An affordable, wearable, fiber-free pulsed-mode diffuse speckle contrast flowmetry (PM-DSCF) sensor for noninvasive measurements of deep cerebral blood flow

TL;DR

This paper introduces a novel pulse-mode diffuse speckle contrast flowmetry sensor that significantly enhances tissue penetration depth, enabling noninvasive, continuous cerebral blood flow monitoring in adult humans with improved safety and performance.

Contribution

The study develops a fiber-free, wearable PM-DSCF system that achieves deeper tissue penetration and reliable CBF measurements in adults, surpassing previous CW-DSCF limitations.

Findings

Maximum source-detector distance increased to 35 mm

Successfully detected CBF variations during head-up tilting

Penetration depth improved from ~7.5 mm to ~17.5 mm

Abstract

Significance: Measuring cerebral blood flow (CBF) is crucial for diagnosing various cerebral diseases. An affordable, wearable, and fiber-free continuous-wave speckle contrast flowmetry (CW-DSCF) technique has been developed for continuous monitoring of CBF variations. However, its application in adult humans is limited by shallow tissue penetration. Aim: To develop an innovative pulse-mode DSCF (PM-DSCF) system for continuous monitoring of CBF variations in adult humans. Approach: The PM-DSCF utilizes an 808 nm laser diode and a small NanEye camera to capture diffuse laser speckle fluctuations caused by red blood cell movement in the brain (i.e., CBF). Operating in short-pulse mode (duty cycle < 5%), the system maximizes peak pulse light power for deeper tissue penetration, while ensuring that the average power density remains within ANSI safety standards for skin exposure. The PM-DSCF was evaluated on tissue-simulating phantoms and in adult humans. Results: The maximum effective source-detector distance increased from 15 mm (CW-DSCF) to 35 mm (PM-DSCF). The PM-DSCF successfully detected CBF variations in adult brains during head-up-tilting experiments, consistent with physiological expectations. Conclusions: Switching from CW mode to PM mode significantly increases the maximum tissue penetration depth from ~7.5 mm (CW-DSCF) to ~17.5 mm (PM-DSCF), enabling successful CBF measurements in adult humans.