Stimulation of the globus pallidus internus in the treatment of Parkinson's disease: Long-term results of a monocentric cohort.

BACKGROUND: Pallidal deep brain stimulation (DBS) has shown to be beneficial in patients with advanced levodopa-responsive Parkinson's disease (PD) in several short-term studies. However, reported long-term outcomes of pallidal DBS for PD are limited and contradictory. METHODS: Eighteen consecutive PD patients were treated with unilateral or bilateral stimulation of the internal part of the globus pallidus (GPi). Assessments were carried out before and six months after neurosurgery, and annually thereafter for up to 16 years (mean follow-up time: 6 years). Primary outcomes included motor signs (Unified PD Rating Scale [UPDRS]-III), activities of daily living (ADL, UPDRS-II), and levodopa-induced motor complications (UPDRS-IV). RESULTS: The results show that GPi stimulation improves levodopa-responsive PD motor signs (UPDRS-III), levodopa-induced motor complications (UPDRS-IV), and ADL (UPDRS-II) in advanced PD. Among motor signs, tremor showed the best response to pallidal stimulation. Levodopa-induced motor complications and tremor showed improvements for more than 10 years after neurosurgery. CONCLUSIONS: The overall findings in our cohort demonstrate that pallidal stimulation is effective in reducing parkinsonian motor signs (UPDRS-III), particularly in the 'off'-medication state. Although the beneficial effects on bradykinesia, rigidity and ADL may be limited to 5-6 years, the follow up results indicate that the improvements of levodopa-induced motor complications (UPDRS-IV) and tremor can be sustained for more than 10 years.

TDM-controlled ring resonator arrays for fast, fixed-wavelength optical biosensing.

A novel control concept for serial ring resonator arrays based on a time-division multiplex (TDM) approach is presented. It allows fast sampling rates in terms of biological kinetics. The novelty consists of using both thermal tuning of the effective refractive index and thermo-optical multiplexing for the silicon-on-insulator (SOI) ring resonator arrays, without the need for a tunable laser source. Using a fixed wavelength, fast read-out rates of 100 Hz are demonstrated for each ring.

Time-domain model of quantum-dot semiconductor optical amplifiers for wideband optical signals.

We present a novel theoretical time-domain model for a quantum dot semiconductor optical amplifier, that allows to simulate subpicosecond pulse propagation including power-based and phase-based effects. Static results including amplified spontaneous emission spectra, continuous wave amplification, and four-wave mixing experiments in addition to dynamic pump-probe simulations are presented for different injection currents. The model uses digital filters to describe the frequency dependent gain and microscopically calculated carrier-carrier scattering rates for the interband carrier dynamics. It can be used to calculate the propagation of multiple signals with different wavelengths or one wideband signal with high bitrate.

Design rules for p-i-n diode carriers sweeping in nano-rib waveguides on SOI.

In this paper we present a detailed analysis of the carrier lifetime for a p-i-n junction on silicon nano-rib waveguides. Several factors determining efficiency of carriers removal from the waveguiding region will be discussed. We compare different structure geometries and spacings between p and n doped regions to show the way to optimize electrons and holes sweeping for CW nonlinear optical devices.

Ultrashort pulse generation from diode pumped mode-locked Yb3+:sesquioxide single crystal lasers.

We present diode pumped SESAM supported Kerr-lens mode locked laser operation based on Yb3+:Sc2O3 and Yb3+:Lu2O3 single crystals. Pulses as short as 71 fs with an average power of 1.09 W were obtained from an Yb3+:Lu2O3 single crystal. Yb3+:Sc2O3 delivered pulses as short as 81 fs with an average power of 840 mW. The mode locked laser operation was stable for longer than 2 hours.

Continuous-wave and modelocked Yb:YCOB thin disk laser: first demonstration and future prospects.

Yb:YCOB is a very attractive material for femtosecond pulse generation given its broad emission bandwidth. We demonstrate continuous-wave power scaling in the thin disk geometry to the 100-W level with a 40% optical-to-optical efficiency in multi-mode operation. Furthermore, we present initial modelocking results in the thin disk geometry, achieving pulse durations as short as 270 fs. The modelocked average power is, however, limited to less than 5 W because of transverse mode degradation. This is caused by anisotropic thermal aberrations in the 15% Yb-doped thin disks which were 300 to 400 µm thick. This result confirms the potential of Yb:YCOB to generate short femtosecond pulses in the thin disk geometry but also makes clear that significantly thinner disks are required to overcome the thermal limitations for high power operation.

