Diffeomorphic Metric Mapping of High Angular Resolution Diffusion Imaging based on Riemannian Structure of Orientation Distribution Functions

In this paper, we propose a novel large deformation diffeomorphic registration algorithm to align high angular resolution diffusion images (HARDI) characterized by orientation distribution functions (ODFs). Our proposed algorithm seeks an optimal diffeomorphism of large deformation between two ODF fields in a spatial volume domain and at the same time, locally reorients an ODF in a manner such that it remains consistent with the surrounding anatomical structure. To this end, we first review the Riemannian manifold of ODFs. We then define the reorientation of an ODF when an affine transformation is applied and subsequently, define the diffeomorphic group action to be applied on the ODF based on this reorientation. We incorporate the Riemannian metric of ODFs for quantifying the similarity of two HARDI images into a variational problem defined under the large deformation diffeomorphic metric mapping (LDDMM) framework. We finally derive the gradient of the cost function in both Riemannian spaces of diffeomorphisms and the ODFs, and present its numerical implementation. Both synthetic and real brain HARDI data are used to illustrate the performance of our registration algorithm

Multi-modality cardiac image computing: a survey

Multi-modality cardiac imaging plays a key role in the management of patients with cardiovascular diseases. It allows a combination of complementary anatomical, morphological and functional information, increases diagnosis accuracy, and improves the efficacy of cardiovascular interventions and clinical outcomes. Fully-automated processing and quantitative analysis of multi-modality cardiac images could have a direct impact on clinical research and evidence-based patient management. However, these require overcoming significant challenges including inter-modality misalignment and finding optimal methods to integrate information from different modalities. This paper aims to provide a comprehensive review of multi-modality imaging in cardiology, the computing methods, the validation strategies, the related clinical workflows and future perspectives. For the computing methodologies, we have a favored focus on the three tasks, i.e., registration, fusion and segmentation, which generally involve multi-modality imaging data, either combining information from different modalities or transferring information across modalities. The review highlights that multi-modality cardiac imaging data has the potential of wide applicability in the clinic, such as trans-aortic valve implantation guidance, myocardial viability assessment, and catheter ablation therapy and its patient selection. Nevertheless, many challenges remain unsolved, such as missing modality, modality selection, combination of imaging and non-imaging data, and uniform analysis and representation of different modalities. There is also work to do in defining how the well-developed techniques fit in clinical workflows and how much additional and relevant information they introduce. These problems are likely to continue to be an active field of research and the questions to be answered in the future

Analysis of the developing brain using image registration

Imperial Users onl

Segmentation of images with low-contrast edges

A vast amount of the current research in medical image analysis has aimed to develop improved techniques of image segmentation. Of the existing approaches, active contour methods have proven effective by incorporating edge or region information from the image into a level set formulation. However, complications arise in images containing regions of low-contrast due to noise, occlusions, or partial volume effects, which are often unavoidable in practical applications. Incorporating prior shape information into the segmentation framework provides a more accurate and robust solution by constraining the evolving contour to resemble a target shape. Two methods are presented to incorporate a shape prior into existing active contour segmentation methods, including the edge-based geodesic active contours model and a fast update implementation of the region-based Chan-Vese model. Applying these methods to synthetic and real images demonstrates that an improved result can be obtained for images containing low-contrast edge regions

Karakterizacija predkliničnega tumorskega ksenograftnega modela z uporabo multiparametrične MR

