Exploration of movement artefacts in handheld laser speckle contrast perfusion imaging

Abstract

Functional performance of handheld laser speckle contrast imaging (LSCI) is compromised by movement artefacts. Here we quantify the movements of a handheld LSCI system employing electromagnetic (EM) tracking and measure the applied translational, tilt and on-surface laser beam speeds. By observing speckle contrast on static objects, the magnitudes of translation and tilt of wavefronts are explored for various scattering levels of the objects. We conclude that for tissue mimicking static phantoms, on-surface speeds play a dominant role to wavefront tilt speed in creation of movement artefacts. The ratio depends on the optical properties of the phantom. Furthermore, with the same applied speed, the drop in the speckle contrast increases with decreasing reduced scattering coefficient, and hence the related movement artefact increases.

Handheld versus mounted laser speckle contrast perfusion imaging demonstrated in psoriasis lesions

“…4 f). In a previous study, the average on-surface speed for handheld measurements by 10 healthy operators on a static object was calculated as 9 mm/s where the measurement distance was 20 cm 18 . In this study, the calculated value is 12.7 mm/s with the measurement distance of 40 cm.…”

“…Left, a front view of the handheld probe. Middle, handheld probe without a cap (reprinted from 18 ). Right, schematic drawing of the handheld probe.…”

“…In a previous work, we measured movements of the LSCI system during handheld experiments using an electromagnetic (EM) tracker. We analyzed movement artefacts in response to on-surface beam speed, that is the speed of the light beam on the surface caused by translation and rotation of the probe, and wavefront tilting for media with various scattering levels 18 . In addition, we explored the influence of wavefront types on movement artefacts employing three types of illumination, namely scrambled, spherical and planar wavefronts 19 .…”

Modeling movement artefacts in handheld laser speckle contrast perfusion imaging: influence of wavefront types

“…Therefore, there is a need to model movement artefact so that their occurrence can be prevented and/or compensated. In other studies, we experimentally showed that movement artefacts caused by translation depend on the optical properties of the medium [9] as well as the type of illumination [10]. In this work, we use the concept of optical Doppler effect to predict speckle contrast drop due to linear motion, and for static objects.…”

Reliability of handheld laser speckle contrast perfusion imaging demonstrated in psoriasis lesions

“…Then, using motorized measurements on static tissue-mimicking phantoms, we found that on-surface speeds play a more dominant role in speckle contrast drop compared to tilt of wavefronts. We also concluded that optical properties of the medium matters when studying movement artefacts such that a measurement on an opaque surface may not be sufficient to correct for movement artefacts [17]. Then, we studied the influence of wavefront types on movement artefacts in handheld LSCI.…”