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Biomedical subjects

B Jean

Publications and source records attributed to B Jean.

At least 19 recordsLinked to original sources
PubMed2006

Melanin granule models for the processes of laser-induced thermal damage in pigmented retinal tissues. I. Modeling of laser-induced heating of melanosomes and selective thermal processes in retinal tissues.

The computer modeling was applied for investigation of the processes of laser-induced tissue damage. The melanin granule models for the processes of laser-induced thermal damage and the results of computer modeling of the optical, thermophysical, and thermochemical processes during selective laser interaction with melanoprotein granules (melanosomes) in retinal pigment epithelium are presented in this paper. Physical-mathematical model and system of equations are formulated which describe thermal interaction processes for "short" laser pulses of duration t (p)<10(-6) s and for " long' pulses of duration t(p) > 10(-6) s. Results of numerical simulation of the processes give the space-time distributions of temperature and degrees of thermodenaturation of the protein molecules inside and around melanosomes and in the volume of irradiated tissues. Energy absorption, heat transfer and thermochemical (thermodenaturation, coagulation) processes occurring during the interaction of laser pulses with pigmented spherical and spheroidal granules in heterogeneous tissues are theoretically investigated. The possibility for selective interaction of short laser pulses with pigmented granules is discussed which results in the formation of denaturation microregions inside and near the pigmented granules (granular thermodenaturation) without origination of a continuous macroscopic thermodenaturation lesion in tissue. Analytical model of heating of single spherical and spheroidal granule under laser pulse is presented. Simple equations for time dependencies of particle temperature are obtained. The presented results are of essential interest for laser applications in and can be used for investigation of laser interaction with pigmented tissues in different fields of laser medicine.

Computer Simulation↗
PubMed2006

Giant and large peripheral cerebral aneurysms: etiopathologic considerations, endovascular treatment, and long-term follow-up.

BACKGROUND AND PURPOSE: Giant/large peripheral cerebral aneurysms beyond the circle of Willis and middle cerebral artery (MCA) bifurcation are rare lesions, their etiopathogenesis is not completely elucidated, and their treatment is often difficult. We reviewed the etiopathologic findings available in the literature and report the results and long-term follow-up in 10 patients with a giant/large peripheral aneurysm treated by parent artery occlusion. METHODS: Four aneurysms were on the MCA, 2 on the anterior cerebral artery, and 4 on the posterior cerebral artery (PCA). Two patients presented with bleeding. An occlusion test was performed in 7 patients. Occlusion of the parent artery was performed by using coils in 8 patients; and liquid coils and glue, in 2. Imaging follow-up was available from 1.5 to 4.5 years; and clinical outcome, from 1.5 to 7 years. RESULTS: All aneurysms were excluded. One patient developed a partial homonymous hemianopsia after PCA occlusion. A transient deficit was observed in 2 other patients. In the partially thrombosed aneurysms, follow-up imaging showed shrinkage of the thrombosed compartment of the aneurysm and disappearance of the mass effect. No patient experienced progression of symptoms and/or bleeding during the follow-up period. At long-term follow-up, 6 patients presented with a modified Rankin Scale score of 0; 3, with score of 1; and 1, with score of 2. CONCLUSION: The endovascular occlusion of the parent artery appears a relatively safe and efficacious technique in the treatment of these lesions. Long-term follow-up studies confirm persistent exclusion of the aneurysm and good clinical tolerance to the vessel occlusion.

Adolescent↗
PubMed2005

[Acutely ruptured intracranial aneurysms treated with GDC coils. Results from a single center over a period of 5 years].

PURPOSE: We prospectively reviewed the clinical results of acutely ruptured cerebral aneurysms treated with GDC over a 5 year period, in order to characterize death and dependency factors. METHODS: Between 1997 and 2002, 229 patients (254 aneurysms treated, 140 females, 89 males; mean age: 51 years) with aneurysmal subarachnoid hemorrhage were treated with GDC (Boston Scientific Neurovascular, Fremont, CA) once the anatomical conditions of feasibility had been achieved. Over 90% of the aneurysms treated (mean size: 5,8 mm) were located in the anterior circulation. The anterior communicating artery complex (87 cases), the posterior aspect of the internal carotid artery (65 cases), and the middle cerebral artery (49 cases) were most commonly treated. RESULTS: At the end of the initial hospitalization period, 14 patients (6.1%) died. Major procedural complications were associated with perforation of the aneurysmal sac in 9 patients (3.9%), thromboembolic events in 10 patients (4.3%) which resulted in 2 deaths (0.8%) and permanent neurologic morbidity in 7 patients (3%). The univariate analysis demonstrated no correlation between death and time-to-treatment, the topography of the aneurysm, or the occurrence of treatment related complications. The results of the logistical regression model demonstrated that the clinical score upon entry, and the occurrence of delayed ischemia were the only independent factors correlated with patient death. The prognostic factors affecting the degree of sequellae identified by the logistical regression model were the clinical score upon admission, age, treatment related complications, and pulmonary complications. CONCLUSIONS: Endovascular treatment of ruptured anterior circulation aneurysms with GDC, including MCA aneurysms, is associated with low morbidity and allows good overall outcomes in patients with subarachnoid hemorrhage. A better understanding of dependency factors associated with endovascular coiling will foster further technical advances in order to improve the treatment of small and medium sized ruptured aneurysms.

