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Biomedical subjects

M Frenz

Publications and source records attributed to M Frenz.

At least 19 recordsLinked to original sources
PubMed2006

Treatment of haemorrhagic radiation-induced proctopathy using small volume topical formalin instillation.

BACKGROUND: Between 2 and 5% of patients undergoing pelvic radiotherapy develop chronic radiation proctopathy, occurring as a result of damage to the rectal mucosa during the treatment. Rectal bleeding of varying severity can occur as a consequence. There have been no formal trials of treatment for haemorrhagic radiation proctopathy and a variety of methods are currently used. AIM: In a retrospective study of 20 patients treated at a single centre, we assessed the efficacy of small volume topical formalin instillation to control bleeding from radiation proctopathy. METHOD: Patients were treated by a single operator using 20 mL of a 5% solution of formalin instilled into the rectum via a flexible sigmoidoscope for 3 min. Patients were followed up for an average of 22.7 months (range: 2-69). RESULTS: A single session of formalin treatment was effective in 13 of 20 (65%) patients and a further four (20%) patients responded to a second treatment. No complications of the treatment was identified. CONCLUSION: Small volume formalin instillation therapy appears to be safe and effective in the context of haemorrhagic radiation proctopathy. The technique is simple, inexpensive, quick and requires no sedation. We suggest that it should be considered as a first line for patients presenting with this distressing condition.

Administration, Topical↗
PubMed2006

A comparison of laser-ultrasound detection system sensitivity with a broad-band ultrasonic source for biomedical applications.

BACKGROUND: Laser ultrasound detection systems are used for noninvasive imaging of internal structures and function of soft tissues. The detection systems with a high sensitivity can be used for detecting small tumors located deeply in human tissues, such as the breast. In this study, the sensitivity of existing ultrasonic detection systems has been compared experimentally by using thermoelastic waves as a broadband ultrasonic source. METHODS: For the comparison, an optical stress transducer, a polyvinylidene difluoride (PVDF) sheet and a calibrated PVDF needle hydrophone were used. To ensure that all detection systems were interrogated by the same ultrasonic field, a small optical instrument was constructed to fix the generating laser head. The sensitivity was evaluated by measuring signal-to-noise ratios (SNRs) and noise equivalent pressures (NEPs). RESULTS: The PVDF system, with a 4 kPa NEP, has a 22-dB better performance than the optical stress transducer. The optical stress transducer showed nearly the same sensitivity as the hydrophone for detecting ultrasound waves at a 1-cm distance. CONCLUSIONS: PVDF detection system provides a useful tool for imaging of soft tissues because of its high sensitivity and broadband detection range.

Biomedical Technology↗
PubMed2001

Laser solder welding of articular cartilage: tensile strength and chondrocyte viability.

BACKGROUND AND OBJECTIVE: The surgical treatment of full-thickness cartilage defects in the knee joint remains a therapeutic challenge. Recently, new techniques for articular cartilage transplantation, such as mosaicplasty, have become available for cartilage repair. The long-term success of these techniques, however, depends not only on the chondrocyte viability but also on a lateral integration of the implant. The goal of this study was to evaluate the feasibility of cartilage welding by using albumin solder that was dye-enhanced to allow coagulation with 808-nm laser diode irradiation. STUDY DESIGN/MATERIALS AND METHODS: Conventional histology of light microscopy was compared with a viability staining to precisely determine the extent of thermal damage after laser welding. Indocyanine green (ICG) enhanced albumin solder (25% albumin, 0.5% HA, 0.1% ICG) was used for articular cartilage welding. For coagulation, the solder was irradiated through the cartilage implant by 808-nm laser light and the tensile strength of the weld was measured. RESULTS: Viability staining revealed a thermal damage of typically 500 m in depth at an irradiance of approximately 10 W/cm(2) for 8 seconds, whereas conventional histologies showed only half of the extent found by the viability test. Heat-bath investigations revealed a threshold temperature of minimum 54 degrees C for thermal damage of chondrocytes. Efficient cartilage bonding was obtained by using bovine albumin solder as adhesive. Maximum tensile strength of more than 10 N/cm(2) was achieved. CONCLUSIONS: Viability tests revealed that the thermal damage is much greater (up to twice) than expected after light microscopic characterization. This study shows the feasibility to strongly laser weld cartilage on cartilage by use of a dye-enhanced albumin solder. Possibilities to reduce the range of damage are suggested.

Animals↗
PubMed2001

Comparative in vitro study of tissue welding using a 808 nm diode laser and a Ho:YAG laser.

