José Correa

Enhancement of chest and breast radiographs by automatic spatial filtering

The authors present a new algorithm to enhance the edges and contrast of chest and breast radiographs while minimally amplifying image noise. The algorithm consists of a linear combination of an original image and two smoothed images obtained from it by using different masks and parameters, followed by the application of nonlinear contrast stretching. The result is an image which retains the high median frequency local variations (edge and contrast-enhancing).

Computer-assisted diagnosis: the classification of mammographic breast parenchymal patterns.

We have developed a method for the quantification of breast texture by using different algorithms to classify mammograms into the four patterns described by Wolfe (N1, P1, P2 and Dy). The computerized scheme employs craniocaudal views of conventional screen-film mammograms, which are digitized by a laser scanner. We used discriminant analysis to select among different feature-extraction techniques, including Fourier transform, local-contrast analysis, and grey-level distribution and quantification. The method has been evaluated on 117 clinical mammograms previously classified by five radiologists as to mammographic breast parenchymal patterns (MBPPS). The results show differences in agreement among radiologists and computer classification, depending on the Wolfe pattern: excellent for Dy (kappa = 0.77), good for P2 (kappa = 0.52) and N1 (kappa = 0.52) and poor for P1 (kappa = 0.22). Our quantitative texture measure as calculated from digital mammograms may be valuable to radiologists in their assessment of MBPP and therefore useful in establishing an index of risk for developing breast carcinoma.

Liquid—liquid equilibria of the system water + acetic acid + methyl ethyl ketone at several temperatures

Abstract This article reports the solubilities and equilibrium data of the ternary mixture water + acetic acid + methyl ethyl ketone at 25, 35 and 45°C, and the equilibrium data of the binary system water + methyl ethyl ketone over the range 20–55°C. NRTL and UNIQUAC equations have been fitted to the experimental data for the ternary system, which are also compared with the values predicted by the UNIFAC method.

Supervised Reinforcement Learning: Application to a Wall Following Behaviour in a Mobile Robot

In this work we describe the design of a control approach in which, by way of supervised reinforcement learning, the learning potential is combined with the previous knowledge of the task in question, obtaining as a result rapid convergence to the desired behaviour as well as an increase in the stability of the process. We have tested the application of our approach in the design of a basic behaviour pattern in mobile robotics, such as that of wall following. We have carried out several experiments obtaining goods results which confirm the utility and advantages derived from the use of our approach.

Digital radiography of the chest: state of the art

Digital image acquisition possesses a number of advantages over conventional systems in radiographic examination of the chest, the most important of which is its greater dynamic range. In addition, one digital images are acquired, they can be processed by computer in ways that cannot be rivalled by conventional analog techniques. Finally, digital images can be stored, retrieved and transmitted to local or remote sites. Here the status of the different digital systems employed in chest radiology and commonly used image processing techniques are reviewed. Also discussed are the current clinical applications of integrating digital chest radiography with a picture archiving and communication system (PACS) along with the difficulties typically encountered. Studies with a variety of digital techniques have been carried out on several fronts. Computer radiography based on photostimulabe phosphor (CR) has replaced screen-film imaging in certain applications (i.e. bedside imaging). However, CR has limitations, namely its poor X-ray utilisation efficiency at high X-ray tube voltages and sensitivity to scatter; therefore, it is not ideal for all applications. Recently, a dedicated digital chest unit with excellent X-ray utilisation efficiency at high X-ray tube potentials has been introduced. On the basis during the past decade, recommendations are made regarding the most desirable equipment specifications for dedicated and bedside digital chest radiography.

Enhancement of Chest Images by Automatic Adaptive Spatial Filtering

Postprocessing of the image data is an exciting capability of digital radiography that may improve diagnostic performance. We present a new algorithm that selectively enhances edges and contrast in both lungs and mediastinum while minimally amplifying noise in chest images. Using different size kernels, two smoothed images are generated from the original chest image. The two regions of interest (lungs and mediastinum) are identified based on the distribution of pixel values in the image. A modified nonlinear unsharp mask subtraction technique is then applied. The resulting image has enhanced high- and middle-frequency information in the mediastinum without distorting lung parenchyma or significantly enhancing noise. We consider that the technique employed in this study could be suitable for routine use although its true effectiveness in improving diagnostic accuracy awaits observer-performance evaluation that is currently under way.

Probabilistic and Count Methods in Map Building for Autonomous Mobile Robots

In this paper two computationally efficient methods for building a map of the occupancy of a space based on measurements from a ring of ultrasonic sensors are presented. The first is a method based on building a histogram of the occurrence of free and occupied space. The second is based on the calculation of the rate between occupied space measurements with respect to the total. The resulting occupancy maps have been compared with those obtained with other well-known methods, bothcoun t as well as Bayes-rule-based ones, in static environments. Free space, occupied space and unknown labels were also compared subsequent to the application of a simple segmentation algorithm. The results obtained gave rise to statistically significant differences between all the different types on comparing the resulting maps. In the case of comparing occupancy labels, no differences were found between the following pairs of methods: RATE and SUM (p - value = 0.157), ELFES and RATE (p - value = 0.600) and ELFES and SUM (p - value = 0.593).

Implementation of a Basic Reactive Behavior in Mobile Robotics Through Artificial Neural Networks

In this work we describe the design and implementation in a Nomad200 mobile robot of a reactive behavior aimed at wall following. A detailed analysis of the application domain has allowed us to modularize the design, conjugating in its. synthesis the potential of artificial neural networks for sensorial abstraction with other decision modules. We have carried out several experiments both in simulated and in real environments, obtaining very good results in different and unfavorable situations, which proves the robustness and flexibility of the system.

Comparison of real and computer-simulated clustered microcalcifications on digital mammograms. ROC study

The authors propose a model to simulate clustered microcalcifications on digital mammograms. The simulation model is based on the gray-level, size and number of microcalcifications per cluster. All the parameters describing the individual microcalcifications and clusters were randomly sampled from the values of the real clustered microcalcifications (extracted in a feature analysis process) present in the mammogram, the exception being the center of the cluster, that was interactively positioned to ensure the location of all the microcalcifications inside the breast. Subsequently, a database of clustered microcalcifications was created. These clusters of microcalcifications from this database were tested from indistinguishability from real ones. Two radiologists and one physicist were asked to indicate wether the microcalcifications were either real or simulated. The responses of the readers were evaluated with an ROC analysis, and the area under the curve was calculated. The average ROC area was 0.54/spl plusmn/0.05, indicating that there was no statistical difference between real and simulated clustered microcalcifications.