Adomian decomposition solution for propulsion of dissipative magnetic Jeffrey biofluid in a ciliated channel containing a porous medium with forced convection heat transfer

Physiological transport phenomena often feature ciliated internal walls. Heat, momentum and multi-species mass transfer may arise and additionally non-Newtonian biofluid characteristics are common in smaller vessels. Blood (containing hemoglobin) or other physiological fluids containing ionic constituents in the human body respond to magnetic body forces when subjected to external (extra-corporeal) magnetic fields. Inspired by such applications, in the present work we consider the forced convective flow of an electrically-conducting viscoelastic physiological fluid through a ciliated channel under the action of a transverse magnetic field. The flow is generated by a metachronal wave formed by the tips of cilia which move to and fro in a synchronized fashion. The presence of deposits (fats, cholesterol etc) in the channel is mimicked with a Darcy porous medium drag force model. The two-dimensional unsteady momentum equation and energy equation are simplified with a stream function and small Reynolds' number approximation. The effect of energy loss is simulated via the inclusion of viscous dissipation in the energy conservation (heat) equation. The non-dimensional, transformed moving boundary value problem is solved with appropriate wall conditions via the semi-numerical Adomian decomposition method (ADM). The velocity, temperature and pressure distribution are computed in the form of infinite series constructed by ADM and numerically evaluated in a symbolic software (MATHEMATICA). Streamline distributions are also presented. The influence of Hartmann number (magnetic parameter), Jeffrey first and second viscoelastic parameters, permeability parameter (modified Darcy number), and Brinkman number (viscous heating parameter) on velocity, temperature, pressure gradient and bolus dynamics is visualized graphically. The flow is decelerated with increasing with increasing Hartmann number and Jeffery first parameter in the core flow whereas it is accelerated in the vicinity of the walls. Increasing permeability and Jeffery second parameter are observed to accelerate the core flow and decelerate the peripheral flow near the ciliated walls. Increasing Hartmann number elevates pressure gradient whereas it is reduced with permeability parameter. Temperatures are elevated with increasing magnetic parameter, Brinkman number and Jeffery second parameter. Increasing magnetic field is also observed to reduce the quantity of trapped boluses. Increasing permeability parameter suppresses streamline amplitudes. Both the magnitude and quantity of trapped boluses is elevated with an increase in both first and second Jeffery parameters

Doctor of Philosophy

dissertationCine phase contrast (PC) magnetic resonance imaging (MRI) is a useful imaging technique that allows for the quantitative measurement of in-vivo blood velocities over the cardiac cycle. Velocity information can be used to diagnose and learn more about the mechanisms of cardio-vascular disease. Compared to other velocity measuring techniques, PC MRI provides high-resolution 2D and 3D spatial velocity information. Unfortunately, as with many other MRI techniques, PC MRI su ers from long acquisition times which places constraints on temporal and spatial resolution. This dissertation outlines the use of temporally constrained reconstruction (TCR) of radial PC data in order to signi cantly reduce the acquisition time so that higher temporal and spatial resolutions can be achieved. A golden angle-based acquisition scheme and a novel self-gating method were used in order to allow for exible selection of temporal resolution and to ameliorate the di culties associated with external electrocardiogram (ECG) gating. Finally, image reconstruction times for TCR are signi cantly reduced by implementation on a high-performance computer cluster. The TCR algorithm is executed in parallel across multiple GPUs achieving a 50 second reconstruction time for a very large cardiac perfusion data set

Loop radiofrequency coils for clinical magnetic resonance imaging at 7 TESLA

To date, the 7 T magnetic resonance imaging (MRI) scanner remains a pure research system and there is still a long way ahead till full clinical integration. Key challenges are the absence of a body transmit radiofrequency (RF) coil as well as of dedicated RF coils in general, short RF wavelengths of the excitation field in the order of the dimensions of a human body leading to signal inhomogeneities, and severe limitations with respect to the specific absorption rate. They all result in a strong need for RF engineering and sequence optimization to explore the potential of MRI at 7 T, and to pave the way for its future clinical application. In this thesis, high-resolution MRI with a rather small field-of-view (FOV) in the head and neck region (parotid gland/duct and carotid arteries), and of the musculoskeletal system as well as with a very large FOV in the abdomen (spine) were presented. Therefore, a variety of RF coils were used: from a commercially available single-loop coil to novel, specially developed phased array coils each consisting of eight loop elements. Methods to thoroughly characterize and test the developed RF coils were presented, including numerical simulations, bench and MRI measurements. Characterization with respect to performance for parallel acquisition techniques and an extensive compliance testing for patient safety were described in detail. All aspects of the engineering part, from design to optimization, and finally, to the in vivo application in volunteers and patients were covered. Since clinical applicability has always been the purpose, optimized imaging protocols along with a discussion on the clinical relevance was included in each study. The presented RF loop coils widely expand the options for clinical research at 7 T and advance the integration of this technology in a clinical setting