In vitro porcine arteries and veins have been welded end-to-end using either a 808 nm diode laser combined with an indocyanine green enhanced albumin solder, or with a continuous-wave (cw) Ho:YAG laser without biological solder. The vascular stumps were approached to each other over a coronary dilatation catheter in order to obtain a precise alignment and good coaptation. Standard histology revealed for both welding techniques lateral tissue damage between 2 and 3 mm caused by laser-induced heat. Good solder attachment to the tissue was observed by the use of a scanning electron microscope. The vessels soldered with the 808 nm diode laser using albumin solder showed considerably higher tensile strength (1 N compared to 0.3 N) than vessels welded exclusively by Ho:YAG laser radiation. In contrast, leaking pressure (350 +/- 200 mmHg) and bursting pressure (457 +/- 200 mmHg) were found to be independent of the welding technique used. This study demonstrates that fast (total welding time about 2-5 min), stable and tight microvascular anastomosis can be achieved with the use of a dye-enhanced albumin laser soldering technique and an ancillary coronary dilatation catheter.

Anastomosis, Surgical↗
PubMed2001

Internal limiting membrane ablation in pig eyes with the Er:YAG laser under perfluorodecalin.

PURPOSE: The aim of our study was to evaluate the in vivo feasibility of non-contact Er:YAG laser ablation of the internal limiting membrane (ILM), which is recommended for the treatment of macular holes. METHOD: Vitrectomy was performed in 16 eyes of 15 pigs. After perfluorodecalin filling, it was attempted to remove the ILM using a free-running fiber-guided Er:YAG laser (lambda=2.94 microm, pulse length 250 micros, repetition rate 1.7 Hz, radiant exposure 0.6-2.05 J/cm2). The eyes were enucleated either immediately (11 eyes, group 1) or 2 weeks after laser therapy (5 eyes, group 2). Furthermore, in one additional pig eye the retina was carefully treated with microforceps after vitrectomy to assess the damage produced by conventional techniques of ILM peeling. All eyes were examined histologically. RESULTS: Group 1: Nine eyes could be examined (problems with fixation in two eyes). In four of nine eyes, the ILM was either removed or detached, in one eye there was a superficial retinal hemorrhage, and in four eyes the ILM was still intact. In the latter cases, there was no intraoperative whitening or bleeding and no posterior vitreous detachment was present histologically. Group 2: Four eyes (problems with fixation in one eye) could be examined. The ILM was either removed or detached in three eyes. In one eye there was a superficial retinal hemorrhage. In one eye the ILM was not removed and there had neither been intraoperative whitening or hemorrhage nor histologically visible posterior vitreous detachment. In both groups, the nerve fiber layer in treated areas was thicker than in adjacent untreated retina. In one eye the retina was gently manipulated with microforceps in an attempt to perform ILM peeling. This led to damage to all layers of the retina. CONCLUSIONS: Removal of the ILM by Er:YAG laser is possible in vivo. However, the variability of the laser effects calls for further improvement such as a reliable indicator of ablation depth. In any case, any damage to the retina was lesser than that produced by microforceps.

Animals↗
PubMed2001

Temporal backward projection of optoacoustic pressure transients using fourier transform methods.

In medical imaging different techniques have been developed to gain information from inside a tissue. Optoacoustics is a method to generate tomography pictures of tissue using Q-switched laser pulses. Due to thermal and pressure confinement, a short light pulse generates a pressure distribution inside tissue, which mirrors absorbing structures and can be measured outside the tissue. Using a temporal back-projection method, the pressure distribution measured on the tissue surface allows us to gain a tomography picture of the absorbing structures inside tissue. This study presents a novel computational algorithm, which, at least in principle, yields an exact reconstruction of the absorbing structures in three-dimensional space inside the tissue. The reconstruction is based on 2D pressure distributions captured outside at different delay times. The algorithm is tested in a simulation and back-projection of pressure transients of a small absorber and a single point source.

Acoustics↗
PubMed2001

Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model.

BACKGROUND: The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur after laser meniscectomy. The objective of the present study was to evaluate the effect of laser wavelength and energy on cartilage injury in an ex vivo model. METHODS: Fresh bovine articular cartilage was exposed to either holmium:yttrium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Both lasers were operated in a free-running mode and at a pulse-repetition rate of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG at 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by conventional histological analysis and by confocal microscopy. Thermal damage was assessed by determining cell viability. RESULTS: The extent of thermal damage demonstrated by confocal microscopy was much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than that after Er:YAG-laser irradiation, which was associated with almost no damage. In addition, the ablation depth was greater after treatment with the Er:YAG laser than after treatment with the Ho:YAG laser. CONCLUSIONS: In the present study, histological analysis underestimated thermal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery.

