Scanning electron microscopy and thermal characteristics of dentin ablated by a short-pulse XeCl excimer laser

The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated. The dependence of surface temperatures and temperature gradients into the treated teeth on laser parameters such as fluence (0.5J/cm2-7J/cm2), pulse repetition rate (1Hz-35Hz), and spot size (0.004cm2-0.12cm2) was studied. Additionally, the effect of fluence and pulse repetition rate on dentin microstructure was studied using scanning electron microscopy (SEM). It is demonstrated that this "cold ablation" excimer laser can result in significant thermal modification in the dentin surfaces. Changes include the formation of melted dentin grains, which uniformly cover the surface and the exposed dentin tubules. Maximum temperatures of the ablated surfaces, however, remained relatively low at most laser parameters used. Also, the immediate neighborhood of the root canal was essentially undisturbed at most laser parameters. These observations suggest that with the appropriate choice of parameters XeCl lasers can be effective in producing surface structures that may prove useful in enhancing bond strength or other applications in dentistry, without exposing tooth pulp to significant temperature elevation.

Effects of pulse width on erbium:YAG laser photothermal trabecular ablation (LTA)

An erbium (Er):YAG laser can remove trabecular meshwork (TM) by photothermal ablation with minimal contiguous thermal damage. A variable pulse width Er:YAG laser was used to investigate the effect of varying pulse width on ablation of human TM. Trabecular photothermal ablation was performed on tissue obtained from eye bank eyes at pulse widths of 50, 150, and 250 microseconds, with energy held constant at 4 mJ. At this energy, a single laser pulse was sufficient for full-thickness ablation of TM. Laser energy was delivered through a 200-microns diameter optical fiber held in apposition to the tissue sample, which was immersed in physiologic saline. High-speed photography of the resultant steam bubbles also was performed. Light microscopy and scanning electron microscopy of TM ablated at 50 microseconds revealed the greatest variability in size (0-140 microns) of the full-thickness ablated areas and demonstrated blast effects, tissue shredding and < or = 10 microns thermal damage. At 150 microseconds, the full-thickness ablated areas were more consistent size (115-120 microns), showed no blast effects and 10 to 20 microns thermal damage. At 250 microseconds, the largest ablations were found (180-220 microns) and showed no blast damage; however, a significant amount of thermal damage (< or = 50 microns) was evident. The steam bubbles produced by the laser energy were largest at 50 microseconds and did not begin to collapse until well over twice the original pulse interval. At 150 and 250 microseconds, the steam bubbles were successively smaller and dissipated at the end of the laser pulse.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon dioxide laser ablation combined with doxorubicin hydrochloride treatment for vaginal fibrosarcoma in a dog

The combined use of CO2 laser ablation and doxorubicin hydrochloride (30 mg/m2) administered twice, 4 weeks apart, resulted in complete remission of vaginal fibrosarcoma in a 10-year-old Miniature Poodle. The tumor had redeveloped when only CO2 ablation was used for treatment and doxorubicin hydrochloride alone has had marginal influence on fibrosarcomas; however, use of both treatments in this dog resulted in a 20-month, disease-free period. This treatment combination was minimally traumatic to the dog, easily accomplished, and effective, and it allowed retention of the normal anatomy and function of the urogenital tract.

Laser vs. suture nerve anastomosis

The repair of injured or transected nerves is frequently encountered in head and neck surgery. Recently, CO2 lasers with milliwatt capability and micrometer spot sizes have been developed that may be used in nerve anastomosis. A comparative study was performed between microsuture and CO2 laser repair of transected sciatic nerves in rats. Nerve regeneration was measured in terms of morphology, electrophysiology, and function. Histologic studies revealed no difference in the size and number of regenerated axons, although there was less scar tissue formation at the anastomotic site with the laser repair. EMG and nerve conduction velocity were similar for the two repair methods. Functional recovery, as determined objectively using measurements of gait footprints, showed no difference between suture and laser repair. Laser-repaired nerves did have a higher dehiscence rate, although this problem can probably be prevented by splinting the rats postoperatively. However, laser repair was faster and simpler than suture repair and required less manipulation of the nerve. This study shows laser repair of peripheral nerves is possible with results comparable to conventional microsuture neurorrhaphy. Laser nerve anastomosis may be an effective alternative to suture nerve repair.

