Computerized analysing system using the active contour in ultrasound measurement of carotid artery intima-media thickness Arno Schmidt-Trucksa Èss 1 , Da-chuan Cheng 2 , Markus Sandrock 1 , Ju È rgen Schulte-Mo È nting 3 , Rainer Rauramaa 4 , Martin Huonker 1 and Hans Burkhardt 2 1 Centre for Internal Medicine, Department of Prevention, Rehabilitation and Sports Medicine, Freiburg University Hospital, Freiburg, Germany, 2 Computer Science Department, Freiburg University, Freiburg, Germany, 3 Department of Medical Biometry and Computer Science, Freiburg University, Freiburg, Germany, and 4 Kuopio Research Institute of Exercise Medicine and Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, Kuopio, Finland Received 16 October 2000; accepted 17 March 2001 Correspondence: Arno Schmidt-Trucksa È ss MD, PhD, Centre for Internal Medicine, Department of Prevention, Rehabilitation and Sports Medicine, Freiburg University Hospital, Hugstetter strasse 55, 79106 Freiburg, Germany ............................................................................................................................................................................................................................................................................................................................ Summary Background and purpose B-mode measurement of the carotid intima-media (IM) thickness (T) based on manual tracing (MT) procedures are dependent on the subjectivity of the reader and the existing auto- matic tracing procedures often fail to detect the IM boundaries accurately. The purpose of this study was to compare the tracing results of the IM boundaries of the carotid wall with a new automatic identi®cation (AI) procedure, based on an active contour model, and computer-assisted manual tracing (MT). Methods The detection of the IM boundaries was performed with both procedures in 126 ultrasound images [63 each of the common carotid artery (CCA) and carotid bulb] along the far wall of the distal CCA and the carotid bulb. Intra- and inter-reader variabi- lity for mean and maximum IMT with AI and MT and accuracy of identi®cation of both IM boundaries were evaluated. Results Using MT the intra- and inter-reader vari- ability amounted to 0á01±0á03 and 0á03±0á07 mm, respectively. The variability was slightly higher in the carotid bulb than in the CCA. Using AI the variability was almost eliminated. Mean and maximum IMT were measured systematically lower by AI compared with MT in all regions by 0á01 mm. The accuracy of identi®cation was similar for both IM boundaries, but lower in the carotid bulb region than in the CCA. Conclusions The new AI procedure identi®es both IM boundaries in the region of the far wall of the CCA and carotid bulb with high precision, and eliminates most of the intra- and inter-reader variability of the IMT measurement using MT. Keywords: atherosclerosis, automatic analysis, carotid bulb, common carotid artery, pattern recognition, ultrasonics. Introduction The intima-media thickness (IMT) of the carotid tree has been measured increasingly with B-mode ultrasound as an index of the atherosclerotic burden of the vascular system (Gibbons & Dzau, 1994; Howard et al., 1998; Greenland et al., 2000), as a surrogate endpoint in clinical trials with interven- tions on the atherosclerotic progress (Byington et al., 1995) and as a powerful predictor of major cardio- vascular disease (O'Leary et al., 1999). The meas- urement of the IMT in research studies has been predominantly performed by well-trained readers with manual tracing procedures, and seems to be as good as automatic measurements. However, there remains a 11% of the total within-subject variability for each outcome measure of IMT performed with manual tracing (Espeland et al., 1996). This is of importance because an increase in the variability of a ............................................................................................................................................................................................................................................................................................................................ Clinical Physiology 21, 5, 561±569 ·Ó 2001 Blackwell Science Ltd 561