Accuracy evaluation of RBC velocity measurement in nail-fold capillaries

• Published in: Microvascular research Vol. 81; no. 3; pp. 252 - 260
• Main Authors: Wu, Chih-Chieh, Lin, Wen-Chen, Zhang, Geoffrey, Chang, Chin-Wen, Liu, Ren-Shyan, Lin, Kang-Ping, Huang, Tzung-Chi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2011
• Subjects: Bias; Blood Flow Velocity - physiology; Capillaries - physiology; Cross-correlation; Erythrocytes - cytology; Humans; Image Interpretation, Computer-Assisted - methods; Microscopic Angioscopy - methods; Nails - blood supply; Optical flow; Red blood cell velocity; Reproducibility of Results; Tourniquets; Visual inspection; Red blood cell velocity; Optical flow; Cross-correlation; Visual inspection
• ISSN: 0026-2862; 1095-9319; 1095-9319
• DOI: 10.1016/j.mvr.2011.01.003

Cutaneous red blood cell velocity in vivo can be measured by using capillaroscopy with image processing techniques. However, unlike simulated blood flow images, there is no standard to determine the accuracy of the techniques for computing blood flow velocities. In this paper, we quantitatively evaluated the accuracy of previously proposed optical flow method for measuring red blood cell velocity in nail-fold capillaries. Blood flow images of subjects under normal and occlusion-release conditions were examined by a capillaroscope. To obtain velocity values, the images were further analyzed by using optical flow, cross-correlation and visual inspection methods, respectively. Visual inspection method was taken as the golden standard to determine the accuracy of blood flow velocity measurement using optical flow and cross-correlation techniques. Results showed that optical flow estimation provided superior accuracy to cross-correlation when assessing real blood flow velocity in nail-fold capillaries. Optical flow estimation is able to measure red blood cell velocity with a high accuracy of 91% and 86% when the observed velocity is less than 0.5 mm/s under normal and occlusion-release conditions, respectively. In addition, optical flow method showed good agreement with visual inspection in determining blood flow velocity in both normal and occlusion-release conditions when the high-velocity zone is excluded. Relative errors of cross-correlation and optical flow estimations of RBC velocity in normal condition. [Display omitted] ►Visual inspection was also applied to estimate the RBC velocity which was taken as a reference for the evaluation and comparison. ►The good agreement of optical flow and visual inspection methods was reflected in the Bland–Altman plot. ►OFM presented higher accuracy than CCM in RBC velocity estimation in normal (91%) and occluding-releasing blood flow conditions (86%).