Analysis of Variance↗
PubMed2003

Spiral versus J-shaped coils for neurovascular embolisation-an in-vitro study.

Our purpose was to compare the characteristics of J-shaped detachable platinum coils with those of spiral coils in in-vitro vascular models. J-shaped coils consist of distal semicircular and proximal straight segments, the latter extending for most of the length of the coil. Spiral coils have a helical shape memory and are thus limited in expansion. In in-vitro silicone vascular models simulating intracranial aneurysms and dural arteriovenous fistulae, we compared J-shaped and spiral coils with regard to ease of delivery, anchoring and folding patterns, and stability in various types of vascular lumen. Delivery and retrieval were comparable. In large and irregular aneurysms and venous sinuses, J-shaped coils could form a more complex basket which conformed to the shape of the vascular cavity. The J-shaped coil was always in contact with the vessel wall. In wide-necked aneurysms, coil protrusion was more frequent with J-shaped coils, while spiral coils tended to stay compact and circular. Arteries were occluded in a shorter segment with spiral coils. J-shaped coils were safe and superior for large and irregular aneurysms or sinuses. Spiral coils were preferable for spherical aneurysms and segmental occlusion of arteries.

Angiography↗
PubMed2000

[Endovascular occlusion and percutaneous treatment of vasospasm].

Current available minimal invasive endovascular technology allows for percutaneous treatment of cerebral aneurysms and of vasospasm, the associated disease fo cerebral arteries secondary to subarachnoid hemorrhage. Multicentric evaluation of standardized treatment techniques using platinum coils have shown that a high success rate is now obtained for certain forms of aneurysms, mostly those which have a small base (4 mm or less) of implantation of the vessel. Treatment of arterial vasospasm by techniques including angioplasty using soft silicon balloons, or intraarterial application of spasmolytics, or both may be very successful, when performed prior to establishment of irreversible ischemic damage to the brain tissue. An intensive patient monitoring during the posthemorrhagic period is therefore critical for the correct timing of such a procedures.

Constriction↗
PubMed1999

Vertebroplasty: clinical experience and follow-up results.

This study was undertaken to report the clinical experience with percutaneous minimal invasive vertebroplasty using polymethyl-methacrylcate (PMMA) for a consecutive group of patients. Over the period of the last 4 years, 40 patients were treated at 68 vertebral segment levels with the intention to relieve pain related to vertebral body lesions. Reduced vertebral body height and destruction of the posterior vertebral wall were not considered to be exclusion criterias. The vertebroplasty procedure was performed under general anesthesia and in prone position with imaging control using mostly biplane DSA fluoroscopic guidance, and rarely with single-plane mobile DSA combined with computed tomographic guidance. Unilateral, but more frequently bilateral, transpedicular introduction of a 2-3-mm OD needle was followed by an injection of polymethyl-methacrylcate (PMMA). PMMA preparation involved a diluted mixture (20 mL powder for 5 mL liquid) allowing for an extended polymerization time of up to 8 min. The PMMA was mixed with metallic powder to enhance its radio-opacity. Before PMMA injection, a vertebral phlebography was obtained to evaluate the filling pattern and identify sites of potential PMMA leakage. Injection of opacified PMMA was performed under continuous visual control with fluoroscopy to obtain adequate filling and to avoid important PMMA leakage. Clinical follow-up involved an evaluation using a questionnaire for assessment of pain, pain medication, and mobility. One to six levels were treated in one to three treatment sessions for patients with metastatic, osteoporotic, and hemangiomatous lesions of the vertebral bodies who presented with pain. The results observed matched those reported previously with a success rate of approximately 80% and a complication rate below 6% per treated level. Treatment failure and complications observed were related to leakage, insufficient pretreatment evaluation, anesthesia, or patient position during treatment. Image guidance with fluoroscopy was efficient both for precise transpedicular approach and PMMA implantation control. Vertebroplasty is very efficient for treatment of pain. Treatment failure was mostly related to insufficient pretreatment clinical evaluation, and complication due to excessive PMMA volume injection. Control of PMMA volume seems to be the most critical point for avoiding complications. A good fluoroscopy control is therefore mandatory.

