Intravascular Near-Infrared Spectroscopy: A Possible Tool for Optimizing the Management of Carotid Artery Disease

Abstract

Stroke is the second most common cause of morbidity and mortality in the Western nations. It is estimated that approximately one-fifth of all strokes or transient ischemic attacks are caused by carotid artery disease. Thus, treatment of carotid artery disease as a mean of stroke prevention is extremely important. Since the introduction of carotid endarterectomy, debate has persisted over the treatment strategy for carotid artery disease. Current recommendations have many potential flaws because they are often based on older trials performed before the introduction of modern pharmacotherapy and are mostly based on the angiographic degree of stenosis, without an emphasis on the pathophysiology of the disease. Most carotid events are caused by rupture or distal embolization of the content of an unstable atherosclerotic plaque with a large lipid pool. Thus, it is plausible that the information regarding the composition of the atherosclerotic plaque could play an important role in deciding on a treatment strategy. In this review article, we provide information about near-infrared spectroscopy, a new invasive imaging modality, which seems to be capable of providing such information.

Keywords: carotid artery stenting; intravascular ultrasound; near-infrared spectroscopy.

Figures

Fig. 1

The near infrared spectroscopy imaging device consisted of the following three main parts: a dual-modality 3.2 F imaging catheter that incorporates both near-infrared spectroscopy and intravascular ultrasound; a device for the mechanical pullback and rotation of the catheter through a vessel; and finally, a console with which one can observe the results of both imaging modalities in real time in the catheterization laboratory.

Fig. 2

The results of the intravascular ultrasound examination has two outputs. From the tomographic ultrasound image (panel A) of the vessel, we can learn about the anatomical structure of the vessel, including the dimensions of the lumen (red line) and the external elastic membrane (blue line). We can additionally calculate the lesion plaque burden as a fraction of the two parameters. The longitudinal intravascular ultrasound cross-section provides additional information about the lesion extent and severity (panel B).

Fig. 3

The near-infrared spectroscopy data are presented as a chemogram. Every pixel of this rectangular color-coded probability map represents the probability of the presence of lipids at a given location. Low probabilities of lipids are depicted as red, while the other extreme of the scale is represented by yellow. The X-axis of the chemogram indicates the pullback position in millimeters, while the Y-axis represents the circumferential position in degrees as though the coronary vessel has been incised along its longitudinal axis. The lipid-core burden index was established to satisfy the need for the quantification of the presence of lipids, defined as the fraction of yellow and red pixels on the chemogram multiplied by one thousand. The maximal lipid core burden index per 4 mm describes the region with the highest lipid burden.