Frequency domain near-infrared multiwavelength imager design using high-speed, direct analog-to-digital conversion

Abstract

Abstract. Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (

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

“…The hardware-integrated dDOS system developed here utilizes direct digital signal generation and detection and wavelength multiplexing, with frequency sweep measurements rates up to 97 Hz, allowing rapid physiological changes to be detected well above the cardiac rate. Previous systems achieving high sampling rates have utilized a small number of discrete modulation frequencies and wavelengths, 14,21 whereas the dDOS system sweeps a range of hundreds of modulation frequencies and utilizes six discrete wavelengths. The dDOS system performance is comparable to previous systems.…”

“…Zimmerman et al recently developed a FD NIR high speed imaging system that utilized two wavelengths, two modulation frequencies, and an array of detectors; with this system, a measurement rate of 90 Hz was achieved, compared to the 97-Hz measurement rate achieved in the dDOS system with six wavelengths and a sweep of modulation frequencies. 14 In the future, the portability of the system can be further improved by implementing miniaturized fiber-coupled laser diodes and miniaturized current driver modules that can be housed in a portable device enclosure. This will help to more easily measure patients in a clinical setting for a range of applications, such as chemotherapy monitoring or rapid hemodynamic analysis.…”

“…Although this is not the preferred data acquisition mode, because utilizing additional modulation frequencies improves model fit accuracy, it provides a useful comparison to other FD systems, which utilize single modulation frequencies. 3,4,8,10,14,21 A summary of the performance specifications is given in Table 2. Torjesen, Istfan, and Roblyer: Ultrafast wavelength multiplexed broad bandwidth.…”

“…Although some analog systems have been successfully miniaturized, 12,13 the difficulties involved in RF system design potentially limit the adoption of these techniques. Furthermore, FD-DOS instruments often have slow measurement acquisition speeds compared to their CW counterparts, and although recent improvements have been made in data acquisition rates for single modulation frequency measurements, 14 data acquisition speeds are limited for broad modulation frequency bandwidth FD-DOS systems. 1,10,15 We recently demonstrated the feasibility of FD-DOS measurements using all digital signal generation and detection using direct digital synthesizer (DDS) integrated circuits and a 3.6-gigasample∕s two-channel analog-to-digital converter (ADC).…”

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).…”