A Clinician's Contribution to Biomedical Engineering in Experimental Echocardiography

The research of this thesis has been focused on the biomedical engineering aspects of new techniques of echocardiography. In close collaboration with the engineers of the Experimental Echocardiography Department of the Thoraxcentre, Erasmus University, Rotterdam, new methods to measure coronary blood flow and arterial wall elasticity with intravascular ultrasound (IVUS) have been developed. We have also investigated the clinical application of these measurements and have tried to improve traditional techniques based on intracoronary Doppler wires. In another field, we have developed a method to determine the radiation dose delivered in the wall of coronary arteries treated with brachytherapy. in collaboration with the Emory University, Atlanta, GA. This method utilizes 3-dimensional IVUS reconstruction combined with radiotherapy treatment planning. Finally, the tools developed for the recording of the signals of intracoronary Doppler wires have been adapted, during a stay at the Cleveland Clinic Foundation, OK for the study of left ventricular mechanics and the compliance of the large arteries. This has been achieved by simultaneous acquisition of non-invasive pressure (with tonometry) and flow (with transthoracic Doppler echocardiography) signals. The fruits of an old and close collaboration with the Institute Biomedical Technology of the Ghent University can also be found in different chapters. This work is subdivided in five major parts, and a detailed introductory chapter precedes each one

An electronically steered, wearable transcranial doppler ultrasound system

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 137-144).This thesis details the design of a transcranial Doppler (TCD) ultrasound system to measure cerebral blood flow velocity (CBFV) at the middle cerebral artery (MCA). TCD sonography has been clinically indicated in a variety of neurovascular diagnostic applications. Acceptance of conventional TCD methods, however, has been primarily impeded by several constraints, including restrictive system form factors, measurement reliability concerns, and the need for a highly-skilled operator. The goal of this work is to reduce the effects of such limitations through the development of a highly-compact, wearable TCD ultrasound system for autonomous CBFV measurement. A first-generation, eight channel printed circuit board prototype system has been designed, fabricated, and experimentally tested. Characterization of the prototype system using a Doppler flow phantom resulted in a normalized root-mean-square error of < 3.5% over the range of expected in vivo MCA flow velocities. Extension of the initial prototype to higher channel count systems and the development of phased array beamformation and algorithmic vessel location are also examined in this work. The emergence of simple, robust, and non-invasive neurovascular diagnostic methods presents an enormous opportunity for the advancement of neurovascular monitoring, particularly in applications where - due to restrictions in current diagnostic modalities - standard monitoring procedures have not yet been established.by Sabino Joseph Pietrangelo.S.M

Mechanics of the mitral valve after surgical repair-an in vitro study

Mitral valve disease is widely prevalent among pediatric and adult population across the world, and it encompasses a spectrum of lesions which include congenital valve defects, degenerative valve lesions, and valve dysfunction due to secondary pathologies. Though replacement of the diseased mitral valves with artificial heart valves has been the standard of care until early 1990's, current trends have veered towards complete surgical repair. These trends are encouraging, but current repair techniques are plagued with lack of durability and high rates of failure within 10 years after repair. With increasing number of patients receiving mitral valve repair, there is now an immediate need to understand the mechanisms of repair failure, and assess the role of several clinical risk factors on valve repair. In this thesis, an in vitro pulsatile left heart simulator was developed to mimic the congenital and adult mitral valve pathological morphologies in normal porcine valves, and simulate the pathological valve hemodynamics and mechanics. Different surgical repair techniques were used to correct the valve lesions, and the post repair valve hemodynamics, mechanics and geometry were assessed using quantitative measurement techniques. The extent to which each repair restores physiological valve function and mechanics was assessed, and the impact of different pathological risk factors on repair failure mechanisms was investigated. It is expected that the knowledge from this thesis would play an important role in the evolution of mitral valve surgical repair, and guide the development of more effective and long-lasting heart valve repair technologies.Ph.D.Committee Chair: Yoganathan, Ajit; Committee Member: Adams, David; Committee Member: Del Nido, Pedro; Committee Member: Gleason, Rudolph; Committee Member: Oshinski, John; Committee Member: Thourani, Vino

VAD in failing Fontan: simulation of ventricular, cavo-pulmonary and biventricular assistance in systolic/diastolic ventricular dysfunction and in pulmonary vascular resistance increase.

Aim: Due to the lack of donors, VADs could be an alternative to heart transplantation for Failing Fontan patients (PTs). Considering the complex physiopathology and the type of VAD connection, a numerical model (NM) could be useful to support clinical decisions. The aim of this work is to test a NM simulating the VADs effects on failing Fontan for systolic dysfunction (SD), diastolic dysfunction (DD) and pulmonary vascular resistance increase (PRI). Methods: Data of 10 Fontan PTs were used to simulate the PTs baseline using a dedicated NM. Then, for each PTs a SD, a DD and a PRI were simulated. Finally, for each PT and for each pathology, the VADs implantation was simulated. Results: NM can well reproduce PTs baseline. In the case of SD, LVAD increases the cardiac output (CO) (35%) and the arterial systemic pressure (ASP) (25%). With cavo-pulmonary assistance (RVAD) a decrease of inferior vena cava pressure (IVCP) (39%) was observed with 34% increase of CO. With the BIVAD an increase of ASP (29%) and CO (37%) was observed. In the case of DD, the LVAD increases CO (42%), the RVAD decreases the IVCP. In the case of PRI, the highest CO (50%) and ASP (28%) increase is obtained with an RVAD together with the highest decrease of IVCP (53%). Conclusions: The use of NM could be helpful in this innovative field to evaluate the VADs implantation effects on specific PT to support PT and VAD selection