Stéphane G. Carlier

Numerical Study of the Uniformity of Balloon-Expandable Stent Deployment

Stents are small tubelike structures, implanted in coronary and peripheral arteries to reopen narrowed vessel sections. This endovascular intervention remains suboptimal, as the success rate is limited by restenosis. This renarrowing of a stented vessel is related to the arterial injury caused by stent-artery and balloon-artery interactions, and a local subsequent inflammatory process. Therefore, efforts to optimize the stent deployment remain very meaningful. Several authors have studied with finite element modeling the mechanical behavior of balloon-expandable stents, but none of the proposed models incorporates the folding pattern of the balloon. We developed a numerical model in which the CYPHER stent is combined with a realistic trifolded balloon. In this paper, the impact of several parameters such as balloon length, folding pattern, and relative position of the stent with respect to the balloon catheter on the free stent expansion has been investigated. Quantitative validation of the modeling strategy shows excellent agreement with data provided by the manufacturer and, therefore, the model serves as a solid basis for further investigations. The parametric analyses showed that both the balloon length and the folding pattern have a considerable influence on the uniformity and symmetry of the transient stent expansion. Consequently, this approach can be used to select the most appropriate balloon length and folding pattern for a particular stent design in order to optimize the stent deployment. Furthermore, it was demonstrated that small positioning inaccuracies may change the expansion behavior of a stent. Therefore, the placement of the stent on the balloon catheter should be accurately carried out, again in order to decrease the endothelial damage.

Challenges in tissue characterization from backscattered intravascular ultrasound signals

Plaque characterization through backscattered intravascular ultrasound (IVUS) signal analysis has been the subject of extensive study for the past several years. A number of algorithms to analyze IVUS images and underlying RF signals to delineate the composition of atherosclerotic plaque have been reported. In this paper, we present several realistic challenges one faces throughout the process of developing such algorithms to characterize tissue type. The basic tenet of ultrasound tissue characterization is that different tissue types imprint their own signature on the backscattered echo returning to the transducer. Tissue characterization is possible to the extent that these echo signals can be received, the signatures read, and uniquely attributed to a tissue type. The principal difficulty in doing tissue characterization is that backscattered RF signals originating as echoes from different groups of cells of the same tissue type exhibit no obvious commonality in appearance in the time domain. This happens even in carefully controlled laboratory experiments. We describe the method of acquisition and digitization of ultrasound radiofrequency (RF) signals from left anterior descending and left circumflex coronary arteries. The challenge of obtaining corresponding histology images to match to specific regions-of-interest on the images is discussed. A tissue characterization technique based on seven features is compared to a full spectrum based approach. The same RF and histology data sets were used to evaluate the performances of these two techniques.

Methods in Atherosclerotic Plaque Characterization Using Intravascular Ultrasound Images and Backscattered Signals

We will review existing supervised as well as unsupervised image- and spectrumderived algorithms in the context of atherosclerotic plaque characterization and detection of vulnerable plaques. We will further elaborate more on challenges involved in characterization of plaques from tissue preparation, data collection, and registration toward classification.

Hemolab: a custom built diagnostic tool for non-invasive, synchronized recording and real-time monitoring of a Doppler spectrogram, an electrocardiogram and arterial tonometry

In clinical diagnostic practice, various medical devices are designed for specific investigations and have no margin for adding other input signals or profound post-processing. Although information obtained from these signals separately is useful, using them in a combined way allows for a more profound analysis of the cardiovascular system. Our goal was to build an affordable, compact and easy-to-use diagnostic tool enabling a synchronized acquisition of arterial pressure and flow waveforms, combined with an electrocardiogram (ecg), all in non-invasive way and to be used in a routine diagnostic setting without prolonging testing protocols or adding discomfort to the patient. The combination of the beat-to-beat pressure and velocity information allows to calculate hemodynamic parameters that can quantify mechanical characteristics of the arterial system such as compliance and resistance. In this study, we used an applanation tonometer, an ecg recorder and an ultrasound device. We built a handy diagnostic tool called Hemolab that can combine the output of several stand-alone medical monitoring devices. A synchronized acquisition of a Doppler spectrogram, an electrocardiogram and a continuous pressure signal could already be acquired non-invasively, monitored in real-time and saved for later processing. This work contributes to obtain diagnostic information from non-invasive hemodynamical parameter analysis.