Evaluation of techniques for the presentation of laboratory data: support of pattern recognition.

Two tabular and two graphical techniques for the presentation of laboratory test results were compared in a reaction-time experiment with 22 volunteers. The experimental setup was designed to determine whether one or more of the presentation techniques facilitated the recognition of four predefined combinations of abnormal test results. Using a conventional, tabular presentation technique as a reference, faster median response times were obtained with each of the other three presentation techniques, irrespective of pattern. The effect on accuracy was less clear, possibly due to the small number of errors made.

Assessment of body position to quantify its effect on nocturnal blood pressure under ambulatory conditions.

BACKGROUND: Nocturnal blood pressure readings may be influenced by body position because of variation in the vertical distance between heart and cuff level. OBJECTIVES: To quantify the effect of body position on nocturnal blood pressure and to assess whether this effect influences the reproducibility of nocturnal blood pressure. PATIENTS AND METHODS: In 16 individuals (three normotensive and 13 hypertensive) 24 h ambulatory measurement of blood pressure and body position was performed twice, separated by an interval of 2-6 weeks. Body position was measured with five acceleration sensors, which were mounted on the trunk and legs. RESULTS: During the first night, 43 +/- 31% of blood pressure values were measured while participants were in the supine position, 29 +/- 28% when they were lying on their side with the cuffed arm down and 28 +/- 29% when they were lying on their side with the cuffed arm up. During the second night these percentages were 40 +/- 29%, 32 +/- 29% and 28 +/- 25% respectively. Blood pressure readings obtained while individuals were lying with the cuffed arm up were about 10 mmHg lower than those obtained with the individual in either the supine position or lying with the cuffed arm down. After correction for the underestimation attributable to 'cuff-up' readings, nocturnal blood pressure increased by 3 mmHg and the number of non-dippers increased from two to four. Correction did not affect the reproducibility of nocturnal blood pressure measurements (standard deviation of the differences 8.3 mmHg for systolic and 6.0 mmHg for diastolic blood pressure after correction). Dipping status was reproduced in 88% of individuals before correction, and in 87% after correction. CONCLUSIONS: Under ambulatory conditions, a highly variable but sometimes substantial number of blood pressure readings are taken with the cuffed arm above heart level. These readings result in underestimation of nocturnal blood pressure and hence influence dipper-non-dipper classification. However, body position does not seem to have an important influence on the reproducibility of nocturnal blood pressure or dipping status.

A re-appraisal of the tri-axial chart for monitoring arterial acid-base values.

OBJECTIVE: To demonstrate the practicability of a tri-axial chart for the graphical and quantitative monitoring of arterial pH, arterial carbon dioxide partial pressure (PaCO2) and actual arterial bicarbonate-ion concentration (a[HCO3-]) in intensive care patients. DESIGN: Case report. SETTING: A general intensive care unit (ICU). METHODS: Using a standard mathematical transformation, a data set of pH, log PaCO2 and log a[HCO3-] values can be transformed in such a way that a graphical display of all three variables is possible while being faithful to their linear relationship. Remarkably, the graphical display closely resembles the tri-axial chart that Hastings and Steinhaus described in 1931 for studying displacements of the acid-base balance. Two new monitoring parameters based on the chart and the transformation are described. One monitors the abnormality of the acid-base status while the other monitors the rate of acid-base changes. CONCLUSIONS: With the tri-axial acid-base chart, the complete acid-base status can be faithfully monitored. Moreover, the proposed monitoring parameters provide extra information about the arterial acid-base status that, otherwise, would remain hidden.

Texture analysis in radiographs: the influence of modulation transfer function and noise on the discriminative ability of texture features.

