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At least 37 records · Page 2Linked to original sources
PubMed2000

Influence of the laser fluence in infrared matrix-assisted laser desorption/ionization with a 2.94 microm Er : YAG laser and a flat-top beam profile.

The dependence of the signal intensity of analyte and matrix ions on laser fluence was investigated for infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry using a flat-top laser beam profile. The beam of an Er : YAG laser (wavelength, 2.94 microm; pulse width, 90 ns) was coupled into a sapphire fiber and the homogeneously illuminated end surface of the fiber imaged on to the sample by a telescope. Three different laser spot sizes of 175, 350 and 700 microm diameter were realized. Threshold fluences of common IR matrices were determined to range from about 1000 to a few thousand J m(-2), depending on the matrix and the size of the irradiated area. In the MALDI-typical fluence range, above the detection threshold ion signals increase strongly with fluence for all matrices, with a dependence similar to that for UV-MALDI. Despite the strongly different absorption coefficients of the tested matrices, varying by more than an order of magnitude at the excitation laser wavelength, threshold fluences for equal spot sizes were found to be comparable within a factor of two. With the additional dependence of fluence on spot size, the deposited energy per volume of matrix at threshold fluence ranged from about 1 kJ mol(-1) for succinic acid to about 100 kJ mol(-1) for glycerol.

Angiotensin I↗
PubMed1999

Laser shaping of corneal transplants in vitro: area ablation with small overlapping laser spots produced by a pulsed scanning laser beam using an optimizing ablation algorithm.

Area laser lathing and trephination of donor corneas is used to produce different types of grafts for human transplantation. 193 nm (ArF excimer) laser radiation is used, since this is known to give a non-thermal laser-tissue interaction with a minimal zone of tissue damage. To guarantee the highest degree of flexibility concerning the overall shape of the grafts as well as their thickness profiles, we use a small (compared with the area to be ablated) scanning laser spot. For area lathing of the tissue we have developed a new ablation algorithm (optimized scanning laser ablation, OSLA) that can be applied to lathe and perforate any tissue--with concave (as in this application), convex or plane surface geometry--where surface precision and smoothness are key issues. Using OSLA with the Excimer Laser Corneal Shaping System (a tool for in vitro fabrication of all kinds of corneal transplants like donor buttons for keratoplasty, lamellar grafts for epikeratoplasty and refractive lenticules) enabled us to produce all types of corneal grafts with very high precision. This is considered to be a major improvement towards the production of refractive lenticules.

Algorithms↗
PubMed2006

New improvements in methane detection using a Helmholtz resonant photoacoustic laser sensor: a comparison between near-IR diode lasers and mid-IR quantum cascade lasers.

Atmospheric methane was detected by combining a photoacoustic (PA) sensor with several lasers emitting in both the near- and mid-infrared spectral ranges to check the achievable detection limits. The PA spectrometer is based on differential Helmholtz resonance. Near-infrared telecommunication-type laser diodes of increasing power, from Sensors Unlimited Inc. and Anritsu, were first used to scan the 2 nu(3) band of CH(4) near 1.65 microm. The best achieved detection limit is 0.15 ppm of methane at atmospheric pressure and with a 1s integration time. The PA sensor was then operated in conjunction with a quantum cascade laser from Alpes Lasers emitting near 7.9 microm on the nu(4) band of CH(4). The achieved detection limit is then of 3 ppb. The dramatic improvement in the detection limit obtained with the QC laser is due to the stronger optical power as well as to the capability of reaching the fundamental bands of methane lying in the mid-infrared spectral range.

Acoustics↗
PubMed2002

Laser blepharoplasty: diamond laser scalpel compared to the free beam CO2 laser.

BACKGROUND: Blepharoplasty has long been employed for functional and cosmetic purposes. Different modalities have been utilized to incise and remove excess eyelid tissue in an attempt to improve surgical technique. OBJECTIVE: This study compares a free beam CO2 laser to a diamond surgical scalpel combined with a CO2 laser for performance of blepharoplasty. METHODS: Ten patients underwent bilateral upper lid blepharoplasty. One side was randomly assigned to the free beam CO2 laser technique, while the other side was performed with the diamond laser scalpel. Intraoperative surgical times and hemostasis were measured. Masked observers assessed postoperative parameters at day 1, week 1, week 2, week 4, and month 4. These assessments were analyzed clinically and statistically. RESULTS: The two modalities produced similar results for the intraoperative and postoperative parameters studied. CONCLUSION: The diamond laser scalpel has the advantage of tactile feedback and the option of use without coagulation.

