MAESTROS II, a multispectral Time-Domain NIRS system for non-invasive placental monitoring

Objective: To enable bedside, depth-resolved monitoring of placental oxygenation and metabolism, we redesigned the first-generation MAESTROS platform into MAESTROS II, a multispectral time-domain near-infrared spectroscopy (TD-NIRS) system. Methods: MAESTROS II combines a 6.5 W supercontinuum laser and acousto-optic tuneable filters with a four-channel detection block built around hybrid photomultiplier tubes and eight-channel TCSPC electronics. Hardware optimisation, including collimated fibre coupling and an inline reference arm, boosted responsivity and narrowed the instrument-response-function width by more than 40 %. A two-step analysis pipeline, comprising spectrally constrained two-layer modelling followed by gated Beer–Lambert estimation, yields absolute chromophore concentrations and dynamic changes in superficial and placental compartments. Results: Basic Instrument Protocol (BIP) and MEDPHOT testing showed improved light harvesting and a narrower instrument response function (IRF), translating into mean absolute errors below 10% in the retrieval of μa and μs′ in homogeneous media. Monte Carlo simulations across 356 patient-informed anatomies predicted an averaged placental sensitivity of 7.30 ± 12.31% across all anatomies. Two-layer blood phantoms demonstrated separation of superficial and deep oxygenation with the current method. In preliminary clinical use (n = 185 monitoring sessions), a support vector machine (SVM) using both optical features and available metadata achieved 92.1% accuracy for risk prediction and 78% for outcome prediction. A separate model estimated placental depth directly from optical data with mean error 0.42 cm. Restricting analysis to cases with ultrasound or optically measured placental depth below 3.5 cm increased accuracy for both risk and outcome to 93.3% and 78.9%, respectively. Conclusion: MAESTROS II improves photon harvest, temporal response, and clinical usability, enabling longitudinal, radiation-free assessment of in-vivo placental physiology. Significance: These first results are encouraging and outline a practical path toward early detection of placental insufficiency; ongoing work will tighten absolute accuracy and generalisability through refined phantoms, algorithmic updates, and expanded clinical validation.