Animals↗
PubMed2001

Endonasal and transcanalicular Er:YAG laser dacryocystorhinostomy.

In the last 10 years different types of lasers were used for dacryocystorhinostomy (DCR). Between April 1998 and August 1999, a fibreoptic erbium laser DCR was performed on 12 patients. Eight cases were for a presaccal stenosis and 4 cases for a postsaccal stenosis. An erbium laser with a specially designed handpiece was used endonasaly and transcanaliculary. Preoperative epiphora was present in all patients. Double bicanalicular nasal silicone tubes were placed during surgery in all cases. The 3 cases of postoperative failure included 2 cases of presaccal stenosis and 1 case of the postsaccal group; failure manifested with recurrent epiphora/dacryocystitis; the onset of symptom recurrence varied from 9 weeks to 11 weeks postoperatively. Laser-assisted DCR includes the avoidance of a cutaneous incision, excessive tissue injury, the advantage of short operation time and precision. Suitable indications for the erbium laser are stenoses in the canaliculi, in the sac, but also for bone lacrimal bone cutting.

Adult↗
PubMed2000

Acute and chronic effects of transmyocardial laser revascularization in the nonischemic pig myocardium by using three laser systems.

BACKGROUND AND OBJECTIVE: Transmyocardial laser revascularization (TMLR) improves symptoms in patients with coronary heart disease. It is based on the hypothesis of direct perfusion of ischemic myocardium by means of laser-created channels. Three different lasers were used to study alternative effects on myocardium. STUDY DESIGN/MATERIALS AND METHODS: The present study was conducted to evaluate comprehensively and compare the short and long-term tissue effects and the basic interaction mechanisms of CO2, Ho:YAG, and Er:YAG laser radiation with myocardium. The dynamics of laser-induced impacts in gel used as tissue phantom was visualized by time-resolved flash photography. Pressure measurements performed during perforation of myocardium in vitro revealed the explosive character of the ablation process. Channels made into the left ventricle of normal pig hearts were examined immediately and 6 weeks after creation. RESULTS: Regardless of laser source, all channels became occluded within 6 weeks by scar. Minimal acute thermal damage by Er:YAG laser corresponded to smaller scars. Pulsed Ho:YAG caused stronger tissue tearing than continuous wave CO2 irradiation. An increased volume density of intramyocardial vessels was found about the scars 6 weeks after treatment with all lasers. CONCLUSION: The laser sources permitted to study outcome of pressure effects and thermal damage in vivo. There were only minor differences between the three laser systems used. Rapid channel occlusion suggests that rather than revascularization, subsidiary physiologic tissue effects elicited by the thermal, oxidative, or mechanical action of the laser impact may contribute to the beneficial clinical effects of TMLR.

Animals↗
PubMed2000

Erbium: YAG laser ablation of retinal tissue under perfluorodecaline: determination of laser-tissue interaction in pig eyes.

PURPOSE: To evaluate the effect of Er;YAG laser on pig retina using a perfluorodecaline/retina interphase with the goal of precisely determining the extent of retinal tissue ablation. METHODS: Free running (tau = 250 microsec) Er:YAG laser pulses were transmitted through a zirconium fluoride (ZrF4) fiber guarded by quartz rod (d = 1000 microm). Laser pulses were applied to the retinal surface of enucleated pig eyes. Eyes were mounted in a specially designed rotating sample holder. The fiber probe was elevated 1.0 +/- 0.3 mm above the retinal surface with perfluorodecaline serving as transmitting medium. The laser energy was applied in a circular pattern with a radius of 3.0 mm. Radiant exposures were set to 1, 3, 5, and 10 J/cm2. RESULTS: Tissue ablation linearly increased with radiant exposure from 3.2 +/- 3.7 microm at 1 J/cm2 up to 40.9 +/- 12.9 microm at 10 J/cm2. Thermal tissue changes extended 70 +/- 10 microm vertically into the retina and 25 +/- 5 microm horizontally. Distortion of outer photoreceptor segments was noticed when the retina was exposed to radiant exposures of 3 J/cm2 or higher. CONCLUSIONS: The Er:YAG laser in combination with perfluorodecaline produced precise ablation of the pig retina, which suggests the feasibility of this technique for safe ablation of epiretinal membranes.

Animals↗
PubMed1999

Advantages and dangers of erbium laser application in stapedotomy.

