Diffuse correlation spectroscopy (DCS) is an established diffuse optical technique that uses the analysis of temporal speckle intensity fluctuations to measure blood flow in tissue. DCS cerebral blood flow measurements in clinical applications have shown promise, but measurements contain contamination of the signal from changes in superficial blood flow. Recent studies have shown that moving to wavelengths beyond the water absorption peak at 970 nm when making DCS measurements improves SNR and reduced influence of superficial flow. Here, we present a DCS system operating at 1064 nm utilizing two InGaAs SPADs to calculate the cross correlation to address detector non-idealities.
Diffuse correlation spectroscopy (DCS) is an established diffuse optical technique that uses the analysis of temporal speckle intensity fluctuations to measure blood flow in tissue. Recent advances in the field have seen the introduction of iDWS/iDCS, which have allowed for the use of conventional photodetectors to replace the single photon counting detectors required to measure the traditional, homodyne DCS signal. Here we detail a high framerate, highly parallel iDCS system at 1064 nm which allows for improved signal to noise ratio at extended source detector separations.
When monitoring patients with a skin contact sensor it is important to ensure that this is properly attached to the skin. This is important both for patient safety and data quality. We have developed a skin-contact sensitive technology that exploits the capacitive coupling of the sensor to detect the quality of the attachment to the subject’s skin and ensure galvanic isolation between patient and sensor. The developed technology can be easily embedded in any optical probe design without adding weight of bulkiness to the probe and provides the capability to detect optical probe displacements and alert user/operators/ hospital staff.
Recently, we developed a time-domain diffuse correlation spectroscopy (TD-DCS) method for neurovascular sensing with higher brain sensitivity. In this paper, laser pulse shaping was designed and demonstrated for TD-DCS at 1064 nm. A quantum superconducting nanowire single-photon detector (SNSPD) with high photon detection efficiency (PDE) and low jitter collects the back-scattered light from the brain. The presented approach is the first step towards scaling up a full fiber optic cap with 96 source channels and 192 custom-made single-photon detectors which will cover most of an adult head.
Diffuse correlation spectroscopy (DCS) is an established diffuse optical technique that uses the analysis of temporal speckle intensity fluctuations to measure blood flow in tissue. As a non-invasive technique, DCS has been used to monitor patient cerebral blood flow at the bedside. Though an effective measurement tool, extra-cerebral contamination of the DCS signal limits the sensitivity to changes in brain blood flow. In order to overcome this depth sensitivity challenge, we present a method, overlapping volumes, acousto-optic modulated DCS (AOM-DCS), to improve sensitivity to deeper tissue structures.
Diffuse correlation spectroscopy (DCS) is an established diffuse optical technique that uses the analysis of temporal speckle intensity fluctuations to measure blood flow in tissue. DCS has been shown to be an effective monitor of cerebral blood flow in many neuro-monitoring applications, though still suffers from depth sensitivity issues. Recent studies have shown that moving to 1064 nm when making DCS measurements improves SNR and sensitivity to depth, but detector challenges have slowed the change to that wavelength. Here, we present on a multipixel, interferometric DCS (iDCS) system that improves measurement capabilities at this wavelength.
The capability to achieve high count rates has become an imperative in the most areas where near-infrared single-photon counters are required to detect photons up to 1.7 μm. Hence, afterpulsing mitigation is a dominant theme in recent works concerning systems based on InGaAs/InP SPADs. Given the challenges inherent in reducing the density of defects that give rise to the carrier trapping events causing afterpulsing, the only viable approach is to reduce the potential number of carriers that can be trapped by limiting the charge flow per avalanche event. In this paper we present a sine-wave gating system based on the balanced detector configuration. The gate frequency is programmable in a wide range (1.0 – 1.6 GHz) for allowing synchronization with an external laser system and for exploring the best trade-off between afterpulsing and photon detection efficiency. The long-term stability can be achieved with a stable cancelation of the gate feedthrough. In this work this is guaranteed by a feedback loop that continuously monitors the residual output power at the gate frequency and adjusts the amplitude and phase of the two sinusoids fed to the SPAD-dummy couple.
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