Nonlinear spectroscopic properties of Yb3+-doped sesquioxides Lu2O3 and Sc2O3.

We report on the measurements of near-UV excited-state absorption (ESA) spectra and refractive index changes (RICs) in the two ytterbium doped laser crystals Yb:Lu2O3 and Yb:Sc2O3. ESA is assigned to ligand-to-metal charge transfer (LMCT) absorption transitions and RICs to the polarizability changes experienced by the Yb3+ ions due to these strong electric-dipole allowed absorption bands.

Femtosecond Yb:Lu(2)O(3) thin disk laser with 63 W of average power.

We present successful power-scaling of an Yb:Lu(2)O(3) thin disk laser to record high-power levels both in cw and mode-locked operation. In a simple multimode resonator we achieved 149 W of output power in cw operation with 73% optical-to-optical efficiency (eta(opt)). Building an 81 MHz fundamental transverse mode resonator with dispersion compensation and a semiconductor saturable absorber mirror (SESAM) for passive mode locking we achieved 63 W of average power in 535 fs pulses (eta(opt)=35%). The output beam is nearly diffraction limited (M(2)<1.2). The 0.78 microJ pulses with a peak power of 1.28 MW had a central wavelength of 1034 nm and were close to the Fourier transform limit. With an SESAM with a larger modulation depth we obtained pulses as short as 329 fs at 40 W average power corresponding to a pulse energy of 0.49 microJ and a peak power of 1.32 MW.

Efficient femtosecond high power Yb:Lu(2)O(3) thin disk laser.

We demonstrate the first passively mode-locked thin disk laser based on Yb:Lu(2)O(3). The laser generates 370-fs pulses with 20.5 W of average power in a diffraction-limited beam (M(2) < 1.1). The nearly transform-limited pulses have a spectral bandwidth of 3.4 nm centered near 1034 nm. With slightly longer pulses (523 fs) we obtained 24 W of average power at a pump power of 56 W, resulting in an optical-to-optical efficiency of 43%, which is higher than for any previously mode-locked thin disk laser.

Passively mode-locked Yb:Lu(2)O(3) laser.

Given its specific thermal characteristics, the sesquioxide crystal Lu(2)O(3) is a particularly promising laser host material. We demonstrate mode locking of a Yb:Lu(2)O(3) laser by use of a semiconductor saturable-absorber mirror. The laser emits up to 470 mW in the picosecond regime, corresponding to a pump efficiency as high as 32%. With dispersion compensation, pulses as short as 220 fs at an average power of 266 mW are obtained at 1033.5 nm. To our knowledge, this is the first demonstration of a femtosecond oscillator based on Yb:Lu(2)O(3).

Calibrated electro-optic E-field sensors for hyperthermia applications.

E-field measurements are an important task for the investigation of newly developed hyperthermia applicators as well as for online control of hyperthermia treatments. Compact and non-perturbing integrated optical E-field sensors based on LiNbO3 as well as optical E-field sensors based on infrared emitting diodes and light bulbs are suitable for nearfield measurements of hyperthermia antennas. In order to investigate their properties a calibration cell with transverse electromagnetic (TEM) waves has been constructed. By using this cell, calibration curves and directional patterns for all sensors have been measured. Due to the threshold behaviour of the IRED and light bulb sensor, only the LiNbO3 sensor is capable of measuring weak fields inside an applicator or a homogeneous phantom.

Scanning E-field sensor device for online measurements in annular phased-array systems.

