High frame rate photon counting using the PF32 to parallelise diffuse correlation spectroscopy (DCS) measurements.
DCS is a non-invasive technique for measuring blood flow in tissue. This involves coupling laser light from a fiber into the tissue and measuring the scattered light at a distance from the input, also via fiber. The further from the input, the deeper the light will have travelled and the less light emerges: single-photon detection required.
Whilst most applications that use a PF32 exploit the 55ps accuracy time-stamping mode, the following 2 papers use the PF32’s photon counting mode and high frames rate to record single-photon images at over 300kfps.
Facebook Reality Labs are using the PF32 in their work towards a brain-computer interface. By using the PF32 they have demonstrated a 32x increase in SNR. Without the high frame rate capability of the PF32, these measurements would not have been possible.
Above left shows the experimental setup to mimic measuring in tissue, whilst above right shows the gains in SNR as the number of pixels used for the measurement is increased. All images copyright of Facebook, the paper can be found here.
Duke University’s work on DCS with the PF32 has shown realtime measurement of blood flow in human tissue as shown below.
In (a) they show their setup for in vivo forehead blood flow. The result in (b) uses the PF32, whilst (c) shows the validation of these results by comparing them with that from a commercial electrocardiogram monitor.