Alexander Serov

Laser Doppler perfusion imaging with a complimentary metal oxide semiconductor image sensor

We utilized a complimentary metal oxide semiconductor video camera for fast flow imaging with the laser Doppler technique. A single sensor is used for both observation of the area of interest and measurements of the interference signal caused by dynamic light scattering from moving particles inside scattering objects. In particular, we demonstrate the possibility of imaging the distribution of the moving red blood cell concentration. This is a first step toward laser Doppler imaging without scanning parts, leading to a much faster imaging procedure than with existing mechanical laser Doppler perfusion imagers.

Prediction of the photodetector signal generated by Doppler-induced speckle fluctuations: theory and some validations

A theoretical framework is proposed for describing the laser Doppler photodetector signal. The theory allows for predicting the power of the photocurrent fluctuations. It is valid for a detector of arbitrary size. The input data required for application of the theory are the angular distribution of the detected light, the fraction of Doppler-shifted photons, and the active detector size. The theory is based on the time-domain approach to the statistics of dynamic speckle patterns on the photodetector. An experiment was carried out to validate some aspects of our theory. The consequences of the speckle dynamics for the various modes of laser Doppler flowmetry are discussed.

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. In this paper, the design of the laser Doppler perfusion monitor is described and its performance is evaluated. We demonstrate our perfusion monitor to be less sensitive to subject motion than a commercial fiber-optic device. For medium and high perfusion levels, the performance of our integrated probe is comparable to the fiber-optic flowmeter containing a normal edge-emitting laser diode. For very low perfusion levels, the signal-to-noise ratio of the fiber-optic device is higher. This difference can mainly be attributed to the shorter coherence length of the VCSEL compared with the edge-emitting laser diode

Method for estimation of the fraction of Doppler-shifted photons in light scattered by a mixture of moving and stationary scatterers

A method for the absolute determination of the fraction of Doppler-shifted photons in light scattered by mixture of moving and stationary scatterers is proposed. It based on the theoretical approach developed in our group to predict the signal power fluctuations of an integrated Doppler- induced speckle pattern on the photodetector. A benefit of using a multimode step-index optical fiber as a scattering sample-to-detector interface is considered. An experimental validation of the method has been performed and experimentally obtained data are in a good agreement with the theory. As one of a practical application of the method the fraction of Doppler-shifted photons in light backscattered from human skin has been measured and the results are reported.

Dynamic speckle patterns formed by a mixture of moving and stationary scatterers : theory and experiment

A theoretical framework is proposed for the description of the photodetector signal generated by Doppler-induced speckle fluctuations. The theory allows for predicting the power of the photo current fluctuations. It is valid for a detector of arbitrary size. The input data required for application of the theory are the angular distribution of the detected light, the fraction of Doppler shifted photons and the active detector size. The theory is based on the time domain approach to the statistics of dynamic speckle patterns on the photodetector. An experiment has been carried out to validate some aspects of our theory. The consequences of the speckle dynamics for the various modes of laser Doppler Flowmetry are discussed. As one of a practical application of the theory the fraction of Doppler- shifted photons in light back scattered from human skin has been measured in vivo. .

New generation of integrated probes for laser Doppler perfusion monitoring: construction and in-vivo results

Integrated probes have been developed containing the essential optoelectronic components necessary for monitoring tissue perfusion using the laser Doppler principle. The device contains a VCSEL for illumination, and a chip with photodetectors, amplifiers for signal enhancement, and digital circuitry for external probe control. VCSEL and detector chip are mounted on a common ceramic platform. A Peltier element may be included for temperature stabilisation, or thermal cycling for physiological purposes. Two special chips have been developed: one containing an array of five detectors, at various distances from the laser, which will allow for some degree of depth discrimination, and a single detector chip. In this paper the probe designs are presented and some results of in vivo measurements are shown.

Integrated probes containing a VCSEL and a multidetector chip for laser Doppler tissue perfusion monitoring

An integrated probe has been developed containing the essential optoelectronic components necessary for monitoring tissue perfusion using the laser Doppler principle. The device includes a VCSEL for illumination, and a chip containing photodetectors, analog amplifiers for signal enhancement, and digital circuitry for external probe control. VCSEL and detector chip are mounted on a common ceramic platform, which also includes an integrated temperature sensor. A Peltier element may be included for temperature stabilization, or thermal cycling for physiological purposes. Two special chips have been developed: one containing an array of five detectors, at various distances from the laser, which will allow for some degree of depth discrimination, and a single detector chip. In this paper the multidetector chip and the probe design are presented.

Dynamic light scattering: a quantitative approach to determination of the fraction of Doppler-shifted photons

We suggest a method for quantitative determination of the total fraction of Doppler-shifted photons in light scattered by an object containing both moving and static scatterers. The method is based on two approaches: time-varying speckle and laser Doppler were we consider the speckle fluctuations as the primary phenomenon with the Doppler effect being the main cause of these fluctuations. A validation of the method and one of its practical applications is demonstrated. The total fraction of Doppler-shifted photons in light backscattered from human skin has been measured in vivo.