Among different types of lasers, the erbium laser exhibits particularly favourable characteristics for ear surgery. Experiments with application of erbium laser pulses to the isolated stapes connected to an inner ear model confirmed that there was virtually no thermal effect to the inner ear liquid and that the border damage zone on the stapes footplate perforation did not exceed 5-10 microm. Erbium laser pulses, however, produce pressure waves due to the explosive ablation of tissue. Pulses of 10 to 17 J/cm2 producing pressure waves between 140 and 160 dB appear to be a limit for clinical application. With these criteria, an in-house built erbium YAG laser with a fiberoptic delivery device was used in 15 patients for stapedotomy. A special microhandpiece, where a zirconium fluoride fiber was connected to a quartz tip, was developed. In addition, three patients had stapedotomy with a commercially available Zeiss (Opmi TwinER) microscope equipped with a micromanipulator-operated erbium laser beam. One year after surgery, the air-bone gap was closed in all patients to within 20 dB between 0.5 and 3 kHz with only minor permanent bone conduction threshold losses (< 20 dB). However, we observed an immediate postoperative middle and high frequency loss of up to 75 dB on bone conduction threshold measurements 2 h after surgery, suggesting an acoustic traumatization by the erbium laser. This threshold shift recovered close to preoperative values within 6 h. These observations prompted us to discontinue the clinical use of erbium laser for stapedotomy until the problem of temporary acoustic traumatization is resolved.

Adult↗
PubMed1997

Laser-tissue interaction during transmyocardial laser revascularization.

BACKGROUND: The clinical procedure known as transmyocardial revascularization has recently seen its renaissance. Despite the promising preliminary clinical results, the associated mechanisms are subject to much discussion. This study is an attempt to unravel the basics of the interaction between 800-W CO2 laser radiation and biological tissue. METHODS: Time-resolved flash photography was used to visualize the laser-induced channel formation in water and in vitro porcine myocardium. In addition, laser-induced pressures were measured. Light microscopy and birefringence microscopy were used to assess the histologic characteristics of laser-induced thermal damage. RESULTS: The channel depth increased logarithmically with time (ie, with pulse duration) in water and porcine myocardium. Pressure measurements showed the occurrence of numerous small transients during the laser pulse, which corresponded with channel formation, as well as local and partial channel collapse during the laser pulse. Twenty millimeters of myocardium was perforated in 25 ms. Increasing the pulse duration had a small effect on the maximum transversable thickness, but histologic analysis showed that thermal damage around the crater increased with increasing pulse duration. CONCLUSIONS: Several basic aspects of the interaction of high-power CO2 laser radiation with myocardial tissue and tissue phantoms were studied in vitro. Although the goal of this study was not to unravel the mechanisms responsible for the beneficial effects of transmyocardial revascularization, it provided important information on the process of channel formation and collapse and tissue damage.

Animals↗
PubMed1997

Mucus quality on horse tracheal epithelium: microscopic grading based on transparency.

The aim of this ex-vivo study on excised tracheas of healthy horses was to characterise the microscopic heterogeneity of mucus quality by a visual grading system based on transparency and to determine whether differences in mucus quality, assessed by a visual grading system, influence tracheal mucus velocity (TMV). Small pieces of each trachea were mounted into a humidified chamber under a microscope. Mucus quality was visually subdivided into four grades (MG) and ciliary beat frequency and TMV were determined. Mucus on excised horse tracheal epithelium does not form a homogenous layer. We observed flakes and streams of a great heterogeneity, which by the characteristic of transparency can be qualified and quantified. Visual characterisation of mucus was able to explain a considerable part of TMV variation. Therefore, it can be considered as a suitable non-invasive method for the evaluation of mucus quality and transport effectiveness.

Animals↗
PubMed1996

Temperature and pressure effects during erbium laser stapedotomy.

BACKGROUND AND OBJECTIVES: Laser-assisted stapedotomy has become a well-established alternative to the mechanical drilling method. The goal of this study is to quantify the mechanical and thermal tissue effects and to determine optimum erbium laser parameters for safe clinical treatment. STUDY DESIGN/MATERIALS AND METHODS: On an inner ear model, time-resolved pressure measurements and Schlieren optical flash photography were performed during the perforation of the stapes foot plate using an erbium laser at 2.79 microns. The laser radiation was transmitted via an optical zirconium fluoride fiber. The laser-treated foot plates were investigated by light microscopy and scanning electron microscopy to visualise the laser-induced tissue effects. RESULTS: Perforation of the stapes foot plate can be performed with a few erbium laser pulses with high precision and a thermal damage zone of < 10 microns. Strong pressure transients were found to be generated by the bone ablation process and the collapse of a vapor channel created in the perilymph after fenestration. CONCLUSION: From the comparison of the laser-induced pressure with the limit graph to avoid hearing defects published by Pfander, an unobjectionable use of the erbium laser is deduced for fluences < 10 J/cm2. The erbium laser seems to represent an ideal instrument for middle ear surgery with all the advantages (precision, fiber optic transportable, high ablation efficiency, safety) desired for clinical application.

