Intravascular ultrasound combined with Raman spectroscopy to localize and quantify cholesterol and calcium salts in atherosclerotic coronary arteries

Coronary intravascular ultrasound (IVUS) can assess arterial wall architect ure and localize large intravascular deposits, but it does not provide quan titative chemical information, which is essential in the evaluation of athe rosclerotic lesions. Previously, it has been shown that Raman spectroscopy can be used to accurately quantify the relative weights of cholesterol, cal cium salts, triglycerides, and phospholipids in homogenized arterial tissue . In the present study, we explore some benefits of combining IVUS and Rama n spectroscopy to evaluate the intact arterial wall. IVUS images were colle cted in vitro from human coronary arterial segments in various stages of di sease (n=7), The images were divided into radial segments (11 to 28 per ima ge, 332 in total), each of which was classified visually as calcified or no ncalcified tissue. The arteries were opened longitudinally, and Raman spect ra were collected from locations at 0.5-mm intervals across the arterial lu minal circumference. The spectra were used to calculate the chemical compos ition of the arterial wall at the examined locations. Generally, locations containing large amounts of calcium salts, as determined with Raman spectro scopy, were classified as calcified with IVUS. However, small calcific depo sits (<6% of weight) were not readily detected with IVUS. The amounts and l ocation of cholesterol determined with Raman spectroscopy were correlated c losely with the presence of cholesterol observed by histochemistry, but the se deposits could not be located accurately by IVUS. The combination of Ram an spectroscopy and IVUS applied in vitro provides detailed information abo ut the amount and location of calcific deposits and lipid pools in atherosc lerotic plaques. Future advances in optical fiber technology may allow simu ltaneous collection of Raman spectra and IVUS images through the same cathe ter in vivo.