Photodynamic therapy of experimental subchoroidal melanoma using chloroaluminum sulfonated phthalocyanine

Although photodynamic therapy has shown great promise for the treatment of a variety of malignant neoplasms, the role of this new therapeutic modality in the clinical management of intraocular tumors remains incompletely understood. This study examines the effects of photodynamic therapy using chloroaluminum sulfonated phthalocyanine on Greene hamster melanoma transplanted into the subchoroidal space in rabbits. Twenty-four hours after intravenous administration of chloroaluminum sulfonated phthalocyanine (5 mg/kg), tumors were irradiated with 675 nm of light at total light doses of 7 to 60 J/cm2. The results show that tumor growth was arrested at total light doses of 22 to 60 J/cm2. At total light doses of 15 to 21 J/cm2, tumor growth was initially arrested. However, regrowth of these tumors was apparent within 7 days. Total light doses of less than 15 J/cm2 showed no response. Complications of photodynamic therapy, such as intraretinal or subretinal hemorrhages and retinal detachment, were seen only in animals who received total light doses in excess of 43 J/cm2.

Acute ultrastructural changes of cornea after excimer laser ablation

Corneal ultrastructural changes induced by an argon fluoride excimer laser using different parameters were investigated. Twenty-eight rabbit corneas were ablated at light doses per pulse and repetition rates ranging from 25-800 mJ/cm2 and 1-100 Hz, respectively, at four different total light doses (25-150 J/cm2). Transmission electron microscopy showed that corneal ablations done at subthreshold light doses per pulse with repetition rates higher than 30 Hz and with an exposure more than 100 sec caused significant surface coagulation and an increase in pseudomembrane thickness. These changes were not observed in ablations done above threshold light doses per pulse, regardless of repetition rate and exposure time. However, repetition rates as high as 80 Hz caused damage to the endothelium and Descemet's membrane at the same ablation depth that did not cause such damage using repetition rates under 40 Hz. It appears that high repetition rates used during excimer laser corneal surgery may cause irreversible damage to the cornea.

Ab-interno neodymium:YAG versus erbium:YAG laser sclerostomies in a rabbit model

This study was undertaken to determine whether thermally-induced tissue necrosis was a factor in ab-interno contact-laser sclerostomy failure. A rabbit model was used to compare the continuous-wave Neodymium (Nd):YAG with the pulsed Erbium (Er):YAG laser with respect to such failure. Laser energy was focused into a fused-silica fiber optic (400 microns) for the Nd:YAG laser (12 W; 3 to 5 seconds), and into a single-crystal, uncladded sapphire fiber optic (250 microns) for the Er:YAG laser (7 to 8 mJ; 250 microseconds; 6 to 8 pulses). The Nd:YAG and Er:YAG lasers required from 21 to 35 J and from 42 to 64 mJ, respectively, to create the sclerostomies. Filtering blebs and intraocular pressure reduction lasted longer (log-rank test; P less than .03) and surgical complications were fewer in the Er:YAG group than in the Nd:YAG group. By creating sclerostomies with minimal thermal damage, the Er:YAG laser may offer significant clinical advantages over lasers producing larger thermal effects.

Optical trapping in animal and fungal cells using a tunable, near-infrared titanium-sapphire laser

We have compared two different laser-induced optical light traps for their utility in moving organelles within living animal cells and walled fungal cells. The first trap employed a continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser at a wavelength of 1.06 micron. A second trap was constructed using a titanium-sapphire laser tunable from 700 to 1000 nm. With the latter trap we were able to achieve much stronger traps with less laser power and without damage to either mitochondria or spindles. Chromosomes and nuclei were easily displaced, nucleoli were separated and moved far away from interphase nuclei, and Woronin bodies were removed from septa. In comparison, these manipulations were not possible with the Nd-YAG laser-induced trap. The optical force trap induced by the tunable titanium-sapphire laser should find wide application in experimental cell biology because the wavelength can be selected for maximization of force production and minimization of energy absorption which leads to unwanted cell damage.

