Usability of optical coherence tomography, clinical photography, thermal imaging, and laser speckle contrast imaging in the evaluation of i.d. injections
Subjects were acclimatized in a temperature-controlled room (21°C) for 15 minutes with bare legs. The sequence of measurements was (starting with the least invasive to minimize disturbance of the subsequent measurements): (1) thermography; (2) cutaneous micro circulation; (3) 3D photography; (4) multispectral imaging; and (5) skin morphology. Details of skin imaging methods are described below.
Skin micro circulation was quantified by LSCI (PeriCam PSI NR system, Perimed, Sweden). Laser speckle is the interference pattern returning from erythrocytes, resulting in a speckle pattern that differs under changes in blood flow (17). Recordings of 40 seconds were taken from a distance of 15 cm with a reading frame of 7 by 7 cm. Analysis was performed using the internal software (PimSoft, Perimed, Sweden) and regions of interest were selected based on the most predominant injection site reaction.
Skin temperature was quantified by infrared thermography (FLIR X6540sc camera, FLIR Systems Inc., USA). After calibration for room temperature using a black body, 10 second recordings were taken from a distance of 80 cm. Recordings were averaged for analysis.
Skin morphology was assessed by OCT (D-OCT VivoSight, Michelson Diagnostics, UK). Thirty second scans were performed with a 6 mm diameter probe. Three automatically calculated parameters were used to quantify morphology (attenuation compensation, blood flow at depth and skin roughness). Qualitative analysis was performed by two clinical scientists with experience in analyzing D-OCT images.
Erythema and swelling were quantified using a multispectral camera (Antera 3D, Miravex, Ireland), and a 3D stereophotogrammetry camera (3D LifeViz, QuantifiCare, USA). The multispectral camera was placed over the skin creating a closed environment with the lesion in the centre of the frame. Erythema was measured using the CIELab *a value. CIELab is a standardized quantitative method to discriminate colours using an XYZ-axis system. CIELab *a value is represented on the red/green axis and is correlated to skin erythema (18,19). Three-dimensional images were taken from a distance of 20 cm with use of a guidance laser and analyzed in imaging processing software (DermaPix Software, QuantifiCare, Valbonne, France).