Lübeck, Germany
Lübeck, Germany

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Hagen-Eggert M.,Medical Laser Center Lubeck | Hillmann D.,Thorlabs GmbH Lubeck | Koch P.,Thorlabs GmbH Lubeck | Huttmann G.,Institute of Biomedical Optics Lubeck
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2011

Diffusion-sensitive optical coherence tomography (DS-OCT) is presented as a functional extension to OCT. Fluctuations of signal intensity and phase, which are caused by Brownian motion, are analysed by an autocorrelation function similar to dynamic light scattering measurements. Based on an ultra-fast Fourier-domain OCT, DS-OCT can determine quantitatively diffusion properties with high depth resolution, e.g. the hydrodynamic diameter of colloidal suspensions. Performance of DS-OCT is demonstrated with polystyrene particle suspensions and compared to conventional DLS measurements. Applications for DS-OCT may be found in the measurement of particle size distributions of inhomogeneous samples or measurements of diffusion properties at boundary surfaces. Additionally, the method has the capability to become a useful benefit in clinical diagnostics, especially in ophthalmology, where the molecular compositions and pathological changes of anterior eye components could be detected. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Lange B.,Medical Laser Center Lubeck | Cordes J.,University of Lübeck | Brinkmann R.,Medical Laser Center Lubeck | Brinkmann R.,University of Lübeck
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2015

Holmium lasers are nowadays the gold standard for endoscopic laser lithotripsy. However, there is a risk of damaging or perforating the ureter or kidney tissue when the vision is poor. An automatic tissue/stone differentiation would improve the handling and safety of the procedure. To achieve this objective, an easy and robust real-time discrimination method has to be found which can be used to realize a feedback loop to control the laser system. Two possible approaches have been evaluated: White light reflectance and fluorescence spectroscopy. In both cases, we use the treatment fiber for detection and evaluate the possibility to decide whether the fiber is placed in front of tissue or calculus by the signal that is delivered by the surface in front of it. White light reflectance spectroscopy uses the standard light source for endourologic surgeries: Radiation of a Xenon light source is coupled to the ureteroscope via a liquid light guide. The part of the white light that is reflected back into the fiber is spectroscopically analyzed. In a clinical proof of concept study reflection signals were measured in vivo in 8 patients. For differentiation of stone and tissue via autofluorescence, excitation as well as detection was done via the treatment fiber. A suitable excitation wavelength was chosen with in vitro measurements (UV / visible) on several human renal calculi and porcine tissues. For verification of the positive results with green excitation in a clinical proof of concept study, a measurement set-up was realized which allows the recording of fluorescence signals during an endourological intervention. © COPYRIGHT SPIE-OSA.


Horstmann J.,Medical Laser Center Lubeck | Brinkmann R.,Medical Laser Center Lubeck | Brinkmann R.,University of Lübeck
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2014

We introduce an innovative detection approach for photoacoustic tomography. The pressure induced surface displacement is obtained in 2D by Electronic Speckle Pattern Interferometry (ESPI) in a repetitive measurement with a variable time delay between excitation- and detection pulses. The detection approach works without any physical contact to the object surface and is very versatile in terms of an adjustable object surface area and an adjustable temporal sampling rate. Furthermore, the approach is potentially very fast by the use of a high speed camera and a high repetition laser excitation and detection. In a proof of concept measurement, transparent silicone cubes with black silicone sphere absorbers are measured. In order to validate the acquired displacement data, the pressure is measured using a lipstick needle hydrophone and correlated to the measured displacement. © 2014 SPIE.


Koinzer S.,University of Kiel | Schlott K.,University of Lübeck | Ptaszynski L.,Medical Laser Center Lubeck | Bever M.,Medical Laser Center Lubeck | And 10 more authors.
Investigative Ophthalmology and Visual Science | Year: 2012

