In vivo kinetics of microbubbles of SH U 508 A (Levovist): comparison with indocyanine green in rabbits

Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

Ultrasound provides a valuable tool for medical diagnosis offering real-time imaging with excellent spatial resolution and low cost. The advent of microbubble contrast agents has provided the additional ability to obtain essential quantitative information relating to tissue vascularity, tissue perfusion and even endothelial wall function. This technique has shown great promise for diagnosis and monitoring in a wide range of clinical conditions such as cardiovascular diseases and cancer, with considerable potential benefits in terms of patient care. A key challenge of this technique, however, is the existence of significant variations in the imaging results, and the lack of understanding regarding their origin. The aim of this paper is to review the potential sources of variability in the quantification of tissue perfusion based on microbubble contrast-enhanced ultrasound images. These are divided into the following three categories: (i) factors relating to the scanner setting, which include transmission power, transmission focal depth, dynamic range, signal gain and transmission frequency, (ii) factors relating to the patient, which include body physical differences, physiological interaction of body with bubbles, propagation and attenuation through tissue, and tissue motion, and (iii) factors relating to the microbubbles, which include the type of bubbles and their stability, preparation and injection and dosage. It has been shown that the factors in all the three categories can significantly affect the imaging results and contribute to the variations observed. How these factors influence quantitative imaging is explained and possible methods for reducing such variations are discussed.

Estimation of forward and backward mitral flow using indicator dilution technique: a theoretical feasibility study

A new theoretical algorithm is presented for high-resolution mitral flow determination based on the indicator dilution principle. The algorithm allows forward as well as backward time-dependent mitral flow estimation with a beat-to-beat resolution. Indices of normal/subnormal left heart functioning, including total stroke volume (TSV), cardiac output (CO), total ejection fraction (TEF), mitral regurgitation volume (MRV) and mitral regurgitation fraction (MRF), are determined. Knowledge of left atrium and ventricle indicator concentration versus time dependencies and the end systolic left atrium and ventricle volumes are sufficient to determine the mitral flow pattern. However, the non-dimensional index of the total ejection fraction can be calculated on the basis of only the indicator concentration. The algorithm was validated by applying it to blood flows and heart chamber volumes derived from a computer simulation of the cardiovascular circulation. First left heart concentrations versus time data were obtained by determining the distribution over a cardiovascular tract of an ideal indicator, a bolus of which was intravenously injected into one of the arms. Then the backward problem of finding mitral flow was solved. The accuracy of the mitral flow estimation depends on the accuracy of end systolic left atrium and ventricle volume data. The method is applicable over a wide range of aortic regurgitation, up to 20% of cardiac output, suggesting that the algorithm might become a robust technique of non-invasive mitral flow assessment, replacing traditional techniques such as nuclear radiography.

Ultraschallkontrastmittel: Substanzklassen, Pharmakokinetik, klinische Anwendungen, Sicherheitsaspekte

Ultrasound contrast agents (UCA) have undergone constant development and improvement in recent years. Greater mechanical stability and improved acoustic properties, combined with new contrast-specific ultrasound sequences, have broadened the potential fields for investigation considerably. Contrast-enhanced ultrasound studies will no longer be complementary investigations, but will be considered as primary techniques. This review article provides a survey of the different drugs used, their chemical properties, and their pharmacokinetic aspects. Summarized are the most important established and published indications for the use of UCA together with an outlook for future applications. Finally this paper discusses the safety profile of these agents, which has become important due to the increasing use of these agents.