Tissue structures, represented by textures in radiographs, can be quantified using texture analysis methods. Different texture analysis methods have been used to discriminate between different aspects of various diseases in primarily x rays of chest, bone, and breasts. However, most of these methods have not specifically been developed for use on radiographs. Certain characteristics of the radiographic process, e.g., noise and blurring, influence the visible texture. In order for a texture analysis method to be able to discriminate between different underlying textures, it should not be too sensitive for such processes as image noise and blur. In this study, we investigated the sensitivity of four different texture analysis methods for image noise and blur. First, a baseline measurement was performed of the discriminative performance of the Spatial Gray-Level Dependence method, the Fourier Power Spectrum, the Fractal Dimension, and the Morphological Gradient Method on images, which were not affected by radiographic noise and blur. Two types of images were used: fractal and Brodatz. Whereas the Brodatz images represent very different textures, the differences between the fractal images are more gradual. We assume that the behavior of the different texture analysis methods on the fractal images is representative for their performance on radiologic textures. On these types of images we simulated the effect of four different noise levels and the effect of two different modulation transfer functions, corresponding with different screenfilm combinations. The influence on the discriminative performance of the four texture analysis methods was evaluated. The influence of noise on the discriminative performance is, as expected, dependent on the image type used; the discrimination of more gradually different images, such as the fractal images, is already lowered for relatively low noise levels. In contrast, when the images are more different, only high noise levels decrease the discriminative performance. The discriminative power of the Morphological Gradient Method is least affected by image blur. We conclude that the discriminative performance of the Morphological Gradient Method is superior to that of other methods in circumstances which mimic the conditions prevailing in radiographs.

Recognition of daily life motor activity classes using an artificial neural network.

OBJECTIVE: To investigate a possible role of artificial neural networks for the automated recognition and classification of daily life activities (eg, sitting, lying, standing, walking, etc) in an attempt to reduce the cost of manual recognition and classification. METHODS: Data from sessions of about 10 hours of continuous recording of eight ambulatory patients were used to train and evaluate eight probabilistic neural networks, each of which is configured for one subject. To provide the reference data for building the training set, the instrumented subject follows a 15- to 30-minute protocol consisting of several daily life activities. To properly evaluate the networks, the remaining manually labeled data of each subject were compared with the output of each trained network. RESULTS: The average recognition rate of the trained neural networks was equal to 95% good classification of all presented cases of the daily life activity. Automatic misclassification of 5% resulted from certain activities being too short or the occurrence of activities that were not included in the training set. CONCLUSION: The preliminary results of the trained neural networks have indicated that the probabilistic neural network is a potentially useful tool for the recognition of daily life motor activities.

A computer program for constructing multivariate reference models.

From a statistical point of view the simultaneous interpretation of multiple variables should be performed with a multivariate reference model rather than with multiple univariate reference intervals. A computer program for constructing and testing multivariate reference models is described. The use of the computer program is illustrated with a data set of total serum calcium concentrations and serum albumin concentrations from 222 2nd year medical students. Using a single univariate reference interval for total serum calcium, 17 students were classified as having an abnormal calcemic status while using a bivariate reference model for total serum calcium and serum albumin, 13 of these 17 students had in fact normal total serum calcium concentrations, taking into account their serum albumin concentrations.

Analysis of metacarpophalangeal profiles by pattern recognition techniques.

RATIONALE AND OBJECTIVES: The author introduces a number of techniques well known in exploratory pattern recognition that can be used for the analysis of the shape of metacarpophalangeal profiles. It is shown that the classic Q-scores must be adapted for such techniques to be applicable. METHODS: A new set of scores (P-scores) describing the shape of metacarpophalangeal profiles is derived. The application of various pattern-recognition techniques that use P-scores is described, using a collection of metacarpophalangeal length measurements in patients with various pathologic conditions. RESULTS: Different pattern-recognition techniques highlight different aspects of the profiles, which, when interpreted together, yield a consistent understanding of the data set and insight in individual patients' peculiarities. CONCLUSIONS: The use of scale-invariant scores is imperative when the shape of profiles is to be analyzed, especially in data sets with large variations in the scale factor. Methods of pattern recognition using such scores are of potential clinical interest.

Metacarpophalangeal pattern (MCPP) profile analysis in a family with triphalangeal thumb.

