for T1ρ and T2 measurements were 0.922 and 0.617 for observer A and 0.914 and 0.628 for observer B, respectively. In the comparison of the aforementioned ICCs, ICCs of interobserver and test-retest reproducibility for T1ρ mapping were significantly higher than T2 mapping (p < 0.001).
CONCLUSION: The interobserver and test-retest reproducibility of T1ρ mapping were significantly higher than those of T2 mapping for the quantitative assessment of nuclei pulposi of lumbar intervertebral discs.ope
3d-Fse Isotropic Mri Of The Lumbar Spine: New Application Of An Existing Technology
Daniel J. Blizzard, Andrew H. Haims, Andrew W. Lischuk, Rattalerk Arunakul, Joshua W. Hustedt, and Jonathan N. Grauer. Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT.
The purpose of this study was to assess the diagnostic performance of three-dimensional, isotropic fast/turbo spin-echo (3D-TSE) in routine lumbar spine MR imaging.
Conventional 2D-FSE MRI requires independent acquisition of each desired imaging plane. This is time consuming and potentially problematic in spine imaging, as the plane of interest varies along the vertical axis due to lordosis, kyphosis, or possible deformity. 3D-TSE provides the capability to acquire volumetric datasets that can be dynamically reformatted to create images in any desired plane.
Eighty subjects scheduled for routine lumbar MRI were included in a retrospective trial. Each subject underwent both 3D-TSE and conventional 2D-FSE axial and sagittal MRI sequences. For each subject, the 3D-TSE and 2D-FSE sequences were separately evaluated (minimum 4 weeks apart) in a randomized order and read independently by four reviewers. Images were evaluated using specific criteria for stenosis, herniation, and degenerative changes.
The inter-method reliability for the four reviewers was 85.3%. Modified inter-method reliability analysis, disregarding disagreements between the lowest two descriptors for appropriate criteria (equivalent to none and mild ), revealed average overall agreement of 94.6%.
Using the above, modified criteria, inter-observer variability for 3D-TSE was 89.1% and 88.3% for 2D-FSE (p=0.05), and intra-observer variability for 3D-TSE was 87.2% and 82.0% for 2D-FSE (p\u3c0.01). The inter-method agreement between 3D-TSE and 2D-FSE was statistically non-inferior to intra-observer 2D-FSE variability (p\u3c0.01).
This systematic evaluation showed there is a very high degree of agreement between diagnostic findings assessed on 3D-TSE and conventional 2D-FSE sequences. Overall, inter-method agreement was statistically non-inferior to the intra-observer agreement between repeated 2D-FSE evaluations.
Overall, this study shows that 3D-TSE performs equivalently, if not superiorly to 2D-FSE sequences. Reviewers found particular utility for the ability to manipulate image planes with the 3D-TSE if there was greater pathology or anatomic variation
Segmentation of the Cerebrospinal Fluid from MRI Images for the Treatment of Disc Herniations
About 80 percent of people are affected at some point in their lives by lower back pain, which is one of the most common neurological diseases and reasons for long-term disability in the United States. The symptoms are primarily caused by overly heavy lifting and/or overstretching of the back, leading to a rupture and an outward bulge of an intervertebral disc, which puts pressure on and pinches the nerve fibers of the spine. The most common form is a lumbar disc herniation between the fourth and fifth lumbar vertebra and between the fifth lumbar vertebra and the sacrum. In recent years the diagnosis of lower back pain has improved, mainly due to enhanced imaging techniques and imaging quality, but the surgical therapy remains hazardous. Reasons for this include low visibility when accessing the lumbar area and the high risk of causing permanent damage when touching the nerve fibers. A new approach for increasing patient safety is the segmentation and visualization of the cerebrospinal fluid in the lower lumbar region of the vertebral column. For this purpose a new fully-automatic and a semi-automatic approach were developed for separating the cerebrospinal fluid from its surroundings on T2-weighted MRI scans of the lumbar vertebra. While the fully-automatic algorithm is realized by a model-based searching method and a volume-based segmentation, the semi-automatic algorithm requires a seed point and performs the segmentation on individual axial planes through a combination of a region-based segmentation algorithm and a thresholding filter. Both algorithms have been applied to four T2-weighted MRI datasets and are compared with a gold-standard segmentation. The segmentation overlap with the gold-standard was 78.7 percent for the fully-automatic algorithm and 93.1 percent for the semi-automatic algorithm. In the pathological region the fully-automatic algorithm obtained a similarity of 56.6 percent, compared to 87.8 percent for the semi-automatic algorithm
Procedures for finite element mesh generation from medical imaging: application to the intervertebral disc
Dissertação de mestrado integrado em Engenharia BiomédicaThe paramount goal of this ‘half-year’ work is the development of a set of methodologies
and procedures for the geometric modelling by a finite element (FE) mesh of the bio-structure of a
motion segment (or functional spinal unit), i.e., two vertebrae and an intervertebral disc, from
segmented medical images (processed from medical imaging).