PURPOSE. Retinal laser photocoagulation carries the risk of overtreatment due to effect variation of identically applied lesions. The degree of coagulation depends on the induced temperature increase and on exposure time. We introduce temperature controlled photocoagulation (TCP), which uses optoacoustics to determine individually exposure times necessary to create reproducible lesions. METHODS. Optoacoustic temperature measurement relies on pressure waves that are excited in the retinal tissue by repetitive low-energy laser pulses. Signal amplitudes correlate with tissue temperature and are detected by a transducer in the laser contact lens. We used a continuous wave (CW) photocoagulator for treatment irradiation and superimposed probe laser pulses for simultaneous temperature measurement. Optoacoustic data of 1500 lesions (rabbit) were evaluated to develop an algorithm that controls exposure times automatically in TCP. Lesion diameters of 156 TCP lesions were compared to 156 non-controlled lesions. Histology was performed after 1 hour, and 1 and 4 weeks. RESULTS. TCP resulted in exposure times from 4 to 800 ms depending on laser power chosen. Ophthalmoscopic and histologic lesion diameters were independent of power between 14 and 200 mW. TCP lesions barely were visible with a mean diameter equal to the treatment beam (130 lm). In contrast, standard lesion diameters increased linearly and statistically significantly with power. Histology confirmed sparing of the ganglion and nerve fiber layers in TCP. CONCLUSIONS. TCP facilitates uniform retinal lesions over a wide power range. In a clinical setting, it should generate soft and reproducible lesions independently of local tissue variation and improve safety, particularly at short exposure times. © 2012 The Association for Research in Vision and Ophthalmology, Inc.


Rohde I.,University of Lübeck | Theisen-Kunde D.,Medical Laser Center Lubeck | Brinkmann R.,University of Lübeck | Brinkmann R.,Medical Laser Center Lubeck
Laser Physics Letters | Year: 2012

A Q-switched Ho:YAG laser, longitudinally in-band pumped by a thulium fiber laser at a wavelength of λ = 1920 nm was designed in order to temporally stretch the Q-switched pulses at the fundamental wavelength. This was realized by two different methods: (a) wavelengths with a small cross section for stimulated emission have been selected, which leads to a pulse duration of 162 ns at 2128 nm compared to 32 ns at a wavelength of 2098 nm with energies around 1 mJ, (b) additionally intracavity second harmonic generation in the overcoupling regime has been used to further increase the pulse duration up to 300 ns at 1 mJ. © 2012 by Astro, Ltd.


Rohde I.,University of Lübeck | Brinkmann R.,University of Lübeck | Brinkmann R.,Medical Laser Center Lubeck
Journal of Optics (United Kingdom) | Year: 2014

An intracavity frequency doubled, Q-switched Nd:YLF emitting at a wavelength of 527 nm was designed with the goal to temporally stretch the Q-switched pulses up to some microseconds at pulse energies of several millijoules. With different resonator configurations pulse durations between 12 μs and 3 μs with energies of 1 mJ-4.5 mJ have been achieved, which is demanded for an application in ophthalmology. For tighter intracavity foci and high pump power, however, strong power modulations by trains of picosecond pulses on the rear flank of the microsecond pulses were observed, indicating the occurrence of cascading nonlinearities and mode-locking. Simultaneously a significant increase of the fundamental spectrum up to 5 nm was found. A similar effect, which is referred to as gain broadening, has previously been observed by using ppKTP for intracavity second harmonic generation. This is, to the best of our knowledge, the first observation of this effect with unpoled second harmonic media. © 2014 IOP Publishing Ltd.


Schlott K.,University of Lübeck | Koinzer S.,University of Kiel | Baade A.,Medical Laser Center Lubeck | Birngruber R.,University of Lübeck | And 2 more authors.
Journal of Biomedical Optics | Year: 2016

Laser photocoagulation is an established treatment for a variety of retinal diseases. However, when using the same irradiation parameter, the size and strength of the lesions are unpredictable due to unknown inter- and intraindividual optical properties of the fundus layers. The aim of this work is to investigate a feedback system to generate desired lesions of preselectable strengths by automatically controlling the irradiation time. Optoacoustics were used for retinal temperature monitoring. A 532-nm continuous wave Nd:YAG laser was used for photocoagulation. A 75-ns/523-nm Q-switched Nd:YLF laser simultaneously excited temperature-dependent pressure transients, which were detected at the cornea by an ultrasonic transducer embedded in a contact lens. The temperature data were analyzed during the irradiation by a LabVIEW routine. The treatment laser was switched off automatically when the required lesion strength was achieved. Five different feedback control algorithms for different lesion sizes were developed and tested on rabbits in vivo. With a laser spot diameter of 133 μm, five different lesion types with ophthalmoscopically visible diameters ranging mostly between 100 and 200 μm, and different appearances were achieved by automatic exposure time control. The automatically controlled lesions were widely independent of the treatment laser power and the retinal pigmentation. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).


