Development and Validation of a Continuous Real-Time Optical Sensor for Indocyanine Green Clearance Measurement...

Liver transplantation remains the only curative treatment for end-stage liver failure, yet its impact is constrained by organ shortages and graft non-utilization. Machine perfusion (MP) enables ex vivo liver assessment; however, current viability criteria rely on intermittent sampling, limiting temporal resolution and accuracy. Indocyanine green (ICG), a clinically validated dye cleared exclusively by hepatocytes, provides a continuous index of hepatic function beyond initial injury.

We present a non-invasive, clamp-on optical sensor that demonstrates the first continuous, real-time quantification of ICG clearance during MP. The sensor consists of a clamp-on module with an 808 nm laser and phototransistor connected to a microcontroller and computer for real-time plotting. The raw phototransistor signal was linearised to a unitless absorbance signal proportional to perfusate ICG; bi-exponential fitting yielded plasma disappearance rate (PDR_bi, %/min) and the 15-min residual fraction (R₁₅).

Across 10 whole and 3 split human livers (45 boluses; 13 paired with spectrophotometry), the sensor closely matched spectrophotometric measurements (pooled R² = 0.994; range 0.983-0.999). The sensor resolved expected physiological trends: ICG clearance rate increased from subnormothermic to normothermic temperatures (ΔPDR_bi + 14.41% ± 9.53%/min, ΔR₁₅ -22.35 ± 9.97 percentage points; n = 4). The continuous sensor signal also revealed early mixing dynamics and medication-related effects missed by intermittent sampling.

This optical sensor enables accurate, real-time monitoring of ICG clearance during ex vivo perfusion. The ex vivo setting is uniquely positioned to validate ICG clearance models, enhance clinical interpretation, and support informed graft assessment during perfusion.