Real-time assessment of liver fat content using a filter-based Raman system operating under ambient light through lock-in amplification

Abstract

During liver procurement, surgeons mostly rely on their subjective visual inspection of the liver to assess the degree of fatty infiltration, for which misclassification is common. We developed a Raman system, which consists of a 1064 nm laser, a handheld probe, optical filters, photodiodes, and a lock-in amplifier for real-time assessment of liver fat contents. The system performs consistently in normal and strong ambient light, and the excitation incident light penetrates at least 1 mm into duck fat phantoms and duck liver samples. The signal intensity is linearly correlated with MRI-calibrated fat contents of the phantoms and the liver samples.

Evaluation of minimum-to-severe global and macrovesicular steatosis in human liver specimens: a portable ambient light-compatible spectroscopic probe

“…Additionally, the untested performance of the Raman system in operating room conditions, despite its proven resistance to 10,000 lm LED light in laboratory settings, leaves a significant gap in understanding its comprehensive compatibility. 26…”

“…Navigating the challenges associated with weak signal detection and fluorescence interferences, we engineered a filter-based 1064-nm Raman system validated through examinations using phantom models and duck liver samples. 26 In our previous study, employing readily interpretable voltage intensities to quickly quantify the relative fat content within the examined liver samples, this multi-channel system functioned reliably (r 2 = 0.934) under normal and intense ambient light conditions 26 .…”

“…The liver specimens were refrozen at -80 degrees Celsius and thawed again for TG quantification. Given that the penetration depth of the incident laser beam was at least 1mm, 26 only specimens heavier than 10 mg (thicker than 1 mm) were included to avoid the insufficiency to quantify TG of low-mass specimens 27,28 . The fat content derived from the analyses using the Raman and reflectance channels was then compared with the TG quantification results to assess the Raman system's accuracy in steatosis estimation.…”

Potential of Raman-reflectance combination to quantify liver steatosis and fat droplet size: evidence from Monte Carlo simulations and phantom studies

“…Our study employed a custom-developed spectroscopic system compatible with ambient light, as detailed in previous publications. [26,27] This optical setup incorporated a continuous-wave laser at 1064 nm for sample illumination, a portable hand-held probe, and an optical filtering system for characteristic wavelength selection. To enhance signal detection, a benchtop lock-in amplifier SR510 (Stanford Research Systems, Sunnyvale, CA, USA) was utilized to amplify and isolate the detected voltage signals by InGaAs photodiodes (in together with a customized transimpedance amplifier).…”

“…Spectroscopic methods, due to their non-invasiveness and immediacy, are hopeful for realizing non-invasive real-time quantification of HS. [18] Infrared (IR) spectroscopy, [19][20][21] reflectance spectroscopy, [22][23][24] and Raman spectroscopy [25][26][27] were all reported valid in quantifying liver fat; however, size measurements of fat droplets using these spectroscopic methods lack investigation. This could be due to the limitations of current data analysis techniques, which may not be enough to simultaneously interpret both fat content and fat droplet size from the same spectroscopic data.…”