Introduction: In small animal studies multiple imaging modalities can be combined to complement each other in providing information on anatomical structure and function. Non-invasive imaging studies on animal models are used to monitor progressive tumor development. This helps to better understand the efficacy of new medicines and prediction of the clinical outcome. The aim was to construct a framework based on longitudinal multi-modal parametric in vivo imaging approach to perform tumor tissue characterization in mice. Materials and Methods: Multi-parametric in vivo MRI dataset consisted of T1-, T2-, diffusion and perfusion weighted images. Image set of mice (n=3) imaged weekly for 6 weeks was used. Multimodal image registration was performed based on maximizing mutual information. Tumor region of interested was delineated in weeks 2 to 6. These regions were stacked together, and all modalities combined were used in unsupervised segmentation. Clustering methods, such as K-means and Fuzzy C-means together with blind source separation technique of non-negative matrix factorization were tested. Results were visually compared with histopathological findings. Results: Clusters obtained with K-means and Fuzzy C-means algorithm coincided with T2 and ADC maps per levels of intensity observed. Fuzzy C-means clusters and NMF abundance maps reported most promising results compared to histological findings and seem as a complementary way to asses tumor microenvironment. Conclusions: A workflow for multimodal MR parametric map generation, image registration and unsupervised tumor segmentation was constructed. Good segmentation results were achieved, but need further extensive histological validation.Uvod Eden izmed pomembnih stebrov znanstvenih raziskav v medicinski diagnostiki predstavljajo eksperimenti na živalih v sklopu predkliničnih študij. V teh študijah so eksperimenti izvedeni za namene odkrivanja in preskušanja novih terapevtskih metod za zdravljenje človeških bolezni. Rak jajčnikov je eden izmed glavnih vzrokov smrti kot posledica rakavih obolenj. Potreben je razvoj novih, učinkovitejših metod, da bi lahko uspešneje kljubovali tej bolezni. Časovno okno aplikacije novih terapevtikov je ključni dejavnik uspeha raziskovane terapije. Tumorska fiziologija se namreč razvija med napredovanjem bolezni. Eden izmed ciljev predkliničnih študij je spremljanje razvoja tumorskega mikro-okolja in tako določiti optimalno časovno okno za apliciranje razvitega terapevtika z namenom doseganja maksimalne učinkovitosti. Slikovne modalitete so kot raziskovalno orodje postale izjemno popularne v biomedicinskih in farmakoloških raziskavah zaradi svoje neinvazivne narave. Predklinične slikovne modalitete imajo nemalo prednosti pred tradicionalnim pristopom. Skladno z raziskovalno regulativo, tako za spremljanje razvoja tumorja skozi daljši čas ni potrebno žrtvovati živali v vmesnih časovnih točkah. Sočasno lahko namreč s svojim nedestruktivnim in neinvazivnim pristopom poleg anatomskih informacij podajo tudi molekularni in funkcionalni opis preučevanega subjekta. Za dosego slednjega so običajno uporabljene različne slikovne modalitete. Pogosto se uporablja kombinacija več slikovnih modalitet, saj so medsebojno komplementarne v podajanju željenih informacij. V sklopu te naloge je predstavljeno ogrodje za procesiranje različnih modalitet magnetno resonančnih predkliničnih modelov z namenom karakterizacije tumorskega tkiva. Metodologija V študiji Belderbos, Govaerts, Croitor Sava in sod. [1] so z uporabo magnetne resonance preučevali določitev optimalnega časovnega okna za uspešno aplikacijo novo razvitega terapevtika. Poleg konvencionalnih magnetno resonančnih slikovnih metod (T1 in T2 uteženo slikanje) sta bili uporabljeni tudi perfuzijsko in difuzijsko uteženi tehniki. Zajem slik je potekal tedensko v obdobju šest tednov. Podatkovni seti, uporabljeni v predstavljenem delu, so bili pridobljeni v sklopu omenjene raziskave. Ogrodje za procesiranje je narejeno v okolju Matlab (MathWorks, verzija R2019b) in omogoča tako samodejno kot ročno procesiranje slikovnih podatkov. V prvem koraku je pred generiranjem parametričnih map uporabljenih modalitet, potrebno izluščiti parametre uporabljenih protokolov iz priloženih tekstovnih datotek in zajete slike pravilno razvrstiti glede na podano anatomijo. Na tem mestu so slike tudi filtrirane in maskirane. Filtriranje je koristno za izboljšanje razmerja med koristnim signalom (slikanim živalskim modelom) in ozadjem, saj je skener za zajem slik navadno podvržen različnim izvorom slikovnega šuma. Uporabljen je bil filter ne-lokalnih povprečij Matlab knjižnice za procesiranje slik. Prednost maskiranja se potrdi v naslednjem koraku pri generiranju parametričnih map, saj se ob primerno maskiranem subjektu postopek bistveno pospeši z mapiranjem le na želenem področju. Za izdelavo parametričnih map je uporabljena metoda nelinearnih najmanjših kvadratov. Z modeliranjem fizikalnih pojavov uporabljenih modalitet tako predstavimo preiskovan živalski model z biološkimi parametri. Le-ti se komplementarno dopolnjujejo v opisu fizioloških lastnosti preučevanega modela na ravni posameznih slikovnih elementov. Ključen gradnik v uspešnem dopolnjevanju informacij posameznih modalitet je ustrezna poravnava parametričnih map. Posamezne modalitete so zajete zaporedno, ob različnih časih. Skeniranje vseh modalitet posamezne živali skupno traja več kot eno uro. Med zajemom slik tako navkljub uporabi anestetikov prihaja do majhnih premikov živali. V kolikor ti premiki niso pravilno upoštevani, prihaja do napačnih interpretacij skupnih informacij večih modalitet. Premiki živali znotraj modalitet so bili modelirani kot toge, med različnimi modalitetami pa kot afine preslikave. Poravnava slik je izvedena z lastnimi Matlab funkcijami ali z uporabo funkcij iz odprtokodnega ogrodja za procesiranje slik Elastix. Z namenom karakterizacije tumorskega tkiva so bile uporabljene metode nenadzorovanega razčlenjevanja. Bistvo razčlenjevanja je v združevanju posameznih slikovnih elementov v segmente. Elementi si morajo biti po izbranem kriteriju dovolj medsebojno podobni in se hkrati razlikovati od elementov drugih segmentov. Za razgradnjo so bile izbrane tri metode: metoda K-tih povprečij, kot ena izmed enostavnejšihmetoda mehkih C-tih povprečij, s prednostjo mehke razčlenitvein kot zadnja, nenegativna matrična faktorizacija. Slednja ponuja pogled na razčlenitev tkiva kot produkt tipičnih več-modalnih značilk in njihove obilice za vsak posamezni slikovni element. Za potrditev izvedenega razčlenjevanja z omenjenimi metodami je bila izvedena vizualna primerjava z rezultati histopatološke analize. Rezultati Na ustvarjene parametrične mape je imela poravnava slik znotraj posameznih modalitet velik vpliv. Zaradi dolgotrajnega zajema T1 uteženih slik nemalokrat prihaja do premikov živali, kar brez pravilne poravnave slik negativno vpliva na mapiranje modalitet in kasnejšo segmentacijo slik. Generirane mape imajo majhno odstopanje od tistih, narejenih s standardno uporabljenimi odprtokodnimi programi. Klastri pridobljeni z metodama K-tih in mehkih C-tih povprečij dobro sovpadajo z razčlenbami glede na njihovo inteziteto pri T2 in ADC mapah. Najobetavnejše rezultate po primerjavi s histološkimi izsledki podajata metoda mehkih C-povprečij in nenegativna matrična faktorizacija. Njuni segmentaciji se dopolnjujeta v razlagi tumorskega mikro-okolja. Zaključek Z izgradnjo ogrodja za procesiranje slik magnetne resonance in segmentacijo tumorskega tkiva je bil cilj magistrske naloge dosežen. Zasnova ogrodja omogoča poljubno dodajanje drugih modalitet in uporabo drugih živalskih modelov. Rezultati razčlenitve tumorskega tkiva so obetavni, vendar je potrebna nadaljna primerjava z rezultati histopatološke analize. Možna nadgradnja je izboljšanje robustnosti poravnave slik z uporabo modela netoge (elastične) preslikave. Prav tako je smiselno preizkusiti dodatne metode nenadzorovane segmentacije in dobljene rezultate primerjati s tukaj predstavljenimi