Triphalangeal thumb (TPT) is a rare congenital disorder characterised by a long, finger-like thumb with three phalanges instead of two. It can occur as an isolated defect, in association with other abnormalities of the hands and feet, or as a part of a syndrome. Sporadic cases have been described, but it is usually inherited as an autosomal dominant trait. In order to examine skeletal morphology in different phenotypic variations of this disorder, we performed metacarpophalangeal pattern profile analysis in one kindred with this disorder. A characteristic profile occurred in all affected people, based on the individual lengthening or shortening of the thumb bones. Comparison of the affected and unaffected people from this family with people with a different genetic background suggests that the described profile is specific for TPT and could be used as a helpful diagnostic tool in syndromes which include TPT.

Evaluation of techniques for the presentation of laboratory data. I: Time needed for interpretation.

Four tabular and two graphical techniques for the presentation of laboratory test results were evaluated in a reaction-time experiment with 25 volunteers. Artificial variables and values were used to represent sets of 12 laboratory tests to eliminate the possible effects of clinical experience. Analyses focused on reaction times for correctly classified sets of data. For comparable data sets, Presentation Techniques (PT) that use color, always allow faster interpretation than PTs that do not use color, or use only a simple marker. Color-coded tables yielded an improvement in median reaction time of approximately six times or better, as compared to the reference PT (a tabular PT without any hints). For the color-coded graphs, the improvement rate was approximately 2.5 or better.

Evaluation of techniques for the presentation of laboratory data. II: Accuracy of interpretation.

Four tabular and two graphical techniques for the presentation of laboratory test results were evaluated in a reaction time experiment with 25 volunteers. Artificial variables and values were used to represent sets of 12 laboratory tests to eliminate the possible effects of clinical experience. Analyses focused on four types of errors in interpretation. Color-coded tables and one of the color-coded graphs greatly (2.8 times or better) reduced the number of incorrectly classified test results, as compared to the reference presentation technique. This was mainly due to a reduction of the number of abnormal test results that were not noticed by the subjects when using these presentation techniques.

Unraveling the role of structure and density in determining vertebral bone strength.

The strength of bone is determined not only by bone density but also by structure. Therefore, quantification of the structure in radiographs by texture parameters may result in a better prediction of fracture risk. Since in radiographs density and structure are strongly correlated, the predictive power of texture parameters should be corrected for the influence of BMD to determine the additional information conveyed by these parameters. In this study, we evaluated the predictive power of various texture parameters based on the Grey-Level Dependence Method and the Morphological Gradient Method. This study was performed on 67 vertebrae obtained from 20 male and 12 female human cadaver thoracolumbar spines. BMD and area of the vertebral body were determined from QCT images and texture parameters were derived from direct magnification (DIMA) radiographs. The fracture force, measured under conditions simulating the in vivo situation, was corrected with the area of the vertebra to yield the fracture stress (FS). Results of the study indicate that BMD correlates significantly with FS r = 0.82 (P < 0. 001, n = 24) and r = 0.94 (P < 0.001, n = 43) for female and male vertebrae, respectively. Correlation coefficients of the investigated texture parameters were as high as 0.80 (P < 0.001) and 0.67 (P < 0.001) for the female and male vertebrae, respectively. Multiple regression analysis showed that in female vertebrae, the addition of one texture parameter to BMD results in a better prediction of strength. The multiple correlation coefficient was 0. 87 (P < 0.001) in this case. In male vertebrae, BMD was the best predictor of fracture stress. These results suggest that texture parameters, as measured in magnification radiographs, can predict bone strength. Whereas in all cases BMD is the best single predictor of bone strength, for women texture parameters contain useful additional information.

New developments and applications in quantitative electron spectroscopic imaging of iron in human liver biopsies.

