We have employed near-infrared optical methods to measure noninvasively the dynamics of muscle blood flow and oxygen saturation $(StO2)$ during cuff occlusion and plantar flexion exercise. Relative muscle oxygen consumption $(rVO2)$ was also computed from these data. Diffuse correlation spectroscopy provides information about blood flow, and diffuse reflectance spectroscopy provides information about blood oxygenation. Ten healthy subjects and one patient with peripheral arterial disease (PAD) were studied during 3-min arterial cuff occlusion of arm and leg, and during 1-min plantar flexion exercise. Signals from different layers (cutaneous tissues and muscles) during cuff occlusion were differentiated, revealing strong hemodynamic responses from muscle layers. During exercise in healthy legs, the observed $∼4.7$ fold increase in relative blood flow (rBF) was significantly lower than the corresponding increase in $rVO2$$(∼7$ fold). The magnitudes of rBF and $rVO2$ during exercise in the PAD patient were $∼1/2$ of the healthy controls, and the $StO2$ recovery time was twice that of the controls. The hybrid instrument improves upon current technologies for measuring muscle responses by simultaneously measuring rBF and $StO2.$ The instrument thus provides a method for evaluation of microcirculation and muscle metabolism in patients with vascular diseases. © 2005 Society of Photo-Optical Instrumentation Engineers.

Approximately 30,000 infants are born each year in the United States with congenital heart disease (CHD), with about a third requiring major surgical repair in the first few months of life.¹ Recent advances in cardiac surgery for complex CHD have minimized infant mortality. Thus, the current focus in the clinical community is oriented toward preventing neurologic injury and improving neurocognitive outcome in these high-risk babies who grow up to face various medical and academic challenges.^{2, 3}

We combine diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) to noninvasively monitor early hemodynamic response to neoadjuvant chemotherapy in a breast cancer patient. The potential for early treatment monitoring is demonstrated. Within the first week of treatment (day 7) DOS revealed significant changes in tumor/normal contrast compared to pretreatment (day 0) tissue concentrations of deoxyhemoglobin $(rctHHbT∕N=69±21%)$, oxyhemoglobin $(rctO2HbT∕N=73±25%)$, total hemoglobin $(rctTHbT∕N=72±17%)$, and lipid concentration $(rctLipidT∕N=116±13%)$. Similarly, DCS found significant changes in tumor/normal blood flow contrast $(rBFT∕N=75±7%$ on day 7 with respect to day 0). Our observations suggest the combination of DCS and DOS enhances treatment monitoring compared to either technique alone. The hybrid approach also enables construction of indices reflecting tissue metabolic rate of oxygen, which may provide new insights about therapy mechanisms.

Traumatic brain injury (TBI) is a leading cause of childhood morbidity and mortality in the United States, with an annual rate of $\sim 200$ per 100,000 children requiring hospitalization.¹ The increasing monetary costs result not only from the acute intensive care for these patients but also from long-term care that is often necessary. Brain injuries in these patients result from both the primary trauma and secondary insults, such as reductions in cerebral blood flow, derangements in cerebral metabolism, and the ensuing ischemic injuries that continue to progress well after the traumatic event. Optimal therapeutic efficacy thus requires knowledge of cerebral blood flow, oxygen supply, and oxygen consumption in patients after TBI. In this study, we explored the feasibility of two diffuse optical techniques, diffuse reflectance spectroscopy (DRS) and diffuse correlation spectroscopy (DCS), for continuous, noninvasive measurement of cerebral blood flow and blood oxygenation at the bedside.

In this study we evaluate the influences of optical property assumptions on near-infrared diffuse correlation spectroscopy (DCS) flow index measurements. The optical properties, absorption coefficient (µ_a) and reduced scattering coefficient (µ_s′), are independently varied using liquid phantoms and measured concurrently with the flow index using a hybrid optical system combining a dual-wavelength DCS flow device with a commercial frequency-domain tissue-oximeter. DCS flow indices are calculated at two wavelengths (785 and 830 nm) using measured µ_a and µ_s′ or assumed constant µ_a and µ_s′. Inaccurate µ_s′ assumptions resulted in much greater flow index errors than inaccurate µ_a. Underestimated/overestimated µ_s′ from −35%/+175% lead to flow index errors of +110%/−80%, whereas underestimated/overestimated µ_a from −40%/+150% lead to −20%/+40%, regardless of the wavelengths used. Examination of a clinical study involving human head and neck tumors indicates up to +280% flow index errors resulted from inter-patient optical property variations. These findings suggest that studies involving significant µ_a and µ_s′ changes should concurrently measure flow index and optical properties for accurate extraction of blood flow information.

This pilot study explores the potential of noninvasive diffuse correlation spectroscopy (DCS) and diffuse reflectance spectroscopy (DRS) for monitoring early relative blood flow $(rBF)$, tissue oxygen saturation $(StO2)$, and total hemoglobin concentration $(THC)$ responses to chemo-radiation therapy in patients with head and neck tumors. $rBF$, $StO2$, and $THC$ in superficial neck tumor nodes of eight patients are measured before and during the chemo-radiation therapy period. The weekly $rBF$, $StO2$, and $THC$ kinetics exhibit different patterns for different individuals, including significant early blood flow changes during the first two weeks. Averaged blood flow increases $(52.7±9.7)%$ in the first week and decreases $(42.4±7.0)%$ in the second week. Averaged $StO2$ increases from $(62.9±3.4)%$ baseline value to $(70.4±3.2)%$ at the end of the second week, and averaged $THC$ exhibits a continuous decrease from pretreatment value of $(80.7±7.0)$$[μM]$ to $(73.3±8.3)$$[μM]$ at the end of the second week and to $(63.0±8.1)$$[μM]$ at the end of the fourth week of therapy. These preliminary results suggest daily diffuse-optics-based therapy monitoring is feasible during the first two weeks and may have clinical promise.