Project Description: In vivo chemical analysis and high-resolution imaging of atherosclerotic plaques using a near-IR fiber-optic catheter

The two AVI movies available below were generated from near-infrared scans of arteries from research subjects maintained on a high-cholesterol diet. This research is supported by the

American Heart Association

[Jump right to the movies]

New imaging algorithms for massively parallel supercomputers and intraarterial fiber-optic cameras are the most recent technological discoveries in this project. The nondestructive chemical analysis of single lesions over time virtually guarantees a new understanding of the mechanisms of lesion formation and growth. In these studies, subjects are maintained on a high-cholesterol diet to create fatty streaks and lesions in their arteries. The catheters are inserted into the femoral artery and advanced to the aortic arch. As the catheters are slowly withdrawn, near-IR chemical analyses of the lesion can be performed. With all other traditional techniques, vascular tissue must be removed from the animal before cholesterol and ox-LDL can be assayed. The advantage of the near-IR technique is that repeated analyses are possible of the same lesion in the same animal during lesion formation and/or treatment. The technique will make possible tests of theories of lesion formation that are not possible with traditional techniques.

Recent work on this project includes testing of catheters in rabbits that have been maintained for 6 weeks on high-cholesterol chow. The light source in these experiments is a laser system consisting of a MIRAGE 3000B Mid-Infrared Optical Parametric Generator and a Continuum NY81-10 Nd:YAG Pump Laser. The system provides tunable near-IR light with a wavelength from 1.4 to 4.1 micrometers with an effective power of 3.3 million watts. This first phase of experimentation involves scanning the aorta with the laser and catheter in vivo, then removing the heart and aorta of the animal. The excised heart and aorta are photographed and scanned with a conventional spectrometer as a control for the laser procedure. The lipoproteins in the lesion are then extracted and analyzed by ultracentrifugation and SDS-PAGE. Rabbits are anesthetized with atropine sulfate as a preanesthetic (0.1 mg/kg, i.m.) followed by ketacet (35 mg/kg, i.v.) and xylazine (5 mg/kg, i.v.). With the rabbit anesthetized, an incision near the femoral artery provides access to the aorta. The catheter is basically a small near-IR fiber-optic probe that is connected to the tunable laser and a detector, fast A/D, and computer. The catheter is inserted into the artery, and advanced to the aortic arch. Spectra are collected as the catheter is slowly withdrawn. The laser is necessary to provide enough light to obtain usable spectra through the blood and rabbit tissue. Following the in vivo portion of the experiment, the animal is euthanized by an overdose of anesthetic, and the heart and aorta are removed. The artery is scanned and measured again with a conventional spectrometer for comparison purposes. Following scanning of the excised artery, the aorta is measured and examined and all physical aspects recorded. A suture tied on the catheter enables penetration to aortic arch to be determined. Following this second scanning, sections are removed for analysis by protein extraction, centrifugation, and electrophoresis.

The AVI movies below are animations constructed from the image data obtained from one cholesterol subject and one control subject as the catheters were moved through the arteries. Increasing uptake of LDL is represented as increasing red color (gray areas = little LDL, red areas = increased LDL). The uptake of LDL is a natural process, making pink areas visible even in the control vessel. Although six weeks on high-choloesterol chow is not long enough for the subject to develop actual lesions, analysis of the near-IR results did show significantly increased LDL uptake by the experimental subject as compared to the control, even at this early stage.

Click here for movie of Cholesterol subject.

Click here for movie of Control subject.