| The invention of the stethoscope marked the beginning of the era of modern clinical diagnosis. Clinicians learned to recognize disease by listening for sounds known as bruits and murmurs caused by abnormal blood flow in the heart and the circulatory system. Even after two centuries, these sounds continue to be important early indicators of diseases such as atherosclerosis, coronary artery disease, valvular disease, renovascular hypertension, aneurysms, peripheral artery disease and vascular trauma. Modern medical imaging technology has provided the ability to noninvasively image the anatomic and blood flow characteristics associated with various diseases. However, the vascular sounds that were the traditional cornerstone of diagnosis have largely been ignored in medical imaging thus far.; In this dissertation, new techniques were investigated for imaging and analyzing the tissue vibrations associated with cardiovascular sounds using the principles of Doppler ultrasound. Techniques were developed for real-time imaging of tissue vibrations produced by abnormalities in the blood flow through arteries and the heart. The feasibility of ultrasonic tissue vibration imaging was demonstrated through numerical simulations and experimental studies. Experimental results in animals showed that active internal bleeding is associated with soft tissue vibrations that are caused by eddies in the extravasating blood from arterial punctures and organ incisions. Vibration characteristics depend upon the bleeding rate. Ultrasonic measurement of vibrations offers significant advantages over conventional Doppler ultrasound and can potentially have a significant impact in trauma care as a tool for initial assessment.; In a preliminary clinical study, myocardial vibrations were observed in patients with coronary artery disease and the location of the vibrations correlated well with angiographically-confirmed coronary artery stenoses. If these preliminary results are confirmed by future clinical trials, tissue vibration imaging could potentially enable rapid and noninvasive bedside diagnosis of coronary artery disease. In addition, this technology can enable the analysis of the source and characteristics of cardiac murmurs in vivo in more detail than previously possible, which could lead to new insight into cardiac function and coronary artery disease. |