Reliable iron concentration data can be obtained by quantitative analyses of image sequences, acquired by electron spectroscopic imaging. A number of requirements are formulated for the successful application of this recently developed in situ quantitative type of analysis. A demonstration of the procedures is given. By application of the technique it is established that there are no significant differences in the average iron loading of structures analysed in liver parenchymal cells of a patient with an iron storage disease, before and after phlebotomy. This supports the hypothesis that the process of iron unloading is an organelle specific process. Measurement of the binary morphology, represented by the area and contour ratio of the iron containing objects revealed no information about differences between the objects. This finding contradicts the visual suggestion that ferritin clusters are more irregularly shaped than the other iron objects. Also, no differences could be found in this sense between the situations before and after phlebotomy. With respect to the density appearance, objects that have an inhomogeneous iron loading averagely contain more iron. This observation does correspond well with the visual impression of the increasingly irregular appearance of more well-loaded structures.

Computerized analysis of daily life motor activity for ambulatory monitoring.

The primary goal of an ambulatory monitoring of motor activities (AMMA) system is to document the occurrence of random and spontaneous motor activities (e.g., sitting, lying, standing, walking, running, etc.) of the ambulatory subject in natural environmental circumstances. Much progress has been made in recording fidelity, reduction in energy requirement, fixation of the accelerometers, equipment size and weight, memory capacity and data acquisition. At present, our laboratory is interested in developing an automated off-line AMMA-signal analysis system. The system has to take care of activity (wave) detection, recognition of onsets and endpoints of the various activities (waves), and computation of a set of relevant clinical parameters (e.g., total walking time, number of times rising from a chair, etc.) from long-term recorded data. Two methods are currently being used for computerizing the off-line analysis system: using an artificial neural network and using a set of selected features extracted from the input data. The present paper is aimed at the latter method. The method was successfully applied to long-term recorded data sets of eight male amputees and three other subjects. The primary results indicate that the method is a potentially useful too to computerize the off-line analysis system.

Quantitative electron spectroscopic imaging in bio-medicine: evaluation and application.

Electron spectroscopic imaging (ESI) with the energy-filtering transmission electron microscope enables the investigation of chemical elements in ultrathin biological sections. An analysis technique has been developed to calculate elemental maps and quantitative distributions from ESI sequences. Extensive experience has been obtained with a practical implementation of this technique. A procedure for more robust element detection has been investigated and optimized. With the use of Fe-loaded Chelex beads, the measurement system has been evaluated with respect to the linearity of the element concentration scale, the reproducibility of the measurements and the visual usage of image results. In liver specimens of a patient with an iron storage disease the detectability of iron was tested and we tried to characterize iron-containing components. The concentration measurement scale is approximately linear up to a relative section thickness of approximately equal to 0.5. Monitoring of this parameter is therefore considered to be important. The reproducibility was measured in an experiment with Fe-Chelex. The iron concentration differed by 6.4% between two serial measurements. Element distributions are in many applications interpreted visually. For this purpose the frequently used net-intensity distributions are regarded as unsuitable. For the quantification and visual interpretation of concentration differences mass thickness correction has to be performed. By contrast, for the detection of elements the signal-to-noise ratio is the appropriate criterion. Application of ESI analysis demonstrated the quantitative chemical capabilities of this technique in the investigation of iron storage diseases. Based on an assumed ferritin iron loading in vivo, different iron components can be discerned in liver parenchymal cells of an iron-overloaded patient.

Estimation of fractal dimension in radiographs.

In the last decade, the fractal dimension has become a popular parameter to characterize image textures. Also in radiographs, various procedures have been used to estimate the fractal dimension. However, certain characteristics of the radiographic process, e.g., noise and blurring, interfere with the straightforward application of these estimation methods. In this study, the influence of quantum noise and image blur on several estimation methods was quantified by simulating the effect of quantum noise and the effect of modulation transfer functions, corresponding with different screen-film combinations, on computer generated fractal images. The results are extrapolated to explain the effect of film-grain noise on fractal dimension estimation. The effect of noise is that, irrespective of the noise source, the fractal dimension is overestimated, especially for lower fractal dimensions. On the other hand, blurring results in an underestimation of the dimensions. The effect of blurring is dependent on the estimation method used; the dimension estimates by the power spectrum method are lowered with a constant value, whereas the underestimation by the methods working in the spatial domain is dependent on the given dimension. The influence of the MTF and noise on fractal dimension estimation seriously limits the comparability of fractal dimensions estimated from radiographs which differ in noise content or MTF. Only when the power spectrum method is used, it is possible to correct for the influence of different MTFs of screen-film combinations. It is concluded that only when using the same object-focus distance, the same exposure conditions, the same digitizer at the same resolution, can fractal dimensions as estimated in radiographs be reliably compared.