Adult↗
PubMed1999

Pathology findings with acrylic implants.

We report the pathological findings in cases of acrylic implants obtained by direct intratumoral injection of polymethyl-methacrylate (PMMA) and N-butyl-cyano-acrylate (NBCA). Direct intratumoral injection of acrylic implants was performed for a variety of primary and secondary bone lesions. These types of treatments have been used at our institution in the last 4 years for 40 vertebroplasty (PMMA) procedures and for nine bone lesions of other locations (PMMA, NBCA). Postmortem histology became available for 1 case of PMMA and for 5 cases with NBCA intratumoral acrylic implants. The pathological findings associated with PMMA and NBCA were evaluated and compared. PMMA exhibited a macroscopic and microscopic rim of tumor necrosis, 6 months after implantation. NBCA exhibited compressive effects on the nearby tumor tissue, however, without signs of significant necrosis outside the acrylic tumor cast. Tumor captured inside the acrylic cast showed extensive to near complete necrosis. Acrylic implants may lead to necrosis when injected directly in tumors. The necrotizing effect may extend beyond the limits of an implant in the case of PMMA. Such an extended effect of PMMA, when compared with NBCA, may be due to the variable toxicity of acrylic implants, including the different degrees of the exothermic reaction during polymerization.

Adenocarcinoma↗
PubMed1999

[Impairment of mesopic vision following photorefractive keratectomy of myopia].

PURPOSE: Halos, glare disability and problems during night driving are significant side effects of photorefractive keratectomy, caused by increasing optical aberrations under reduced conditions of luminiscence. In a previously performed retrospective study an impairment of mesopic vision in most of the investigated eyes was found. To prove these results, a prospective study was conducted. METHODS AND PATIENTS: In a prospective, consecutive study mesopic function was investigated in 41 myopic patients, who were interested in PRK. 26 patients underwent surgery (Summit ExciMed UV200LA, optical zone 5 mm), which was performed in 30 eyes. Mesopic function (contrast vision, glare sensitivity) was measured by using the Mesoptometer II test in all 30 eyes preoperatively and 6 to 9 months postoperatively. Additionally, 21 eyes were examined after 12 to 15 months of follow up. RESULTS: There was a statistically significant reduction of contrast vision and increase of glare sensitivity after 6 to 9 and 12 to 15 months. The Mesoptometer II contrast level of 1:5 (with and without glare) can be used as a critical parameter for the decision, whether mesopic function is markedly reduced or not. Before surgery, contrast level of 1:5 without glare was not recognized in 30%, with glare in 40%. After 6 to 9 months, this contrast level was not recognized in 73% of the 30 eyes without glare, with glare in 80%. Out of these 30 eyes, 21 eyes were followed over 12 to 15 months. Whereas 38% of these eyes (with glare 48%) did not recognized the critical contrast level before surgery, this rate increased to 67% (with glare 81%) 12 to 15 months after surgery. CONCLUSIONS: Impairment of mesopic function has to be considered as a possible side effect of PRK (optical zone 5 mm). Although further investigations are needed, the indication for PRK in special professions (pilots, professional drivers) should be very critical discussed.

Adult↗
PubMed1999

[Current status of infrared photoablation of the cornea].

BACKGROUND: IR-photothermal ablation has, for some time, been described as an alternative to UV photoablation with Excimer lasers. Both procedures are based on different laser-tissue-interactions. IR solid state lasers have cost advantages over UV laser technology and allow a broader clinical use. New beam shaping principals had to be developed. IN-VITRO: Systematic biophysical investigations, recently using tunable Free Electron Lasers, have described the ablation efficiency, the collateral thermal adverse effects, the surface properties and particle size, and the dynamic behaviour of the particle ejection, all as a function of wavelengths (and thus of different absorbers in the corneal tissue), of energy and of different pulselengths. The free running Er:YAG laser is suitable and well investigated, the optic parametrical oscillator (OPO) with supershort pulses a more recent alternative. IN VIVO: First in vivo photoablation with different Er:YAG lasers has proved the principle feasibility of IR photoablation. Histology of enucleated human eyes indicates that the wound healing and repair after IR photoablation is not principally different from UV-PRK. The evaluation of the achievable optical quality of the cornea in vivo as well as data on the stability resp. regression of the ablation profiles are still pending.

