The diffuse correlation spectroscopy (DCS) and diffuse near infrared spectroscopy (DNIRS) are the contemporary non-invasive optical methods which have turned out now to be ones of the most required optical tools for assessing tissue health, in regards to mammography, brain, and deep tissue injury. Earlier we reported on an observation, within the DCS technics, of development of pressure injuries measuring dermal and subcutaneous red blood cell motion; the data obtained has produced remarkably a characteristic decay time of the light intensity temporal correlation function being five times larger for patients of the group with developing open pressure injuries as compared with the group exhibiting healthier stage. The quantitative determination of the characteristic time required a definite picture of scatterer motion. For quantitative study the crucial problem to solve is a proper account for the scattering anisotropy. We perform comparative simulations of the diffuse photon density wave (DPDW) signals and the temporal intensity correlation functions either with the Henyey-Greenstein (HG) or Rayleigh-Gans (RG) phase functions, which we consider is more appropriate as the hard sphere suspension model for imitating a tissue. We find that for a half space geometry the results obtained for these two scattering patterns turn to be quite close; however for finite size tissue geometries results of simulations of the source-detector plot for backscattered intensity differ noticeably at small distances; simulating the temporal correlation function with these two phase functions we find the blood flow to be different for different scattering patterns in case of spatial restrictions. The DPDW methodology is widely used in a number of biomedical applications. Here we present results of Monte Carlo simulations that employ an effective numerical procedure, based upon a description of radiative transfer in terms of the Bethe-Salpeter equation, and compare them with measurements from Intralipid aqueous solutions. We find the Monte Carlo simulations and measurements to be in a very good agreement for a wide range of source-detector separations.
Pressure injuries (PIs) originate beneath the surface of the skin at the interface between bone and soft tissue. We used diffuse correlation spectroscopy (DCS) and diffuse near-infrared spectroscopy (DNIRS) to predict the development of PIs by measuring dermal and subcutaneous red cell motion and optical absorption and scattering properties in 11 spinal cord injury subjects with only nonbleachable redness in the sacrococcygeal area in a rehabilitation hospital and 20 healthy volunteers. A custom optical probe was developed to obtain continuous DCS and DNIRS data from sacrococcygeal tissue while the subjects were placed in supine and lateral positions to apply pressure from body weight and to release pressure, respectively. Rehabilitation patients were measured up to four times over a two-week period. Three rehabilitation patients developed open PIs (POs) within four weeks and eight patients did not (PNOs). Temporal correlation functions in the area of redness were significantly different (p<0.01) during both baseline and applied pressure stages for POs and PNOs. The results show that our optical method may be used for the early prediction of ulcer progression.
Microcirculation is essential for proper supply of oxygen and nutritive substances to the biological tissue and the removal of waste products of metabolism. The determination of microcirculatory blood flow (mBF) is therefore of substantial interest to clinicians for assessing tissue health; particularly in pressure ulceration and suspected deep tissue injury. The goal of this pilot clinical study was to assess deep-tissue pressure ulceration by non-invasively measuring mBF using Diffuse Correlation Spectroscopy (DCS). DCS provides information about the flow of red blood cells in the capillary network by measuring the temporal autocorrelation function of scattering light intensity. A novel optical probe was developed in order to obtain measurements under the load of the subject’s body as pressure is applied (ischemia) and then released (reperfusion) on sacrococcygeal tissue in a hospital bed. Prior to loading measurements, baseline readings of the sacral region were obtained by measuring the subjects in a side-lying position. DCS measurements from the sacral region of twenty healthy volunteers have been compared to those of two patients who initially had similar non-blanchable redness. The temporal autocorrelation function of scattering light intensity of the patient whose redness later disappeared was similar to that of the average healthy subject. The second patient, whose redness developed into an advanced pressure ulcer two weeks later, had a substantial decrease in blood flow while under the loading position compared to healthy subjects. Preliminary results suggest the developed system may potentially predict whether non-blanchable redness will manifest itself as advanced ulceration or dissipate over time.
KEYWORDS: Monte Carlo methods, Scattering, Sensors, Diffusion, Modulation, Diffuse photon density waves, Anisotropy, Signal detection, Photon transport, Tissues
Diffuse photon density wave (DPDW) methodology is widely used in a number of biomedical applications. Here, we present results of Monte Carlo simulations that employ an effective numerical procedure based upon a description of radiative transfer in terms of the Bethe–Salpeter equation. A multifrequency noncontact DPDW system was used to measure aqueous solutions of intralipid at a wide range of source–detector separation distances, at which the diffusion approximation of the radiative transfer equation is generally considered to be invalid. We find that the signal–noise ratio is larger for the considered algorithm in comparison with the conventional Monte Carlo approach. Experimental data are compared to the Monte Carlo simulations using several values of scattering anisotropy and to the diffusion approximation. Both the Monte Carlo simulations and diffusion approximation were in very good agreement with the experimental data for a wide range of source–detector separations. In addition, measurements with different wavelengths were performed to estimate the size and scattering anisotropy of scatterers.
