Small separation frequency-domain near-infrared spectroscopy for the recovery of tissue optical properties at millimeter depths

• Type of Material: Article
• Authors: Seung Yup Lee, Georgia Institute of Technology; Corey Zheng, Georgia Institute of Technology; Rowan Brothers, Georgia Institute of Technology; Erin Buckley, Emory University
• Language: English
• Date: 2019-10-01
• Publisher: OPTICAL SOC AMER
• Publication Version: Final Published Version
• Copyright Statement: © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
• Final Published Version (URL): http://dx.doi.org/10.1364/BOE.10.005362
• Title of Journal or Parent Work: BIOMEDICAL OPTICS EXPRESS
• Volume: 10
• Issue: 10
• Start Page: 5362
• End Page: 5377
• Grant/Funding Information: National Heart, Lung, and Blood Institute10.13039/100000050 (R21-HL138062); National Institute of Neurological Disorders and Stroke10.13039/100000065 (R21-NS104801); Children's Healthcare of Atlanta10.13039/100012423 (Junior Faculty Award); American Heart Association10.13039/100000968 (19POST34380337).
• Keywords: Radiology, Nuclear Medicine & Medical Imaging; DETECTOR; Life Sciences & Biomedicine; OXYGEN EXTRACTION FRACTION; Science & Technology; Biochemistry & Molecular Biology; TURBID MEDIA; CEREBRAL-BLOOD-FLOW; Biochemical Research Methods; ABSORPTION; REFLECTANCE; PHANTOM; Optics; BRAIN; Physical Sciences; SPECTRA; DIFFUSE CORRELATION SPECTROSCOPY
• Research Categories: Chemistry, Biochemistry; Health Sciences, Radiology

Abstract

Millimeter-depth sensitivity with frequency domain near-infrared spectroscopy has been challenging due to the breakdown of the diffusion equation for source-detection separations < 1cm. To overcome this challenge, we employ a Monte-Carlo lookup table-based inverse algorithm to fit small separation (3-6 mm) frequency-domain near-infrared spectroscopy (FDNIRS) data for absorption and reduced scattering coefficients. We verify this small separation FDNIRS method through a series of in vitro and in vivo studies. In vitro, we observed a root mean squared percent error (RMSE) in estimation of the reduced scattering coefficient and absorption coefficient of 2.8% and 7.6%, respectively, in liquid phantoms consisting of Intralipid and Indian ink, and a RMSE in estimation of oxygen saturation and total hemoglobin concentrations of 7.8 and 11.2%, respectively, in blood-mixed liquid phantoms. Next, we demonstrate one particularly valuable in vivo application of this technique wherein we non-invasively measure the optical properties of the mouse brain (n = 4). We find that the measured resting state cerebral oxygen saturation and hemoglobin concentration are consistent with literature reported values, and we observe expected trends during a hyper-/hypoxia challenge that qualitatively mimic changes in partial pressure of oxygen (pO2) measured simultaneously with an invasive pO2 sensor. Further, through simulations of the mouse head geometry, we demonstrate that the skull and scalp exert minimal influence on the estimate oxygen saturation, while leading to small but systematic underestimation of total hemoglobin concentration. In total, these results demonstrate the robustness of small separation FDNIRS to assess tissue optical properties at millimeter depth resolution.