Detection of calcified atherosclerotic plaque by laser‐induced plasma emission

Abstract

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.

Autofluorescence spectroscopy using a XeCl excimer laser system for simultaneous plaque ablation and fluorescence excitation

“…In 1985, Kittrell and colleagues [26] reported normal arterial wall in vitro by analyzing autoa spectrofluorimeter. Subsequently, various lasers were used as light Sources for the in vitro excitation of arterial fluorescence: an argon ion laser operating at 458 nm [27], a nitrogen laser at 337 nm [28, 291, a dye laser emitting between 305 and 310 nm [301 or at 476 nm ~311, or a H~-c~ laser operating at 325 nm [32][33][34][35][36]. The H~-c~ A two-laser system with a dye laser emitting at a of480 nm for tissue ablation and autofluorescence has been evaluated in patients with peripheral vascular disease of the lower ex-and for lipid plaques were essentially the Same as according to algorithm (I1) for media and lipid that a fibrous plaque could be differentiated from fluorescence spectra after excitation a t 480 nm in lesions in cave knee, there was a peak at 470 nm followed by laser was also used in viva on humans [37].…”

Optical feedback signal for ultrashort laser pulse ablation of tissue

“…Fluorescence [14], [15] and plasma luminescence [16]- [18] have been used for detection of calcified atherosclerotic plague with high sensitivity in angioplasty. A major drawback of using fluorescence spectroscopy is interference with blood clots and need for additional diagnostic light source [14], [17]. Plasma luminescence during pulsed laser ablation leads to a characteristic spectrum determined by tissue composition, A major disadvantage for longer pulse ablation system in using luminescence spectra in tissue diagnosis is that it requires an ablative laser fluence which might not be well-suited since it causes significant thermaVmechanical damage to the surrounding tissue.…”

Immunophotodynamic therapy: Current developments and future prospects

“…The concept of targeted drug delivery was first elaborated by Paul Ehrlich in the early 20 th century [Himmelweit, 1957]. Recent efforts to effect targeted delivery include local photosensitizer administration [Amano et al, 1988], intra-arterial drug administration [Deckelbaum et al, 1990], choice of route of administration [Bachor et al, 1992], photosensitizer activation with green visible light to avoid substantial normal tissue penetration [Nseyo et al, 1993;Veenhuizen et al, 1997], and two-photon excitation in the near-infrared [Fisher et al, 1997]. It has been suggested that the inherently lower pH of many tumors [Wike-Hooley et al, 1984;Thistlethewaite et al, 1985] may be exploited to identify photosensitizers with preferential tumor uptake [Pottier and Kennedy, 1990].…”