Effects Of Large Blood Vessels Research Articles

Numerical analysis of a clinically-extracted vascular tissue during cryo-freezing using immersed boundary method

In this paper, the effects of the blood vessel structure and injected nanoparticles on the cryo-freezing of a clinically-extracted vascular tissue are numerically investigated. A hybrid two-dimensional (2D) finite difference analysis combined with immersed boundary method has been developed to accurately simulate the cryo-freezing process. Based on the measured experimental temperature field, the numerical results compared well with the experimental data with a maximum error of 3.04%. This improved cryo-freezing model is able to significantly simplify the mesh generation process at the boundary resulting in improved computational efficacy. For simulating the temperature profile of a tumor that is sited in a dominantly vascularized tissue, our model is able to capture with ease the thermal effect at junctions of the blood vessels. We also analyzed the effects of blood vessel complexity and nanoparticles on iceball deformation which cannot be easily quantified through clinical experiments. Results indicated that the thermal effects of large blood vessels, especially for a more complex blood vessel boundary, remarkably affect the temperature and deformation distributions. In addition, the numerical results showed that, the inclusion of nanoparticles enlarged the cryo-freezing area as they enhance the thermal conductivity and thermal capacity of tissue.

Evaluation of the Contribution of Signals Originating from Large Blood Vessels to Signals of Functionally Specific Brain Areas.

The fusiform face area (FFA) is known to play a pivotal role in face processing. The FFA is located in the ventral region, at the base of the brain, through which large blood vessels run. The location of the FFA via functional MRI (fMRI) may be influenced by these large blood vessels. Responses of large blood vessels may not exactly correspond to neuronal activity in a target area, because they may be diluted and influenced by inflow effects. In this study, we investigated the effects of large blood vessels in the FFA, that is, whether the FFA includes large blood vessels and/or whether inflow signals contribute to fMRI signals of the FFA. For this purpose, we used susceptibility-weighted imaging (SWI) sequences to visualize large blood vessels and dual-echo gradient-echo echo-planar imaging (GE-EPI) to measure inflow effects. These results showed that the location and response signals of the FFA were not influenced by large blood vessels or inflow effects, although large blood vessels were located near the FFA. Therefore, the data from the FFA obtained by individual analysis were robust to large blood vessels but leaving a warning that the data obtained by group analysis may be prone to large blood vessels.

Thermal-structure coupling simulation during ex-vivo hypothermic perfusion of kidney

In this paper, the temperature variation and consequent thermal stress and deformation during hypothermic perfusion are numerically investigated. Hypothermic perfusion is the first step of preservation techniques that washes out of the vascular system and provides the supply of substrates and cools the kidney to the preservation temperature. A three-dimensional (3D) finite element analysis using the anatomical CAD model of kidney is developed to accurately simulate the hypothermic perfusion process. Based on the temperature field, the time evolution of thermal stress and deformation distribution are obtained. In addition, we analyze the effect on the thermal stress and deformation which cannot be easily acquired through clinical experiments. The results indicate that the thermal effects of large blood vessels could remarkably affect the temperature, thermal stress and deformation distributions. Increasing the perfusion rate could enlarge the thermal deformation, which causes the injury to the kidney. These results provide a guideline to the basic and applied research for the thermal effect on the hypothermic perfusion of kidney.

Temperature evolution in tissues embedded with large blood vessels during photo-thermal heating

During laser-assisted photo-thermal therapy, the temperature of the heated tissue region must rise to the therapeutic value (e.g., 43°C) for complete ablation of the target cells. Large blood vessels (larger than 500 micron in diameter) at or near the irradiated tissues have a considerable impact on the transient temperature distribution in the tissue. In this study, the cooling effects of large blood vessels on temperature distribution in tissues during laser irradiation are predicted using finite element based simulation. A uniform flow is assumed at the entrance and three-dimensional conjugate heat transfer equations in the tissue region and the blood region are simultaneously solved for different vascular models. A volumetric heat source term based on Beer–Lambert law is introduced into the energy equation to account for laser heating. The heating pattern is taken to depend on the absorption and scattering coefficients of the tissue medium. Experiments are also conducted on tissue mimics in the presence and absence of simulated blood vessels to validate the numerical model. The coupled heat transfer between thermally significant blood vessels and their surrounding tissue for three different tissue-vascular networks are analyzed keeping the laser irradiation constant. A surface temperature map is obtained for different vascular models and for the bare tissue (without blood vessels). The transient temperature distribution is seen to differ according to the nature of the vascular network, blood vessel size, flow rate, laser spot size, laser power and tissue blood perfusion rate. The simulations suggest that the blood flow through large blood vessels in the vicinity of the photothermally heated tissue can lead to inefficient heating of the target.

