Biomedical Engineering and Bioengineering Commons^™

Accurate Quantification Of Steady And Pulsatile Flow With Segmented K-Space Magnetic Resonance Velocimetry, Haosen Zhang, Sandra S. Halliburton, James R. Moore, Orlando P. Simonetti, Paulo R. Schvartzman, Richard D. White, George P. Chatzimavroudis

Chemical & Biomedical Engineering Faculty Publications

Conventional non-segmented magnetic resonance phase velocity mapping (MRPVM) is an accurate but relatively slow velocimetric technique. Therefore, the aim of this study was to evaluate the accuracy of the much faster segmented k-space MRPVM in quantifying flow. The axial velocity was measured in four straight tubes (inner diameter: 5.6–26.2 mm), using a segmented MRPVM sequence with seven lines of k-space per segment. The flow rate and flow volume were accurately quantified (errorssteady (r²=0.99) and pulsatile flow (r²=0.98), respectively. The measured velocity profiles and flow rates from the segmented sequence agreed …

Ultrafast Flow Quantification With Segmented K-Space Magnetic Resonance Phase Velocity Mapping, Haosen Zhang, Sandra S. Halliburton, James R. Moore, Orlando P. Simonetti, Paulo R. Schvartzman, Richard D. White, George P. Chatzimavroudis

Chemical & Biomedical Engineering Faculty Publications

Magnetic resonance (MR) phase-velocity mapping (PVM) is routinely being used clinically to measure blood flow velocity. Conventional nonsegmented PVM is accurate but relatively slow (3–5 min per measurement). Ultrafast k-space segmented PVM offers much shorter acquisitions (on the order of seconds instead of minutes). The aim of this study was to evaluate the accuracy of segmented PVM in quantifying flow from through-plane velocity measurements. Experiments were performed using four straight tubes (inner diameter of 5.6–26.2 mm), under a variety of steady (1.7–200 ml/s) and pulsatile (6–90 ml/cycle) flow conditions. Two different segmented PVM schemes were …

In Vivo Flow Dynamics Of The Total Cavopulmonary Connection From Three-Dimensional Multislice Magnetic Resonance Imaging, Shiva Sharma, Ann E. Ensley, Katherine Hopkins, George P. Chatzimavroudis, Timothy M. Healy, Vincent K.H. Tam, Kirk R. Kanter, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

Background. The total cavopulmonary connection (TCPC) design continues to be refined on the basis of flow analysis at the connection site. These refinements are of importance for myocardial energy conservation in the univentricular supported circulation. In vivo magnetic resonance phase contrast imaging provides semiquantitative flow visualization information. The purpose of this study was to understand the in vivo TCPC flow characteristics obtained by magnetic resonance phase contrast imaging and compare the results with our previous in vitro TCPC flow experiments in an effort to further refine TCPC surgical design.

Methods. Twelve patients with TCPC underwent sedated three-dimensional, multislice …

Evaluation Of The Precision Of Magnetic Resonance Phase Velocity Mapping For Blood Flow Measurements, George P. Chatzimavroudis, John N. Oshinski, Robert H. Franch, Peter G. Walker, Ajit P. Yoganathan, Roderic I. Pettigrew

Chemical & Biomedical Engineering Faculty Publications

Evaluating the in vivo accuracy of magnetic resonance phase velocity mapping (PVM) is not straightforward because of the absence of a validated clinical flow quantification technique. The aim of this study was to evaluate PVM by investigating its precision, both in vitro and in vivo, in a 1.5 Tesla scanner. In the former case, steady and pulsatile flow experiments were conducted using an aortic model under a variety of flow conditions (steady: 0.1–5.5 L/min; pulsatile: 10–75 mL/cycle). In the latter case, PVM measurements were taken in the ascending aorta of ten subjects, seven of which had aortic regurgitation. Each velocity …

Fluid Mechanic Assessment Of The Total Cavopulmonary Connection Using Magnetic Resonance Phase Velocity Mapping And Digital Particle Image Velocimetry, Ann E. Ensley, Agnès Ramuzat, Timothy M. Healy, George P. Chatzimavroudis, Carol Lucas, Shiva Sharma, Roderic Pettigrew, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

The total cavopulmonary connection (TCPC) is currently the most promising modification of the Fontan surgical repair for single ventricle congenital heart disease. The TCPC involves a surgical connection of the superior and inferior vena cavae directly to the left and right pulmonary arteries, bypassing the right heart. In the univentricular system, the ventricle experiences a workload which may be reduced by optimizing the cavae-to-pulmonary anastomosis. The hypothesis of this study was that the energetic efficiency of the connection is a consequence of the fluid dynamics which develop as a function of connection geometry. Magnetic resonance phase velocity mapping (MRPVM) and …

Mri Techniques For Cardiovascular Imaging, Roderic I. Pettigrew, John N. Oshinski, George P. Chatzimavroudis, W. Thomas Dixon