Design and representation of multivariate patient-based reference regions for arterial pH, PCO2 and base excess values.

OBJECTIVES: To determine and compare the shape and location of three data sets of arterial pH, PCO2, and BE values from intensive care patients in a new acid-base chart for the purpose of deriving multivariate reference regions. DESIGN AND METHODS: The new chart is constructed by applying a statistical technique called principal component analysis (PCA). Three different data sets, each comprised of 1500 arterial pH, PCO2, and BE values, were subjected to PCA. The 3 data sets were collected in a respiratory intensive care unit (ICU) of a University Hospital, in a general ICU of a District Hospital, and in a neonatal ICU of a Children's Hospital. RESULTS: The outlines of the resulting charts are similar for all 3 data sets, but the representations of the three distributions in the new chart are highly dissimilar, both in shape and in location. CONCLUSIONS: PCA can be used to derive a patient-based reference region for arterial pH, PCO2, and BE values. Furthermore, the new chart may be useful for the graphical monitoring of acid-base data because distances between consecutive observations are faithfully represented.

A computer program for the multivariate and graphical monitoring of acid-base data in an intensive care unit.

Monitoring the arterial acid-base status of ICU patients is done by measuring and calculating the acid-base variables pH, the partial pressure of carbon-dioxide (PCO2) and the bicarbonate-ion concentration ([HCO-3]). Univariate normal reference ranges exist for these values. However, it is well known that an exact linear relationship exists between pH, the logarithm of PCO2 and the logarithm of [HCO-3] values. We developed a computer program for the multivariate evaluation and graphical monitoring of these values in an intensive care setting that takes this intrinsic two-dimensionality into account. A composite index is introduced for the monitoring of all three laboratory values. Moreover, using this index, a multivariate statistical reference region based on an unselected population of ICU patients was derived.

A new representation of acid-base disturbances.

The acid-base status of intensive care patients is monitored on the basis of three quantities. The graphical representation which may be of help for the monitoring task is therefore cumbersome. The classical Siggaard-Andersen acid-base chart is such a representation, but it is only suited for evaluating one acid-base status at a time and not for representing acid-base paths. A new representation, obtained after a principal components transformation is presented. It is shown that the representation is characteristic for the laboratory instrument used. Its most attractive feature is that it is distortionless with respect to the three-dimensional configuration.

Energy-filtering transmission electron microscopy as a tool for structural and compositional analysis of isolated ferritin particles.

Structural and compositional analysis of isolated horse-spleen ferritin particles was performed by energy filtering transmission electron microscopy (EFTEM). Ferritin particles were collected in ultrathin (2 nm thick) chromium films and analyzed without any additional stain by electron energy-loss spectroscopy (EELS) for iron and carbon and by electron-spectroscopic imaging (ESI) for carbon. The ultrastructure of the proteinaceous shell of the ferritin particle, as obtained by the carbon net-intensity electron spectroscopical and carbon concentration-distribution images, was qualitatively compared to the structure as acquired by a negative-staining procedure. Quantitative analysis of the number of carbon atoms in the ferritin-shell proteins was carried out through an ESI-acquisition protocol and processing procedure with calibrated attenuation filters in the optical path to the TV camera. This procedure included images acquired with calibrated attenuation filters for the compensation of shading and the non-linear performance of the TV camera used in the analytical part of the procedure. A new ¿ESI-Spectra¿ program is proposed that allows element-related spectra to be generated at any place and with any frame size in a contrast-sensitive or other type of image present on the computer monitor screen.