At an initial stage, a three-dimensional voxel-based geometric model of a goat motion
segment was created from magnetic resonance imaging (MRI) data. An imaging processing
software (ScanIP/Simplewire) was used for imaging segmentation (identification of different
structures and tissues), both in images with lower (normal MRI) and higher (micro-MRI) resolutions.
It shall be noticed that some soft-tissues, such as annulus fibrosus or nucleus pulposus, are very
hard to isolate and identify given that the interface between them is not clearly defined. At the end
of this stage, images with different resolutions allowed to generate different 3D voxel-based
geometric models.
Thereafter, a procedure for the FE mesh generation from the aforementioned voxelized
data should be studied and applied. However, as the original geometry was only approximately
known from real medical imaging, it was difficult to objectively quantify the quality of the FE
meshing procedure and the accuracy between source geometry and target FE mesh. In order to
overcome such difficulties, and due to the lack of quality of the available medical imaging, a
“virtualization” procedure was developed to create a set of segmented 2D medical images from a
well-defined geometry of a motion segment. The main idea was to create the conditions to quantify
the quality and the accuracy of the developed FE meshing procedure, as well to study the effect of
imaging resolution.
Starting from the virtually generated 2D segmented images, a 3D voxel-based structure
was achieved. Given that initial domains are now clearly defined, there is no need for further image
processing. Then, a two-step FE mesh generation procedure (generation followed by simplification)
allows to create an optimized tetrahedral FE mesh directly from 3D voxelized data. Finally, because
the virtualization procedure allowed to know the initial geometry, one is able to objectively quantify the quality and the accuracy of the final simplified tetrahedral FE mesh, and thus to understand
and quantify: a) the role of the medical image resolution on the FE geometrical reconstruction, b)
the procedure and parameters of the FE mesh generation step, and c) the procedure and
parameters of the FE mesh simplification step, and thus to give a clear contribution in the
definition of the procedure for the FE mesh generation from medical imaging in case of an
intervertebral disc.O objetivo fundamental deste trabalho de seis meses é o desenvolvimento de um conjunto
de metodologias e procedimentos para a modelação geométrica, através de uma malha de
elementos finitos (EF) de uma bio-estrutura de um motion segment (ou unidade funcional da
coluna), ou seja, duas vértebras e um disco intervertebral, a partir de imagens médicas
segmentadas (processadas a partir de imagiologia médica).
Numa fase inicial, um modelo geométrico tridimensional baseado em voxels de um motion
segment de uma cabra foi criado a partir de informação de imagens médicas de ressonância
magnética (RM). Um software de processamento de imagem (ScanIp/Simplewire) foi usado para
segmentação de imagens (identificação de diferentes estruturas e tecidos), em imagens de menor
(RM normal) e maior (micro-RM) resolução. Deve ser referido que alguns tecidos moles, como o
anel fibroso e o núcleo pulposo são muito difíceis de isolar e identificar, dado que as fronteiras
destes não estão claramente definidas. No final desta etapa, as imagens com diferentes
resoluções permitiram gerar diferentes modelos geométricos 3D baseados em voxels.
Posteriormente, um procedimento para geração de malha de EF, a partir da informação
voxelizada acima mencionada, deveria ser estudado e aplicado. No entanto, como a geometria
original era aproximadamente conhecida a partir de imagens médicas reais, foi difícil quantificar
objetivamente a qualidade do procedimento de geração de malha de EF e a precisão entre a
geometria de origem e a malha de EF de destino. A fim de superar tais dificuldades, e devido à
falta de qualidade de imagens médicas disponíveis, um procedimento de “virtualização” foi
desenvolvido para criar um conjunto de imagens médicas 2D segmentadas a partir de uma
geometria de um motion segment bem conhecida. A principal ideia foi criar as condições para
quantificar a qualidade e a precisão do procedimento de geração de malha de EF desenvolvido,
bem como estudar o efeito da resolução da imagem médica.
A partir das imagens 2D segmentadas, geradas virtualmente, uma estrutura de voxels 3D
pode ser conseguida. Dado que os domínios iniciais estão agora claramente definidos, não há
necessidade de processamento de imagem adicional. Por conseguinte, um procedimento de geração de malha de EF de duas etapas (geração seguida por simplificação) permite criar uma
malha de EF tetraédrica otimizada diretamente a partir de informação 3D voxelizada.
Por fim, como o procedimento de virtualização permitiu conhecer a geometria inicial, é
possível quantificar objetivamente a qualidade e exatidão da malha de EF tetraédrica final
simplificada, e assim, compreender e quantificar: a) o papel da resolução da imagem médica na
reconstrução geométrica de EF; b) o procedimento e os parâmetros da etapa de geração de malha
de EF; c) o procedimento e os parâmetros da etapa de simplificação de malhas de EF, e assim,
dar uma contribuição clara na definição do procedimento para a geração de malha de EF a partir
de imagem médica, no caso de um disco intervertebral.European Project : NP Mimetic - Biomimetic
Nano-Fiber Based Nucleus Pulposus Regeneration for the Treatment of Degenerative Disc Disease,
funded by the European Commission under FP7 (grant NMP3-SL-2010-246351
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