Turgut Durduran

Multidistance diffuse correlation spectroscopy for simultaneous estimation of blood flow index and optical properties

Abstract. Traditionally, diffuse correlation spectroscopy (DCS) measures microvascular blood flow by fitting a physical model to the measurement of the intensity autocorrelation function from a single source-detector pair. This analysis relies on the accurate knowledge of the optical properties, absorption, and reduced scattering coefficients of the medium. Therefore, DCS is often deployed together with diffuse optical spectroscopy. We present an algorithm that employs multidistance DCS (MD-DCS) for simultaneous measurement of blood flow index, as well as an estimate of the optical properties of the tissue. The algorithm has been validated through noise-free and noise-added simulated data and phantom measurements. A longitudinal in vivo measurement of a mouse tumor is also shown. MD-DCS is introduced as a stand-alone system for small source-detector separations (<2u2009u2009cm) for noninvasive measurement of microvascular blood flow.

Compact, multi-exposure speckle contrast optical spectroscopy (SCOS) device for measuring deep tissue blood flow

Speckle contrast optical spectroscopy (SCOS) measures absolute blood flow in deep tissue, by taking advantage of multi-distance (previously reported in the literature) or multi-exposure (reported here) approach. This method promises to use inexpensive detectors to obtain good signal-to-noise ratio, but it has not yet been implemented in a suitable manner for a mass production. Here we present a new, compact, low power consumption, 32 by 2 single photon avalanche diode (SPAD) array that has no readout noise, low dead time and has high sensitivity in low light conditions, such as in vivo measurements. To demonstrate the capability to measure blood flow in deep tissue, healthy volunteers were measured, showing no significant differences from the diffuse correlation spectroscopy. In the future, this array can be miniaturized to a low-cost, robust, battery operated wireless device paving the way for measuring blood flow in a wide-range of applications from sport injury recovery and training to, on-field concussion detection to wearables.

Hardware simulator for optical correlation spectroscopy with Gaussian statistics and arbitrary correlation functions

We present a new hardware simulator (HS) for characterization, testing and benchmarking of digital correlators used in various optical correlation spectroscopy experiments where the photon statistics is Gaussian and the corresponding time correlation function can have any arbitrary shape. Starting from the HS developed in [Rev. Sci. Instrum. 74, 4273 (2003)], and using the same I/O board (PCI-6534 National Instrument) mounted on a modern PC (Intel Core i7-CPU, 3.07GHz, 12GB RAM), we have realized an instrument capable of delivering continuous streams of TTL pulses over two channels, with a time resolution of Δt = 50ns, up to a maximum count rate of 〈I〉 ∼ 5MHz. Pulse streams, typically detected in dynamic light scattering and diffuse correlation spectroscopy experiments were generated and measured with a commercial hardware correlator obtaining measured correlation functions that match accurately the expected ones.

Pre-clinical longitudinal monitoring of hemodynamic response to anti-vascular chemotherapy by hybrid diffuse optics

The longitudinal effect of an anti-vascular endothelial growth factor receptor 2 (VEGFR-2) antibody (DC 101) therapy on a xenografted renal cell carcinoma (RCC) mouse model was monitored using hybrid diffuse optics. Two groups of immunosuppressed male nude mice (seven treated, seven controls) were measured. Tumor microvascular blood flow, total hemoglobin concentration and blood oxygenation were investigated as potential biomarkers for the monitoring of the therapy effect twice a week and were related to the final treatment outcome. These hemodynamic biomarkers have shown a clear differentiation between two groups by day four. Moreover, we have observed that pre-treatment values and early changes in hemodynamics are highly correlated with the therapeutic outcome demonstrating the potential of diffuse optics to predict the therapy response at an early time point.

A new method utilizing novel single-photon avalanche diode arrays for multi-exposure laser speckle flowmetry

A new approach for multi-exposure laser speckle contrast imaging (MESI) which exploits a novel single-photon avalanche diode array is presented. High frame-rate and sensitivity allow rapid single-shot acquisition MESI in phantoms and small animals.

Simultaneous, non-invasive measurement of local tissue hemodynamics, oxygen metabolism and gold nanorod concentration in vivo

A hybrid broadband diffuse optical and diffuse correlation spectroscopy system is used to measure local tissue hemodynamics, oxygen metabolism and gold nanorod concentration. The objective is to pr ...

Practical height correction for diffuse optical spectroscopy to account for curved tissue surfaces

Non-contact broadband diffuse optical spectroscopy that is meant for longitudinal study of superficial tumor models suffers from systematic errors due to tissue surface. We propose a practical heig ...

Bedside monitoring of cerebral blood flow in the hyper-acute phase of ischemic stroke

Diffuse correlation spectroscopy is used to monitor cerebral blood flow changes at the hyper-acute phase of ischemic stroke (1) detecting local hemodynamic changes due to recanalization and (2) in cerebrovascular response to orthostatic challenges.

The effect of obstructive sleep apnea on the cerebral blood flow response to orthostatic stress

Changes in cerebral blood flow in response to orthostatic stress in obstructive sleep apnea patients were measured using diffuse correlation spectroscopy. Clinical indices derived from arterial oxygen saturation alter the cerebrovascular response.

Speckle contrast optical tomography (SCOT): Reconstructing the three dimensional distribution of blood flow in deep tissues

A novel tomographic imaging method called speckle contrast optical tomography (SCOT) to image blood flow in deep tissue is presented. Method is based on Born approximation and is validated using the tissue simulating phantoms.