Glucose administration combined with photodynamic therapy of cancer improves therapeutic efficacy

Both the scope and the levels of activity in basic research and in the clinical applications of PDT, have grown enormously during the past few years. Several studies have examined the synergism of hyperthermia and chemotherapeutic agents in combination with PDT to enhance tumor eradication. The present study investigates the synergism of glucose administration combined with phototherapy. The results of this study suggest that glucose administration is simple and well tolerated, and combined with PDT produces a larger percentage of animals cured than using PDT alone. Furthermore, the results indicate that this approach requires lower amounts of light and might enable dosage reduction of photosensitizer for optimal response, with minimal side effects, to the treatment of cancer.

Demonstration of synergistic effects of hyperthermia and photodynamic therapy using the chick chorioallantoic membrane model

The chick chorioallantoic membrane (CAM) model was used to study vascular effects of photodynamic therapy (PDT) and hyperthermia (HPT) and the synergism of these modalities. The CAM is a convenient medium for monitoring the modifications of the vasculature. It is possible to view the CAM and to examine structural changes of individual blood vessels in real time. Moreover, the CAM is a closed system which lends itself to mathematical modeling of the temporal and spatial temperature profile and in which HPT can be performed quantitatively and to a selected depth, using different lasers. A porphyrin-type photosensitizer solution was applied to areas of the CAM, defined by teflon O-rings placed on the surface. Uptake dynamics of the sensitizer into the CAM was determined by analyzing its fluorescence in vivo. The CAM area was irradiated with a dual-wavelength laser system composed of a dye laser at 644 nm (to induce PDT) and a CO2 laser at 10.6 microns (to bring about HPT). Damage to the CAM vasculature, due to combined PDT+HPT, was compared to the outcome of the separate modalities, and a synergistic effect of about 40% was observed.

Micromanipulation of mitotic chromosomes in PTK2 cells using laser-induced optical forces ("optical tweezers")

To study the potential use of optical forces to manipulate chromosome movement, we have used a Nd:YAG laser at a wavelength of 1.06 microns focused into a phase contrast microscope. Metaphase and anaphase chromosomes were exposed while being monitored by video microscopy. The results indicated that when optical forces were applied to late-moving metaphase chromosomes on the side closest to the nearest spindle pole, the trapped chromosomes initiated movement to the metaphase plate. The chromosome velocities were two to eight times the normal rate depending on the chromosome size, geometry, and trapping site. At the initiation of anaphase, a pair of chromatids could be held by the optical trap and kept motionless throughout anaphase while the other pairs of chromatids separated and moved to opposite spindle poles. As a result, the trapped chromosome either was incorporated into one of the daughter cells or was lost in the cleavage furrow, or the two chromatids eventually separated and moved to their respective daughter cells. If the trap was removed at the beginning of anaphase B, the chromosome moved back to the poles. Our experiments demonstrate that the laser-induced optical force trap is a potential new technique to study noninvasively the mitotic spindle of living cells.

Direct experimental evidence for the existence, structural basis and function of astral forces during anaphase B in vivo

The existence, structural basis and function of astral forces that are active during anaphase B in the fungus, Nectria haematococca, were revealed by experiments performed on living cells. When one of the two asters of a mitotic apparatus was damaged, the entire mitotic apparatus migrated rapidly in the direction of the opposing astral forces, showing that the force that accelerated spindle pole body separation in earlier experiments is located in the asters. When a strong solution of the antimicrotubule drug, MBC, was applied at anaphase A, tubulin immunocytochemistry showed that both astral and spindle microtubules were destroyed completely in less than a minute. As a result, separation of the spindle pole bodies during anaphase B almost stopped. By contrast, disrupting only the spindle microtubules with a laser microbeam increased the rate of spindle pole body separation more than fourfold. Taken together, these two experiments show that the astral forces are microtubule-dependent. When only one of the two or three bundles of spindle microtubules was broken at very early anaphase B, most such diminished spindles elongated at a normal rate, whereas others elongated at an increased rate. This result suggests that only a critical mass or number of spindle microtubules needs be present for the rate of spindle elongation to be fully governed, and that astral forces can accelerate the elongation of a weakened or diminished spindle.