Blepharoplasty↗
PubMed2003

Combined ultrapulse CO2 laser and Q-switched alexandrite laser compared with Q-switched alexandrite laser alone for refractory melasma: split-face design.

BACKGROUND: : Melasma is common and can cause major psychological impact. To date, the mainstay of treatment, including various hypopigmenting agents and chemical peels, is ineffective and can cause adverse effects. Laser is a new approach and is yet to be explored for its efficacy and safety. OBJECTIVE: : To compare combined Ultrapulse CO2 laser and Q-switched alexandrite laser (QSAL) with QSAL alone in the treatment of refractory melasma. METHODS: : Six Thai females were treated with combined Ultrapulse CO2 laser and QSAL on one side of the face and QSAL alone on the other side. The outcome was evaluated periodically for up to 6 months using the modified Melasma Area and Severity Index score and the modified Melasma Area and Melanin Index score. RESULTS: : The side with combination treatment had a statistically significant reduction of both scores. On the QSAL side, the score reduction was not significant. Two cases developed severe postinflammatory hyperpigmentation and were effectively treated with bleaching agents. Transient hypopigmentation and contact dermatitis were observed with the combination treatment side. CONCLUSIONS: : Combined Ultrapulse CO2 laser and QSAL showed a better result than QSAL alone but was associated with more frequent adverse effects. Long-term follow-up and a larger number of cases are required to determine its efficacy and safety for refractory melasma.

Adult↗
PubMed1981

Comparative histological studies of the tunable dye (at 577 nm) laser and argon laser: the specific vascular effects of the dye laser.

This study compares the histological changes occurring after argon laser and dye laser (operating at 577 nm) treatment of normal human skin. The initial effect of the argon laser is a diffuse nonspecific epidermal and upper dermal necrosis with subsequent cell death and a neutrophilic response at 48 hr. These changes occur at 15 joules/cm2 and their extent closely correlates with the energy applied. In sharp contrast, the immediate effect of the dye laser is erythrocyte aggregation, vessel rupture, and hemorrhage. At 48 hr, there is a pattern of acute vasculitis in the upper dermis and a prominent perivascular neutrophilic response in the mid-dermis. Focal epidermal necrosis does occur but is relatively minimal, while skin appendages and collagen are preserved. The energy to produce these alterations is relatively small, approximately 3 J/cm2. Thus, the dye laser at 577 nm can selectively damage the cutaneous vascular plexus and may provide a basis for treatment of cutaneous vascular lesions.

Argon↗
PubMed1998

Holmium:YAG laser resection of the prostate versus visual laser ablation of the prostate and transurethral ultrasound-guided laser induced prostatectomy: a retrospective comparative study.

BACKGROUND: Transurethral resection of the prostate (TUR-P) is the gold standard for treating symptomatic benign prostatic hyperplasia (BPH) despite some perioperative morbidity. As a minimally-invasive alternative to TUR-P, a neodymium:YAG laser, and more recently a holmium:YAG laser, have been used in transurethral surgery for BPH. In order to assess the safety and efficacy of various BPH treatments, the outcome in patients treated with transurethral ultrasound-guided laser induced prostatectomy (TULIP), visual laser ablation of the prostate (VLAP) and holmium:YAG laser resection of the prostate (HoLRP) were retrospectively compared. METHODS: From May 1995 to August 1996, 60 patients with symptomatic BPH underwent TULIP (n=20), VLAP (n=20), and HoLRP (n=20). All patients were evaluated preoperatively and at 1 and 3 months postoperatively by the International Prostate Symptom Score (IPSS), the IPSS quality-of-life score (QOL), maximum flow rate (MFR), prostate volume, and residual urine volume. RESULTS: The preoperative mean IPSS was 18.5, 19.3, and 19.6 and the mean MFR was 6.3, 6.9, and 6.1 mL/sec in the TULIP, VLAP, and HoLRP groups, respectively. At 1 month after surgery, the mean IPSS was 10.2, 9.5, and 4.7 and the mean MFR was 9.6, 13.4, and 18.7 mL/sec while at 3 months the mean IPSS was 6.2, 6.1, and 3.6 and the mean MFR was 14.1, 16.0, and 21.5 mL/sec in patients treated with TULIP, VLAP, and HoLRP, respectively. No serious complication occurred in any patient. CONCLUSION: Although HoLRP requires expertise, it appears to be a promising treatment modality for BPH.

