Intracoronary saline infusion should be incorporated into all excimer laser coronary angioplasty procedures.

By discriminating atherosclerotic from normal tissue and by confirming catheter-tissue contact and saline hemodilution, fluorescence feedback should minimize irradiation of normal tissue and/or blood and enhance the safety and efficacy of laser angioplasty.

Picosecond time-resolved fluorescence measurements were performed on fibrous and calcified atherosclerotic plaque and normal arteiy with 35 1 nm picosecond excitation of a mode-locked Nd-glass laser. Double exponential decay profiles were measured. The fast component of lifetimes of fibrous plaque is different than that of normal artery or calcified plaque and can be used to discriminate fibrous plaque from normal artery. 1.INTRODUCTIONTime resolved fluorescence spectroscopy has been used to study the various dynamical processes in biological metha"2. Tissues contain several fluorophores creating complex spectral emission profiles which cannot be easily identified to well-defined species, especially with steady state fluorescence alone. Time resolved fluorescence spectroscopy is thus another method which could help evaluate the heterogeneous nature of the emission.Earlier work on normal artery and white fibrous atherosclerotic plaque revealed a difference in the fluorescence spectra3'4. These differences were used to guide selective ablation during in vitro laser angioplast. However, steady-state fluorescence is not capable of accurately discriminating all subtypes of plaque, such as calcified plaque, from normal artery, which may limit its ability to accurately guide ablation. To understand and characterize the nature of the emission and assist in identification of the different chromophores present, or to obtain information of the physical processes occurring, time resolved fluorescence measurements were performed. 2.EXPERIMENTAL SET-UPPicosecond time-resolved fluorescence from artery tissue were measured using a streak camera with iOps resolution upon excitation with a 5ps third harmonic at 35mm of a modelocked Nd-glass laser2. The energy of the pulse was about 20 microjoules at the sample site. The sample size was about 5mm x 5mm x 1.5mm. The samples consisted of normal artery, fibrous atherosclerotic plaque and calcified atherosclerotic plaque. 2 / SPIE Vol. 1425 Diagnostic and Therapeutic Cardiovascular lnterventions(1991) O-8194-0515-9/91/$4.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/26/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

The use of fluorescence spectroscopy to discriminate atherosclerotic from normal tissue is limited by a lower sensitivity for calcified than noncalcified atherosclerotic plaque (65% vs. 93%, respectively). To evaluate plasma emission as a means to detect calcified plaque, 325 normal and atherosclerotic cadaveric aortic sites were irradiated through a 100-micron silica fiber in blood by a pulsed holmium laser (lambda = 2.1 microns, fluence = 4 J/mm2). A photodiode positioned near the proximal end of the fiber detected plasma emission during a laser pulse. Plasma emission was detected at 0% (0/110) of normal, 0% (0/107) of noncalcified atherosclerotic tissue, and 91% (98/108) of calcified atherosclerotic sites. Spectroscopic analysis confirmed the presence of calcium lines in the plasma emission from calcified atherosclerotic plaque. Although ablative fluences (greater than 3 J/mm2) were required for plasma generation, a single laser pulse ablated only to a depth of 67 +/- 16 microns in normal tissue. In an additional 10 calcified atherosclerotic sites, laser ablation was continued as long as plasma emission was detected. In all cases, plaque ablation was terminated before arterial perforation. Furthermore, the adjunctive use of plasma detection improved the accuracy of fluorescence spectroscopic classification of normal and atherosclerotic tissue. In conclusion, plasma detection has a high sensitivity (91%) and specificity (100%) for calcified atherosclerotic plaque and may be a useful adjunct for laser angioplasty guidance. Furthermore, plasma detection can be implemented both simply and inexpensively.