Multimodality and Nonrigid Image Registration with Application to Diffusion Tensor Imaging

The great challenge in image registration is to devise computationally efficient algorithms for aligning images so that their details overlap accurately. The first problem addressed in this thesis is multimodality medical image registration, which we formulate as an optimization problem in the information-theoretic setting. We introduce a viable and practical image registration method by maximizing a generalized entropic dissimilarity measure using a modified simultaneous perturbation stochastic approximation algorithm. The feasibility of the proposed image registration approach is demonstrated through extensive experiments. The rest of the thesis is devoted to nonrigid medical image registration. We propose an informationtheoretic framework by optimizing a non-extensive entropic similarity measure using the quasi-Newton method as an optimization scheme and cubic B-splines for modeling the nonrigid deformation field between the fixed and moving 3D image pairs. To achieve a compromise between the nonrigid registration accuracy and the associated computational cost, we implement a three-level hierarchical multi-resolution approach in such a way that the image resolution is increased in a coarse to fine fashion. The feasibility and registration accuracy of the proposed method are demonstrated through experimental results on a 3D magnetic resonance data volume and also on clinically acquired 4D computed tomography image data sets. In the same vein, we extend our nonrigid registration approach to align diffusion tensor images for multiple components by enabling explicit optimization of tensor reorientation. Incorporating tensor reorientation in the registration algorithm is pivotal in wrapping diffusion tensor images. Experimental results on diffusion-tensor image registration indicate the feasibility of the proposed approach and a much better performance compared to the affine registration method based on mutual information, not only in terms of registration accuracy in the presence of geometric distortions but also in terms of robustness in the presence of Rician noise

