A.A.C.M. Kalker

Cardiac image segmentation for contrast agent videodensitometry

Indicator dilution techniques are widely used in the intensive care unit and operating room for cardiac parameter measurements. However, the invasiveness of current techniques represents a limitation for their clinical use. The development of stable ultrasound contrast agents allows new applications of the indicator dilution method. Ultrasound contrast agent dilutions permit an echographic noninvasive measurement of cardiac output, ejection fraction, and blood volumes. The indicator dilution curves are measured by videodensitometry of specific regions of interest and processed for the cardiac parameter assessment. Therefore, the major indicator dilution imaging issue is the detection of proper contrast videodensitometry regions that maximize the signal-to-noise ratio of the measured indicator dilution curves. This work presents an automatic contour detection algorithm for indicator dilution videodensitometry. The algorithm consists of a radial filter combined with an outlier correction. It maximizes the region of interest by excluding cardiac structures that act as interference to the videodensitometric analysis. It is fast, projection independent, and allows the simultaneous detection of multiple contours in real time. The system is compared to manual contour definition on both echographic and magnetic resonance images.

Identification of ultrasound contrast agent dilution systems for ejection fraction measurements

Left ventricular ejection fraction is an important cardiac-efficiency measure. Standard estimations are based on geometric analysis and modeling; they require time and experienced cardiologists. Alternative methods make use of indicator dilutions, but they are invasive due to the need for catheterization. This study presents a new minimally invasive indicator dilution technique for ejection fraction quantification. It is based on a peripheral injection of an ultrasound contrast agent bolus. Left atrium and left ventricle acoustic intensities are recorded versus time by transthoracic echocardiography. The measured curves are corrected for attenuation distortion and processed by an adaptive Wiener deconvolution algorithm for the estimation of the left ventricle impulse response, which is interpolated by a monocompartment exponential model for the ejection fraction assessment. This technique measures forward ejection fraction, which excludes regurgitant volumes. The feasibility of the method was tested on a group of 20 patients with left ventricular ejection fractions going from 10% to 70%. The results are promising and show a 0.93 correlation coefficient with echographic bi-plane ejection fraction measurements. A more extensive validation as well as an investigation on the method applicability for valve insufficiency and right ventricular ejection fraction quantification will be an object of future study.

Intra-thoracic blood volume assessment by dilution of ultrasound contrast agents

The blood volume assessment provides important information on the circulatory system condition. Especially the intra-thoracic blood volume (ITBV) is related to the symmetry of the cardiac efficiency. The ITBV measurement, nowadays, is made by use of trans-pulmonary indicator dilution techniques, such as thermo- and dye-dilution. Since catheterization is required, these techniques are very invasive. The tracer is injected into a central vein and detected in the aorta. The detected indicator concentration-versus-time curve is referred to as indicator dilution curve (IDC). The mean transit time (MTT) of the IDC multiplied by the cardiac output (CO) gives the blood volume between the injection site (central vein) and the aorta, i.e., the ITBV plus the average volume of all the cardiac chambers. This paper presents a new non-invasive technique for the measurement of blood volumes in the circulatory system. The tracer is an ultrasound contrast agent (UCA) detected by an ultrasound transducer. The acoustic or video intensity analysis of the B-mode output of ultrasound scanners allows the measurement of UCA IDCs. Several cardiac echo-views permit the measurement of different IDCs from different sites. The blood volume between two different sites is given by the product of the blood flow (CO) times the MTT that the contrast takes to go from the first to the second site. For the ITBV assessment, two IDCs can be measured simultaneously in the right and left side of the heart. The system is validated by in-vitro experimentation. A Sonos 5500 ultrasound scanner is used to detect SonoVue/spl reg/ contrast agent IDCs. The results show very accurate volume measurements with a standard deviation smaller than 4% of the volume for a wide range of flows. Initial in-vivo application of the system in humans shows promising results.

Blood volume measurements by videodensitometric analysis of ultrasound-contrast-agent dilution curves

The assessment of blood volumes provides useful information on the circulatory system. Especially the intra-thoracic blood volume (ITBV), which is measured by invasive trans-pulmonary indicator dilution techniques, is related to the symmetry of the cardiac efficiency. This paper presents a new non-invasive indicator dilution technique for blood volume measurements. The indicator is an ultrasound contrast agent, which is detected by videodensitometric analysis of echocardiographic videos. Different indicator dilution curves (IDC) are measured simultaneously in different sites. The mean transit time (MTT) of the contrast between the measurement sites is multiplied by the blood flow to determine the blood volumes. The local density random walk model is used to fit and interpret the IDC. The MTT is easily derived from the fitted model. A specific fast and accurate least-square fitting algorithm is adopted. The in-vitro results show very accurate volume measurements with standard deviation smaller than 4.8% of the volume. The in-vivo application of the system in humans shows promising results too.

Identification of ultrasound-contrast-agent dilution systems for cardiac quantification

This study presents a new minimally-invasive indicator dilution technique for cardiac quantification. An ultrasound contrast agent bolus is injected in a peripheral vein and detected by an ultrasound transducer. Several acoustic-intensity time curves are measured in specific regions of interest. After calibration, the resulting curves are processed by a Wiener deconvolution filter to identify the dilution system between different measurement sites, which is characterized by its impulse response function. This is interpolated and interpreted by specific models for the assessment of ejection fraction (EF) and pulmonary blood volume. The EF assessment is tested on a group of 20 patients with left ventricular EF going from 10% to 70%. The results show a 0.93 correlation coefficient with echographic hi-plane measurements. Blood volume measurements are validated in vitro and show a 0.99 correlation coefficient with the real volumes. The method feasibility is also tested in patients with promising results. In conclusion, the echographic identification of biological dilution systems is feasible. It allows a minimally invasive measurement of pulmonary blood volume and EF. The promising results encourage further validation and investigation for new applications.