Micromanipulation of gametes using laser microbeams

Various microsurgical procedures at the cellular and subcellular levels using laser non-touch techniques are presented and reviewed. In these procedures, the beams of light, varying in their wavelength (range: 14 ns to continuous wave), were directed via microscopes towards the target area. Micromanipulation of human spermatozoa with a laser-generated optical trap enabled the assessment of possible effects on sperm motility and measurements of the relative force generated by each single spermatozoon. Furthermore, the optical trap also provides a new approach to the measurements of intracellular forces without physically touching the cell or its organelles, and inducing chromosome movement during cell division is also possible. Laser beams in a specific configuration are able to induce minimal superficial damage to the zona pellucida of oocytes from various species. This manipulation is aimed at increasing the fertilization rate following insemination with low-quality spermatozoa. Another intracellular application of the laser beams is the destruction of extra pronuclei in polyspermic fertilized human oocytes. These procedures require special equipment which is not commonly available. However, simpler devices may be developed if the advantages of this novel technology are demonstrated.

Infrared laser sclerostomies

Four solid-state lasers with three fiberoptic delivery systems were used to perform laser sclerostomies in an acute-injury rabbit model and in fresh human globes. The lasers used were continuous-wave neodymium:yttrium aluminum garnet (YAG, 1.06 microns) and pulsed holmium:yttrium scandium galliam garnet (YSGG) (2.10 microns), erbium:YSGG (2.79 microns), and erbium:YAG (2.94 microns). Thermal damage to tissue and total laser energy required to produce sclerostomies decreased with increasing wavelength. In human tissue using a 600-microns fused silica fiberoptic, maximum thermal damage (greater than or equal to 100 microns) was noted at 1.06 microns with a total energy of 21 J at a power density of 2.5 kW/cm2. In addition, focal damage to the iris and ciliary body was noted at this wavelength. The least amount of thermal damage (15-20 microns) and lowest total energies needed were found at 2.94 microns. A 250-microseconds pulse length and pulse radiant exposures of 3.6 J/cm2 and 14.3 J/cm2 were used for the low hydroxyl-fused silica (500 microns) and zirconium fluoride (250 microns) fiberoptics, respectively. Although zirconium fluoride fibers have high through-put efficiencies that facilitate study of laser tissue interactions at 2.94 microns, problems encountered with fragility and solubility of the bare tip in aqueous media limit its usefulness. A high attenuation rate with the low hydroxyl-fused silica fiber limited its usable length to 35 cm at 2.94 microns. Tissue damage during sclerostomy formation was minimized at 2.94 microns, reaching a maximum at 1.06 microns. Minimizing tissue damage theoretically could decrease subconjunctival scarring and filtration failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of macrophages by Photofrin II during photodynamic therapy

In order to obtain information about the activation of macrophages (M phi s) during photodynamic therapy (PDT), the influence of Photofrin II (Pf II) on the viability of thioglycollate-elicited murine M phi s and the subsequent generation of superoxide anion was studied. Irradiations were performed at an energy density of 5 J cm-2, a power density of 150 mW cm-2 and a wavelength of 405 nm. Viability of M phi s was assessed using the acridine orange-ethidium bromide assay. Superoxide anion generation was determined using ferricytochrome c (cyt c) and nitroblue tetrazolium (NBT) reduction. Our results indicate that the M phi s are highly susceptible to PDT as their viability is decreased to approximately 30% by 1 microgram ml-1 Pf II at the energy density indicated above. Within the first 30 min of addition of the photosensitizer, a reducing agent is generated intracellularly by the stimulation of the M phi s. An extracellular release of superoxide anion does not occur, as measured by the cyt c assay. Preincubation of the cells for 1 or 24 h with Pf II and a second challenge with phorbol myristate acetate (PMA) does not enhance the reduction of NBT. Thus, Pf II exerts an immediate effect on the M phi s which could be interpreted as a first step for subsequent reactions.

Thoracoscopic carbon dioxide laser treatment of bullous emphysema

A new technique of thoracoscopic laser ablation of pulmonary bullae suitable for patients with multiple bullae and diffuse emphysema was developed and assessed in 22 patients. 20 of 22 patients survived. Pre-operative and postoperative functional evaluation is available for the 11 patients followed up for more than a month; at 1 to 3 months postoperatively there were increases in FVC (mean 2.0 litres pre-operatively to 2.7 litres postoperatively, p less than 0.001), in FEV1 (0.74 to 1.06 litres, p = 0.01), and in maximum exercise treadmill times (5.4 min to 8.0 min, p less than 0.01). Postoperative air leaks lasted a mean of 13 days and usually resolved spontaneously. Other complications were bleeding (1 patient) and unilateral acute lung injury (1 patient). These results suggest that selected patients with diffuse emphysema and pulmonary bullae may benefit from thoracoscopic carbon dioxide laser ablation.

