1. Field of the Invention
The present invention relates generally to the field of medical device. More specifically, the present invention relates to a device that employs palpography technology to characterize vulnerable plaque and other biological tissue such as cancer tissue.
2. Description of the Related Art
Atherosclerosis, a process underlying coronary artery disease, myocardial infarction and cerebrovascular disease, is a leading cause of morbidity and mortality in industrialized countries. The atherosclerotic plaque is often indolent and progressive and may destabilize without warning. This is defined as progressing from a pre-plaque to a vulnerable plaque. Cellular and molecular characteristics and the structure of the atherosclerotic plaque determine its vulnerability to rupture. Imaging techniques currently available utilize invasive and non-invasive methods to characterize coronary artery stenosis.
Current technique for vulnerable plaque detection may include combinations of thermography, NIR (near infrared) spectrum imaging, IVUS (intravascular ultrasound) imaging, nuclear labeling, chemical coding, micro-coil MRI, focal ELISA, and measurement of C-reactive protein, oxidized chemicals, lactate or pH. Detection, however, usually occurs late in the course of disease after symptoms have presented. Through early detection and a targeted treatment strategy, it is hoped that the burden of ischemic heart disease can be reduced. (Fischer et al., 2000; Naghavi et al. 2001).
Vulnerable atherosclerotic plaques are known to be inflamed and have higher temperature than the adjacent areas. A thermography catheter with an expandable basket having 4 to 8 expandable basket members, each of which was equipped with two thermocouples have been developed. It was reported that temperature heterogeneity was detected in five in-bred atherosclerotic dogs and ten Watanabe rabbits. A thermo-elastography system provides thermal, structure and elasticity data for detection of plaques and determination of their functional status (Gul et al., 2001).
Hence, inflamed vulnerable atherosclerotic plaques can be detected based on their increased temperature. An infrared angio-thermography catheter for imaging the thermal characteristics of arterial walls has been reported. The system has a thermal resolution of 0.01° C. and spatial resolution of 100 microns. It was reported that a side-viewing thermography using a 4 French infrared fiber optic bundle catheter is feasible. A realtime imaging reconstruction software continuously records the linear images obtained through the 1 mm window and processes them into two-dimensional and virtual longitudinal color-coded thermographic images of the lumen (Naghavi et al., 2001).
Plaque hypoxia and ischemia have been identified and correlated for a long time. Activated macrophages, in particular those incubated with Ox-LDL, produce enormous amounts of lactate and reduce their environmental pH to acidic levels. Near infrared spectroscopy is one of the few available non-destructive techniques for in vivo measurement of tissue pH. A near-infrared fiber optic catheter with the capability to measure reflectance spectra from the vessel wall has been developed to study the spectroscopic characteristics of lactate and pH in human carotid atherosclerotic plaques. The catheter has the capability to image lactate and pH distribution in the plaque with the help of a specialized software program (Khan et al., 2001).
Human carotid endarterectomized plaque, atherosclerotic rabbit aorta, and ApoE-deficient mice aorta show marked temperature heterogeneity due to inflammation in contrast to normal arterial wall. Plaque temperature and pH are inversely correlated, suggesting that hot plaques are acidic. Plaques with a large lipid core, macrophage infiltration, and no calcification (vulnerable plaques) have lower pH than calcified and fibrotic (stable) plaques (Naghavi et al., 2002).
There are currently several feasible and accurate methods to study the arterial wall morphology like angiography and intravascular ultrasounds. Diamantopoulos et al. developed a 3F intracoronary catheter that can slide over a conventional angioplasty guidewire. This catheter is equipped with an array of electrically isolated ultra-thin metallic film rings using the capacitometry principles. It was reported that the plaque morphology is well correlated with the images acquired by IVUS. The method can distinguish calcified areas, areas with fatty content and other tissues for in vivo assessment of a vulnerable plaque (Diamantopoulos et al., 2001).
Simultaneous thermal and morphology mapping of the coronary arteries in vivo have been reported by using a catheter system combining intravascular ultrasound and multi-point thermography at the same time and position. The system includes a 3.5F catheter using 4 thermisters to study the temperature at 360° of the arterial wall, and an ultrasound scanning system for the simultaneous acquisition of intravascular images. The 2D plots and 3D re-constructions are automatically provided from a study of 10 non-atherosclerotic rabbits (Diamantopoulos et al., 2001).
Plaque temperature has been associated with plaque vulnerability. A new insight into plaque vulnerability by means of thermography and advanced computer algorithms has been reported. A new catheter-based system that has the capability of simultaneous intravascular echogram and temperature sampling at the same location is used in 5 atherosclerotic rabbits. A 3-D color-coded thermal mapping of the atherosclerotic plaque verified the existence of temperature heterogeneity inside the individual plaques (Diamantopoulos et al., 2001).
Known vulnerable plaques are more likely to be soft plaques. In contrast, stable plaques are likely to be fibrotic and calcified (hard plaque). The present invention discloses a method and apparatus for screening hot and soft plaques to identify vulnerable plaques. This system is designated as thermo-elastography catheter and may be superior and more cost-effective compared to an intravascular sono-elastography described by Cespedes and de Korte (de Korte et al., 2002 Mar; de Korte et al., 2002 April) or a combination of thermosensors and IVUS elastography currently investigated by Serruys and Diamontapolos.
The prior art offers means to characterize arterial walls and atherosclerotic plaques including the use of thermo-elastography, sono-elastography and near infrared spectroscopy techniques. The present invention provides a diagnostic device for studying tissue environments, including tissue environments enclosing a body lumen. In particular, the present invention further provides a device that enhances the technology of prior art to detect and diagnose atherosclerotic plaques; thereby, fulfulling a long standing need and desire in the art.