Impact of Experimental Conditions on Noncontact Laser Recordings in Microvascular Studies GUILLAUME MAHE ´ , *,  SYLVAIN DURAND, à ANNE HUMEAU-HEURTIER, § GEORGES LEFTHERIOTIS, *,  AND PIERRE ABRAHAM *,  * Laboratoire d’Explorations Fonctionnelles Vasculaires, Centre Hospitalier Universitaire, Angers, France;   Biologie Neurovasculaire et Mitochondriale Inte ´gre ´e (BNMI), L’UNAM Universite ´, Faculte ´ de Me ´decine, Angers, France; à L’UNAM Universite ´, Laboratory ‘‘Motricite ´, Interactions, Performance’’, Faculty of Sport Sciences, University of Le Mans, Le Mans, France; § L’UNAM Universite ´, Laboratoire d’Inge ´nierie des Syste `mes Automatise ´s (LISA), Universite ´ d’Angers, Angers, France Address for correspondence: Guillaume Mahe ´, Laboratory of Vascular Investigations, University Hospital, 4, rue Larrey, 49933 Angers Cedex 9, France. E-mail: maheguillaume@yahoo.fr Received 16 September 2011; accepted 13 June 2012. ABSTRACT Microcirculation, especially skin microcirculation, is a window toward systemic vascular function in magnitude and underlying mechanisms. Different techniques have been developed to assess the microcirculation. Among these techniques, laser technology is used to perform noninvasive microvascular assessments. In the 1970s, the laser Doppler flowmetry (LDF) technique was proposed to monitor microvascular blood flow. More recently, noncontact technologies including laser Doppler perfusion imaging (LDI) and laser speckle contrast imaging (LSCI) have improved the reproducibility of the microcirculation measurements and facilitated some clinical evaluations such as on wounds and ulcers. However, due to the absence of contact between tissue and sensors, it is likely that different technical and environmental conditions may interfere with microvascular recordings. This review presents major technical and environmental conditions, which may interfere with noncontact laser recordings in microvascular studies. Key words: laser Doppler, laser speckle, microcirculation, skin, experimental conditions, methods, iontophoresis, blood flow. Abbreviations used: ACh, acetylcholine; CBF, cutaneous blood flow; CCD, charged coupled device; CV, coefficient of variation; LDF, laser Doppler flowmetry; LDI, laser Doppler imaging; LH-T, distance, laser head to tissue distance; LIPU, laser imager perfusion unit; LSCI, laser speckle contrast imaging; LSPU, laser speckle perfusion unit; MSV, measured signal values; PORH, post- occlusive reactive hyperemia; ROI, region of interest; TOI, time of interest. Please cite this paper as: Mahe ´ G, Durand S, Humeau-Heurtier A, Leftheriotis G, Abraham P. Impact of experimental conditions on noncontact laser recordings in microvascular studies. Microcirculation 19: 669–675, 2012. INTRODUCTION Assessment of microvascular function is of particular interest in humans and animals to understand physiologi- cal and pathophysiological processes [38]. Methods for the noninvasive investigation of microcirculation are mainly based on optical microscopy and laser techniques [21]. Since 1975, LDF has been proposed for in vivo monitoring of blood flow [36]. LDF is a contact tech- nique that relies on the Doppler effect: a coherent laser light is led via optical fibers (most often) to a probe posi- tioned on the tissues. Some photons are scattered by sta- tic tissues, while others are scattered by moving blood cells. For the latter photons, a Doppler shift generates a modification in their wavelength. The interference of the Doppler-shifted and non-Doppler-shifted photons on a detector results in a beat frequency. The first moment of the power spectrum for the fluctuations of the photode- tector current gives the LDF signal [5,15,26]. However, due to the regional heterogeneity of skin perfusion and the small measurement volume of single-point LDF probes (<1 mm 3 for a 780-nm laser wavelength [24], a high spatial variability exists in LDF skin perfusion values [39]. This gives a relatively poor reproducibility of the single-point LDF technique [29,31]. Moreover, LDF is a contact technique and thus necessitates the positioning of a probe on the tissues limiting the perfusion monitoring on injuries. To reduce these drawbacks, LDI has been proposed [8,43]. In brief, a laser Doppler image is a collection of LDF points (pixels) placed together on a color-coded map. Con- ventional laser Doppler imagers achieve the perfusion DOI:10.1111/j.1549-8719.2012.00205.x Review ª 2012 John Wiley & Sons Ltd 669 The Official Journal of the Microcirculatory Society, Inc. and the British Microcirculation Society