PURPOSE: A measurement device for noninvasive and simultaneous control of antennas during regional radiofrequency (rf) hyperthermia and, subsequently, the estimation of the power distribution in the interior of patients are essential preconditions for further technological progress. Aiming at this, the feasibility of an electro-optical electric field sensor was investigated during clinical rf hyperthermia. MATERIAL AND METHODS: The electro-optical electric field (E-field) sensor is based on lithiumniobate crystals and the Mach-Zehnder interferometer structure, and was tested in an earlier phantom study. For this study, a mechanical scanning device was developed allowing the registration of the E-field during clinical application. Data were recorded along a curve in the water bolus of the SIGMA 60 applicator of the annular phased-array system BSD-2000 (BSD Medical Corp., Salt Lake City, UT) close to the base points of the flat biconical dipole antennas. The results were compared with modeling calculations using the finite-difference time-domain (FDTD) method. For the latter, different antenna models were assumed. For systematic registration of the E-field curves in amplitude and phase, we employed an elliptical lamp phantom with fat-equivalent ring (filled with saline solution) and an elliptical polyacrylamide phantom with acrylic glass wall. Further measurements were carried out during the treatment of 5 patients with 20 hyperthermia treatments. RESULTS: Data of both phantom and patient measurements can be satisfactorily described by the FDTD method, if the antenna model is refined by taking into account the conical form of the dipoles and the special dielectric environment of the feeding point. Phase deviations can be entered ex posteriori for correction in the calculation algorithm. A comparison of amplifier power measurement (forward and backward power) and bolus E-field scans near the antenna base points demonstrates that E-field measurements between antennas and patient are a necessity for the appropriate characterization of antenna radiation properties. These measurements are sensitive to variations of the lossy medium in position and shape, and can be correctly predicted with current models. However, the differences between different patients are moderate and unspecific in both calculations and measurements, with fluctuations at maximum of 30 degrees in phases and 40% in amplitudes. CONCLUSIONS: The measurement method presented here turned out to be a practical tool for online registration of E-fields in phases and amplitudes along arbitrary curves in a water bolus or phantom. It can be utilized to evaluate antenna design and modeling calculations and leads, thus, to a better understanding of complicated multiantenna systems. In clinical routine, it can be employed as input for patient-specific hyperthermia planning and, finally, for the realization of online control with subsequent optimization of the power distribution in the patient.

Multicenter German reference data base for peripheral quantitative computer tomography.

The wide spread use of bone densitometers in Germany and other European countries has required the establishment of a validated reference population data base. A semianthropomorphic forearm cross-calibration phantom (EFP), developed during a concerted research action of the European Union's programme in Biomedical Engineering (COMAC-BME), was used to cross-calibrate the peripheral quantitative computer tomography (pQCT) devices at four German centers participating in the multicenter study. In total, 723 women and 208 men were included in the normal data base. No significant regional differences were found between the data of the different centers. In addition to the manufacturers calibration standard, proper calibration of the pQCT devices could be monitored during collection of the normal female and male data base. As a merit of the COMAC-BME study the measurements obtained with all pQCT devices thus ensured an uniform reference data base for distal radius measurements in Germany.

Noninvasive prediction of SAR distributions with an electro-optical E field sensor.

An integrated electro-optical (eo) E field sensor is developed on the basis of a Ti:LiNbO3 Mach-Zehnder interferometer. A measuring device based on the lock-in principle is introduced to register the E field in phase and amplitude using this E field probe. Segmented electrodes are used to minimize influences from the dielectric surroundings on the base point capacitance of the receiving dipole. The operating point is stabilized against drift phenomena resulting from optical damage and pyroelectric effect. Sensitivity, dynamic range, harmonic distortions and mechanical properties of a prototype of this electro-optical E field sensor are evaluated. A phantom setup in the SIGMA-60 applicator was developed to test this electro-optical sensor for hyperthermia applications. Power deposition patterns of various standard adjustments of the SIGMA ring are visualized in an elliptical lamp phantom. Simultaneously, E field in phase and amplitude is determined on a closed curve in 10 degrees steps around the phantom in a substitute bolus. The numbers are stored and utilized as boundary conditions in a two-dimensional finite elements code which calculates the SAR distribution on an appropriate triangular grid inside the closed curve. An excellent qualitative agreement is obtained between visualized and calculated SAR patterns. This novel measurement method is therefore suitable for noninvasive monitoring of SAR patterns during clinical application of regional radiofrequency hyperthermia.

Sensitivity of a fiber-optic gyroscope to environmental magnetic fields.

It is shown that environmental magnetic fields may cause a considerable error for the detected rotation rate even though the line integral of the magnetic field along the fiber vanishes. Experimentally, it has been shown that the earth's magnetic field yields a bias uncertainty of about 10 degrees /h, which can be reduced by at least 1 order of magnitude if the fiber coil is protected against environmental magnetic fields.

Intensity-dependent nonreciprocal phase shift in fiber-optic gyroscopes for light sources with low coherence.

It is shown that light sources of low coherence will exhibit intensity fluctuations similar to those of thermal light, at least after traveling through a fiber with material dispersion. These fluctuation yield a vanishing intensity-dependent nonreciprocal phase shift for fiber gyroscopes.