Method for Improving the Lateral Resolution of Near-Infrared (NIR) Single Optods: Application to Subcutaneous Vein Detection and Localization

Yasser S Fawzy

doi:10.4236/opj.2012.24044

Abstract

NIR backscattering measurements using single source-detector optical probe (optods) can detect absorption areas within deep tissue layer. However, such optods, are characterized by large separation distance between the source and detectors (>2 cm) and poor lateral resolution (>1 cm), which limits its usage for the localization of small absorption volumes embedded deep within the tissue such as subcutaneous veins. In this work a method to improve the accuracy of locating such absorption volumes (areas) using backscattered NIR measurements is suggested and investigated with the aim of developing an optical sensor for detecting and localizing large subcutaneous veins. The method is based on measuring the differential signal from three overlapping source-detector pairs arranged within the probe such that the total photon sensitivity profile of the probe is maximized along a narrow width area (within the central of the probe) and minimized along its sides. The location of the absorption areas is then determined when a peak maximum of the measured signal is detected. Monte Carlo simulation and light transport modeling was used to determine the optimum arrangement of each source-detector pair within the probe to create the required spatial sensitivity profile and demonstrate the validity of the method. The results showed that the differential optode has more than two times improvement in the lateral resolution compared to the standard optode. The result also showed that the differential probe can locate subcutaneous veins with diameter ~5 mm and embedded at ~1.5 cm depth. The method could have a potential for designing and developing an optical backscattering sensors for detecting and localizing large subcutaneous veins embedded 2 cm depths

Highlights

NIR diffuse reflectance measurements and spectroscopy is simple and portable optical diagnostic technique that can be used to detect and to monitor the alteration in tissue physiology and/or pathology, by measuring the change in absorption coefficient related to such alteration
NIR backscattering measurements using single source-detector optical probe can detect absorption areas within deep tissue layer. Such optods, are characterized by large separation distance between the source and detectors (>2 cm) and poor lateral resolution (>1 cm), which limits its usage for the localization of small absorption volumes embedded deep within the tissue such as subcutaneous veins
The results showed that the differential optode has more than two times improvement in the lateral resolution compared to the standard optode

Summary

Introduction

NIR diffuse reflectance measurements and spectroscopy is simple and portable optical diagnostic technique that can be used to detect and to monitor the alteration in tissue physiology and/or pathology, by measuring the change in absorption coefficient related to such alteration. The lateral spatial resolution for such single sourcedetector arrangement is typically larger than 1 cm for absorption areas located within such depths [10,11] This would limit the application of such probes in the applications that require detecting as well as localizing the lateral position of the measured absorption areas within deep tissue layers. The aim of this work is to develop a method of reflectance probe design and measurement that could improve the lateral spatial resolution to the detected NIR diffuse reflectance signal obtained from large depths within the tissue. For that respect we have investigated the possibility of using multiple source-detector pairs arranged in certain design such that the spatial sensitivity profile of the measured signal is maximized along certain localized area (volume) within the tissue. Monte Carlo simulation was used to determine the optimum distances to produce the required spatial sensitivity profile and to verify the improvement in the spatial resolution using simulated data

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