Current role of contrast echocardiography in the diagnosis of cardiovascular diseases

High-resolution functional imaging with ultrasound contrast agents based on RF processing in an in vivo kidney experiment

Knowledge of the relative tissue perfusion distribution is valuable in the diagnosis of numerous diseases. Techniques for the assessment of the relative perfusion distribution, based on ultrasound (US) contrast agents, have several advantages compared to established nuclear techniques. These are, among others, a better spatial and temporal resolution, the lack of exposure of the patient to ionizing radiation and the relatively low cost. In the present study, US radiofrequency (RF) image sequences are acquired, containing the signal intensity changes associated with the transit of a bolus contrast agent through the microvasculature of a dog kidney. The primary objective is to explore the feasibility of calculating functional images with high spatial resolution. The functional images characterize the transit of the contrast agent bolus and represent distributions of peak time, peak value, transit time, peak area, wash-in rate and wash-out decay constant. For the evaluation of the method, dog experiments were performed under optimized conditions where motion artefacts were minimized and an IA injection of the contrast agent Levovist was employed. It was demonstrated that processing of RF signals obtained with a 3.5-MHz echo system can provide functional images with a high spatial resolution of 2 mm in axial resolution, 2 to 5 mm in lateral resolution and a slice thickness of 2 mm. The functional images expose several known aspects of kidney perfusion, like perfusion heterogeneity of the kidney cortex and a different peripheral cortical perfusion compared to the inner cortex. Based on the findings of the present study, and given the results of complimentary studies, it is likely that the functional images reflect the relative perfusion distribution of the kidney.

The future of bedside monitoring

Today's intensivists are provided with more information than ever before, yet current monitors present data from multiple sources in a relatively raw form with virtually no intelligent data integration and processing. In the next century, technological advances in miniaturization, biosensors and computer processing, coupled with an improved understanding of critical illnesses at the molecular level, will lead to the development of a new generation of monitors. Monitoring will move from the traditional macroscopic invasive approach to a noninvasive, molecular analysis of evolving critical disease processes. It is likely that disturbances in homeostasis will become known immediately or before they would otherwise be manifest clinically. Nanotechnology will permit monitoring of critical changes in the intracellular environment or the by-products of cellular metabolism and signal messaging. This article discusses monitoring technologies that hold promise for further development in the next century and point out techniques likely to be abandoned.

Visualization and quantification of myocardial mass at risk using three-dimensional contrast echocardiography

OBJECTIVE

Three-dimensional echocardiographic assessment of myocardial ischemia using contrast echocardiography has been hampered by limitations of available contrast agents and analytic software. In the study presented, a three-dimensional perfusion imaging method was evaluated in the porcine model of myocardial ischemia using a novel contrast agent.

METHODS

Three-dimensional echocardiography was performed in eight open-chested pigs before, during and after left anterior descending (six animals) or circumflex (two animals) coronary artery occlusion. The intramyocardial contrast effect was obtained by left atrial injection of Myomap, a deposit contrast agent.

RESULTS

Myocardial opacification was visible in all studies and retained in all three-dimensional datasets. Three-dimensional intensity analysis demonstrated a significant difference, exceeding 20 intensity units in every animal (in 127-level scale), between perfused and non-perfused myocardium. Reperfusion followed by contrast reinjection resulted in homogenous myocardial enhancement. Myocardial mass at risk was clearly delineated in all studies and measured with a mean error of -0.1 +/- 2.0 g against real mass (p = non-significant). Spatial extent of ischemia could be displayed in volume-rendered reconstruction of separate perfusion territories.

CONCLUSIONS

Quantitative analysis of myocardial contrast enhancement from three-dimensional datasets is feasible and allows accurate measurement of myocardial mass at risk.