Horstmann J.,Medical Laser Center Lubeck | Brinkmann R.,Medical Laser Center Lubeck | Brinkmann R.,University of Lübeck
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2013

An innovative very fast non-contact imaging technique for Photoacoustic Tomography is introduced. It is based on holographic optical speckle detection of a transiently altering surface topography for the reconstruction of absorbing targets. The surface movement is obtained by parallel recording of speckle phase changes known as Electronic Speckle Pattern Interferometry. Due to parallelized 2-D camera detection and repetitive excitation with variable delay with respect to the image acquisition, data recording of whole volumes for Photoacoustic Imaging can be completed in times far below one second. The size of the detected area is scalable by optical magnification. As a proof of concept, an interferometric setup is realized, capable of surface displacement detection with an axial resolution of less than 3 nm. The potential of the proposed method for in vivo Photoacoustic Imaging is discussed.


Schlott K.,University of Lübeck | Koinzer S.,University of Kiel | Ptaszynski L.,Medical Laser Center Lubeck | Bever M.,Medical Laser Center Lubeck | And 6 more authors.
Journal of Biomedical Optics | Year: 2012

Laser coagulation is a treatment method for many retinal diseases. Due to variations in fundus pigmentation and light scattering inside the eye globe, different lesion strengths are often achieved. The aim of this work is to realize an automatic feedback algorithm to generate desired lesion strengths by controlling the retinal temperature increase with the irradiation time. Optoacoustics afford non-invasive retinal temperature monitoring during laser treatment. A 75 ns/523 nm Q-switched Nd:YLF laser was used to excite the temperature-dependent pressure amplitudes, which were detected at the cornea by an ultrasonic transducer embedded in a contact lens. A 532 nm continuous wave Nd:YAG laser served for photocoagulation. The ED50 temperatures, for which the probability of ophthalmoscopically visible lesions after one hour in vivo in rabbits was 50%, varied from 63°C for 20 ms to 49°C for 400 ms. Arrhenius parameters were extracted as ΔE = 273 J mol-1 and A = 3 · 1044 s-1. Control algorithms for mild and strong lesions were developed, which led to average lesion diameters of 162 ± 34 μm and 189 ± 34 μm, respectively. It could be demonstrated that the sizes of the automatically controlled lesions were widely independent of the treatment laser power and the retinal pigmentation. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE).


Klatt C.,University of Kiel | Saeger M.,University of Kiel | Oppermann T.,University of Kiel | Porksen E.,University of Kiel | And 6 more authors.
British Journal of Ophthalmology | Year: 2011

Aims: To evaluate selective retina therapy (SRT) as a treatment of acute central serous chorioretinopathy. Methods: 30 eyes of 30 patients with central serous chorioretinopathy of at least a 3 months' duration were recruited. 14 eyes were randomised to an SRT group (Q-switched neodymium-doped yttrium lithium fluoride (Nd:YLF) laser, wavelength 527 nm, t=1.7 μs, energy 100-370 μJ, spot diameter 200 mm, pulse repetition rate 100 Hz,) and 16 eyes to a control group. After 3 months of follow-up, patients in the control group with persistence of subretinal fluid (SRF) were allocated to a cross-over group, treated with SRT and followed up for further 3 months. The main outcome measures were change of best-corrected Early Treatment Diabetic Retinopathy Study visual acuity (BCVA) and SRF. Results: At 3 months of follow-up, the mean (SD) improvement of BCVA was significantly greater after SRT than in the control group: 12.7 (7.2) versus 6.3 (8.9) letters (p=0.04). SRF had decreased significantly more after SRT as compared with that the control group: 203 (136) μm versus 41 (150) μm (p=0.005). In eight eyes allocated to the cross-over group, the mean BCVA had increased during 3 months of follow up before SRT by 1.4 (5.2) letters and continued to increase during 3 months following SRT by 7.4 (6.3) letters, while SRF increased by 39.5 (160.2) μm before SRT and decreased by 151.5 (204.9) μm after SRT. In six of the eight eyes, SRF had completely resolved 3 months after SRT. Conclusions: SRT appears to expedite functional recovery and the re-absorption of SRF as compared with that in untreated controls. A larger prospective, randomised phase 3 confirmative patient study is warranted. Trial registration number NCT00987077.

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