Ultrafast wavelength multiplexed broad bandwidth digital diffuse optical spectroscopy for in vivo extraction of tissue optical properties

Abstract

, "Ultrafast wavelength multiplexed broad bandwidth digital diffuse optical spectroscopy for in vivo extraction of tissue optical properties," J. Biomed. Opt. Abstract. Frequency-domain diffuse optical spectroscopy (FD-DOS) utilizes intensity-modulated light to characterize optical scattering and absorption in thick tissue. Previous FD-DOS systems have been limited by large device footprints, complex electronics, high costs, and limited acquisition speeds, all of which complicate access to patients in the clinical setting. We have developed a new digital DOS (dDOS) system, which is relatively compact and inexpensive, allowing for simplified clinical use, while providing unprecedented measurement speeds. The dDOS system utilizes hardware-integrated custom board-level direct digital synthesizers and an analog-to-digital converter to generate frequency sweeps and directly measure signals utilizing undersampling at six wavelengths modulated at discrete frequencies from 50 to 400 MHz. Wavelength multiplexing is utilized to achieve broadband frequency sweep measurements acquired at over 97 Hz. When compared to a gold-standard DOS system, the accuracy of optical properties recovered with the dDOS system was within 5.3% and 5.5% for absorption and reduced scattering coefficient extractions, respectively. When tested in vivo, the dDOS system was able to detect physiological changes throughout the cardiac cycle. The new FD-dDOS system is fast, inexpensive, and compact without compromising measurement quality. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Quantitative real-time pulse oximetry with ultrafast frequency-domain diffuse optics and deep neural network processing

“…1(a). This hardware is described in detail in our previous publication [16]. Briefly, five near infrared lasers (690, 785, 808, 830, and 850 nm) were modulated at different radio frequencies using five direct digital synthesis boards (DDS) controlled by a single board computer (MircoZed Zynq-7010 SOC).…”

“…Aliasing did not lead to any loss of information in this case because the laser modulation frequencies always mapped to unique and non-overlapping frequencies in the baseband. Since the modulated signals are narrow-band with known frequencies, the amplitude and phase could be extracted from the undersampled signals [16]. While theoretically only one modulation frequency is necessary to separate absorption from scattering [17], other groups have found that using multiple frequencies resulted in measurements that were less susceptible to noise [15,18].…”

“…In this work we overcome these limitations to develop a new technique that is capable of noninvasively quantifying and displaying absolute concentrations of oxy-and deoxy-hemoglobin in real-time. To accomplish this, we have leveraged our recent work in the development of ultrafast FD-DOS hardware [16], together with new developments in real-time firmware data processing, as well as an unprecedented improvement in the speed of optical property extractions through a new deep neural network (DNN) inversion algorithm. In the following sections, we will show that the integration of these advances enables the calculation and display of quantitative hemoglobin concentrations at a rate of up to 27 Hz.…”

Frequency-Domain Techniques for Cerebral and Functional Near-Infrared Spectroscopy

“…Recent developments in FD-NIRS instrumentation include implementations based on a compact frequency-sweeping circuit board (No et al, 2008), digital heterodyning (Arnesano et al, 2012), direct digital sampling (Roblyer et al, 2013;Zimmermann et al, 2016), frequency division multiplexing (Torjesen et al, 2017;Zhao et al, 2018), CMOS integrated circuitry (Sthalekar and Joyner Koomson, 2013;Yun and Joyner Koomson, 2013), and vertical cavity surface emitting lasers (VCSEL) (Sultan et al, 2013;Kitsmiller et al, 2018).…”

Single snapshot of optical properties image quality improvement using anisotropic two-dimensional windows filtering

“…Optical imaging methods capable of providing real-time information related to functional and structural conditions of living tissues are becoming increasingly popular. [1][2][3][4][5][6] Some medical fields in particular, such as surgery, are driving this need for realtime interpretable information content to aid decision-making in a time-constrained environment. [7][8][9][10][11][12] Several solutions have been investigated to fulfill this need, each with their pros and cons, ranging from raster scanning of microscopic information to wide-field acquisitions of diffused information.…”