Fabrice Manns

OPTICAL PROFILOMETRY OF POLY(METHYLMETHACRYLATE) SURFACES AFTER RESHAPING WITH A SCANNING PHOTOREFRACTIVE KERATECTOMY (SPRK) SYSTEM

A prototype frequency-quintupled Nd:YAG laser was used with a scanning system to create, on poly(methylmethacrylate) (PMMA) blocks, ablations corresponding to a correction of 6 diopters of myopia by photorefractive keratectomy. The topography of the ablated samples was measured with an optical profilometer to evaluate the smoothness and accuracy of the ablations. The ablation depth was larger than expected. With a 50% to 70% spot overlap, large valleylike variations with a maximum peak-to-peak amplitude of 20 µm were observed. With an 80% spot overlap, the rms surface roughness was 1.3 µm, and the central flattening was 7 diopters. This study shows that optical profilometry can be used to determine precisely the ablation per pulse and the smoothness and accuracy of surface ablations. Knowing the exact ablation per pulse is necessary to produce a smooth and accurate corneal surface by scanning photorefractive keratectomy.

Laser induced photochemical surface modification of PMMA for fibrin free intraocular lens

The central part of a PMMA or acrylic resin lens was modified into hydrophobic and the peripheral part to be phydrophilic using teh ArF laser and excimer lamp. PMMA or acrylic resin lens have been used as an intraocular lens for 50 years and is the golden standard in ophthalmology. However, protein and fat are stuck onto the IOL surface after long-term implantation and opacify the surface )after-cataract). Therefore, the central part of the IOL was modified to be hydrophobic to prevent fat and protein deposition; the periphery was made hydrophilic to develop affinity for tissue.

Development of a tissue phantom for experimental studies on laser interstitial ThermoTherapy of breast cancer

A tissue phantom for experimental studies in Laser Interstitial ThermoTherapy (LITT) for the treatment of small breast tumors was developed and evaluated. The tissue phantom consists of a polyacrylamide/acrylate hydrogel matrix containing various concentrations of an absorber (Nigrosin) and a scatterer (Intralipid 10% solution), allowing the optical properties to be varied in accordance to experimental need. Temperature measurements in the phantom were performed with a thermocouple array placed symmetrically around the fiber axis during laser irradiation for different output powers, treatment duration, and different concentrations of absorber. A 980 nm diode laser system was used in conjunction with an REM LightStic 360 diffusing tip fiber. The polyacrylamide/acrylate matrix tissue phantom remained stable during laser irradiation and produced reproducible results. The behavior of the temperature curves produced by the phantom during laser irradiation was similar to the behavior of the temperature curves in ex-vivo tissue. Therefore, this tissue phantom can be used as a model for the thermal response of tissue during laser interstitial thermotherapy. The phantom will be used as an experimental model to determine a set of optimum laser treatment parameters for laser interstitial thermotherapy of breast cancer.

Predictions of tissue denaturation during experimental laser interstitial thermotherapy for breast tumors

The purpose of these preliminary experiments was to calculate the activation energy and the frequency factor constants of the Arrhenius equation for prediction of the denaturation zone produced by laser interstitial thermotherapy in female breast tissue models. In a first step, pairs of parameters consisting of the activation energy (ΔE) and frequency factor (A) were calculated for different half denaturation times at 50°C and 60°C. Pairs of parameters were eliminated if the calculated time of denaturation at 70°C was excessively short (<0.1s). In a second step, denaturation was calculated over time for each remaining pair of parameters using temperature measurements performed during a laser heating experiment in ex-vivo porcine mammary chain tissue. The zone of denaturation in the tissue after laser heating was 2.0 cm x 3.5 cm. One pair of Arrhenius parameters was chosen whose denaturation plot showed no denaturation outside the experimentally-observed denaturation zone, 50% denaturation at the border of the experimental denaturation zone, and 100% denaturation within the experimental denaturation zone after 1200 seconds. The activation energy and frequency factor which best fit our experimental data were ΔE=3.02x105 J mol-1 and A=1.18x1044 s-1, respectively. These values fall within the general range given in the literature.

Microsurgical laser Doppler probe for simultaneous intraoperative monitoring of cochlear blood flow and electrocochleography from the round window

The aim of this project is the development of a microsurgical laser Doppler (LD) probe that simultaneously monitors blood flow and Electrocochleography (ECochG) from the round window of the ear. The device will prevent neurosensory hearing loss during acoustic neuroma surgery by preventing damage to the internal auditory nerve and to the cochlear blood flow supply. A commercially available 0.5 mm diameter Laser-Doppler velocimetry probe (LaserFlo, Vasamedics) was modified to integrate an ECochG electrode. A tube for suction and irrigation was incorporated into a sheath of the probe shaft, to facilitate cleaning of the round window (RW) and allow drug delivery to the round window membrane. The prototype microprobe was calibrated on a single vessel model and tested in vivo in a rabbit model. Preliminary results indicate that the microprobe was able to measure changes in cochlear blood flow (CBF) and ECochG potentials from the round window of rabbits in vivo. The microprobe is suitable for monitoring cochlear blood flow and auditory cochlear potentials during human surgery.

