Methodological concerns with laser speckle contrast imaging in clinical evaluation of microcirculation

Abstract

BackgroundLaser Speckle Contrast Imaging (LSCI) is a non-invasive and fast technique for measuring microvascular blood flow that recently has found clinical use for burn assessment and evaluation of flaps. Tissue motion caused by for example breathing or patient movements may however affect the measurements in these clinical applications, as may distance between the camera and the skin and tissue curvature. Therefore, the aims of this study were to investigate the effect of frame rate, number of frames/image, movement of the tissue, measuring distance and tissue curvature on the measured perfusion.MethodsMethyl nicotinate-induced vasodilation in the forearm skin was measured using LSCI during controlled motion at different speeds, using different combinations of frame rate and number of frames/image, and at varying camera angles and distances. Experiments were made on healthy volunteers and on a cloth soaked in a colloidal suspension of polystyrene microspheres.ResultsMeasured perfusion increased with tissue motion speed. The relation was independent of the absolute perfusion in the skin and of frame rate and number of frames/image. The measured perfusion decreased with increasing angles (16% at 60°, p = 0.01). Measured perfusion did not vary significantly between measurement distances from 15 to 40 cm (p = 0.77, %CV 0.9%).ConclusionTissue motion increases and measurement angles beyond 45° decrease the measured perfusion in LSCI. These findings have to be taken into account when LSCI is used to assess moving or curved tissue surfaces, which is common in clinical applications.

Assessment of the test‐retest reliability of human gingival blood flow measurements by Laser Speckle Contrast Imaging in a healthy cohort

“…Unexpectedly, the incidence angle has some effect on the mean of the measurements. Contrary to our study on the gingiva, the incidence angle does not influence LSCI measurements in the skin even when a much wider range of angles (up to 45 degrees) is used . In our experiment, the patient's head was turned by only 10 degrees approximately, a limit imposed by the field of view.…”

“…These values (5.4%‐6.0%) were very similar to the residual error of LSCI measurements in animal experiments where most clinical factors (retraction, reflection, most of the movements) can be eliminated. This suggests that it is difficult to further reduce this component which may include not only technical factors such as the selection of regions by visual inspection, motion artefacts, the internal error of the LSCI instrument, but also short‐term biological variation due to breathing, pulse, and vasomotion.…”

“…To eliminate the pulse effect, 1 snapshot included 20 consecutive images within a 2‐second time interval. Such rapid imaging facilitated multiple measurements at each session and reduced the risk of movement artefacts . GBF was expressed in LSPU.…”

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.…”

Blood Flow Dynamics in Burns

“…A description of LSCI can be found in the introduction section on page 13. This system has previously been described in detail [58] and potential sources of error during routine measurement have also been investigated [75].…”