Portable Near-Infrared Technologies and Devices for Noninvasive Assessment of Tissue Hemodynamics

Abstract

Tissue hemodynamics, including the blood flow, oxygenation, and oxygen metabolism, are closely associated with many diseases. As one of the portable optical technologies to explore human physiology and assist in healthcare, near-infrared diffuse optical spectroscopy (NIRS) for tissue oxygenation measurement has been developed for four decades. In recent years, a dynamic NIRS technology, namely, diffuse correlation spectroscopy (DCS), has been emerging as a portable tool for tissue blood flow measurement. In this article, we briefly describe the basic principle and algorithms for static NIRS and dynamic NIRS (i.e., DCS). Then, we elaborate on the NIRS instrumentation, either commercially available or custom-made, as well as their applications to physiological studies and clinic. The extension of NIRS/DCS from spectroscopy to imaging was depicted, followed by introductions of advanced algorithms that were recently proposed. The future prospective of the NIRS/DCS and their feasibilities for routine utilization in hospital is finally discussed.

Improved accuracy of cerebral blood flow quantification in the presence of systemic physiology cross-talk using multi-layer Monte Carlo modeling

“…5,8 DCS takes advantage of this physical phenomenon to monitor time-varying blood flow non-invasively and is currently being used in various research applications. 5,[8][9][10][11][12][13][14][15] A particularly successful application area is the CBF monitoring of neonates, for whom the relatively thin skull results in high brain sensitivity. 16,17 Extending the application of DCS to bedside brain monitoring of adults, however, requires accounting for the influence of systemic variations of scalp blood flow (SBF) that have the potential to strongly contaminate changes in the calculated cerebral blood flow index (CBF i ).…”

Diffuse correlation spectroscopy and frequency-domain near-infrared spectroscopy for measuring microvascular blood flow in dynamically exercising human muscles

“…Unfortunately, DCS is highly sensitive to motion artifacts that distort signals coming from the exercising muscle. Very recently, 11 studies carried out on human skeletal muscle, utilizing integrated NIRS/DCS instru-ments, were reviewed by Hou et al (27). In most of those studies, BF i was measured during and/or after cuff occlusion.…”

“…In the last 20 years a complementary optical technique, near-infrared diffuse correlation spectroscopy (DCS), has been developed for the continuous measurement of BF in tissue. Applications to human skeletal muscle, breast cancer, and the brain cortex (11,27,37) have been demonstrated. DCS uses the temporal fluctuations of diffusely reflected light to quantify the motion of moving scatterers, which in tissue is dominated by the motion of red blood cells; DCS provides a noninvasive estimate of deep tissue microvascular BF as a BF index (BF i ) with units cm 2 /s.…”

“…Regarding the application of the hybrid FDNIRS-DCS system for human skeletal muscle studies, so far, the instrument has been utilized only to measure relative BF i changes in flexor digitorum superficialis muscle BF during the 10-s end-stage resting periods of exercise of varying power (24). In the latter (24) and in most of the prior studies (utilizing noncommercial devices), recently reviewed by Hou et al (27), DCS has never been used continuously during dynamic exercise because of the large motion artifacts inherent to the DCS method, which mask the motion of the red blood cells. In fact, previous works have limited BF i analysis to short intervals during the exercise, in which the muscle is not contracted and not moving, or during plantar flexion exercise (21,38).…”

Simultaneous measurements of tissue blood flow and oxygenation using a wearable fiber-free optical sensor

“… 6 – 11 There are also growing interests in simultaneous measurements of blood flow and oxygenation alterations as more comprehensive biomarkers for tissue health/injury than one single parameter alone. 12 – 14 Furthermore, a combination of tissue blood flow and oxygenation allows to estimate the metabolic rate of tissue oxygen consumption, 12 , 15 another important functional parameter highly associated with tissue pathology.…”