Abstract:Density is defined as mass per unit volume. The classical technique to measure the density of fluids consists of a determination of mass and volume. Blood density is proportional to hematocrit or, more exactly, to the total protein concentration of blood; only to a minor extent is blood density influenced by other plasma solutes. Since the introduction of the mechanical oscillator technique for the continuous recording of fluid density a sizeable amount of experience has accumulated. This review summarizes rec… Show more
“…Newtonian fluid) [Wells and Merril, 1962] and a density of 1080 kg/m 3 [Kenner, 1989]. From the velocity profiles in the MRI measurements, the Reynolds number based on inlet diameter, ranged from 200 at late diastole to 7500 at peak systole, with a mean of 1600.…”
shear stress (WSS) has been correlated to the development of atherosclerosis in arteries. As WSS depends on the blood flow dynamics, it is sensitive to pulsatile effects and local changes in geometry. The aim of this study is therefore to investigate if the effect of wall motion changes the WSS or if a rigid wall assumption is sufficient. Magnetic resonance imaging (MRI) was used to acquire subject specific geometry and flow rates in a human aorta, which were used as inputs in numerical models. Both rigid wall models and fluid-structure interaction (FSI) models were considered, and used to calculate the WSS on the aortic wall. A physiological range of different wall stiffnesses in the FSI simulations was used in order to investigate its effect on the flow dynamics. MRI measurements of velocity in the descending aorta were used as validation of the numerical models, and good agreement was achieved. It was found that the influence of wall motion was low on time-averaged WSS and oscillating shear index, but when regarding instantaneous WSS values the effect from the wall motion was clearly visible. Therefore, if instantaneous WSS is to be investigated, a FSI simulation should be considered.
“…Newtonian fluid) [Wells and Merril, 1962] and a density of 1080 kg/m 3 [Kenner, 1989]. From the velocity profiles in the MRI measurements, the Reynolds number based on inlet diameter, ranged from 200 at late diastole to 7500 at peak systole, with a mean of 1600.…”
shear stress (WSS) has been correlated to the development of atherosclerosis in arteries. As WSS depends on the blood flow dynamics, it is sensitive to pulsatile effects and local changes in geometry. The aim of this study is therefore to investigate if the effect of wall motion changes the WSS or if a rigid wall assumption is sufficient. Magnetic resonance imaging (MRI) was used to acquire subject specific geometry and flow rates in a human aorta, which were used as inputs in numerical models. Both rigid wall models and fluid-structure interaction (FSI) models were considered, and used to calculate the WSS on the aortic wall. A physiological range of different wall stiffnesses in the FSI simulations was used in order to investigate its effect on the flow dynamics. MRI measurements of velocity in the descending aorta were used as validation of the numerical models, and good agreement was achieved. It was found that the influence of wall motion was low on time-averaged WSS and oscillating shear index, but when regarding instantaneous WSS values the effect from the wall motion was clearly visible. Therefore, if instantaneous WSS is to be investigated, a FSI simulation should be considered.
“…The fluid had a density of 1,151.5 kg/m 3 and a viscosity of 10.3 mPa â s. Since the density of blood is 1,050 kg/m 3 (21) and with the assumption that in vivo the viscosity is constant at 4 mPa â s (22)(23)(24), the flow had to be adjusted to match in vivo conditions according to the Reynolds analogy (25). An in vivo blood flow rate of 2.3 mL/second in a vessel with a radius of 1.9 mm corresponding to the inlet radius of the model was assumed, yielding a constant Reynolds number of about 200.…”
Purpose:To verify the accuracy of velocity mapping with three-dimensional (3D) phase-contrast magnetic resonance angiography (PC-MRA) for steady flow in a realistic model of a cerebral artery aneurysm at a 3T scanner.
Materials and Methods:Steady flow through an original geometry model of a cerebral aneurysm was mapped at characteristic positions by state-of-the-art laser Doppler velocimetry (LDV) as well as 3D PC-MRA at 3T. The spatial distributions and local values of two velocity components obtained with these two measurement methods were compared.
Results:The 3D PC-MRA velocity field distribution and mean velocity values exhibited only minor differences to compare to the LDV measurements in straight artery regions for both main and secondary velocities. The differences increased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the main flow direction.Conclusion: 3D PC-MRA can provide reliable measurements of velocity components of steady flow in small arteries. The accuracy of such measurements depends on the artery size and the measurement plane positioning.
“…Aside from conduction, heat is removed via blood perfusion, assumed to be at a relatively constant incoming temperature of 37 C. Heat dissipation via perfusion is dependent on blood density 32 (1060 kg/m 3 ), blood specific heat 33 (3600 J/kg/K), and flow rate. Flow rate was assumed to be temperature-independent but tissue-dependent (Table II).…”
Purpose: A recently completed Phase I clinical trial combined concurrent Mitomycin-C chemotherapy with deep regional heating using BSD-2000 Sigma-Ellipse applicator (BSD Corporation, Salt Lake City, UT, U.S.A.) for the treatment of nonmuscle invasive bladder cancer. This work presents a new treatment planning approach, and demonstrates potential impact of this approach on improvement of treatment quality. Methods: This study retrospectively analyzes a subset of five patients on the trial. For each treatment, expert operators selected "clinical-optimal" settings based on simple model calculation on the BSD-2000 control console. Computed tomography (CT) scans acquired prior to treatment were segmented to create finite element patient models for retrospective simulations with SigmaHyperPlan (Dr. Sennewald Medizintechnik GmbH, Munchen, Germany). Since Sigma-HyperPlan does not account for the convective nature of heat transfer within a fluid filled bladder, an effective thermal conductivity for bladder was introduced. This effective thermal conductivity value was determined by comparing simulation results with clinical measurements of bladder and rectum temperatures. Regions of predicted high temperature in normal tissues were compared with patient complaints during treatment. Treatment results using "computed-optimal" settings from the planning system were compared with clinical results using clinical-optimal settings to evaluate potential of treatment improvement by reducing hot spot volume. Results: For all five patients, retrospective treatment planning indicated improved matches between simulated and measured bladder temperatures with increasing effective thermal conductivity. The differences were mostly within 1.3 C when using an effective thermal conductivity value above 10 W/K/m. Changes in effective bladder thermal conductivity affected surrounding normal tissues within a distance of $1.5 cm from the bladder wall. Rectal temperature differences between simulation and measurement were large due to sensitivity to the sampling locations in rectum. The predicted bladder T90 correlated well with single-point bladder temperature measurement. Hot spot locations predicted by the simulation agreed qualitatively with patient complaints during treatment. Furthermore, comparison between the temperature distributions with clinical and computedoptimal settings demonstrated that the computed-optimal settings resulted in substantially reduced hot spot volumes. Conclusions: Determination of an effective thermal conductivity value for fluid filled bladder was essential for matching simulation and treatment temperatures. Prospectively planning patients using the effective thermal conductivity determined in this work can potentially improve treatment efficacy (compared to manual operator adjustments) by potentially lower discomfort from reduced hot spots in normal tissue.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citationsâcitations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.