Diffuse correlation spectroscopy with a fast Fourier transform-based software autocorrelator

Nanyang Technological University, Division of Bioengineering, School of Chemical and Biomedical Engineering, Singapore 637457, Singapore.
Journal of Biomedical Optics (Impact Factor: 2.86). 09/2012; 17(9):97004-1. DOI: 10.1117/1.JBO.17.9.097004
Source: PubMed


Diffuse correlation spectroscopy (DCS) is an emerging noninvasive technique that probes the deep tissue blood flow, by using the time-averaged intensity autocorrelation function of the fluctuating diffuse reflectance signal. We present a fast Fourier transform (FFT)-based software autocorrelator that utilizes the graphical programming language LabVIEW (National Instruments) to complete data acquisition, recording, and processing tasks. The validation and evaluation experiments were conducted on an in-house flow phantom, human forearm, and photodynamic therapy (PDT) on mouse tumors under the acquisition rate of ∼400  kHz. The software autocorrelator in general has certain advantages, such as flexibility in raw photon count data preprocessing and low cost. In addition to that, our FFT-based software autocorrelator offers smoother starting and ending plateaus when compared to a hardware correlator, which could directly benefit the fitting results without too much sacrifice in speed. We show that the blood flow index (BFI) obtained by using a software autocorrelator exhibits better linear behavior in a phantom control experiment when compared to a hardware one. The results indicate that an FFT-based software autocorrelator can be an alternative solution to the conventional hardware ones in DCS systems with considerable benefits.

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    ABSTRACT: Diffuse correlation spectroscopy (DCS) is an emerging modality for noninvasive deep tissue blood flow monitoring that is becoming increasingly popular; it conducts an autocorrelation analysis of fast fluctuating photon count signals from a single speckle. In this Letter, we show that the same level of deep tissue flow information can be obtained from a much simpler analysis on the spatial distribution of the speckles that is obtained by a CCD camera, which we named diffuse speckle contrast analysis (DSCA). Both the flow phantom experiment and in vivo cuff occlusion data are presented. DSCA can be considered a new optical modality that combines DCS and laser speckle contrast imaging (LSCI), which exploits simple instrumentation and analysis and yet is sensitive to deep tissue flow.
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    ABSTRACT: Recently, diffuse speckle contrast analysis (DSCA) was introduced as a competent modality for deep tissue blood flow measurement, where the speckle contrast is calculated over spatial domain on the CCD image of diffuse reflectance. In this paper, we introduce time-domain DSCA where temporal statistics are used for speckle contrast calculation and results in the same deep tissue flow measurement. This new modality is especially suitable for multi-channel real-time flowmetry, and we demonstrate its performance on human arm during cuff occlusion test. Independent component analysis (ICA) study on multi-channel data shows promising results about underlying physiology.
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