Self-mixing microprobe for monitoring microvascular perfusion in rat brain.

Measuring functional activity in brain in connection with neural stimulation faces technological challenges. Our goal is to evaluate, in relative terms, the real-time variations of local cerebral blood flow in rat brain, with a convenient spatial resolution. The use of laser Doppler flowmetry (LDF) probes is a promising approach but commercially available LDF probes are still too large (450 μm) to allow insertion in brain tissue without causing damage in an extension that may negatively impact local measurements.

Depth-kymography of vocal fold vibrations: part II. Simulations and direct comparisons with 3D profile measurements.

We report novel direct quantitative comparisons between 3D profiling measurements and simulations of human vocal fold vibrations. Until now, in human vocal folds research, only imaging in a horizontal plane was possible. However, for the investigation of several diseases, depth information is needed, especially when the two folds act differently, e.

Time development models for perfusion provocations studied with laser-Doppler flowmetry, applied to iontophoresis and PORH.

Objective: Clinical acceptance of laser-Doppler perfusion monitoring (LDPM) of microcirculation suffers from lack of quantitatively reliable signal data, due to varying tissue constitution, temperature, hydration, etc. In this article, we show that a novel approach using physiological models for response upon provocations provides quantitatively and clinically relevant time constants.

Methods: We investigated this for two provocation protocols: postocclusive reactive hyperemia (PORH) and iontophoresis shots, measured with LDPM on extremities.

New laryngoscope for quantitative high-speed imaging of human vocal folds vibration in the horizontal and vertical direction.

We report the design of a novel laser line-triangulation laryngoscope for the quantitative visualization of the three-dimensional movements of human vocal folds during phonation. This is the first successful in vivo recording of the three-dimensional movements of human vocal folds in absolute values. Triangulation images of the vocal folds are recorded at the rate of 4000 fps with a resolution of 256x256 pixels.

Depth-kymography: high-speed calibrated 3D imaging of human vocal fold vibration dynamics.

We designed and developed a laser line-triangulation endoscope compatible with any standard high-speed camera for a complete three-dimensional profiling of human vocal fold vibration dynamics. With this novel device we are able to measure absolute values of vertical and horizontal vibration amplitudes, length and width of vocal folds as well as the opening and closing velocities from a single in vivo measurement. We have studied, for the first time, the generation and propagation of mucosal waves by locating the position of its maximum vertical position and the propagation velocity.

Normalization of vasomotion in laser Doppler perfusion monitoring.

Laser Doppler flux signals show temporal fluctuations caused by physiological phenomena like heartbeat, respiration, and local variation of vascular tonus, vasomotion. This study investigates the influence of fiber arrangement, equipment and two probe locations on the variations in laser Doppler flux signals in five frequency bands in the absence of provocations. Two probes with detecting optical fibers at several distances from the illuminating source were used, as well as instruments from two manufacturers.

Diffusion model for iontophoresis measured by laser-Doppler perfusion flowmetry, applied to normal and preeclamptic pregnancies.

We present a physical model to describe iontophoresis time recordings. The model is a combination of monodimensional material diffusion and decay, probably due to transport by blood flow. It has four adjustable parameters, the diffusion coefficient, the decay constant, the height of the response, and the shot saturation constant, a parameter representing the relative importance of subsequent shots (in case of saturation).

Integrated optoelectronic probe including a vertical cavity surface emitting laser for laser Doppler perfusion monitoring.

An integrated optoelectronic probe with small dimensions, for direct-contact laser Doppler blood flow monitoring has been realized. A vertical cavity surface emitting laser (VCSEL), and a chip with photodetectors and all necessary electronics are integrated in a miniature probe head connected to a laptop computer. The computer sound processor is utilized for acquisition and digital signal processing of the incoming Doppler signal.

A model for post-occlusive reactive hyperemia as measured with laser-Doppler perfusion monitoring.

To facilitate the quantitative analysis of post-occlusive reactive hyperaemia (PORH), measured with laser-Doppler perfusion monitoring (LDPM) on extremities, we present a flow model for the dynamics of the perfusion of the tissue during PORH, based on three parameters: two time constants (tau1 and tau2) and the ratio of the maximum flux and the resting flux. With these three constants quantitative comparisons between experiments will be possible and, therefore, we propose to adopt this approach as future standard. For this reason, we also developed a computer program to perform the fit of the model to measured data.

Imaging of small vessels using photoacoustics: an in vivo study.

Background And Objectives: The ability to correctly visualize the architectural arrangement of microvasculature is valuable to many diverse fields in medicine. In this study, we applied photoacoustics (PA) to obtain high-resolution images of submillimeter blood vessels.

Study Design/materials And Methods: Short laser pulses are used to generate ultrasound from superficial blood vessels in several animal models.

Photoacoustic imaging of blood vessels with a double-ring sensor featuring a narrow angular aperture.

A photoacoustic double-ring sensor, featuring a narrow angular aperture, is developed for laser-induced photoacoustic imaging of blood vessels. An integrated optical fiber enables reflection-mode detection of ultrasonic waves. By using the cross-correlation between the signals detected by the two rings, the angular aperture of the sensor is reduced by a factor of 1.

Photoacoustic determination of blood vessel diameter.

A double-ring sensor was applied in photoacoustic tomographic imaging of artificial blood vessels as well as blood vessels in a rabbit ear. The peak-to-peak time (tau(pp)) of the laser (1064 nm) induced pressure transient was used to estimate the axial vessel diameter. Comparison with the actual vessel diameter showed that the diameter could be approximated by 2ctau(pp), with c the speed of sound in blood.

Suppression of dynamic laser speckle signals in multimode fibers of various lengths.

The effects of fiber coupling and fiber length on photocurrent fluctuations are studied when the light of a laser diode transmitted to and from a dynamic turbid medium by a step-index multimode fiber is studied. When the laser light is coupled asymmetrically, filling only the higher-order modes, the photocurrent fluctuations are suppressed significantly when fiber lengths of as much as 16 m are added between the laser and the medium. Addition of as much as 16 m of detection fiber, or any fiber in the case of symmetric light coupling, leads to much less or no suppression of the photocurrent fluctuations.

Poly(vinyl alcohol) gels for use as tissue phantoms in photoacoustic mammography.

Materials for solid photoacoustic breast phantoms, based on poly(vinyl alcohol) hydrogels, are presented. Phantoms intended for use in photoacoustics must possess both optical and acoustic properties of tissue. To realize the optical properties of tissue, one approach was to optimize the number of freezing and thawing cycles of aqueous poly(vinyl alcohol) solutions, a procedure which increases the turbidity of the gel while rigidifying it.

Glass-fiber self-mixing intra-arterial laser Doppler velocimetry: signal stability and feedback analysis.

We have developed a blood velocimeter based on the principle of self-mixing in a semiconductor laser diode through an optical fiber. The intensity of the light is modulated by feedback from moving scattering particles that contain the Doppler-shift frequency. Upon feedback the characteristics of the laser diode change.