Quan Liang

A New Automated Computerized Analyzing System Simplifies Readings and Reduces the Variability in Ultrasound Measurement of Intima-Media Thickness

BACKGROUND AND PURPOSE A computerized analyzing system with manual tracing of echo interfaces for measurement of intima-media thickness and lumen diameter in carotid and femoral arteries was previously developed by our research group and has been used for many years in several laboratories. However, manual measurements are not only time consuming, but the results from these readings are also dependent on training and subjective judgement. A further problem is the observed drift in measurements over time. A new computerized technique for automatic detection of echo interfaces was therefore developed. The aim of this study was to evaluate the new automated computerized analyzing system. METHODS The new system is based on dynamic programming and includes optional interactive modification by the human operator. Local measurements of vessel echo intensity, intensity gradient, and boundary continuity are extracted by image analysis techniques and included as weighed terms in a cost function. The dynamic programming procedure is used for determining the optimal location of the vessel interfaces in a way that the cost function is minimized. RESULTS With the new automated computerized analyzing system the measurement results were less dependent on the readers experience, and the variability between readers was less compared with the old manual analyzing system. The measurements were also less time consuming. CONCLUSIONS The new automated analyzing system will not only greatly increase the speed of measurements but also reduce the variability between readers. It should also reduce the variability between different laboratories if the same analyzing program is used. Furthermore, the new system will probably prevent the problem with drift in measurements over time.

A multiscale dynamic programming procedure for boundary detection in ultrasonic artery images

Ultrasonic measurements of human carotid and femoral artery walls are conventionally obtained by manually tracing interfaces between tissue layers. The drawbacks of this method are the interobserver variability and inefficiency. Here, the authors present a new automated method which reduces these problems. By applying a multiscale dynamic programming (DP) algorithm, approximate vessel wall positions are first estimated in a coarse-scale image, which then guide the detection of the boundaries in a fine-scale image. In both cases, DP is used for finding a global optimum for a cost function. The cost function is a weighted sum of terms, in fuzzy expression forms, representing image features and geometrical characteristics of the vessel interfaces. The weights are adjusted by a training procedure using human expert tracings. Operator interventions, if needed, also take effect under the framework of global optimality. This reduces the amount of human intervention and, hence, variability due to subjectiveness. By incorporating human knowledge and experience, the algorithm becomes more robust. A thorough evaluation of the method in the clinical environment shows that interobserver variability is evidently decreased and so is the overall analysis time. The authors conclude that the automated procedure can replace the manual procedure and leads to an improved performance.

A dynamic programming procedure for automated ultrasonic measurement of the carotid artery

Describes a computerized technique for automated ultrasonic measurements of the carotid artery based on dynamic programming. Local measurements vessel echo intensity, edge strength, and continuity were extracted by image analysis techniques and included as weighted terms in a cost function. The dynamic programming procedure was used for determining the locations of the vessel interfaces in a way that the cost function was minimized. Then lumen diameter (LD) and intima-media thickness (IMT) were computed. Inter-method (auto versus manual) variability as well as inter- and intraobserver variability was studied by computing conventional coefficient of variation (CV). Inter-method (n=22), inter-observer (n=50), and intra-observer (n=47) variability of LD measurements were 1.2, 0.90, and 1.0%, respectively. Corresponding values for IMT were 3.2, 4.7, and 3.6%. These results indicate that the carotid artery can be automatically measured with accuracy.<<ETX>>

Implementation and comparison of four different boundary detection algorithms for quantitative ultrasonic measurements of the human carotid artery

In this paper we examine four algorithms for automated ultrasonic boundary detection, and describe the application of these algorithms to the quantification of the intima-media thickness (IMT) in the human carotid artery. The first algorithm uses a dynamic programming approach to identify the boundary that minimizes a certain cost function. The second algorithm is based on finding points of maximum gradient. The third algorithm employs a mathematical model describing the intensity profile perpendicular to the two boundaries defining the IMT. The last algorithm is based on defining a template representing the intensity profile across boundary and applying a matched filter procedure to find the image region that best matches it. The authors also present a quantitative and qualitative comparison between the four algorithms examined. It is shown that the dynamic programming algorithm provides superior performance in terms of accuracy and robustness. The correlation coefficients between automated measurements and manually obtained reference values were 0.96, 0.94, 0.63, and 0.85 for the dynamic programming, the maximum gradient the model-based, and the matched filter algorithm, respectively (n=30).

Isointensity directional smoothing for edge-preserving noise reduction

Isointensity directional smoothing is a novel edge-preserving smoothing method. By fitting a polynomial hypersurface to the local intensity, isointensity bands (isobands) are derived which approximately parallel an edge when the centre pixel is close to the edge. Pixels in the isoband passing through the centre are assigned higher weights, while those in other isobands are assigned lower weights according to a decaying function of the estimated intensity distance between the pixel and the centre. The weighted average of the pixel values is used as the smoothed value at the centre. The proposed method has a strong smoothing effect while causes little blurring of the edge, and the preserved edge has a good formation. The filter also performs well in intensity slope area. Experiments were carried on synthetic and real images. The results showed that the proposed filter has better performance than some well known edge-preserving filters compared in this work.