Aged↗
PubMed1989

The Glaucoma Laser Trial. I. Acute effects of argon laser trabeculoplasty on intraocular pressure. Glaucoma Laser Trial Research Group.

The Glaucoma Laser Trial Research Group has examined the acute effects of argon laser trabeculoplasty on immediate change in intraocular pressure and the formation of peripheral anterior synechiae among the 271 eyes assigned to argon laser trabeculoplasty as initial treatment for primary open angle glaucoma. Argon laser trabeculoplasty was administered in two sessions. Intraocular pressure rises of greater than 5 mm Hg occurred in 34% of eyes after one or both of the treatment sessions; intraocular pressure rises of greater than 10 mm Hg occurred in 12%. Eyes that had an intraocular pressure rise after the first session were more likely to have a rise after the second session than eyes with no rise after the first session. Among the many patient, eye, and treatment characteristics examined, only pigmentation of the trabecular meshwork was strongly associated with intraocular pressure rises. Forty-six percent of eyes developed greater than or equal to 1 degree of peripheral anterior synechiae. Brown iris color and posterior placement of laser burns were associated with higher rates of peripheral anterior synechiae formation.

Adult↗
PubMed2006

Laser and self-Raman-laser oscillations of PBMoO4:Nd3+ crystal under laser diode pumping.

Different regimes of laser operation and stimulated Raman scattering (SRS) for a laser diode (LD)-pumped PbMoO4:Nd3+ crystal have been investigated. Under 1.5 W LD pumping, the output power of the PbMoO4:Nd3+ laser in the free-running mode at 1056 nm reached 0.65 W with a slope efficiency of up to 53%. Using different LiF: F-2 saturable absorbers, we achieved a maximum pulse energy of 11 microJ at a 1.4 ns pulse duration and a maximum output power of 0.35 W (10 microJ) at a 7 ns pulse width in the passively Q-switched mode. PbMoO4:Nd3+ self-Raman-laser operation at 1163 nm (first Stokes) was obtained for the first time, to our knowledge. The self-Raman-laser output pulse energy was measured to be as high as 6 microJ and the pulse duration was estimated to be shorter than 500 ps.

Journal Article↗
PubMed1997

[Transmyocardial laser revascularization. Histopathology of laser channels in 10 postoperatively deceased patients 1 to 18 days after treatment with a CO2 laser].

TMLR (Transmyocardial laser revascularization) is a disputed cardiosurgical technique available in Europe since 1994 that aims to deliver additional blood flow to ischemic myocardium from the left heart chamber. Goal of our study is morphological examination of laser channels in human hearts to answer the questions: Are there patent laser channels with communication to the left chamber and to intramural vessels? We examined hearts of 10 patients who died during the first 18 days after TMLR. Channels were examined in histological serial sections under the light microscope. Laser channels in the first days postoperatively have a lumen diameter of about 1 mm and are surrounded by coagulation necrosis about 500 microns thick. Despite phagocytic removal of necrotic tissue the lumen diameter decreases during the following two weeks. Open intramyocardial channels can be shown in all patients. These channels communicate with intramural vessels, but in no instance with chamber lumen. Our results suggest that clinical benefits are based on improved distribution of coronary blood. Additional blood is not delivered from left chamber lumen to the myocardium. However, our patients represent the small subgroup of the decreased. If similar observations can be made in the majority of patients living symptom free after TMLR remains open.

Angina Pectoris↗
PubMed1997

Laser neck and jowl liposculpture including platysma laser resurfacing, dermal laser resurfacing, and vaporization of subcutaneous fat.

BACKGROUND: Submental tumescent liposculpture alone is not able to achieve the results of rhytidectomy. OBJECTIVE: To improve the results of submental tumescent liposculpture new laser techniques were developed to provide maximum cosmetic results with minimal disability and rapid recovery. METHODS: Extensive tumescent liposculpture of the lower face, jowls, neck, and subplatysma was performed on 100 patients. Platysma fascia and undersurface of the dermis of the neck were laser resurfaced. Septae and platysma insertions were separated. Subcutaneous fat was laser vaporized. Platysma muscle was plicated. Where indicated, a chin implant was inserted. RESULTS: Clinical results far superior to tumescent liposculpture alone included improved cervico-mental angle and marked reduction in laxity of the neck skin, platysma banding, and horizontal neck creases. Patients recovered rapidly with minimal to no bruising, scarring, or pain. CONCLUSION: Laser neck and jowl liposculpture produces superior results to standard submental tumescent liposculpture with no increase in recovery time and no complications to date.

