Improved echocardiographic endocardial border delineation aids in the assessment of ventricular function and wall motion abnormalities. Microbubble-based contrast agents provide excellent echogenicity but a short-lived effect as microbubbles are susceptible to destruction by ultrasound and are rapidly eliminated by the lungs. In contrast, liquid perfluorocarbon (PFC) nanoparticles exhibit long circulatory times and are stable to insonification but have poor echogenicity. Ideally, a contrast agent should demonstrate long circulatory persistence, resistance to ultrasonic destruction, while displaying significant echogenicity.This study demonstrates the effectiveness of biocompatible, liquid PFC nanoparticles as a blood pool contrast agent. When imaged with Power Doppler Harmonic Imaging (PDHI), this agent exhibited marked blood pool enhancement lasting over 1 hour. Furthermore, the contrast enhancement was achieved at doses of 0.7% blood volume; a dose far smaller than had been previously published in studies utilizing liquid PFC nanoparticles with conventional imaging.[I] In order to investigate the influence of particle size on blood pool contrast effect, liquid PFC nanoparticles were formulated with diameters of 232 and 465 nm. The nanoparticles were then administered to canines (N = lo), with 7 canines receiving the 232 nm nanoparticles and the remainder receiving the 465 nm nanoparticles at a dose of 0.5 ml/kg. PDHI revealed marked blood pool enhancement in all three canines receiving the 465 nm nanoparticles but minimal contrast effect in the canines receiving the 232 nm nanoparticles. This data suggests that PFC nanoparticles in conjunction with PDHI may serve as an important adjunct for the assessment of ventricular function and wall motion abnormalities. This study provides the 0-7803-6365-5/00/$10.00 0 2000 IEEE first documented report of liquid PFC nanoparticles utilized as blood pool contrast agents with PDHI.
Myocardial edema is associated with impaired ventricular compliance and diastolic dysfunction. To determine the sensitivity of highfrequency ultrasound to myocardial edema, we employed a model in which edema was induced by Formation of edema after rapid-freezing and thawing immersion of heart tissue in isotonic saline.of myocardium was also evaluated. Rat hearts were arrested at end-diastole and insonified fresh within 15 minutes of excision (n=5) or after being frozen for 24 hours and thawed (n=4). A high-frequency, acoustic microscope was employed to perform ultrasonic measurements of attenuation, backscatter, speed of sound, and tissue thickness at baseline and hourly for 4 hours while immersed in solution. Parametric images of these ultrasonic indices were constructed to monitor changes in microscopic material properties due to edema and to allow identification of localized regions of interest. Fresh tissue demonstrated a greater propensity for the development of edema than frozen tissue. Integrated backscatter increased in both tissues while the magnitude and slope of attenuation decreased as edema evolved. We conclude that highfrequency ultrasound sensitively detects myocardial edema and may prove useful for monitoring and treatment of cardiac edematous disease states.
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