title: Comparison of infrared thermography and laser speckle contrast imaging for the dynamic assessment of digital microvascular function.
abstract: OBJECTIVE
  Laser speckle contrast imaging (LSCI) is a novel non-invasive microvascular imaging modality. The present study evaluates the validity and reliability of LSCI by comparison with infrared thermography (IRT) for the dynamic assessment of digital microvascular function in healthy volunteers.
  
  
  METHODS
  Subjects attended on 3 occasions. Simultaneous assessment of cutaneous perfusion at 3 distinct regions of interest (ROI) within the hands was undertaken using LSCI and infrared thermography (IRT) at baseline, and at 13s intervals over 15 min following a standardised local cold challenge. Endpoints for evaluation included absolute measurements at baseline and following cold stress, in addition to the characteristics of the re-warming curves (maximum % recovery and maximum gradient). Visits 1 and 2 were undertaken in identical conditions (ambient temperature 23°C) to assess reproducibility, whereas visit 3 was undertaken at a lower ambient room temperature of 18°C to evaluate responsiveness to reduction in ambient room temperature.
  
  
  RESULTS
  Fourteen healthy participants completed the study. There was greater variability in the data generated using LSCI compared with the highly damped IRT, reflecting greater sensitivity of LSCI to physiological variation and movement artefact. LSCI and IRT correlated well at baseline and following cold challenge for all endpoints (r(s) for pooled data between 0.5 and 0.65, p<0.00005). Reproducibility of both IRT and LSCI was excellent (ICCs>0.75) for absolute assessments but lower for re-warming curve characteristics. LSCI provides greater spatial resolution than IRT identifying variation in cutaneous perfusion within the hands most likely associated with the presence of arteriovenous anastamoses. Both techniques were responsive to reduction in ambient room temperature. Effect sizes were greatest for IRT than LSCI (e.g. -1.17 vs. -0.85 at ROI 1 at baseline) although this may represent heat transfer rather than altered vascular perfusion.
  
  
  CONCLUSIONS
  In the dynamic assessment of digital vascular perfusion, LSCI correlates well with IRT, is reproducible and responsive to reduction in ambient room temperature. Absolute measurements appear preferable to parameters derived from re-warming curve characteristics when assessing digital perfusion following cold challenge. The greater temporal and spatial resolution of LSCI compared with IRT may facilitate the development of novel assessment tools of autonomic function and digital cutaneous perfusion.
authors.affiliation: Royal National Hospital for Rheumatic Diseases, Bath, UK. John.Pauling@rnhrd.nhs.uk
authors.forename: J D
authors.initials: JD
authors.lastname: Pauling
authors.forename: J A
authors.initials: JA
authors.lastname: Shipley
authors.forename: S
authors.initials: S
authors.lastname: Raper
authors.forename: M L
authors.initials: ML
authors.lastname: Watson
authors.forename: S G
authors.initials: SG
authors.lastname: Ward
authors.forename: N D
authors.initials: ND
authors.lastname: Harris
authors.forename: N J
authors.initials: NJ
authors.lastname: McHugh
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D003080:Cold Temperature; D005260:Female; D005385:Fingers / Q000098:blood supply*; D006801:Humans; D007259:Infrared Rays; D017078:Laser-Doppler Flowmetry / Q000379:methods*; D008297:Male; D008833:Microcirculation; D055806:Microvessels / Q000502:physiology*; D008875:Middle Aged; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature; D013817:Thermography / Q000379:methods*; D013997:Time Factors