Comparative rheology of low- and iso-osmolarity contrast agents at different temperatures.

BACKGROUND: Several contrast media (CM) are used for diagnostic angiography and coronary percutaneous interventions. Catheter miniaturization allows performance of most diagnostic studies using 4-5 F catheters and interventions using 5-6 F catheters. As a result of catheter lumen downsizing and viscosity of CM, the operators are sometimes required to forcefully inject to produce adequate images. METHODS AND RESULTS: The aim of the study is to perform a comparative rheology analysis between three different commonly used CM: iso-osmolar, nonionic iodixanol, Visipaque, (GE Healthcare); low-osmolar, nonionic ioversol, Optiray; and low-osmolar, ionic ioxaglate, Hexabrix, (Tyco Healthcare, US). The viscosity was experimentally assessed for temperature varying from 14 to 40 degrees C. To reproduce clinical use, an experimental set-up was used and the pressure developed to inject CM was evaluated at different temperatures and compared between the three CM. All three agents demonstrated a nonlinear inverse relationship between temperature and viscosity. At 14 degrees C iodixanol showed a twofold increase in viscosity compared with ioversol and ioxaglate. At 40 degrees C, the difference was reduced to 27%. At room temperature (20 degrees C), the difference in pressure needed to inject CM was 10% between iodixanol and ioxaglate and 6% between iodixanol and ioversol. As the temperatures increased, the differences in pressure became less important, becoming negligible (1%) at 37 degrees C. CONCLUSION: The viscosity of the iso-osmolar nonionic contrast agent iodixanol showed a stronger dependence on temperature compared with ioversol and ioxaglate. The impact of differences in viscosity and pressure to inject between CM were minimized at 37 degrees C. This emphasizes the importance of temperature control when using current low-osmolar CM and iso-osmolar CM with smaller sized catheters.

Numerical modeling of coronary drug eluting stents.

One of the principal therapies considered for the control of in-stent restenosis is the use of drug loaded polymer-coated stents for local delivery. We present two-dimensional and three-dimensional numerical models to study local delivery of drug eluting stents. The impact of various stent and flow parameters on the concentration distribution in the wall are investigated including the effect of the strut size, coating thickness, strut inter-distance and strut embedment in the vascular wall, blood flowing speed and the respective diffusion coefficients in the blood, wall and polymer. We also present criteria to assess the drug delivery efficiency based of the concept of the therapeutic window which aims at an spatial homogeneous concentration distribution and we introduce the variables to assess the amount of drug delivered in the wall. The results suggest that advection have a much stronger effect compared to diffusion in the blood media and that drug diffusivity in the arterial wall and in the polymer coating significantly affects the drug distribution. It is also shown that fully-embedded struts provide better spatial drug concentration uniformity after a short period of time and the half-embedded struts have a better temporal uniformity.

Image based biomechanics of coronary plaque.

In this chapter we present recent developments in the modeling of coronary artery biomechanics. We first introduce the pathology and localization of lesions in the circulatory system. Recent fluid and structural modeling of CAD is presented and discussed. At the end of the chapter, we present recent effort in coupling these two modeling domains using fluid-structure interaction (FSI).

Molecular imaging using light-absorbing imaging agents and a clinical optical breast imaging system--a phantom study.

PURPOSE: The aim of the study was to determine the feasibility of using a clinical optical breast scanner with molecular imaging strategies based on modulating light transmission. PROCEDURES: Different concentrations of single-walled carbon nanotubes (SWNT; 0.8-20.0 nM) and black hole quencher-3 (BHQ-3; 2.0-32.0 µM) were studied in specifically designed phantoms (200-1,570 mm(3)) with a clinical optical breast scanner using four wavelengths. Each phantom was placed in the scanner tank filled with optical matching medium. Background scans were compared to absorption scans, and reproducibility was assessed. RESULTS: All SWNT phantoms were detected at four wavelengths, with best results at 684 nm. Higher concentrations (≥8.0 µM) were needed for BHQ-3 detection, with the largest contrast at 684 nm. The optical absorption signal was dependent on phantom size and concentration. Reproducibility was excellent (intraclass correlation 0.93-0.98). CONCLUSION: Nanomolar concentrations of SWNT and micromolar concentrations of BHQ-3 in phantoms were reproducibly detected, showing the potential of light absorbers, with appropriate targeting ligands, as molecular imaging agents for clinical optical breast imaging.

Advanced contour detection for three-dimensional intracoronary ultrasound: a validation--in vitro and in vivo.

Intracoronary ultrasound (ICUS) provides high-resolution transmural images of the arterial wall. By performing a pullback of the ICUS transducer and three-dimensional reconstruction of the images, an advanced assessment of the lumen and vessel wall morphology can be obtained. To reduce the analysis time and the subjectivity of boundary tracing, automated segmentation of the image sequence must be performed. The Quantitative Coronary Ultrasound-Clinical Measurement Solutions (QCU-CMS) (semi)automated analytical software package uses a combination of transversal and longitudinal model- and knowledge-guided contour detection techniques. On multiple longitudinal sections through the pullback stack, the external vessel contours are detected simultaneously, allowing mutual guidance of the detection in difficult areas. Subsequently, luminal contours are detected on these longitudinal sections. Vessel and luminal contour points are transformed to the individual cross-sections, where they guide the vessel and lumen contour detection on these transversal images. The performance of the software was validated stepwise. A set of phantoms was used to determine the systematic and random errors of the contour detection of external vessel and lumen boundaries. Subsequently, the results of the contour detection as obtained in in vivo image sets were compared with expert manual tracing, and finally the contour detection in in vivo image sequences was compared with results obtained from another previously validated ICUS quantification system. The phantom lumen diameters were underestimated by 0.1 mm, equally by the QCU-CMS software and by manual tracing. Comparison of automatically detected contours and expert manual contours, showed that lumen contours correspond very well (systematic and random radius difference: -0.025 +/- 0.067 mm), while automatically detected vessel contours slightly overestimated the expert manual contours (radius difference: 0.061 +/- 0.037 mm). The cross-sectional vessel and lumen areas as detected with our system and with the second computerized system showed a high correlation (r = 0.995 and 0.978, respectively). Thus, use of the new QCU-CMS analytical software is feasible and the validation data suggest its application for the analysis of clinical research.