In vivo measurement of human brain elasticity using a light aspiration device

The brain deformation that occurs during neurosurgery is a serious issue impacting the patient "safety" as well as the invasiveness of the brain surgery. Model-driven compensation is a realistic and efficient solution to solve this problem. However, a vital issue is the lack of reliable and easily obtainable patient-specific mechanical characteristics of the brain which, according to clinicians' experience, can vary considerably. We designed an aspiration device that is able to meet the very rigorous sterilization and handling process imposed during surgery, and especially neurosurgery. The device, which has no electronic component, is simple, light and can be considered as an ancillary instrument. The deformation of the aspirated tissue is imaged via a mirror using an external camera. This paper describes the experimental setup as well as its use during a specific neurosurgery. The experimental data was used to calibrate a continuous model. We show that we were able to extract an in vivo constitutive law of the brain elasticity: thus for the first time, measurements are carried out per-operatively on the patient, just before the resection of the brain parenchyma. This paper discloses the results of a difficult experiment and provide for the first time in-vivo data on human brain elasticity. The results point out the softness as well as the highly non-linear behavior of the brain tissue.Comment: Medical Image Analysis (2009) accept\'

Identification of the Elastic Modulus of an Organ Model Using Reactive Force and Ultrasound Image

制度:新 ; 報告番号:甲3418号 ; 学位の種類:博士(工学) ; 授与年月日:2011/7/28 ; 早大学位記番号:新574

Stress-strain analysis of aortic aneurysms

Tato práce se zabývá problematikou aneurysmat břišní aorty a možností využít konečnoprvkovou deformačně-napěťovou analýzu těchto aneurysmat ke stanovení rizika ruptury. První část práce je věnována úvodu do problematiky, popisu kardiovaskulární soustavy člověka s důrazem na abdominální aortu, anatomii, fyziologii a patologii stěny tepny s důrazem na procesy vedoucí ke vzniku aneurysmatu. Dále se práce věnuje rizikovým faktorům přispívajících ke vzniku aneurysmat spolu s analýzou současných klinických postupů ke stanovení rizika ruptury spolu se srovnáním navrhovaného kritéria maximálního napětí. Dominantní část této disertace je věnována identifikaci faktorů ovlivňujících napjatost a deformaci stěny aneurysmatu spolu s návrhem nových postupů, prezentací vlastních poznatků vedoucích ke zpřesnění určení rizika ruptury pomocí deformačně- napěťové analýzy a metody konečných prvků. Nejprve je analyzován vliv geometrie, vedoucí k závěru, že je nezbytné používání individuálních geometrií pacienta. Dále je pozornost zaměřena na odbočující tepny, které ve stěně působí jako koncentrátor napětí a mohou tedy ovlivňovat napjatost v ní. Jako další podstatný faktor byl identifikován vliv nezatížené geometrie a bylo napsáno makro pro její nalezení, které bylo opět zahrnuto jako standardní součást do výpočtového modelu. Mechanické vlastnosti jak stěny aneurysmatu, tak intraluminálního trombu jsou experimentálně testovány pomocí dvouosých zkoušek. Také je zde analyzován vliv modelu materiálu, kde je ukázáno, že srovnávání maximálních napětí u jednotlivých modelů materiálu není vhodné díky zcela rozdílným gradientům napětí ve stěně aneurysmatu. Dále je zdůrazněna potřeba znalosti distribuce kolagenních vláken ve stěně a navržen program k jejímu získání. Intraluminální trombus je analyzován ve dvou souvislostech. Jednak je ukázán vliv jeho ruptury na napětí ve stěně a jednak je analyzován vliv jeho poroelastické struktury na totéž. Posledním identifikovaným podstatným faktorem je zbytková napjatost ve stěně. Její významnost je demonstrována na několika aneurysmatech a i tato je zahrnuta jako integrální součást do našeho výpočtového modelu.Na závěr jsou pak navrženy další možné směry výzkumu.This thesis deals with abdominal aortic aneurysms and the possibility of using finite element method in assessment of their rupture risk. First part of the thesis is dedicated to an introduction into the problem, description of human cardiovascular system where the abdominal aorta, its anatomy, physiology and pathology is emphasized. There Processes leading to formationing of abdominal aortic aneurysms are also discussed. Risk factors contributing to creation of aneurysms are discussed next. Finally, an analysis of current clinical criteria which determine rupture risk of an abdominal aortic aneurysm is presented and compared with the new maximum stress criterion being currently in development. Main part of the thesis deals with the identification of relevant factors which affect stress and deformation of aneurysmal wall. This is connected with proposals of new approaches leading to predicting the rupture risk more accurately by using finite element stress-strain analysis. The impact of geometry is analyzed first with the conclusion that patient-specific geometry is a crucial input in the computational model. Therefore its routine reconstruction has been managed. Attention is then paid to the branching arteries which were neglected so far although they cause a stress concentration in arterial wall. The necessity of knowing the unloaded geometry of aneurysm is then emphasized. Therefore a macro has been written in order to be able to find the unloaded geometry for any patient-specific geometry of aneurysm. Mechanical properties of both aneurysmal wall and intraluminal thrombus were also experimentally tested and their results were fitted by an isotropic material model. The effect of the material model itself has been also investigated by comparing whole stress fields of several aneurysms. It has been shown that different models predict completely different stresses due to different stress gradients in the aneurysmal wall. The necessity of known collagen fiber distribution in arterial wall is also emphasized. A special program is then presented enabling us to obtain this information. Effect of intraluminal thrombus on the computed wall stress is analyzed in two perspectives. First the effect of its failure on wall stress is shown and also the impact of its poroelastic structure is analyzed. Finally the residual stresses were identified as an important factor influencing the computed wall stress in aneurysmal wall and they were included into patient-specific finite element analysis of aneurysms. Further possible regions of investigation are mentioned as the last part of the thesis.