Advances in Concurrent Motion and Field-Inhomogeneity Correction in Functional MRI.

Head motion and static magnetic field (B0) inhomogeneity are two important sources of image intensity variability in functional MRI (fMRI). Ideally, in MRI, any deviation in B0 homogeneity in an object occurs only by design. However, due to imperfections in the main magnet and gradient coils, and, magnetic susceptibility differences in the object, undesired B0 deviations may occur. This causes geometric distortion in Cartesian EPI images. In addition to spatial shifts and rotations of images, head motion during an fMRI experiment may induce time-varying field-inhomogeneity changes in the brain. As a result, correcting for motion and field-inhomogeneity effects independently of each other with a static field map may be insufficient, especially in the presence of large out-of-plane rotations. Our primary concern is the correction of the combined effects of motion and field-inhomogeneity induced geometric distortion in Cartesian EPI fMRI images. We formulate a concurrent field-inhomogeneity with map-slice-to-volume motion correction, and develop a motion-robust dual-echo bipolar gradient echo static field map estimation method. We also propose and evaluate a penalized weighted least squares approach to dynamic field map estimation using the susceptibility voxel convolution method. This technique accounts for field changes due to out-of-plane rotations, and estimates dynamic field maps from a high resolution static field map without requiring accurate image segmentation, or the use of literature susceptibility values. Experiments with simulated data suggest that the technique is promising, and the method will be applied to real data in future work. In a separate clinical fMRI project, which is independent of the above work, we also formulate a current density weighted index to quantify correspondence between electrocortical stimulation and fMRI maps for brain presurgical planning. The proposed index is formulated with the broader goal of defining safe limits for lesion resection, and is characterized extensively with simulated data. The index is also computed for real human datasets.Ph.D.Electrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60787/1/tbyeo_1.pd

Homogeneity based segmentation and enhancement of Diffusion Tensor Images : a white matter processing framework

In diffusion magnetic resonance imaging (DMRI) the Brownian motion of the water molecules, within biological tissue, is measured through a series of images. In diffusion tensor imaging (DTI) this diffusion is represented using tensors. DTI describes, in a non-invasive way, the local anisotropy pattern enabling the reconstruction of the nervous fibers - dubbed tractography. DMRI constitutes a powerful tool to analyse the structure of the white matter within a voxel, but also to investigate the anatomy of the brain and its connectivity. DMRI has been proved useful to characterize brain disorders, to analyse the differences on white matter and consequences in brain function. These procedures usually involve the virtual dissection of white matters tracts of interest. The manual isolation of these bundles requires a great deal of neuroanatomical knowledge and can take up to several hours of work. This thesis focuses on the development of techniques able to automatically perform the identification of white matter structures. To segment such structures in a tensor field, the similarity of diffusion tensors must be assessed for partitioning data into regions, which are homogeneous in terms of tensor characteristics. This concept of tensor homogeneity is explored in order to achieve new methods for segmenting, filtering and enhancing diffusion images. First, this thesis presents a novel approach to semi-automatically define the similarity measures that better suit the data. Following, a multi-resolution watershed framework is presented, where the tensor field’s homogeneity is used to automatically achieve a hierarchical representation of white matter structures in the brain, allowing the simultaneous segmentation of different structures with different sizes. The stochastic process of water diffusion within tissues can be modeled, inferring the homogeneity characteristics of the diffusion field. This thesis presents an accelerated convolution method of diffusion images, where these models enable the contextual processing of diffusion images for noise reduction, regularization and enhancement of structures. These new methods are analysed and compared on the basis of their accuracy, robustness, speed and usability - key points for their application in a clinical setting. The described methods enrich the visualization and exploration of white matter structures, fostering the understanding of the human brain