Chemical & Biomedical Engineering Faculty Publications

Over the last several years, cardiovascular MRI has benefited from a number of technical advances which have improved routine clinical imaging techniques. As a result, MRI is now well positioned to realize its longstanding promise of becoming the comprehensive cardiac imaging test of choice in many clinical settings. This may be achieved using a combination of basic advanced techniques. In this overview, the basic cardiac MRI techniques which are clinically useful are reviewed, and the recent technical advances which are clinically promising are described. These advances include routine black blood and cine bright blood techniques that are high speed (slice), …

Toward Designing The Optimal Total Cavopulmonary Connection: An In Vitro Study, Ann E. Ensley, Patricia Lynch, George P. Chatzimavroudis, Carol Lucas, Shiva Sharma, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

Background. Understanding the total cavopulmonary connection (TCPC) hemodynamics may lead to improved surgical procedures which result in a more efficient modified circulation. Reduced energy loss will translate to less work for the single ventricle and although univentricular physiology is complex, this improvement could contribute to improved postoperative outcomes. Therefore to conserve energy, one surgical goal is optimization of the TCPC geometry. In line with this goal, this study investigated whether addition of caval curvature or flaring at the connection conserves energy.

Methods. TCPC models were made varying the curvature of the caval inlet or by flaring the anastomosis. …

Quantification Of Mitral Regurgitation With Mr Phase-Velocity Mapping Using A Control Volume Method, George P. Chatzimavroudis, John N. Oshinski, Roderic I. Pettigrew, Peter G. Walker, Robert H. Franch, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase-velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of …

Slice Location Dependence Of Aortic Regurgitation Measurements With Mr Phase Velocity Mapping, George P. Chatzimavroudis, Peter G. Walker, John N. Oshinski, Robert H. Franch, Roderic I. Pettigrew, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

Although several methods have been used clinically to assess aortic regurgitation (AR), there is no “gold standard” for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual …

The Influence Of Acoustic Impedance Mismatch On Post-Stenotic Pulsed-Doppler Ultrasound Measurements In A Coronary Artery Model, S. A. Jones, H. Leclerc, George P. Chatzimavroudis, Y. H. Kim, N. A. Scott, Ajit P. Yoganathan

Chemical & Biomedical Engineering Faculty Publications

Acoustic impedance mismatch at the fluid-wall interface was shown to affect the spectra from an intravascular Doppler device in an in vitro model with a diameter typical of human coronary arteries. Measurements were obtained first under Poiseuille flow conditions with impedance mismatches of 0%, 7% and 12%, and then under stenosed conditions for the 0% and 7% mismatch cases. For the zero mismatch case, the Doppler spectra could be readily interpreted in terms of fluid mechanical phenomena. When mismatch was present, the spectra from Poiseuille flow exhibited multiple peaks which could not be directly related to the velocity profile. Also, …

Lntracrystalline Diffusion Of Benzene In Silicalite : Effect Of Structural Heterogeneity, Dhananjai B. Shah, Chang-Jie Guo, David T. Hayhurst

Chemical & Biomedical Engineering Faculty Publications

The sorption kinetics of benzene in silicalite have been measured gravimetrically using large silicalite crystals of sizes 350 µm × 105 µm × 105 µm and 270 µm × 70 µm × 70 µm in the temperature range 283–343 K. Experiments were performed under conditions that ensured isothermal operation with intracrystalline diffusion control. An analytical expression for the Darken's correction factor (δ In P/δ In a) was derived based on the Hill–de-Boer equation and was used to determine the variation of corrected diffusivity with concentration. The transport diffusivity varied significantly with the adsorbed-phase concentration but the …

Network Analysis Of Intermediary Metabolism Using Linear Optimization. Ii. Interpretation Of Hybridoma Cell Metabolism, Joanne M. Savinell (Belovich), Bernhard O. Palsson

Chemical & Biomedical Engineering Faculty Publications

Analysis of metabolic networks using linear optimization theory allows one to quantify and understand the limitations imposed on the cell by its metabolic stoichiometry, and to understand how the flux through each pathway influences the overall behavior of metabolism. A stoichiometric matrix accounting for the major pathways involved in energy and mass transformations in the cell was used in our analysis. The auxiliary parameters of linear optimization, the so-called shadow prices, identify the intermediates and cofactors that cause the growth to be limited on each nutrient. This formalism was used to examine how well the cell balances its needs for …

On The Orders Of Magnitude Of Epigenic Dynamics And Monoclonal Antibody Production, Joanne M. Savinell (Belovich), Gyun Min Lee, Bernhard O. Palsson

Chemical & Biomedical Engineering Faculty Publications

The hybridoma cell's maximum capacity for monoclonal antibody (MAb) production is estimated to be 2300–8000 MAb molecules/cell/s, using measured rates of transcription and translation, and the limitations imposed by the size of the polymerase molecule and the ribosome. Nearly all the production rates reported in the literature fall into or below this range of production rates. Data from batch cultures of hybridomas demonstrate a constant specific rate of MAb production until the time integral of the viable cell concentration reaches about 10⁸ cells · h/cm³. At this point, some essential nutrients from the standard media …