279 research outputs found

    Laser-enhanced high-intensity focused ultrasound heating in an in vivo small animal model

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    The enhanced heating effect during the combination of high-intensity focused ultrasound (HIFU) and low-optical-fluence laser illumination was investigated by using an in vivo murine animal model. The thighs of murine animals were synergistically irradiated by HIFU and pulsed nano-second laser light. The temperature increases in the target region were measured by a thermocouple under different HIFU pressures, which were 6.2, 7.9, and 9.8 MPa, in combination with 20 mJ/cm2 laser exposures at 532 nm wavelength. In comparison with conventional laser therapies, the laser fluence used here is at least one order of magnitude lower. The results showed that laser illumination could enhance temperature during HIFU applications. Additionally, cavitation activity was enhanced when laser and HIFU irradiation were concurrently used. Further, a theoretical simulation showed that the inertial cavitation threshold was indeed decreased when laser and HIFU irradiation were utilized concurrentl

    Convergence of the Generalized Volume Averaging Method on a Convection-Diffusion Problem: A Spectral Perspective

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    A mixed formulation is proposed and analyzed mathematically for coupled convection-diffusion in heterogeneous medias. Transfer in solid parts driven by pure diffusion is coupled with convection-diffusion transfer in fluid parts. This study is carried out for translation-invariant geometries (general infinite cylinders) and unidirectional flows. This formulation brings to the fore a new convection-diffusion operator, the properties of which are mathematically studied: its symmetry is first shown using a suitable scalar product. It is proved to be self-adjoint with compact resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards −∞ and the other towards +∞, thus resulting in a nonsectorial operator. The decomposition of the convection-diffusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the infinite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operator’s two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization

    CT evaluation of mediastinal masses

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    CT is an important modality for imaging mediastinal masses, and certain CT attenuation features (fat, calcium, or water attenuation, contrast enhancement) are well known to suggest specific diagnoses. In a series of 132 consecutive patients with tissue-proven mediastinal masses, these specific CT features were present in only 16. We evaluated the ability of CT to differentiate soft tissue mediastinal masses based on morphology and distribution of disease. Metastatic disease and lymphoma accounted for 69% of masses in this series, and CT could not generally differentiate them. However, CT was helpful in differential diagnosis in certain settings. CT demonstration of multiple mediastinal masses when conventional radiographs showed a single mass generally excluded diagnoses such as thymoma and teratoma. CT demonstration of a single middle mediastinal mass, frequently missed by conventional radiography, made metastatic disease a much more likely diagnosis than lymphoma. Finally, CT demonstration of certain ancillary findings strongly favored a diagnosis of lymphoma (axillary adenopathy) or metastatic disease (solitary pulmonary mass, focal liver lesions, bone lesions).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26707/1/0000257.pd

    Parameter Estimation for Personalization of Liver Tumor Radiofrequency Ablation

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    International audienceMathematical modeling has the potential to assist radiofrequency ablation (RFA) of tumors as it enables prediction of the extent of ablation. However, the accuracy of the simulation is challenged by the material properties since they are patient-specific, temperature and space dependent. In this paper, we present a framework for patient specific radiofrequency ablation modeling of multiple lesions in the case of metastatic diseases. The proposed forward model is based upon a computational model of heat diffusion, cellular necrosis and blood flow through vessels and liver which relies on patient images. We estimate the most sensitive material parameters, those need to be personalized from the available clinical imaging and data. The selected parameters are then estimated using inverse modeling such that the point to-mesh distance between the computed necrotic area and observed lesions is minimized. Based on the personalized parameters, the ablation of the remaining lesions are predicted. The framework is applied to a dataset of seven lesions from three patients including pre- and post-operative CT images. In each case, the parameters were estimated on one tumor and RFA is simulated on the other tumor(s) using these personalized parameters, assuming the parameters to be spatially invariant within the same patient. Results showed significantly good correlation between predicted and actual ablation extent (average point-to-mesh errors of 4.03 mm)

    An Electrode Array for Limiting Blood Loss During Liver Resection: Optimization via Mathematical Modeling

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    Liver resection is the current standard treatment for patients with both primary and metastatic liver cancer. The principal causes of morbidity and mortality after liver resection are related to blood loss (typically between 0.5 and 1 L), especially in cases where transfusion is required. Blood transfusions have been correlated with decreased long-term survival, increased risk of perioperative mortality and complications. The goal of this study was to evaluate different designs of a radiofrequency (RF) electrode array for use during liver resection. The purpose of this electrode array is to coagulate a slice of tissue including large vessels before resecting along that plane, thereby significantly reducing blood loss. Finite Element Method models were created to evaluate monopolar and bipolar power application, needle and blade shaped electrodes, as well as different electrode distances. Electric current density, temperature distribution, and coagulation zone sizes were measured. The best performance was achieved with a design of blade shaped electrodes (5 × 0.1 mm cross section) spaced 1.5 cm apart. The electrodes have power applied in bipolar mode to two adjacent electrodes, then switched sequentially in short intervals between electrode pairs to rapidly heat the tissue slice. This device produces a ~1.5 cm wide coagulation zone, with temperatures over 97 ºC throughout the tissue slice within 3 min, and may facilitate coagulation of large vessels

    Chaos for the Hyperbolic Bioheat Equation

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    The Hyperbolic Heat Transfer Equation describes heat processes in which extremely short periods of time or extreme temperature gradients are involved. It is already known that there are solutions of this equation which exhibit a chaotic behaviour, in the sense of Devaney, on certain spaces of analytic functions with certain growth control. We show that this chaotic behaviour still appears when we add a source term to this equation, i.e. in the Hyperbolic Bioheat Equation. These results can also be applied for the Wave Equation and for a higher order version of the Hyperbolic Bioheat Equation.The authors are supported in part by MEC and FEDER, Projects MTM2010-14909 and MTM2013-47093-P.Conejero, JA.; Ródenas Escribá, FDA.; Trujillo Guillen, M. (2015). Chaos for the Hyperbolic Bioheat Equation. Discrete and Continuous Dynamical Systems - Series A. 35(2):653-668. doi:10.3934/dcds.2015.35.653S65366835