Selective ablation of atheromas using a flashlamp-excited dye laser at 465 nm.

Abstract

Ablation of human atheromas with laser pulses that had only a small effect on normal artery tissue was shown in vitro in air and under saline using 1-psec pulses at 465 nm from a flashlamp-excited dye laser. At this wavelength, there is preferential absorption in atheromas due to carotenoids. The threshold fluence for ablation was 6.8 ± 2.0 J/cm2 for atheromas and 15.9 ± 2.2 J/cm2 for normal aorta tissue. At a fluence of 18 J/cm2 per pulse, the ablated mass per unit of energy ranged from 161 to 370 ,ug/J for atheromas and from 50 to 74 1Lg/J for normal aorta tissue. Ablation products consisted of cholesterol crystals, shredded collagen fibers, and small bits of calcific material. Most debris was less than 100Mum in diameter, but a few pieces were as large as 300 Mum.High-speed photography of ablation in air suggested explosive ejection of debris, caused by vapor formation, at speeds on the scale of 300 m/sec. Histological analysis showed minimal thermal damage to residual tissue. These data indicate that selective laser ablation of atheromas is possible in vitro.The ability to deliver laser energy to arteries via fine optical fibers offers the possibility of unclogging obstructed arteries without the trauma of surgery or general anaesthesia (1). This procedure, called laser endarterectomy or laser angioplasty, is now being evaluated in early clinical trials (2, 3). Its use thus far, however, has been limited, apparently due to perforations, aneurysms, and other forms of inadvertent laser damage, to adjacent and underlying normal tissues (2-6). Angioscopic (7) and radiographic visualization or other techniques (8) may help in aiming laser radiation at plaque. Laser endarterectomy would be much safer, however, ifthe radiation preferentially ablated atheroma and thrombus. In the ideal case, laser light would be delivered uniformly inside an obstructed artery, and only the obstructing material would be ablated.Preferential ablation of atheromas has previously been accomplished by first staining atheromas with a dye and then ablating with laser radiation that is absorbed by the dye (9, 10). A simpler method of achieving preferential ablation might be to take advantage ofexisting, endogenous, preferential absorption in the atheromas. The waveband from 450 to 500 nm has been identified as having a 2-fold preferential absorption in atheromas due to carotenoid pigments (11). In this study we have characterized preferential ablation of atheromas, in vitro, using a flashlamp-excited dye laser emitting radiation in this waveband at an appropriate pulse width and fluence. METHODS Radiation Source. Laser radiation at 465 nm was provided by a flashlamp-excited dye laser (Candela SLL 500 Coax) with 1.5 x 10-4 M coumarin 445 (Exciton C445) in methanol/distilled water (1:1, vol/vol). This laser generated 1-,usec pulses (full width at half-maximum) at a repetition rate of 1 Hz with energies up to 1.5 J per pulse. Laser wavelength, measured with a grating monochromator (Bausch and Lomb 33-86-76), ranged from 459 to 470 nm w...

Mechanisms of Pulsed Laser Ablation of Biological Tissues

“…When the removal of tissue layers that exhibit pathologic changes from underlying healthy tissue (for example, burn eschar versus normal tissue; plaque versus artery wall) is desired, or when a sensitive tissue structure adjacent to the target structure must be protected (for example, neural tissue in microspinal surgery), it is necessary to confine the ablation to the target structure. Researchers first sought to achieve selective ablation by making use of intrinsic differences in the optical properties of the tissues involved. − Later, online monitoring and active feedback techniques were introduced to discriminate between different tissue types and to automatically stop the ablation procedure when the transition between the layers is reached. Such techniques include the analysis of the acoustic transients in air generated during ablation, ,− fluorescence spectroscopy for discrimination between plaque and vessel wall, plasma spectroscopy to distinguish between bone and nerve tissue, and analysis of the cavitation bubble dynamics at the fiber tip for controlled sclera perforation in glaucoma surgery. , 388…”

“…Researchers first sought to achieve selective ablation by making use of intrinsic differences in the optical properties of the tissues involved. [482][483][484] Later, online monitoring and active feedback techniques were introduced to discriminate between different tissue types and to automatically stop the ablation procedure when the transition between the layers is reached. Such techniques include the analysis of the acoustic transients in air generated during ablation, 276,[485][486][487] fluorescence spectroscopy for discrimination between plaque and vessel wall, 370 plasma spectroscopy to distinguish between bone and nerve tissue, 488 and analysis of the cavitation bubble dynamics at the fiber tip for controlled sclera perforation in glaucoma surgery.…”

Ablation Characteristics of Arterial Vessel Walls Irradiated with the Pulsed Dye Laser - An Analysis of Variance

“…A b latio n thresholds w ere defined as the energy le ve ls at w h ich 5 0% o f the tissue specim ens showed h isto lo g ically confirm ed ablation. M u ltiv aria te an alysis (lo g istic regression, M A N O V A ) w as perform ed w ith S A S V e rsio n 6.08 to assess the effect o f m edium , pulse repetition rate and degree o f arterio sclerotic alterations w h ile adjusting fo r pulse num bers, energy densities, and…”

Effect of blood upon the selective ablation of atherosclerotic plaque witha pulsed dye laser

“…The threshold energies for the ablation for human aorta have been previously characterized for normal and atherosclerotic plaques of various compositions when performed in air or saline [2,3]. In our study, ablation threshold was defined as evidence of tissue removal or crater formation after 40 pulses of laser energy observed under 40 power dissecting microscopy whereas Prince et al examined tissues after a single laser pulse.…”