Animals↗
PubMed1999

[Dielectric spectroscopy for noninvasive examination of corneal tissue].

Dielectric spectroscopy is a non-invasive contact technique that permits the in vivo measurement of the specific electrical properties of biological tissue induced by an external electrical field. Permittivity, relaxation time and specific conductivity as a function of corneal hydration (wet weight/dry weight) and temperature were measured in 10 porcine corneas. Variation of tissue hydration has a minor influence on the signal, with a significant variation of the signal being detectable only for relatively dry tissue. A much greater influence was found for temperature, in particular on relaxation times. Dielectric spectroscopy provides us with an opportunity to detect structural, in particular temperature-induced, changes in living tissue. In the frequency range investigated, hydration has only a small influence on the dielectric properties of the tissue.

Animals↗
PubMed1998

Holmium:YAG thermokeratoplasty: treatment parameters for astigmatism induction based upon spherical enucleated human eyes.

BACKGROUND: The refractive outcome of thermokeratoplasty for astigmatism correction depends upon the optical zone diameter (OZD) and coagulation angle (CA; distance between two coagulation spots around the flat meridian). METHODS: Astigmatism was induced in 36 spherical human eye-bank eyes (Ho:YAG laser, 15 Hz, 20 mJ/pulse, 25 pulses per coagulation spot) with different OZDs and CAs. Thirty eyes received free-hand laser application (marked positions). Six eyes were treated using a suction mask, providing a constant OZD of 8.1 mm and an angle of 22.5 degrees between the laser spots. To compare the results, silicone replicas of the eyes were made pre- and postoperatively and analyzed by video-topometery. RESULTS: With an average decrease of 4 D/mm the refractive change is inversely linear to the OZD. Changes of the CA showed significant variations between 22.5 degrees and 45 degrees, only. Mask guidance leads to the same amount of average refractive change. The deviation is +/- 3.4 D for the freehand application but only +/- 0.8 D for mask guidance. CONCLUSION: The data obtained in this in vitro study are transferred to a treatment nomogram describing the immediate postoperative refractive change, not identical with the final refraction. The results of the study are limited by the fact that astigmatism was induced in spherical corneas, rather than correcting preexisting ones.

Astigmatism↗
PubMed1998

[Diode laser cyclophotocoagulation of secondary glaucoma caused by anterior, necrotizing scleritis].

PATIENT: A 60-year-old female patient presented with recurrent anterior, necrotizing scleritis with inflammation and a newly developed secondary glaucoma in the right eye. Anterior uveitis occurred some years before. Severe scleral thinning was circumferentially present and focal scleral ectasia was found. Physical examination revealed no systemic association of scleritis. Immunosuppressive therapy with metotrexate was initiated and control of scleritis achieved. Intraocular pressure elevation persisted and was refractory to glaucoma medication. Diurnal pressure curve showed IOP-values of 40 mm Hg despite the use of systemic carbonic anhydrase inhibitors. Visual acuity was 20/50 in the right and 20/25 in the left eye. METHOD: Diode laser cyclophotocoagulation (Oculight SLx 810 nm, Iris Medical Instruments Inc. California, USA) was performed under general anaesthesia using reduced parameters for application (12 laser spots, 1 second, 1.25 W). No complications occurred during and after laser application. Postoperatively, intraocular pressure was within normal range between 14 and 18 mm Hg. No reactivation of scleritis or uveitis was seen. CONCLUSION: In our experience, diode laser cyclophotocoagulation is effective and safe in treating secondary glaucoma associated with anterior, necrotizing scleritis with inflammation and uveitis using reduced parameters for application.

Female↗
PubMed1997

Mesopic vision in myopia corrected by photorefractive keratectomy, soft contact lenses, and spectacles.

PURPOSE: To evaluate contrast vision and glare sensitivity under mesopic conditions in eyes having uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia and in eyes corrected by disposable soft contact lenses, soft contact lenses, and spectacles. SETTING: Division of Experimental Ophthalmic Surgery, University of Tübingen, Germany. METHODS: The Mesoptometer II test was used to evaluate mesopic vision (glare sensitivity and contrast vision) in 28 eyes of 14 patients wearing disposable soft contact lenses, 20 eyes of 10 patients wearing soft contact lenses, 39 eyes of 20 patients wearing spectacles, 30 eyes of 15 emmetropic patients, and 33 eyes of 22 patients after PRK with 5.0 mm optical zone. Follow-up was between 15 and 60 months after PRK (mean 34.5 months). RESULTS: The guidelines of the German Ophthalmologic Society state that patients must recognize Mesoptometer II contrast levels of 1:5 or better with and without glare to meet the minimum legal night-driving standards for private cars. All eyes with disposable soft contact lenses and soft contact lenses, all emmetropic eyes, and 38 eyes corrected by spectacles recognized contrast levels of 1:5 or better without glare. In contrast, 18 eyes in the PRK group were unable to recognize contrast level 1:5 without glare. With glare, 1 eye in the disposable soft contact lens group, 1 in the soft contact lens group, and 7 with spectacles were unable to recognize the 1:5 contrast level. All emmetropic eyes recognized contrast levels of 1:5 or better; 22 PRK eyes were unable to recognize contrast level 1:5 with glare. CONCLUSION: Myopic PRK may lead to long-term impairment of mesopic vision, while soft contact lens use does not seem to markedly influence mesopic vision in eyes with low to moderate myopia.