Adipose Tissue↗
PubMedDate not supplied

Experimental results of preparing laser-shaped stromal implants for laser-assisted intrastromal keratophakia in extremely complicated laser in situ keratomileusis cases.

PURPOSE: To evaluate the feasibility of laser-shaped stromal implants from a donor eye for correcting extreme high hyperopia with irregular astigmatism and an exceptionally thin corneal bed. METHODS: Thirty-one fresh enucleated porcine eyes were used. The procedure was initiated with mechanical de-epithelialization followed by a lamellar cut with a microkeratome, resulting in a hinged flap (thickness 150 microm, diameter 9.5 mm). The cornea was photoablated with PRK treatment for +8.00 D sphere (hyperopic lenticule group) and -5.00 D sphere (myopic group) by a scanning spot excimer laser. A customized scanning software algorithm was used to create a circumferential cut with a 6.5-mm internal diameter. The lenticule was removed from the stromal bed and measured by a surface profiling system. A clinical case was performed on a patient with previous LASIK and highly irregular hyperopic astigmatism to verify the clinical utility of the experimental setup. RESULTS: Under the microscope, lenticules seemed round, regular, and transparent. The average surface profile of porcine corneas demonstrated good parabolic shape with individual variations as large as 30 microm, probably due to the corneal size and curvature differences between the porcine eye and the human eye--for which the microkeratome is designed. The patient underwent a topography-guided treatment after laser-assisted intrastromal keratophakia (LAIK) and 1-month follow-up showed an increase of UCVA, BSCVA, and central corneal thickness. CONCLUSIONS: The use of modern scanning-spot excimer lasers and microkeratomes enabled us to produce stromal lenticules of good quality, which might be acceptable to implant into a human eye.

Adult↗
PubMed1990

Direct laser and laser-thermal irradiation of normal canine coronary arteries: implications for laser delivery methods.

Clinical use of laser recanalization has been mostly limited by arterial perforation. Two modifications of the optical fiber were used to decrease the perforation rate: (1) a guidewire to align the fiber in a coaxial position with the vascular lumen and (2) encapsulation of the optical fiber tip with a metal cap. Fourteen dogs were studied. Argon laser radiation was delivered through optical fibers, 9 with a 1.7-mm metal encapsulated fiber (Laserprobe-PLR,¿ Trimedyne, Santa Ana, CA) and 5 with a 2-mm metal encapsulated fiber with a window at the tip (Spectraprobe-PLR). Three dogs served as control, and no guidewire was used. In 11 dogs, laser irradiation was done either in advancing the probe or on pullback over a guidewire. Energy used ranged from 25 to 50 J. In vitro, this raised the probe temperature in blood to a maximum of 500 degrees C. Arterial perforation occurred in 2 of 4 lased arteries without guidewire (p less than 0.05). There was no difference in perforation rated comparing the Laserprobe (1 out of 17 arteries) and Spectraprobe (1 out of 8 arteries) (p greater than 0.05). At high laser energy (50 J), there was an increased incidence of thrombus formation, which appeared to be associated with adherence of the metal cap to the arterial wall (3 out of 6 vs. 1 out of 19, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Laser↗
PubMed1989

Laser recanalization, laser assisted balloon angioplasty and laser angioplasty.

The efficacy of laser recanalization (LR), laser assisted balloon angioplasty (LABA) and laser angioplasty (LA) was evaluated. These procedures were performed a total of 55 times upon 49 patients who had occlusive arterial disease of a lower extremity with a history of incapacitating, intermittent claudication, rest pain or loss of tissue, or all three. Patients with lesions through which a guide wire could be passed were eliminated from this study. Two lesions in the common iliac artery, 44 in the superficial femoral artery, seven in the popliteal artery and two in the infrapopliteal artery were studied. Thirty-nine of 55 lesions (71 per cent), including 12 of 12 stenoses and 27 of 43 occlusions (63 per cent), were successfully recanalized. None of the seven total length occlusions were successfully recanalized (p less than 0.001); perforation occurred in four. Bypass procedures were required in six of 13 and two of 25 lesions treated by LR and LABA, respectively (p less than 0.05). All patients with lesions successfully recanalized using LR, LABA and LA were observed for a period of 15 days to six months, with an 82 per cent patency rate (32 of 39). Total length occlusions are not a good indication for treatment with currently available laser techniques. The addition of balloon dilation in LR decreased the requirement for bypass procedures in a significant number of patients.

