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Biomedical subjects

W Ertmer

Publications and source records attributed to W Ertmer.

16 recordsLinked to original sources
PubMed2001

[Optoacoustic tissue alterations for optimizing laser cyclophotocoagulation. Transscleral detection of laser-induced optoacoustic pressure transients].

BACKGROUND: Considerable problems occur in transscleral laser cyclophotocoagulation concerning energy dosage. We investigated the feasibility of localizing the ciliary body by the detection of thermoelastic pressure transients and of supervising on-line the degree of tissue damage during treatment. METHOD: We used a specially designed handpiece to apply short pulsed laser radiation with low energy levels to enucleated bulbs of rabbits. With an adjusted pressure transducer we examined acoustical transients generated in the area of absorption of the ciliary muscle or the pigmented epithelial layer and measured axial resolution of the method at various distances to the corneoscleral limbus. RESULTS: We detected acoustic transients that allowed rough localization of the target area. A marked change in signal was recorded with increasing level of ciliary destruction. CONCLUSION: This procedure can serve as an essential tool in the on-line supervision of the coagulation process. The laser parameters can thus be adjusted optimally to the progress of the treatment.

Acoustics↗
PubMed2000

Wave packet echoes in the motion of trapped atoms.

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by nonadiabatically shifting the potential and stimulate their reoccurrence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate.

Journal Article↗
PubMed2000

Application of ultrashort laser pulses for intrastromal refractive surgery.

BACKGROUND: Recently, laser systems have become available which generate ultrashort laser pulses with a duration of 100-200 femtoseconds (fs). By generating micro-plasmas inside the corneal stroma with fs pulses, it is possible to achieve a cutting effect inside the tissue while leaving the anterior layers intact. The energy threshold to generate a micro-plasma with fs pulses is some orders of magnitude lower than it is for picosecond or nanosecond pulses. This results in a strong reduction of the thermal and mechanical damage of the surrounding tissue. METHODS: With a titanium:sapphire fs laser system, the cutting effect on corneal tissue from freshly enucleated porcine eye globes was investigated with different pulse energies. The irradiated samples were examined by light and electron microscopy. The laser-induced pressure transients and the laser-induced bubble formation were analysed with a broadband acoustic transducer and by flash photography. RESULTS: With fs laser pulses, the extent of thermal and mechanical damage of the adjacent tissue is in the order of 1 microm or below and therefore comparable with the tissue alterations after ArF excimer laser ablation. Using pulse energies of approximately 1-2 microJ and a spot diameter of 5-10 microm, intrastromal cuts can be performed very precisely in order to prepare corneal flaps and lenticules. CONCLUSION: Femtosecond photodisruption has the potential to become an attractive tool for intrastromal refractive surgery.

Animals↗
PubMed1998

A scanning and rotating slit arF excimer laser delivery system for refractive surgery.

PURPOSE: This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF excimer laser (Nidek EC-5000). METHODS: The ablation patterns on polymethylmethacrylate (PMMA) wafers were examined by scanning electron microscopy. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. RESULTS: The scanning and rotating slit delivery system is tolerant of small-beam non-homogeneities. The ablation rate is sensitive to the dynamics of the ablation plume. CONCLUSIONS: Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue.

Cornea↗
PubMed1994

ArF-excimer laser-induced secondary radiation in photoablation of biological tissue.

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200-800 nm. The intensity of secondary radiation in the range of 200-315 nm (UVC and UVB) is approximately 20% of the total intensity at high laser fluences (> 2 J/cm2), and approximately 50% at moderate laser fluences (< 500 mJ/cm2); 10 muJ/cm2 in the UVC and UVB were measured at the sample surface, at fluences (< 1J/cm2) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (> 5 J/cm2) are required. As a consequence, laser-induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field.

Animals↗
PubMed1993

Q-switched CTE:YAG (2.69 microns) laser ablation: basic investigations on soft (corneal) and hard (dental) tissues.

Ablative infrared lasers either show poor transmission in optical fibers (Er:YAG: 2.94 microns; ErCr:YSGG: 2.79 microns or are characterized by potential relevant thermal side effects (Ho:YAG: 2.1 microns). The CTE:YAG laser (Cr,Tm, Er doted YAG) emits radiation at a wavelength of 2.69 microns. Efficiently high optical fiber transmission is accomplished (attenuation: < 8db/m for Low-Hydroxy-Fused-Silica (LHFS): 0.3 ppm). Since the laser can easily be run in the Q-switch mode (pulse duration: 0.5-2.5 microseconds) thermal side effects of tissue interaction were expected to be low. Laser tissue interaction was studied on soft (porcine and human cornea), as well as on hard (human dental) tissue. Histological and micromorphological examinations were performed by light microscopy and scanning electron microscopy. It was found that ablation rates in corneal tissue increased from 5 to 90 microns/pulse with increasing laser fluences (5.5-20 J/cm2). Collateral thermal damage reached as far as 20 +/- 5 microns, and was higher (up to 50 microns) when craters where processed in the contact mode using LHFS-optical fibers. In comparison to soft tissue ablation, hard dental tissue ablation showed very little increase of ablation rate (1-3 microns/pulse) when higher fluences were applied. In dental tissue processing, the ablative effect was accompanied by a luminescence, indicating the presence of plasma. We conclude that the presented CTE:YAG laser can be considered as an effective tool for a variety of laser surgical applications where high power optical fiber delivery is required and where strong thermal side effects are not desired.