Computational study of thermal effects of large blood vessels in human knee joint

This paper is dedicated to present a comprehensive investigation on the thermal effects of large blood vessels of human knee joint during topical cooling and fomentation treatment. A three-dimensional (3D) finite element analysis by taking full use of the anatomical CAD model of human knee joint was developed to accurately simulate the treatment process. Based on the classical Pennes bio-heat transfer equation, the time evolution of knee joint's temperature distribution and heat flux from large blood vessels was obtained. In addition, we compared several influencing factors and obtained some key conclusions which cannot be easily acquired through clinical experiments. The results indicated that the thermal effects of large blood vessels could remarkably affect the temperature distribution of knee joint during treatment process. Fluctuations of blood flow velocity and metabolic heat production rate affect little on the thermal effects of large blood vessels. Changing the temperature of blood and regimes of treatment could effectively regulate this phenomenon, which is important for many physiological activities. These results provide a guideline to the basic and applied research for the thermally significant large blood vessels in the knee organism.

Effects of large blood vessels on the transient propagation of ultrafast laser pulse in biological tissues

A typical vascular model is established to study the effects of large blood vessels on the transient laser propagation during optical imaging. A time-resolved Monte Carlo algorithm is developed to investigate transient light propagation in biological tissues with embedded tumors and blood vessels. The results indicate that inclusion of the vasculatures could significantly alter light propagation transients from those obtained from the tissue embedded with tumor only.

Disclosure of the significant thermal effects of large blood vessels during cryosurgery through infrared temperature mapping

During cryosurgery the large blood vessels entering the frozen volume can be an important source of temperature non-uniformity and possible under-dosage for the target tissues. In this study, the thermal effects of large vessels during cryosurgery were experimentally investigated by introducing infrared thermography system on monitoring both simulated and animal experiments. For all experiments, the freezing was supplied by a 5 mm diameter cryoprobe with liquid nitrogen running through. Tissue temperature responses during freezing and thawing were recorded by an infrared thermography system. It was demonstrated that for different geometrical configurations between the simulated vessels and the positioning of the cryoprobe, a very different temperature profile will be induced even under the same freezing. The results for the cases with single vessel and with count-current vessel pairs indicated that different vascular models produce significantly different temperature responses for a given freezing pattern. Both the simulated and animal experiments suggested that the heating nature of the flowing blood in the large vessels can produce steep temperature gradients and inadequate cooling to the frozen tissues, and therefore may seriously contribute to failed-killing of tumor during cryosurgery. The physical pictures disclosed in this paper may help planning more successful cryosurgery in the near future.

Numerical Study of the Effects of Large Blood Vessels on Three-Dimensional Tissue Temperature Profiles During Cryosurgery

ABSTRACT Large blood vessels can produce steep temperature gradients in frozen tissues, resulting in inadequate cooling temperatures during cryosurgery. In addition, blocking of blood vessels and/or bleeding due to ruptures of large blood vessels by the iceball during the cryoablation procedure may cause undesired damage to healthy tissues or organs. However, such important issues have received little attention up to now. In this article, several typical vascular models, which have been widely used in simulation of tissue temperature during tumor hyperthermia, are applied to study the effects of large blood vessels on the transient tissue temperature distributions during cryosurgery treatment. The thermal model combines the Pennes bioheat transfer equation describing perfused tissues and the energy equation for single or countercurrent large blood vessels with a constant Nusselt number. A finite-difference algorithm based on the effective heat capacity method is applied to solve these complex heat transfer problems with phase change in biological tissues embedded with large blood vessels. In the algorithm, the tissues are treated as nonideal materials, freezing over a temperature range, and the effects of blood perfusion and metabolic heat generation in the unfrozen tissues are also included. Numerical analyses are then performed to test the influence of the blood vessels on the temperature distributions of tissues. The results indicate that different vascular models produce significantly different temperature transients for a given freezing pattern. Therefore, without careful treatment planning on some specific tumors close to or with large vessels transmitting through, the final cryosurgery may turn out to fail. In other words, insufficient cooling of the targets due to heating of large and warm blood vessels may lead to the regeneration of tumor cells. This study has raised quite a few important issues in modeling the cryosurgical phase-change behavior of living tissues embedded with large blood vessels.

The effects of large blood vessels on temperature distributions during simulated hyperthermia.

Several three-dimensional vascular models have been developed to study the effects of adding equations for large blood vessels to the traditional bioheat transfer equation of Pennes when simulating tissue temperature distributions. These vascular models include "transiting" vessels, "supplying" arteries, and "draining" veins, for all of which the mean temperature of the blood in the vessels is calculated along their lengths. For the supplying arteries this spatially variable temperature is then used as the arterial temperature in the bioheat transfer equation. The different vascular models produce significantly different locations for both the maximum tumor and the maximum normal tissue temperatures for a given power deposition pattern. However, all of the vascular models predict essentially the same cold regions in the same locations in tumors: one set at the tumors' corners and another around the inlets of the large blood vessels to the tumor. Several different power deposition patterns have been simulated in an attempt to eliminate these cold regions; uniform power in the tumor, annular power in the tumor, preheating of the blood in the vessels while they are traversing the normal tissue, and an "optimal" power pattern which combines the best features of the above approaches. Although the calculations indicate that optimal power deposition patterns (which improve the temperature distributions) exist for all of the vascular models, none of the heating patterns studied eliminated all of the cold regions. Vasodilation in the normal tissue is also simulated to see its effects on the temperature fields.(ABSTRACT TRUNCATED AT 250 WORDS)