Mathematical analysis of the temperature field during ex vivo and in vivo experimental laser interstitial thermotherapy (LITT) in breast tissue models

Purpose: Laser interstitial thermotherapy is a promising minimally- invasive technique for the treatment of small cancers of the breast that are currently removed surgically lumpectomy. The purpose of this work was to analyze in situ temperature fields recorded with stainless-steel thermocoupled probes during experimental laser interstitial thermo-therapy (LITT). Methods: Both a CW Nd:YAG laser system emitting 20W for 25 to 30s and a 980 nm diode laser emitting 10 to 20 W for up to 1200s delivered through a fiber-optic probe were used to create localized heating in fatty cadaver pig tissue and milk as phantoms. To quantify an artifact due to direct heating of the thermocouple probes by laser radiation, experiments were also performed in air, water and intralipid solution. The temperature field around the fiber-optic probe during laser irradiation was measured every 0.3 s or 1 s with an array of up to fifteen needle thermocoupled probes. The effect of light absorption by the thermocouples probes was quantified and the time-dependence of the temperature distribution was analyzed. Results: After removal of the thermocouple artifact, the temperature was found to vary exponentially with time with a time constant of 600 to 700 s. Conclusions:The time-dependence of the interstitial temperature can be modeled by exponential functions both during ex vivo and in vivo experiments.

Experimental laser interstitial thermotherapy in ex-vivo porcine tissue at 940 nm

Purpose: the purpose of these experiments was to evaluate the temperature and predicted cell kill distribution during LITT of breast tissue phantoms at 940nm and compare with the results of previous experiments ar 830 nm and 980 nm. Material and Methods: A Dornier Medilas D Skinpulse 940 nm diode lase system coupled to a Dornier D-6111-T2 fiber (Dornier Surgical Products, Phoenix, AZ) was used to irradiate the porcine tissue three times at approximately 5 W for 10 minutes. Results: The initial rate of temperature increase at 940 nm for locations 5, 10, and 15 mm from the fiber axis ranged from 0.076 to 0.142 °C/s, 0.027 to 0.041 °C/s, and 0.008 to 0.013 °C/s, respectively, wile the maximum temperature increase ranged from 37.8 to 46.9 °C, 19.3 to 26.1 °C, 8.6 to 13.0 °C, respectively, temperature curves hed lower slopes at 940 nm than at 830 nm and 980 nm. the maximum temperature increase was higher at 940 nm than at 830 nm. Predicted area of 100% cell kill was approximately 2 cm by 2 cm Conclusion: Results of experiments at 940 nm were more comparable to those at 980 nm than at 830 nm.

In-situ measurement and analysis of the temperature fields in laser interstitial thermotherapy of breast cancer

Temperature increases and the resultant thermal field produced by the irradiation of ex vivo (porcine and human) and in vivo (porcine) tissue models appropriate to the treatment of human breast tissue using Nd:YAG (cw:60W) radiation delivered with an interstitial fiber optic probe were recorded with an array of fifteen 23 gauge needle thermocouple probes connected to a laboratory computer based data acquisition system. Using a stepwise decreasing power cycle to avoid tissue charring, acceptably symmetric thermal fields of repeatable volumetric dimensions were obtained. Reproducible thermal gradients and predictable tissue necrosis without carbonization could be induce din a three centimeter diameter region around the fiber probe during a single treatment lasting only 3 minutes. The time-dependence of the temperature rise of the thermocouples surrounding the LITT probe were quantitatively modeled with simple linear functions during the applied laser heating cycles.

Scleral heating with pulsed midinfrared lasers and temperature-dependent absorption coefficient

We studied the effect of the temperature-dependence of the scleral absorption coefficient on the accuracy of thermal models of laser-induced scleral heating. The scleral surface temperature increase during pulsed Holmium:YAG and Thulium:YAG laser irradiation was calculated with a constant (static model) and temperature-dependent (dynamic model) absorption coefficient. The 1D heat equation was solved with the assumption that thermal diffusion during the pulse is negligible. We found that the dynamic model yields lower temperatures than the static model. For the sclera, the overestimation becomes significant when the surface temperature is above 70 degree(s)C. This study shows that the temperature-dependence of the absorption coefficient must be taken into account to accurately predict laser-induced scleral or corneal heating.

Objective dynamic changes in lens curvature during accommodation using optical coherence tomography images (Conference Presentation)

Purpose: To objectively quantify dynamic changes in lens shape during accommodation using two-dimensional OCT imagesnnMethods: In-vivo responses to an accommodative step stimulus of three subjects (aged 22, 39, and 45) were captured using a custom-made extended-depth SD-OCT system operating at 840 nm following an IRB-approved protocol (Ruggeri et al. 2012). Subjects focused on a visual accommodation target designed to produce an adjustable step stimulus of accommodation. Accommodative responses to 2-D and 4-D stimuli were captured ~1.5s before and ~4.5s after stimulation. Lens thickness, anterior curvature, and posterior curvature were measured using a newly-developed algorithm (validated using a calibration sphere). Dynamic changes in lens thickness and curvature were then fitted with an exponential model to produce time dependent constants.nnResults: All calibration OCT images were automatically analyzed in under 2 seconds. A radius of 7.793mm ± 0.051mm was calculated resulting in a difference of 2.4μm from the reported nominal value of the calibration sphere. Anterior lens radius decreased over time in all subjects. Radius of the posterior lens experienced a slight increase for all subjects. nnConclusion: This study demonstrates the feasibility of quantifying the dynamic changes in lens curvature and thickness during accommodation using extended-depth OCT combined with a step accommodation stimulus and an automated segmentation algorithm.