Quantitation of local myocardial perfusion is essential for the assessment of the extent of myocardial ischemia. The existing noninvasive approaches in myocardial contrast echocardiography (MCE) are significantly hampered by limited reproducibility due to variable attenuation of the harmonic signals emanating from insonated contrast microbubbles. Our long-term objective is to study nonlinear ultrasound signal propagation within the cardiovascular system and develop a robust mathematical model for attenuation compensation. Our preliminary method for decomposing a received broadband signal into the fundamental and harmonic (ie, dual) frequency spectra has resulted in the introduction of a Harmonic-to- Fundamental Ratio peak (HFRp) of the spectral envelope. The HFRp parameter self-compensates for variations in signal attenuation while differentiating perfused and nonperfused myocardium. We hypothesize that an analytical model of linear and nonlinear ultrasound signal propagation can reproducibly correct for harmonic spectrum attenuation. The short-term objective of the present reseach is to test the hypothesis in calibrated tissue phantoms and animal models of myocardial perfusion under defined levels of signal attenuation.
Aim 1 : Characterize changes in the fundamental and harmonic spectra during propagation through a tissue phantom with calibrated attenuation.
Aim 2 : Define the precision and accuracy of variable flow velocity measurements in vivo using attenuation correction by the proposed dual spectrum method.
Aim 3 : Determine the precision and accuracy of the dual spectrum method for estimation of regional myocardial blood flow under varying levels of attenuation.
Aim 4 : Validate the new method for quantitation of myocardial perfusion during coronary stenosis.
Aim 5 : Validate the dual spectrum method for perfusion quantitation in microvascular obstruction. To accomplish these aims, we will analyze digital radiofrequency ultrasound data obtained from tissue perfusion phantoms and beating dog hearts with induced ischemia, determine the region of ischemic risk in stained specimens, and define the reference perfusion flow from local activities of radiolabeled microspheres. The novelty is in the use of the fundamental component of the dual spectra as an immediate """"""""internal reference"""""""" for automatic attenuation compensation of the harmonic """"""""perfusion imaging"""""""" component. Such a principle should allow reproducible quantitation of perfusion by MCE.
