Performance assessment of time-domain optical brain imagers, part 2: nEUROPt protocol.

The nEUROPt protocol is one of two new protocols developed within the European project nEUROPt to characterize the performances of time-domain systems for optical imaging of the brain. It was applied in joint measurement campaigns to compare the various instruments and to assess the impact of technical improvements. This protocol addresses the characteristic of optical brain imaging to detect, localize, and quantify absorption changes in the brain.

Performance assessment of time-domain optical brain imagers, part 1: basic instrumental performance protocol.

Performance assessment of instruments devised for clinical applications is of key importance for validation and quality assurance. Two new protocols were developed and applied to facilitate the design and optimization of instruments for time-domain optical brain imaging within the European project nEUROPt. Here, we present the "Basic Instrumental Performance" protocol for direct measurement of relevant characteristics.

GLM analysis of time resolved NIRS data of motor activation during different motor tasks.

The hemodynamic response to motor activation was investigated by time-resolved NIRS in healthy subjects and patients with unilateral impairment in motor ability. Healthy subjects performed a simple and a complex finger movement task, patients a handgrip task. A General Linear Model approach (GLM) was applied during NIRS data processing.

A multichannel time-domain scanning fluorescence mammograph: performance assessment and first in vivo results.

We present a scanning time-domain fluorescence mammograph capable to image the distribution of a fluorescent contrast agent within a female breast, slightly compressed between two parallel glass plates, with high sensitivity. Fluorescence of the contrast agent is excited using a near infrared picosecond diode laser module. Four additional picosecond diode lasers with emission wavelengths between 660 and 1066 nm allow to measure the intrinsic optical properties of the breast tissue.

Optical bedside monitoring of cerebral perfusion: technological and methodological advances applied in a study on acute ischemic stroke.

We present results of a clinical study on bedside perfusion monitoring of the human brain by optical bolus tracking. We measure the kinetics of the contrast agent indocyanine green using time-domain near-IR spectroscopy (tdNIRS) in 10 patients suffering from acute unilateral ischemic stroke. In all patients, a delay of the bolus over the affected when compared to the unaffected hemisphere is found (mean: 1.

Nonlinear reconstruction of absorption and fluorescence contrast from measured diffuse transmittance and reflectance of a compressed-breast-simulating phantom.

We report on the nonlinear reconstruction of local absorption and fluorescence contrast in tissuelike scattering media from measured time-domain diffuse reflectance and transmittance of laser as well as laser-excited fluorescence radiation. Measurements were taken at selected source-detector offsets using slablike diffusely scattering and fluorescent phantoms containing fluorescent heterogeneities. Such measurements simulate in vivo data that would be obtained employing a scanning, time-domain fluorescence mammograph, where the breast is gently compressed between two parallel glass plates, and source and detector optical fibers scan synchronously at various source-detector offsets, allowing the recording of laser and fluorescence mammograms.

High-power fifth-harmonic generation of femtosecond pulses in the vacuum ultraviolet using a Ti:sapphire laser.

We demonstrate the generation of fifth-harmonic pulses at 161 nm, with an energy of up to 600 nJ and 160 fs pulse duration from a Ti:sapphire laser at 1 kHz repetition rate by four-wave difference-frequency mixing in argon-filled waveguides. The efficiency is greatly improved by coupling to higher-order transverse modes, as well as by coating the inner surface of the waveguide. A numerical model of the process yields an understanding of the main effects influencing the harmonic generation.

Generation of sub-30 fs ultraviolet pulses by Raman induced phase modulation in nitrogen.

We demonstrate compression of ultrashort light pulses in the ultraviolet (UV) by impulsively excited molecular wave-packets in nitrogen filled in a 25 cm long hollow waveguide of 128 microm diameter. After compression with CaF2 prisms the pulse duration was determined by XFROG to be 23 fs with a time-bandwidth product of 0.50.

Ultrafast predissociation dynamics of water molecules excited to the electronic C and D states.

Two-photon excitation with femtosecond laser pulses in the spectral range 240-250 nm was used to prepare vapor phase H(2)O and D(2)O in the C (1)B(1) and D (1)A(1) states. Both states are predissociated via the B (1)A(1) state, forming excited OH/OD(A (2)Sigma(+)) as well as ground state OH/OD(X (2)Pi). We used ultrashort infrared probe pulses (1.