Animals↗
PubMed1993

Internal ablative sinostomy using a fiber delivered Q-switched CTE: YAG laser (2.69 microns).

Current trends of laser technology towards low-thermal photoablative pulsed mid-infrared lasers open new, more adequate approaches to experimental surgical procedures which have already been evaluated in the past. Transcorneal laser ablation of the trabecular meshwork (internal sinostomy) in human autopsy eyes was performed with a Q-switched CTE:YAG laser (wavelength: 2.69 microns, pulse width: 1 microsecond). Beam delivery was achieved with conventional optical quartz fibers (Low-hydroxy-fused-silica: 0.3 ppm, 50 cm length, 200 microns diameter). Light- and scanning-electron-microscopy were used for histological examination and micromorphological analysis. By applying two laser pulses (6 J/cm2) to the functional trabecular meshwork, a round sinostomy with a diameter corresponding to the diameter of the fiber-tip was achieved. It was possible to set several internal sinostomies into the chamber angle opposite to the entering paracentesis of the laser fiber-tip. Collateral thermal tissue alteration reached up to 50 microns, and since fiber-tip contact was maintained during laser application, thermal tissue alteration was also found around the opposite wall of Schlemm's canal. At higher energy fluences mechanical (disruptive vaporization) effects were significantly enhanced. It can be concluded, that low-thermal pulsed mid-infrared lasers are adequate instruments to perform transcorneal trabecular ablation (abinterno sinostomy). The laser used in this study (CTE:YAG) bears the advantage that its radiation can easily be delivered in conventional optical quartz fibers.

Fiber Optic Technology↗
PubMed1993

Q-switched CTE:YAG laser sclerostomies on human autopsy eyes.

Experimental laser sclerostomies were performed on human eye-bank eyes with a new mid-infrared solid-state laser that is characterized by adequate optic-fiber transmission and low-thermal tissue interaction. The laser presented herein works with a chromium thulium erbium-doped (CTE): YAG crystal as the active medium, emitting radiation at a wavelength of 2.69 microns. In the Q-switch mode, the pulse duration is tunable from 0.5 to 2.5 microseconds. The maximal energy is 50 mJ/pulse (1-10 Hz). Attenuation of energy transmission in quartz (0.3 ppm) optic fibers is < 8 dB/m (diameter, 200 microns). Absorption depths of 2.69 microns radiation in water is 12.5 microns. In vitro procedures performed were ab-interno and ab-externo full-thickness sclerostomies. Histological and micro-morphological examination was performed by light microscopy and scanning electron microscopy. Collateral tissue damage in processed sclerostomies did not exceed 50(+/- 10) microns at typical fluences (10 J/cm2). In contact guidance, 10-15 laser pulses were required in the full-thickness ab-externo procedure, whereas up to 50 pulses were required in the ab-interno procedure. The number of laser pulses applied corresponded to the length of the filtration canals created. The canal was significantly longer (2.5 +/- 1 mm) in the ab-interno approach than in the ab-externo approach (1 +/- 0.2 mm). The intraocular ostium of the filtration canal in the ab-externo procedure showed enhanced signs of mechanical deterioration. It is concluded that both the wavelength (2.69 microns) and the pulse duration (0.5-2.5 microseconds) of the CTE: YAG laser are appropriate for laser sclerostomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Eye↗
PubMed1992

[Photodynamic laser therapy with antibody-bound dyes. A new procedure in therapy of gynecologic malignancies].

In the present paper, a new therapeutic concept of photodynamic laser therapy using antibody-linked dyes for the treatment of gynecological malignancies is described. So far, HPD (hematoporphyrin derivative) has been employed in this area, but is associated with toxic systemic reactions. We see a solution to this problem in the linking of a systemically non-toxic dye--known to induce photodynamic reactions while not itself being selectively accumulated within tumor cells--to an antibody directed against a selective tumor-associated antigen. The results of our study demonstrate the efficacy of this therapeutic concept as exemplified by the selective destruction of dye-labeled ovarian carcinoma cells by laser light of a defined wavelength (675 nm). The potential of this form of photodynamic therapy extends far beyond its use in ovarian carcinoma.

Antibodies, Monoclonal↗
PubMed1992

[Laser-induced photoacoustic effects in the dentin].

To study photoacoustic effects in dentin caused by UV-laser ablation, laser-induced shockwaves were measured using piezoelectric PVDF films. Above the tissue-specific energy threshold for photoablation the amplitude of the acoustic shock waves is proportional to the applied laser energy density. Laser energy densities of 2 J/cm2 cause pressure amplitudes of 50 bar, densities of 20 J/cm2 cause pressure amplitudes of 1000 bar. To avoid microcracks in dentine the maximum laser energy density to prepare dentin should be limited to approximately 20 J/cm2.

Biophysical Phenomena↗