Erbium↗
PubMed1996

Effect of pulse duration on bubble formation and laser-induced pressure waves during holmium laser ablation.

BACKGROUND AND OBJECTIVE: One concern during laser ablation of tissue is the mechanical injury that may be induced in tissue in the vicinity of the ablation site. This injury is primarily due to rapid bubble expansion and collapse or due to laser-induced pressure waves. In this study, the effect of laser pulse duration on the thermodynamics of bubble formation and accompanying acoustic pressure wave generation has been investigated. STUDY DESIGN/MATERIALS AND METHODS: Q-switched holmium:YAG laser pulses (pulse duration 500 ns, pulse energy 14 mJ) and free-running holmium:YAG laser pulses (pulse duration 100-1,100 microseconds, pulse energy 200 mJ) were delivered in water and tissue phantoms via a 200- and 400-microns fiber, respectively. The tissue phantoms consisted of polyacrylamide gels with varying mechanical strengths. Bubble formation was recorded with a fast flash photography setup, while acoustic transients were measured with a needle hydrophone. RESULTS: It was observed that, as the pulse length was increased the bubble shape changed from almost spherical for Q-switched pulses to a more elongated cylinder shape for longer pulse durations. The bubble expansion velocity was larger for shorter pulse durations. Only the Q-switched pulse induced a measurable thermo-elastic expansion wave. All pulses that induced bubble formation generated pressure waves upon collapse of the bubble in gels as well as in water. However, the magnitude of the pressure wave depended strongly on the size and geometry of the induced bubble. CONCLUSION: The magnitude of the collapse pressure wave decreased as laser pulse duration increased. Hence it may be possible to reduce collateral mechanical tissue damage by stretching the holmium laser pulse.

Acoustics↗
PubMed1996

Experimental erbium laser surgery in the guinea pig cochlea: its use in the study of afferent cochlear neurotransmitters.

Microiontophoretic techniques were used to examine the changes in activity of inner half cell afferents in the guinea pig following circumscribed penetration of cochlear bone with erbium:YSGG laser pulses. Neuronal responses to the application of the glutamate agonists N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) before laser use and after return to normal spontaneous activity were equivalent, implying total reversibility of the changes occurring. Suppression of laser-induced hair cell activity was possible with NMDA and AMPA receptor antagonists and lasted 10-15 min. These findings suggest a transmitter-related increase of neuronal activity. Our results show that use of the erbium laser in inner ear microsurgery might be possible with low risk if the amount of energy applied is kept under a safe limit of 10 J/cm2.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1996

Treatment of human papillomavirus-associated vulvar disease with the CO2-laser. Physical and histological aspects with use of a new scanning device, the SwiftLase.

The CO2-laser has a successful record in treatment of extensive, refractory vulvar condylomas and vulvar intraepithelial neoplasia. A prerequisite for optimal use of the laser is careful preoperative diagnosis and optimized surgical technique based upon the exact knowledge of the interaction process between laser radiation and tissue. Using a new CO2-laser scanning device, the Sharplan Swift-Lase, this in-vivo study analyses the effects of CO2-laser parameters [average power density (PD), beam size and exposure time] on vulvar skin to determine optimum laser settings. Our histomorphometric analyses reveal a minimal skin destruction (ablation depth 40 microns, extent of irreversible thermal damage 80 microns to 120 microns) after application of the CO2-laser energy with the SwiftLase using a PD of 1000 W/cm2 with a beam size of 1 mm diameter. Previous CO2-laser application techniques required low PD (200 W/cm2 to 750 W/cm2) and a larger beam size (1.5 mm to 2 mm) moving over the epithelial surface as fast as possible to obtain a precise skin destruction. The SwiftLase allows the laser beam to be moved slowly with a beam size of 1 mm and significantly higher PD (up to 5000 W/cm2). These advantageous application conditions guarantee precise, homogeneous vulvar skin treatments with minimal thermal damage to the surrounding normal skin. The SwiftLase enables a less experienced colposcopists to perform vulvar CO2-laser surgery.

Carcinoma in Situ↗