Adolescent↗
PubMed1997

Automated compensation of defocusing errors in videokeratography.

PURPOSE: The reproducibility of videokeratography measurements is mainly dependent on the accuracy of manual adjustment in the focal plane. Videokeratoscopes having small Placido cones show a considerable amount of error when the required working distance between cornea and keratoscope is not maintained. The advantages of small cones (optimal illumination and the reduction of anatomically caused shadows) are in no proportion to the disadvantage-poor depth of focus, resulting in poor reproducibility. METHODS: The Tubingen Color Ellipsoid Topometer compensates with software and hardware for defocusing errors by means of a triangulation measurement. An 8.0 mm sphere (42 D) was measured in a distance range of +/- 1.5 mm around the focal plane with and without compensation. Five measurements were acquired at each position to evaluate the reproducibility of the calculated data. RESULTS: Defocusation in the range of +/-1.5 mm leads to deviation smaller than 0.05 mm (0.25 D). Without compensation, the maximal deviation is increased up to 0.7 mm (3.0 D), and thus is considerably greater. DISCUSSION: Automated compensation of defocusing errors in videokeratography actively compensates for defocusation errors, enhancing precision and avoiding measuring artifacts.

Cornea↗
PubMed1995

Dynamic mechanical spectroscopy of the cornea for measurement of its viscoelastic properties in vitro.

Cylindric samples (3 mm in diameter) of explanted human corneas were biomechanically characterized in the frequency range from 0.1 mHz to 100 Hz with a specially modified viscoelasticity spectrometer. Such spectra of the shear compliance J (the reciprocal value of the shear modulus G) were measured as a function of corneal hydration and temperature. Variation of the hydration from 0.20- to 1.00-mm sample thickness (5-fold) changed the shear compliance 600-fold. Such a strong effect means that the shear-compliance spectra are highly sensitive to changes in the biomechanical properties of the cornea. This is demonstrated by three examples. A myopic cornea (-3D) was significantly softer (by a factor of 7 at lower frequencies and a factor of 4 at higher frequencies) than an emmetropic cornea. An increasing post mortem interval decreased the shear-compliance values (stiffening) obtained at higher frequencies (by a factor of 0.7 per day), whereas the values obtained at lower frequencies were reproduced. The biomechanics of thermal coagulation were studied in detail. The temperature was increased step by step, and at 48 degrees C a first irreversible decrease in the compliance was recorded at lower frequencies (0.8-fold). A further stiffening by a factor of 1/6 at lower frequencies and 1/5 at higher frequencies ended at 64 degrees C with a minimum in the compliance. To provide a new diagnostic tool, the biomechanical spectra of the cornea have to be measured in vivo. Equipment suitable for the megahertz range has been developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1994

Complications of myopic photorefractive keratectomy with the excimer laser.

BACKGROUND: Although many thousands of myopic eyes have been operated on by excimer laser photorefractive keratectomy (PRK), the safety of this procedure is still a concern. METHODS: The results and complications of PRK have been studied for up to 2 years in a prospective trial including 193 eyes in 146 patients. In addition, specific complications of PRK are described that occurred in patients outside the prospective study. RESULTS: Two eyes (1.2%) lost two lines of best-spectacle-corrected visual acuity 1 year after surgery, but at 2 years one of these eyes had regained baseline visual acuity. At 1 year, 12 eyes (7.1%) had lost more than two lines of visual acuity under glare conditions. Significant complications such as manifest scarring, overcorrection, undercorrection, and continued regression are dependent on attempted refraction. Eccentric ablations with resultant induced astigmatism are rare and the incidence is dependent on the experience of the surgeon. Progressive hyperopia did not occur. CONCLUSION: Except in corrections greater than 6 diopters, complications after PRK are rare. Assuming an appropriate patient selection, PRK may be considered a relatively safe procedure compared with other refractive procedures.

Adult↗