Handheld motion stabilized laser speckle imaging

Abstract

Laser speckle imaging (LSI) is a wide-field, noninvasive optical technique that allows researchers and clinicians to quantify blood flow in a variety of applications. However, traditional LSI devices are cart or tripod based mounted systems that are bulky and potentially difficult to maneuver in a clinical setting. We previously showed that the use of a handheld LSI device with the use of a fiducial marker (FM) to account for motion artifact is a viable alternative to mounted systems. Here we incorporated a handheld gimbal stabilizer (HGS) to produce a motion stabilized LSI (msLSI) device to further improve the quality of data acquired in handheld configurations. We evaluated the msLSI device in vitro using flow phantom experiments and in vivo using a dorsal window chamber model. For in vitro experiments, we quantified the speckle contrast of the FM (K FM ) using the mounted data set and tested 80% and 85% of K FM as thresholds for useable images (K FM,Mounted,80% and K FM,Mounted,85% ). Handheld data sets using the msLSI device (stabilized handheld) and handheld data sets without the HGS (handheld) were collected. Using K FM,Mounted,80% and K FM,Mounted,85% as the threshold, the number of images above the threshold for stabilized handheld (38 ± 7 and 10 ± 2) was significantly greater (p = 0.031) than for handheld operation (16 ± 2 and 4 ± 1). We quantified a region of interest within the flow region (K FLOW ), which led to a percent difference of 8.5% ± 2.9% and 7.8% ± 3.1% between stabilized handheld and handheld configurations at each threshold. For in vivo experiments, we quantified the speckle contrast of the window chamber (K WC ) using the mounted data set and tested 80% of K WC (K WC,Mounted,80% ). Stabilized handheld operation provided 53 ± 24 images above K WC,Mounted,80% , while handheld operation provided only 23 ± 13 images. We quantified the speckle flow index (SFI) of the vessels and the background to calculate a signal-to-background ratio (SBR) of the window chamber. Stabilized handheld operation provided a greater SBR (2.32 ± 0.29) compared to handheld operation (1.83 ± 0.21). Both the number of images above threshold and SBR were statistically significantly greater in the stabilized handheld data sets (p = 0.0312). These results display the improved usability of handheld data acquired with an msLSI device.

Sample entropy analysis of laser speckle fluctuations to suppress motion artifact on blood flow monitoring

“…LSI systems like most other physiological signal monitoring devices are susceptible to motion artifacts. Several studies tried to correct motion artifacts [16][17][18] . For example, Mahé et al removed motion artifacts by point-by-point subtraction between the skin surface and adjacent opaque surface [19] , and Richards et al used filtering to correct the pulsatile artifacts in monitoring cerebral blood flow [20] .…”

Exploration of movement artefacts in handheld laser speckle contrast perfusion imaging

“…Movement artefacts during a handheld LSCI measurement are caused by tissue motions [9,11,[20][21][22][23] and motions of the LSCI system [5,12,13]. The former can be caused by breathing or patient movements while the latter are generated in the wrist, elbow and shoulder, and motions due to heartbeat and breathing of the operator.…”

“…However, selecting only proper frames may cause data loss. They recently showed reduction of movement artefacts during handheld LSCI measurement thanks to the gimbal stabilizer which was at the expense of increasing total weight of the system [13].…”

Laser Speckle Contrast Imaging in Reconstructive Surgery

“…The problem of not being able to interpret LSCI measurements in real time without considering possible motion artifacts is still waiting for its solution. [84][85][86][87][88] In study II, even at complete arterial occlusion, the perfusion, measured with both LDF and LSCI, never reached zero PU. Both these techniques have the problem of the biological zero in common.…”