Impact of logarithmic and linear spaced camera exposure durations for multi-exposure speckle imaging

Abstract

Neurosurgical interventions benefit greatly from monitoring of cerebral blood flow (CBF). Laser speckle contrast imaging (LSCI) is a label-free optical imaging technique that can provide continuous, high spatiotemporal maps of flow dynamics, allowing clinicians to monitor changes in CBF without any interruption to the surgical workflow. Multi-exposure speckle imaging (MESI) is an extension of LSCI that collects speckle images at numerous camera exposure times to create reproducible and quantifiable measurements of flow, through a more robust calculation of the correlation time constant. This work is focused on investigating whether the chosen spacing of the camera exposure times can impact the resulting computation of the inverse correlation time (ICT). A microfluidic phantom using a pressure-regulated flow control system is used to generate a 5-step and 7-step flow profile. MESI data is collected with three different exposure time spacings; logarithmic-spaced, linear-spaced, and the ad hoc exposure times from previous research. Using a nonlinear least squares fitting algorithm we fit the measured data to solve for the speckle correlation time constant at each MESI frame. We compare the quantified flow, based on the computed ICT for each exposure time collection method. These results suggest that future research and clinical adaptations should consider implementing logarithmic -spaced exposure times for MESI as it may provide more reliable and accurate estimates of flow, as well as faster acquisition times, without the need for specially chosen exposure times.