Correcting for possible tissue distortion between provocation and assessment in skin testing: The divergent beam UVB photo-test Jim O’Doherty 1 , Joakim Henricson 2 , Magnus Falk 3 and Chris D. Anderson 4 1 Division of Imaging Sciences & Biomedical Engineering, King’s College London, St Thomas’ Hospital, London, SE1 7EH, United Kingdom., 2 Department of Clinical and Experimental Medicine, Link€ oping University, Link€ oping, S581-85, Sweden and 3 Division of Community Medicine, Primary care,Department of Medical and Health Sciences, Link€ oping,S581-85, Sweden Background: In tissue viability imaging (TiVi), an assessment method for skin erythema, correct orientation of skin position from provocation to assessment optimizes data interpretation. Image processing algorithms could compensate for the effects of skin translation, torsion and rotation realigning assessment images to the position of the skin at provocation. Methods: A reference image of a divergent, UVB phototest was acquired, as well as test images at varying levels of trans- lation, rotation and torsion. Using 12 skin markers, an algo- rithm was applied to restore the distorted test images to the reference image. Results: The algorithm corrected torsion and rotation up to approximately 35 degrees. The radius of the erythemal reac- tion and average value of the input image closely matched that of the reference image’s ‘true value’. Conclusion: The image ‘de-warping’ procedure improves the robustness of the response image evaluation in a clinical research setting and opens the possibility of the correction of possibly flawed images performed away from the laboratory setting by the subject/patient themselves. This opportunity may increase the use of photo-testing and, by extension, other late response skin testing where the necessity of a return assess- ment visit is a disincentive to performance of the test. Key words: xxxxx Ó 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd Accepted for publication 7 January 2013 I N CLINICAL and research situations, skin test- ing can be used to assess individual variabil- ity in both innate and adaptive skin reactivity. Type I skin prick testing for the demonstration of Type I allergy is broadly used, with assess- ment being based on readings at 10–20 min after provocation (1). Phototesting and other testing involving assessment hours or days after provocation heighten demands for correct spa- tial orientation in order to make full use of the detailed assessment provided by modern bioen- gineering techniques such as Tissue Viability Imaging (TiVi), laser speckle imaging and laser Doppler imaging (2). Spatially transforming an acquired image to remove an unwanted geometrical effect or to perform image registration is a common issue in many areas of imaging in medicine such as endoscopic surgery (3), ultrasound-guided pros- tate biopsy (4), static and dynamic MRI imaging (5, 6) PET-guided radiotherapy planning (7) and multi-modality diagnostic imaging (8, 9). Image registration in its most basic form, is a transformation which maps all positions in one image plane to positions in a second plane with the choice of transformation involving a compromise between a smooth distortion and a transformation which achieves a good match between planes (10). The trans- formation is a mapping function that estab- lishes a spatial correspondence between all points in a reference image and its distorted counterpart, with a certain geometric relation- ship between each point in the reference and input images. Generally, several pixels in both reference and input images with correspon- dences (i.e. control points marked manually or automatically) are used to derive the unknown transformation. A general mapping function can be given in two forms; either relating the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 1 Skin Research and Technology 2013; 0:1–7 Printed in Singapore  All rights reserved doi: 10.1111/srt.12055 © 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd Skin Research and Technology S R T 1 2 0 5 5 B Dispatch: 19.1.13 Journal: CE: Deepa R Journal Name Manuscript No. Author Received: No. of pages: 7 PE: Ananthavalli