Angioplasty, Balloon↗
PubMed1994

[The CO2 laser in ophthalmology. I. Physical and biological properties and indications for the 20-C CO2 laser made by Pfizer Laser Systems].

The authors describe physical and biological properties of a CO2 laser operating in the infrared area (wave length 10,600 m). The authors discuss the use of this laser in ophthalmology and draw attention to its advantages as well as shortcomings. They describe the apparatus 20-C of Pfizer Laser Systems, incl. safety measures required for operation of the CO2 laser.

Carbon Dioxide↗
PubMed2005

A comparison of two laser-based methods for determination of burn scar perfusion: laser Doppler versus laser speckle imaging.

UNLABELLED: Laser Doppler perfusion imaging (LDI) is an established technique for early assessment of burn depth to help determine a course of treatment. Laser speckle perfusion imaging (LSPI) is an alternative laser based, non-invasive perfusion monitoring technique that offers rapid and high resolution images of tissue. We have evaluated the ability of the LSPI instrument in determining and monitoring burn scar perfusion over time and compared it with the LDI instrument as a standard. METHODS: Ten patients with hypertrophic burn scars (time since injury: 1-8 months) were recruited. Burn scars were scanned with both instruments (LSPI and LDI) monthly over a period of 11 months. Clinical grading of the burn scars was assessed on every scan date using the Vancouver burn scar scale. RESULTS: Comparison of the perfusion values determined by each instrument shows a strong positive correlation, r2=0.86 (n=63). Each instrument's output also correlated significantly with the clinical grading of the scar, indicating the expected decrease in perfusion as the clinical condition of the scars improved with time. SIGNIFICANCE: The new LSPI instrument compared favorably with the established LDI instrument, yielding similar results. The considerably faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor near real-time responses to mechanical or pharmacological interventions to study dynamic vascular changes to burn damaged tissues.

Adult↗
PubMed1998

Holmium laser resection of the prostate versus neodymium:yttrium-aluminum-garnet visual laser ablation of the prostate: a randomized prospective comparison of two techniques for laser prostatectomy.

OBJECTIVES: To directly compare holmium laser resection of the prostate (HoLRP) with neodymium:yttrium-aluminum-garnet visual laser ablation of the prostate (VLAP), which represent two fundamentally different methods of laser prostatectomy. METHODS: In a randomized, prospective comparison, a total of 44 men with symptomatic benign prostatic hyperplasia (BPH) were treated with either HoLRP or VLAP. Standard preoperative assessment included American Urological Association (AUA) symptom score, peak urinary flow rates (Qmax), ultrasound prostate volume, and residual urine measurements. Pressure-flow urodynamics were performed preoperatively and at 3 months postoperatively. Intraoperative and perioperative factors were assessed. The patients were followed at 1, 3, 6, and 12 months following the procedure. RESULTS: There were no significant differences between the patient groups for any preoperative parameter. The mean total operating time was longer in the HoLRP group (52 minutes) compared with the VLAP group (41 minutes) (P <0.01). The mean catheter times were 1.4 days (HoLRP) and 11.6 days (VLAP) (P <0.001). These times included the 9% of patients undergoing HoLRP and 36% of patients undergoing VLAP who required recatheterization. Immediate postoperative dysuria scores were higher in the VLAP group compared with the HoLRP group. There were no significant differences in AUA scores between the two treatment groups at any postoperative interval. The Qmax values were greater at follow-up in the HoLRP group, but statistical significance was not achieved at 12 months. However, both PdetQmax and Schäfer grade measurements taken at 3 months postoperatively were significantly lower in the patients undergoing HoLRP. Three patients (14%) required reoperation in the VLAP treatment arm but no patient who underwent HoLRP has required reoperation to date. CONCLUSIONS: HoLRP results in significantly improved patient outcomes compared to VLAP.

Adult↗