Correcting for motion artifact in handheld laser speckle images

Abstract

Laser speckle imaging (LSI) is a wide-field optical technique that enables superficial blood flow quantification. LSI is normally performed in a mounted configuration to decrease the likelihood of motion artifact. However, mounted LSI systems are cumbersome and difficult to transport quickly in a clinical setting for which portability is essential in providing bedside patient care. To address this issue, we created a handheld LSI device using scientific grade components. To account for motion artifact of the LSI device used in a handheld setup, we incorporated a fiducial marker (FM) into our imaging protocol and determined the difference between highest and lowest speckle contrast values for the FM within each data set (Kbest and Kworst). The difference between Kbest and Kworst in mounted and handheld setups was 8% and 52%, respectively, thereby reinforcing the need for motion artifact quantification. When using a threshold FM speckle contrast value (KFM) to identify a subset of images with an acceptable level of motion artifact, mounted and handheld LSI measurements of speckle contrast of a flow region (KFLOW) in in vitro flow phantom experiments differed by 8%. Without the use of the FM, mounted and handheld KFLOW values differed by 20%. To further validate our handheld LSI device, we compared mounted and handheld data from an in vivo porcine burn model of superficial and full thickness burns. The speckle contrast within the burn region (KBURN) of the mounted and handheld LSI data differed by <4 % when accounting for motion artifact using the FM, which is less than the speckle contrast difference between superficial and full thickness burns. Collectively, our results suggest the potential of handheld LSI with an FM as a suitable alternative to mounted LSI, especially in challenging clinical settings with space limitations such as the intensive care unit.

Comparison of speckleplethysmographic (SPG) and photoplethysmographic (PPG) imaging by Monte Carlo simulations and in vivo measurements

“…Motion artifact can play a major role in signal accuracy for both PPG and SPG. The current processing techniques did not account for motion artifact, but motion artifact has been addressed in both SPG [ 38 ] and PPG [ 39 ] acquisition through the use of alignment. The ideal ROI for each individual varied slightly and representative waveforms were used.…”

Clinical applications of laser speckle contrast imaging: a review

“…This method was later used by others. [23][24][25] The same group later improved this method with an equation that is valid for the studied population that does not require calibration. 26 Using this method, cutaneous microvascular assessment was measured on a patient forearm during exercise.…”

“…27 The forearm was placed on a table while the patient was working out on a home trainer. Whereas Mahe et al used the adhesive opaque patch as a zeroflow reference, and Lertsakdadet et al 25 used a fiducial marker to identify and re-align a subset of speckle images that have an acceptable degree of motion artefact. These methods can be helpful when cutaneous microvascular perfusion is assessed, yet in some cases the tissue of interest cannot have any object stuck to it.…”

Wearable speckle plethysmography (SPG) for characterizing microvascular flow and resistance

“…In this configuration the depth penetrance is typically on the order of 500 -1000 microns [43,44]. Although LSI is very useful for measuring relative perfusion in a given area of tissue, it requires an optical system that can be cumbersome in a clinical environment and is susceptible to motion artifacts [45][46][47][48].…”