We present the application to time-domain diffuse optics of a device composed of 8x256 CMOS SPAD array with 256 7-bit time-to-digital converters. Thanks to its structure and despite the limitation on the maximum repetition rate of the laser (2 MHz), it has been demonstrated to be suitable for fast acquisitions (10 ms) provided that a high photon count-rate is used and pile-up distortion is corrected. We demonstrate that high penetration depth (>30 mm) and good linearity in absorption coefficient retrieval can be achieved. Finally, we were able to clearly record the heart beat in a resting state forehead measurement.
By exploiting the recent components miniaturization trend, we realize a small and cheap multifunctional time-resolved (TR) single-photon detection chain. It is based on 16 channels, which can be configured either as 16 independently located channels for TR diffuse optical tomography or as a linear array for parallel TR fluorescence spectroscopy. Both applications require a detector with high time resolution and high light harvesting capability (i.e., large active area and detection efficiency). Thus, each detection channel contains a 1.3 x 1.3 mm2 active area silicon photomultiplier and its home-made electronics specifically designed for avalanche sensing and amplification, capable of optimizing the single-photon timing resolution despite the miniaturization. In this study we describe the timing performances of a first 8- channel prototype and its first application in fluorescence lifetime sensing. Then, we show the capability of the whole 16-channel array in detecting absorption changes within a homogeneous scattering medium. We have been able to obtain a single-photon timing resolution of almost 60 ps, that is close to the best ever achieved with this kind of detector. For the validation in fluorescence lifetime sensing, the fluorescence signal acquired by the proposed prototype is comparable to the one obtained using a state-of-the-art setup based on a PMT detector. In the validation in diffuse optics, we clearly detected the absorption perturbation. This confirms the suitability of this stackable solid-state detector array for both applications.
Time domain diffuse optics (TD-DO) relies on the injection of ps laser pulses and on the collection of the arrival times of scattered photons. To reach the ultimate limits of the technique (allowing to investigate even structures at depth <5 cm), a large area detector is needed. To this extent, we realized and present a new silicon photomultiplier featuring a 1 cm2 area. To the best of our knowledge, it represents the largest detector ever proposed for TD-DO and shows a light harvesting capability which is more than 1 decade larger than the state-of-the-art technology system. To assess its suitability for TDDO measurements, we tested the detector with several procedures from shared protocols (BIP, nEUROPt and MEDPHOT). However, the light harvesting capability of a detector with large area can be proficiently exploited only if coupled to timing electronics working in sustained count-rate CR (i.e., well above the single photon statistics). For this reason, we study the possibility to work in a regime where (even more than) one photon per laser pulse is detected (i.e., more than 100% laser repetition rate) exploiting in-silico technology. The results show that the possibility to use sustained count-rate represents a dramatic improvement in the number of photons detected with respect to current approaches (where count-rate of 1-5% of the laser repetition rate are used) without significant losses in the measurement accuracy. This represents a new horizon for TD-DO measurements, opening the way to new applications (e.g., optical investigation of the lung or monitoring of fast dynamics never studied before).
Large-area detectors for time-domain diffuse optics are increasingly available, with enormous gain in collected light intensity. Pile-up distortion is nowadays the main limit, here studied to anticipate the possibility of a new working modality.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.