SignificanceMicrofluidic flow phantom studies are commonly used for characterizing the performance of laser speckle contrast imaging (LSCI) instruments. The selection of the flow control system is critical for the reliable generation of flow during testing. The majority of recent LSCI studies using microfluidics used syringe pumps for flow control.AimWe quantified the uncertainty in flow generation for a syringe pump and a pressure-regulated flow system. We then assessed the performance of both LSCI and multi-exposure speckle imaging (MESI) using the pressure-regulated flow system across a range of flow speeds.ApproachThe syringe pump and pressure-regulated flow systems were evaluated during stepped flow profile experiments in a microfluidic device using an inline flow sensor. The uncertainty associated with each flow system was calculated and used to determine the reliability for instrument testing. The pressure-regulated flow system was then used to characterize the relative performance of LSCI and MESI during stepped flow profile experiments while using the inline flow sensor as reference.ResultsThe pressure-regulated flow system produced much more stable and reproducible flow outputs compared to the syringe pump. The expanded uncertainty for the syringe pump was 8 to 20 × higher than that of the pressure-regulated flow system across the tested flow speeds. Using the pressure-regulated flow system, MESI outperformed single-exposure LSCI at all flow speeds and closely mirrored the flow sensor measurements, with average errors of 4.6 % ± 2.6 % and 15.7 % ± 4.6 % , respectively.ConclusionsPressure-regulated flow systems should be used instead of syringe pumps when assessing the performance of flow measurement techniques with microfluidic studies. MESI offers more accurate relative flow measurements than traditional LSCI across a wide range of flow speeds.
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.
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