Tissue metabolism and hemodynamics are known to be abnormal in several pathologies. Peripheral arterial disease is one such example where tissue metabolism is reduced as an adaptive mechanism to hypoxia. In this same disease, pulsatile hemodynamic signatures are deteriorated by progressive arterial obstruction. Interrogating tissue with coherent light sources offers a simple and effective means for noninvasive cardiovascular assessment by directly measuring tissue oxygen metabolism and pulsatile hemodynamics.

In this work we develop a wide-field, noncontact imaging technique that utilizes coherent light and pixel-based detectors to map metabolism and blood flow at high speeds. First, we expand upon previous work on Coherent Spatial Frequency Domain Imaging (cSFDI) by mitigating bottlenecks in data acquisition. Adapting advanced image demodulation techniques along with simplified projection optics, we are able to recover the tissue absorption and reduced-scattering coefficients (µa and µs’, respectively), in addition to speckle contrast from a single snapshot. Next, we extend this technique to two wavelengths allowing for the recovery blood flow, oxyhemoglobin and deoxyhemoglobin at 16 frames per second. We then implement a framework for extracting the tissue metabolic rate of oxygen consumption (tMRO2). We validate tMRO2 measurements using yeast-hemoglobin phantoms in which oxygen is progressively extracted from bovine hemoglobin with baker’s yeast. As a proof of concept, we perform a series of in vivo arterial occlusion protocols and demonstrate sensitivity to metabolic changes caused by transient tissue ischemia. Finally, we sequence a rabbit model of cyanide poisoning showing that cSFDI is capable of recovering metabolic dynamics consistent with mitochondrial uncoupling.

At the same time, we investigate pulsatile signals due to the cardiac cycle using a novel device that measures coherent speckle patterns in transmission geometry; this technique is called Affixed Transmission Speckle Analysis (ATSA). From a single coherent light, source we obtain two signals, one related to blood flow and one related to vascular compliance. We demonstrate sensitivity to arterial stiffness and vascular tone using novel processing methods aimed at characterizing timing offsets between the signals along with embedded harmonic content. Our results suggest that parameters extracted using our processing methods are sensitive to both arterial stiffness and vascular tone. Overall, this work demonstrates that coherent light-based techniques constitute a promising low-cost strategy for noninvasive cardiovascular assessment.

In this work we introduce a modified form of laser speckle imaging (LSI) referred to as affixed transmission speckle analysis (ATSA) that uses a single coherent light source to probe two physiological signals: one related to pulsatile vascular expansion (classically known as the photoplethysmographic (PPG) waveform) and one related to pulsatile vascular blood flow (named here the speckle plethysmographic (SPG) waveform). The PPG signal is determined by recording intensity fluctuations, and the SPG signal is determined via the LSI dynamic light scattering technique. These two co-registered signals are obtained by transilluminating a single digit (e.g. finger) which produces quasi-periodic waveforms derived from the cardiac cycle. Because PPG and SPG waveforms probe vascular expansion and flow, respectively, in cm-thick tissue, these complementary phenomena are offset in time and have rich dynamic features. We characterize the timing offset and harmonic content of the waveforms in 16 human subjects and demonstrate physiologic relevance for assessing microvascular flow and resistance.