Constrained Soft Tissue Simulation for Virtual Surgical Simulation

yesMost of surgical simulators employ a linear elastic model to simulate soft tissue material properties due to its computational efficiency and the simplicity. However, soft tissues often have elaborate nonlinearmaterial characteristics. Most prominently, soft tissues are soft and compliant to small strains, but after initial deformations they are very resistant to further deformations even under large forces. Such material characteristic is referred as the nonlinear material incompliant which is computationally expensive and numerically difficult to simulate. This paper presents a constraint-based finite-element algorithm to simulate the nonlinear incompliant tissue materials efficiently for interactive simulation applications such as virtual surgery. Firstly, the proposed algorithm models the material stiffness behavior of soft tissues with a set of 3-D strain limit constraints on deformation strain tensors. By enforcing a large number of geometric constraints to achieve the material stiffness, the algorithm reduces the task of solving stiff equations of motion with a general numerical solver to iteratively resolving a set of constraints with a nonlinear Gauss–Seidel iterative process. Secondly, as a Gauss–Seidel method processes constraints individually, in order to speed up the global convergence of the large constrained system, a multiresolution hierarchy structure is also used to accelerate the computation significantly, making interactive simulations possible at a high level of details . Finally, this paper also presents a simple-to-build data acquisition system to validate simulation results with ex vivo tissue measurements. An interactive virtual reality-based simulation system is also demonstrated

Characterization and Assessment of Mechanical Properties of Adipose Derived Breast Tissue Scaffolds as a Means for Breast Reconstructive Purposes

Decellularized adipose tissue (DAT) has shown great potential for use as a regenerative scaffold in breast reconstruction following mastectomies or lumpectomies. Mechanical properties of such scaffolds are of great importance in order to mimic natural adipose tissue. This study focuses on the characterization of mechanical properties and assessment of DAT scaffolds for implantation into a human breast. DAT samples sourced from multiple adipose tissue depots within the body were tested and their elastic and hyperelastic parameters were obtained. Subsequently simulations were conducted where the calculated hyperelastic parameters were tested as a real human breast model under two different gravity loading situations (prone-to-supine, and prone-to-upright positions). DAT samples were also modelled for post-mastectomy, and post-lumpectomy reconstruction purposes. Results show that DAT shows similar deformability to that of native tissue, and varying DAT depots exhibited little intrinsic nonlinearity. Finally, contour defects were not observed for the samples under either loading conditions

Comparing Regularized Kelvinlet Functions and the Finite Element Method for Registration of Medical Images to Sparse Organ Data

Image-guided surgery collocates patient-specific data with the physical environment to facilitate surgical decision making in real-time. Unfortunately, these guidance systems commonly become compromised by intraoperative soft-tissue deformations. Nonrigid image-to-physical registration methods have been proposed to compensate for these deformations, but intraoperative clinical utility requires compatibility of these techniques with data sparsity and temporal constraints in the operating room. While linear elastic finite element models are effective in sparse data scenarios, the computation time for finite element simulation remains a limitation to widespread deployment. This paper proposes a registration algorithm that uses regularized Kelvinlets, which are analytical solutions to linear elasticity in an infinite domain, to overcome these barriers. This algorithm is demonstrated and compared to finite element-based registration on two datasets: a phantom dataset representing liver deformations and an in vivo dataset representing breast deformations. The regularized Kelvinlets algorithm resulted in a significant reduction in computation time compared to the finite element method. Accuracy as evaluated by target registration error was comparable between both methods. Average target registration errors were 4.6 +/- 1.0 and 3.2 +/- 0.8 mm on the liver dataset and 5.4 +/- 1.4 and 6.4 +/- 1.5 mm on the breast dataset for the regularized Kelvinlets and finite element method models, respectively. This work demonstrates the generalizability of using a regularized Kelvinlets registration algorithm on multiple soft tissue elastic organs. This method may improve and accelerate registration for image-guided surgery applications, and it shows the potential of using regularized Kelvinlets solutions on medical imaging data.Comment: 17 pages, 9 figure

Controlling the Error on Target Motion through Real-time Mesh Adaptation: Applications to Deep Brain Stimulation

We present an error-controlled mesh refinement procedure for needle insertion simulation and apply it to the simulation of electrode implantation for deep brain stimulation, including brain shift. Our approach enables to control the error in the computation of the displacement and stress fields around the needle tip and needle shaft by suitably refining the mesh, whilst maintaining a coarser mesh in other parts of the domain. We demonstrate through academic and practical examples that our approach increases the accuracy of the displacement and stress fields around the needle without increasing the computational expense. This enables real-time simulations. The proposed methodology has direct implications to increase the accuracy and control the computational expense of the simulation of percutaneous procedures such as biopsy, brachytherapy, regional anesthesia, or cryotherapy and can be essential to the development of robotic guidance.Comment: 21 pages, 14 figure