Photodynamic therapy of spontaneous cancers in felines, canines, and snakes with chloro-aluminum sulfonated phthalocyanine

This is the first report on the photodynamic treatment with a second-generation sensitizer, chloro-aluminum sulfonated phthalocyanine (CASPc) of spontaneously arising tumors and on the photodynamic therapy (PDT) of snake neoplasms. Each of 10 cats, 2 dogs, and 3 snakes presenting with a variety of tumor types (squamous cell carcinoma, mast cell malignant tumor, and mixed carcinoma/sarcoma) was given an intravenous injection of 1 mg of CASPc per kilogram body weight 48 hours prior to irradiation with 675-nm light. Some larger tumors (greater than 1.5 cm deep) were surgically debulked prior to PDT. No significant systemic toxicity or skin photosensitization was observed in any animal. The tumor responses were comparable to those seen with conventional cryotherapy, hyperthermia, or surgery. PDT with CASPc of these cases led to 67% (12 of 18) complete response, 22% (4 of 18) partial response, and 11% (2 of 18) no response (less than 50% reduction in tumor size). Four cases could not be evaluated. Since the overall tumor response to CASPc is very good, and the problem of skin photosensitivity is nonexistent, it is expected that using CASPc-PDT to eradicate human tumors would also yield comparable results. Further studies with long-term follow-up are necessary to optimize the use of CASPc-PDT in veterinary and human medicine.

Laser trabecular ablation (LTA)

As part of a pilot study for glaucoma surgery, the use of 3 infrared solid state lasers with 4 fiber optic delivery systems to ablate human trabecular meshwork was investigated. Laser trabecular ablation (LTA) was attempted with the Erbium:YAG (2.94 microns), Erbium:YSGG (2.79 microns), and Holmium:YSGG (2.1 microns) lasers. Laser energy was delivered as a single pulse (250 microseconds) by tissue fiber optic contact with low hydroxyl-fused silica (200 and 500 microns), zirconium fluoride (250 microns), or sapphire (250 microns) fiber optics. Total energy required and thermal effects decreased as laser wavelength increased. LTA was best achieved at 2.94 microns (4 mJ total energy; energy densities = 8.2-12.7 J/cm2; pulse length 250 microseconds) with average thermal damage zones of 5.3-10.3 +/- 1.3-2.4 microns (means +/- SDs) to contiguous structures. This finding has potential applications in the surgical treatment of open-angle and congenital glaucoma and may minimize failure rates seen in other types of surgery on the trabecular meshwork where disrupted trabecular meshwork is not removed.

Experimental cholelitholysis with the pulsed tunable dye laser

This study evaluates the pulsed tunable dye laser with wavelength 504 nm, frequency 10 Hz, and pulse width 1.2 microseconds for cholelitholysis. Power of 10-40 kW was directed through a 250-microns quartz fiber optic to ablate 55 gallstones (removed from 14 patients). The fiber was positioned in direct contact with the stones under saline. Power delivery was begun at 10 kW and increased in 10-kW increments until litholysis began. The range of power and energy necessary to fragment the gallstones was evaluated on four common bile ducts (fresh autopsy specimens). Following fragmentation, all stones were analyzed. There were 35 cholesterol stones (3 calcified) and 20 bilirubin stones (4 calcified). Size ranged from 0.012 to 7.56 cm3 (mean 0.96 +/- 1.41 cm3). Energy necessary for fragmentation ranged from 0.4 to 11.2 J (exposure time 1.0-28 s). Power necessary for fragmentation was 20 kW for 2/55 stones and 40 kW for 53/55 stones. At 40 kW (40 mJ/pulse), common bile duct perforation occurred within 1.1 +/- 0.1 s (0.44 +/- 0.04 J). The pulsed tunable dye laser can fragment gallstones of all compositions. The threshold for fragmentation is 40 kW, but common bile duct perforation occurs at this power. We conclude that laser radiation sufficient to fragment gallstones can injure the common bile duct.