Videodensitometric methods for cardiac output measurements

Cardiac output is often measured by indicator dilution techniques, usually based on dye or cold saline injections. Developments of more stable ultrasound contrast agents (UCA) are leading to new noninvasive indicator dilution methods. However, several problems concerning the interpretation of dilution curves as detected by ultrasound transducers have arisen. This paper presents a method for blood flow measurements based on UCA dilution. Dilution curves are determined by real-time densitometric analysis of the video output of an ultrasound scanner and are automatically fitted by the Local Density Random Walk model. A new fitting algorithm based on multiple linear regression is developed. Calibration, that is, the relation between videodensity and UCA concentration, is modelled by in vitro experimentation. The flow measurement system is validated by in vitro perfusion of SonoVue contrast agent. The results show an accurate dilution curve fit and flow estimation with determination coefficient larger than 0.95 and 0.99, respectively

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

Novel ultrasound-contrast-agent dilution method for assessment of left ventricular ejection faction

Background: Left ventricular ejection fraction (LVEF) is an important determinant of prognosis. We evaluated the accuracy of a novel fast method for LVEF quantification based on indicator dilution curve (IDC) principles (figure 1) and compared the results with contrast-enhanced biplane LVEF assessment. Method: a 10 ml diluted (1:100) ultrasound-contrast bolus (SonoVue ®) was injected intravenously in thirty patients (pts) (20 male, age 65 ± 10) with known or suspected heart disease. In 22 pts multiple recordings were made and in 12 pts injections were repeated after implantation of a biventricular pacemaker, leading to 68 measurements. The developed algorithm used the left atrium and LV IDC for the LVEF measurement. For the biplane enhanced LVEF measurements a 0.5 ml pure ultrasound-contrast bolus (SonoVue ®) was administered to obtain multiple four- and two-chamber recordings. Results: according to contrast enhanced biplane assessments, the LVEF ranged from 10 to 75 % while the LV end-diastolic volume ranged from 80 to 521 ml. The mean LVEF measured by the biplane and the IDC method was 33 ± 17 % and 35 ± 18 %, respectively. A correlation coefficient r=0.91 was observed between the two methods (figure 2). Conclusion: A new fast method for LVEF assessment based on IDC principles is described and comparison with contrast enhanced biplane LVEF quantification shows accurate results. The proposed method also allows simultaneous quantification of right ventricular EF based on the same IDC principles

RoA:visual analytics support for deconfounded causal inference in observational studies

The gold standard in medical research to estimate the causal effect of a treatment is the Randomized Controlled Trial (RCT), but in many cases these are not feasible due to ethical, financial or practical issues. Observational studies are an alternative, but can easily lead to doubtful results, because of unbalanced selection bias and confounding. Moreover, RCTs often only apply to a specific subgroup and cannot readily be extrapolated. In response, we present Rod of Asclepius (RoA), a novel visual analytics method that integrates modern techniques designed for identification of causal effects and effect size estimation with subgroup analysis. The result is an interactive display designed to combine exploratory analysis with a robust set of techniques, including causal do-calculus, propensity score weighting, and effect estimation. It enables analysts to conduct observational studies in an exploratory, yet robust way. This is demonstrated by means of a use case involving patients undergoing surgery, for which we collaborated closely with clinical researchers

The effect of MySleeve on fluid restriction adherence in hemodialysis patients

In hemodialysis patients, non-adherence to fluid restriction is associated with high interdialytic weight gain (IDWG) and adverse outcomes. Monitoring drinkingbehaviour and direct feedback to the patient can lead to better adherence. We developed the MySleeve, a device that can be wrapped around a drinking glass to monitor fluid intake throughout the day. The MySleeve will also provide a subtle vibration on the glass when the amount drunk exceeds target. The information about drinking behaviour can be found in the accompanying application on a mobile phone. In this study, we investigate the effect of direct feedback and information to the patient on fluid restriction adherence, measured by the IDW