This paper describes a novel, wearable, battery powered ultrasound applicator that was evaluated as a therapeutic tool for healing of chronic wounds, such as venous ulcers. The low frequency and low intensity (~100mW/cm2) applicator works by generating ultrasound waves with peak-to-peak pressure amplitudes of 55 kPa at 20 kHz. The device was used in a pilot human study (n=25) concurrently with remote optical (diffuse correlation spectroscopy - DCS) monitoring to assess the healing outcome. More specifically, the ulcers’ healing status was determined by measuring tissue oxygenation and blood flow in the capillary network. This procedure facilitated an early prognosis of the treatment outcome and – once verified - may eventually enable customization of wound management. The outcome of the study shows that the healing patients of the ultrasound treated group had a statistically improved (p<0.05) average rate of wound healing (20.6%/week) compared to the control group (5.3%/week). In addition, the calculated blood flow index (BFI) decreased more rapidly in wounds that decreased in size, indicating a correlation between BFI and wound healing prediction. Overall, the results presented support the notion that active low frequency ultrasound treatment of chronic venous ulcers accelerates healing when combined with the current standard clinical care. The ultrasound applicator described here provides a user-friendly, fully wearable system that has the potential for becoming the first device suitable for treatment of chronic wounds in patient's homes, which - in turn - would increase patients’ compliance and improve quality of life.
The Diffuse Photon Density Wave (DPDW) methodology is widely used in a number of biomedical applications. Here we present results of Monte Carlo simulations that employ an effective numerical procedure, based upon a description of radiative transfer in terms of the Bethe-Salpeter equation, and compare them with measurements from Intralipid aqueous solutions. In our scheme every act of scattering contributes to the signal. We find the Monte Carlo simulations and measurements to be in a very good agreement for a wide range of source –detector separations.
The ability to determine the depth and degree of cutaneous and subcutaneous tissue damage is critical for medical
applications such as burns and pressure ulcers. The Diffuse Photon Density Wave (DPDW) methodology at near infrared
wavelengths can be used to non-invasively measure the optical absorption and reduced scattering coefficients of tissue at
depths of several millimeters. A multi-frequency DPDW system with one light source and one detector was constructed
so that light is focused onto the tissue surface using an optical fiber and lens mounted to a digitally-controlled actuator
which changes the distance between light source and detector. A variable RF generator enables the modulation frequency
to be selected between 50 to 400MHz. The ability to digitally control both source-detector separation distance and
modulation frequency allows for virtually unlimited number of data points, enabling precise selection of the volume and
depth of tissue that will be characterized. Suspensions of Intralipid and india ink with known absorption and reduced
scattering coefficients were used as optical phantoms to assess device accuracy. Solid silicon phantoms were formulated
for stability testing. Standard deviations for amplitude and phase shift readings were found to be 0.9% and 0.2 degrees
respectively, over a one hour period. The ability of the system to quantify tissue damage in vivo at multiple depths was
tested in a porcine burn model.
A pilot human study is conducted to evaluate the potential of using diffuse photon density wave (DPDW) methodology at near-infrared (NIR) wavelengths (685 to 830 nm) to monitor changes in tissue hemoglobin concentration in diabetic foot ulcers. Hemoglobin concentration is measured by DPDW in 12 human wounds for a period ranging from 10 to 61 weeks. In all wounds that healed completely, gradual decreases in optical absorption coefficient, oxygenated hemoglobin concentration, and total hemoglobin concentration are observed between the first and last measurements. In nonhealing wounds, the rates of change of these properties are nearly zero or slightly positive, and a statistically significant difference (p<0.05) is observed in the rates of change between healing and nonhealing wounds. Differences in the variability of DPDW measurements over time are observed between healing and nonhealing wounds, and this variance may also be a useful indicator of nonhealing wounds. Our results demonstrate that DPDW methodology with a frequency domain NIR device can differentiate healing from nonhealing diabetic foot ulcers, and indicate that it may have clinical utility in the evaluation of wound healing potential.
Changes of optical properties of wound tissue in hairless rats were quantified by diffuse photon density wave methodology at near-infrared frequencies. The diffusion equation for semi-infinite media was used to calculate the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain device. There was an increase in the absorption and scattering coefficients and a decrease in blood saturation of the wounds compared with the nonwounded sites. The changes correlated with the healing stage of the wound. The data obtained were supported by immunohistochemical analysis of wound tissue. These results verified now by two independent animal studies could suggest a noninvasive method to detect the progress of wound healing.
Quantitative non-invasive assessment of the wound healing process in chronic wounds may assist in selection and
monitoring of expensive treatments. The Diffuse Photon Density Wave (DPDW) methodology at near infrared
wavelengths can be used to non-invasively measure the optical absorption and reduced scattering coefficients of tissue at
depths of several millimeters. Changes in the optical properties of tissue at near-infrared wavelengths (685nm-950nm)
are caused by changes in blood volume, oxygenation, and tissue hydration. A four-wavelength DPDW system with a
single source position and four detectors was used to monitor the optical properties of wounds in healthy and
streptozotocin-induced diabetic rats. Optical data obtained after inflicting full-thickness wounds on the dorsal region of
diabetic and control rats indicate that DPDW technology can be used to monitor wound healing and differentiate the rate
of impaired vs. normal wound healing. The concentrations of oxyhemoglobin, deoxyhemoglobin and water were
calculated from the optical absorption coefficients. Changes in hemoglobin concentration may indicate increased
vascularization throughout the wound healing process, while changes in water content may reflect inflammation
following tissue injury. These physiological changes are supported by qualitative immunohistochemical analysis of
wound biopsies.
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