Self-mixing microprobe for monitoring microvascular perfusion in rat brain

Abstract

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 lm) to allow insertion in brain tissue without causing damage in an extension that may negatively impact local measurements. The self-mixing technique coupled to LDF is herein proposed to overcome limitations of the minimal diameter of the probe imposed by non-self-mixing probes (commercial available probes). Our Monte Carlo simulations show that laser photons have a mean penetration depth of 0.15 mm, on the rat brain with the 785 nm laser light microprobe. Moreover, three self-mixing signal processing methods are tested: counting method, autocorrelation method, power spectrum method. The perfusion signal computed shows a good linearity with the scatterers velocity, for the three methods (a determination coefficient close to one is obtained), for the in vitro measurements. Furthermore, we believe that these indicators can be used to monitor local blood flow changes in the rat brain.

Concurrent Reflectance Confocal Microscopy and Laser Doppler Flowmetry to Improve Skin Cancer Imaging: A Monte Carlo Model and Experimental Validation

“…From the diffused photons in the turbid skin medium, some of them make their way out of the tissue and return to the detection system of the LDF, which usually involves an interferometric technique and a photodetector to acquire the beat frequency. Perfusion is defined as the product of the average RBCs’ velocity and concentration and is proportional to the first moment of the power spectrum of the detected signal [ 51 ]: where ω is the angular frequency and is the Doppler power spectrum. By raster scanning the beam on the skin surface, we can create the perfusion map.…”

Laser feedback interferometry and applications: a review

“…The accuracy was better than 0.1 L∕ min in the large range of 0 to 6 L∕ min of clinical interest. Figueiras et al 91 applied the laser self-mixing velocimeter as a microprobe for monitoring microvascular perfusion in rat brain. The mean detection depth was 0.15 mm, and the size of the probe was as small as 785 nm.…”

Potential of Laser Doppler Flowmetry in the Medical Needle Insertion Procedures

“…Laser Doppler Flowmetry (LDF) has been implemented in clinical practice since 1981, when Bonner and Nossal have developed a model for laser Doppler measurements of blood flow in tissue becoming a standard for LDF measurements [6]. Based on this model, LDF has been investigated for static monitoring of skin [7,8], dental tissue [9] and brain [10] microcirculation. Moreover, commercial LDF devices for microvascular research are widely available for clinical use [11].…”