Regular Article Laser speckle contrast imaging accurately measures blood flow over moving skin surfaces Guillaume Mahé a,e , Pascal Rousseau b,e , Sylvain Durand c , Stephanie Bricq d , Georges Leftheriotis a,e , Pierre Abraham a,e, ⁎ a Laboratory of Vascular Investigations, University Hospital of Angers, France b Department of Plastic Surgery, University Hospital of Angers, France c Laboratory “Motricité, Interactions, Performance” EA 4334, University of Le Mans, Faculty of Sport Sciences, Le Mans, France d Groupe ESAIP, Centre d'Études et de Recherche pour l'Aide à la Décision de l'ESAIP, Saint Barthélemy d'Anjou Cedex, France e Biologie Neurovasculaire Intégrée (BNVI), Unité mixte UMR CNRS 6214/INSERM 771, Faculté de Médecine, Angers, France abstract article info Article history: Accepted 30 November 2010 Available online 13 December 2010 Keywords: Skin blood flow Microcirculation Imaging Physiology Methods Cutaneous blood flow (CBF) can be assessed non-invasively with lasers. Unfortunately, movement artefacts in the laser skin signal (LS sk ) might sometimes compromise the interpretation of the data. To date, no method is available to remove movement artefacts point-by-point. Using a laser speckle contrast imager, we simultaneously recorded LS sk and the signal backscattered from an adjacent opaque surface (LS os ). The completion of a first protocol allowed a definition of a simple equation to calculate the CBF from movement artefact-affected traces of LS sk and LS os . We then recorded LS sk and LS os before, during and for 5 min after the tourniquet ischemia, both when subjects (n = 8) were immobile or submitted to external passive movements of random intensity throughout the test. The typical post-occlusive reactive hyperemia trace was not identifiable within the LS sk recordings, with LS sk being 2 to 3 times higher during movements than in the immobile situation. After the calculation of CBF, traces in the immobile versus movement conditions were comparable, with the “r” cross-correlation coefficient being 0.930+/-0.010. Our method might facilitate future investigations in microvascular physiology and pathophysiology, specifically in subjects who have frequent or continuous involuntary movements. © 2010 Elsevier Inc. All rights reserved. Introduction There is an increasing interest in the study of the microvascular function in a broad spectrum of clinical or experimental situations (Fromy et al., 2010; Wingo et al., 2010; Sun et al., 2009; Fredriksson et al., 2010; Nazzaro et al., 2008; Wiles et al., 2010; Mistrik et al., 2010, McGuire and Howdieshell, 2010). Laser Doppler flowmetry can measure cutaneous blood flow (CBF) non-invasively and, when used in conjunction with specific provocation tests (e.g., local heating/cooling, iontophoresis of vasoactive substances, and post-occlusive reactive hyperaemia), is a key tool for evaluating skin microvascular function in clinical studies. Unfortunately, laser flowmetry recordings are highly prone to movement artefacts. Indeed, movements of the subject (e.g., trembling, coughing, shivering, and flinching) or laser probes, even of very small amplitude, result in the appearance of large artefacts in the recorded signal. Although an occasional movement artefact can be easily identified and manually removed, iterative or prolonged movements produce very “noisy” data that are difficult or even impossible to analyse and interpret (Fritzsche and Coyle, 2000). Therefore, CBF measurements should be done either in strictly immobile subjects or after tight immobilisation of the skin areas. To date, the recording of CBF over permanently moving skin areas has never been reported. Laser speckle contrast imaging (LSCI) allows for the continuous recording of CBF over large skin areas (McGuire and Howdieshell, 2010; Roustit et al., in press; Briers, 2001). We hypothesized: (i) that recording of the laser signal backscattered from an opaque surface fixed to the skin (LS os ) would be insensitive to CBF changes and allow for the sole quantification of movement artefacts (ART os ), as suggested in the review paper by Briers (2007), and; (ii) that the laser signal backscattered from adjacent skin (LS sk ) is the sum of CBF and movement artefacts on the skin (ART sk ). If correct, studying the relationship of ART os to ART sk should allow for the removal of movement artefacts from the recorded laser signals. Furthermore, a point-by-point subtraction, as proposed in the present study, has never been previously done. It is of specific interest if one aims at removing transient events related to artefacts and allow for an optimal time-resolution of the resulting de-noised laser signal, and overall at avoiding a manual subjective de-noising of data. We first investigated if the increase in the ART os is proportional to the increase in ART sk during externally-produced movements, when Microvascular Research 81 (2011) 183–188 ⁎ Corresponding author. Laboratory of Vascular Investigations, University Hospital, 4, rue Larrey, 49933 Angers Cedex 9, France. Fax: +33 2 41 35 35 93. E-mail address: piabraham@chu-angers.fr (P. Abraham). 0026-2862/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.mvr.2010.11.013 Contents lists available at ScienceDirect Microvascular Research journal homepage: www.elsevier.com/locate/ymvre