Frontiers in Intravascular Imaging Technologies

Abstract

I n 1971, Bom et al 1 developed one of the first catheterbased real-time imaging techniques for use in the cardiac system. In placing a set of phased-array ultrasound transducers within the cardiac chambers, Bom and colleagues showed that higher frequencies than those used in transthoracic ultrasound imaging could be used to produce high-resolution images of cardiac structures. By the late 1980s, Yock et al 2 had successfully miniaturized a single-transducer system to enable transducer placement within coronary arteries. Since then, intravascular ultrasound (IVUS) has become a pivotal catheter-based imaging technology, having provided practical guidance for percutaneous interventions and scientific insights into vascular biology in clinical settings. Technical developments currently being explored consist of further device improvements, a variety of advanced image analyses, and the extension of this ultrasound-based approach to diverse intravascular imaging techniques with other energy sources. Principles and Device DevelopmentsUltrasound-Based Approaches IVUS systems produce tomographic images by performing a series of pulse/echo sequences, or vectors, in which an acoustic pulse is emitted and the subsequent reflections from the tissue are detected. Each vector is acquired by directing the ultrasound beam from the catheter in a slightly different direction from the previous vector by mechanical or electrical means. A gray-scale IVUS image is made with all the vectors (commonly 256 vectors), with each vector acquired at a different angle of rotation.Several clinically relevant properties of the ultrasound image, such as the resolution, depth of penetration and attenuation of the acoustic pulse by tissue, are dependent on the geometric and frequency properties of the transducer. A crystal transducer emits a signal that spans a range of frequencies. The higher the center frequency, the better the radial resolution (Figure 1) but the lower the depth of penetration. Conventional IVUS catheters used in the coronary arteries have center frequencies that range from 20 MHz to 40 MHz, thus providing theoretical lower limits of resolution (calculated as half the wavelength) of 39 and 19 m, respectively. In practice, the radial resolution is at least 2 to 5 times poorer, as determined by factors such as the length of the emitted pulse and the position of the imaged structures relative to the transducer.For peripheral and intracardiac echocardiographic (ICE) applications, larger imaging catheters with lower center frequencies (8 to 20 MHz) are produced in both mechanical and electrical configurations. In addition, a phased-array intracardiac echocardiography catheter is available that provides a sector image with color/spectral Doppler and multiple frequency imaging (5.0 to 10 MHz) capabilities. Optical Approaches AngioscopyIntracoronary angioscopy is an endoscopic technology that allows direct visualization of the surface color and superficial morphology of atherosclerotic plaque, thrombus, neointima, or stent struts. The ...

Determination of Plaque Distribution in Intravascular Ultrasound Imaging: Visualization of an Unfolded Artery

“…Evaluation of the complex arterial geometry during percutaneous interventions allows to identify detailed in-vivo hemodynamic information [10]. Monitoring of vascular responses following stent implantation is important to determine potential subsequent plaque formation [11].…”

Cognitive AutonomouS CAtheters Operating in Dynamic Environments

“…from fluoroscopy and contrast agent, through catheter-mounted exteroceptive sensing it becomes possible measure and hence exploit this information in a more direct fashion. Amongst the different imaging modalities such as based on ultrasound (intravascular ultrasound or IVUS), 49 optical coherence tomography (OCT), 49 angioscopy, 50 MRI 51 or infrared vision, 52 IVUS is found a mature and widely used technique. Aside from its capability to detect vascular abnormalities, withing CASCADE it is used to capture the entire vessel wall (i.e.…”

Coronary Angioscopic Evaluation for Serial Changes of Luminal Appearance After Pharmacological and Catheter Interventions

“…In recent years, invasive or non-invasive diagnostic imaging technologies have been therefore developed for identifying vulnerable plaques. 3,6,7 According to previous pathological and clinical studies, definite vulnerable plaques demonstrate morphological and functional characteristics as follows: (1) active inflammation with infiltration of monocytes, macrophages, or T-lymphocytes; (2) fibrous cap (≤65 μm) with a large lipid core (thin-cap fibroatheroma: TCFA); (3) endothelial denudation with superficial platelet aggregation; (4) fissured plaque; (5) severe stenosis >90%; (6) superficial calcified nodule; (7) glistening yellow plaque; (8) intraplaque hemorrhage; (9) endothelial dysfunction; or (10) positive remodeling. 5 Histological TCFA is accounted for 60-70% of the culprit lesion in ACS, and then plentiful energy has been invested in identifying TCFA before suffering from ACS.…”