Current wearable optical technologies generally utilize superficial tissue continuous-wave measurements for biological metrics such as heart rate monitoring. There has been limited prior work in wearables that extract quantitative information including tissue optical properties and hemoglobin concentrations. These parameters may assist in tracking physiological status for cardio-pulmonary conditions and cancer. Next-generation optical wearables must meet substantial technical requirements, including small footprint, high sensitivity, and thermal stability. Here we investigate the use of a new multi-wavelength optical laser and compact avalanche photodiode for use in a miniaturized diffuse optical frequency-domain optode (miniOptode). These components represent the most compact fiberless optode for frequency-domain measurements to date. The miniOptode had high SNR (53.5dB at 50 MHz), and achieved high accuracy and precision in optical property extractions (accuracy: μa 0.0018 mm-1 and μs′ 0.0547 mm-1; precision: μa 0.00008mm-1 and μs′ 0.0015 mm-1). It provided high SNR for test measurements taken on nine different anatomic locations and was capable of tracking hemodynamics during a cuff occlusion test. Active thermoelectric cooling was required for thermal stability during longer tissue measurements. This work demonstrates that frequency domain diffuse optical measurements can be achieved in a highly portable format, providing new opportunities for long-term monitoring with quantitative oximetry.
KEYWORDS: Tissue optics, Breast, Sensors, Breast cancer, Hemodynamics, Light emitting diodes, Tissues, Biomedical optics, Oxygen, Signal to noise ratio
We present a new continuous-wave wearable diffuse optical probe aimed at investigating the hemodynamic response of locally advanced breast cancer patients during neoadjuvant chemotherapy infusions. The system consists of a flexible printed circuit board that supports an array of six dual wavelength surface-mount LED and photodiode pairs. The probe is encased in a soft silicone housing that conforms to natural breast shape. Probe performance was evaluated using tissue-simulating phantoms and in vivo normal volunteer measurements. High SNR (71 dB), low source-detector crosstalk (−60 dB), high measurement precision (0.17%), and good thermal stability (0.22% Vrms/°C) were achieved in phantom studies. A cuff occlusion experiment was performed on the forearm of a healthy volunteer to demonstrate the ability to track rapid hemodynamic changes. Proof-of-principle normal volunteer measurements were taken to demonstrate the ability to collect continuous in vivo breast measurements. This wearable probe is a first of its kind tool to explore prognostic hemodynamic changes during chemotherapy in breast cancer patients.
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