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PubMed1984

The control of chiasma distribution.

The question of recombination control has been the subject of intensive investigation over many years. This paper is restricted to an evaluation of the information obtainable from cytological studies of chiasmata, since other approaches are well represented in other papers in this volume. The advantages and disadvantages of chiasmata as means of studying recombination are discussed. Cytological observations reveal many constraints on the distribution of chiasmata, which are interpreted as outward expressions of controls operating at different levels, namely between cells, between bivalents and within bivalents. Detailed descriptions of these constraints are presented as a preliminary to discussing models and mechanisms of control. They include, at the between-bivalent level, over-dispersal of chiasma number per bivalent and the formation of an obligatory minimum of one chiasma per bivalent; and at the within-bivalent level, chiasma localization and chiasma interference. The genetical basis of these constraints is emphasized and evidence presented which suggests that chiasma distribution at different levels is subject to both separate and coordinate genetical controls. These observations lead to the consideration and evaluation of general stochastic models of chiasma control based on the modification of site probabilities for chiasma formation. While these models are a useful approach to thinking about the control of recombination, they do not give a fully satisfactory explanation of all aspects of chiasma control. Finally, specific mechanisms for chiasma distribution control are considered. In a few exceptional species, localized pairing and synaptonemal complexes lead to localized chiasma formation; details of two such cases are presented. In the majority of species, pairing is not localized or restricted and in these species the control of chiasma distribution is more conjectural. Arguments are presented which suggest that even in these cases of full pairing, the pattern of pairing initiation and progression and perhaps the timing of these events could be important factors controlling the distribution of chiasmata.

Animals↗
PubMed1980

Behavioral effects of microwaves.

Microwaves can produce sensations of warmth and sound in humans. In other species, they also can serve as cues, they may be avoided, and they can disrupt ongoing behavior. These actions appear to be due to heat produced by energy absorption. The rate of absorption depends on the microwave parameters and the electrical and geometric properties of the subject. We, therefore, cannot predict the human response to microwaves based on data from other animals without appropriate scaling considerations. At low levels of exposure, microwaves can produce changes in behavior without large, or even measureable, changes in body temperature. Thermoregulatory behavior may respond to those low levels of heat, and thereby affect other behavior occurring concurrently. There are no data that demonstrate that behavioral effects of microwaves depend on any mechanism other than reactions to heat. Our interpretation of whether a reported behavioral effect indicates that microwaves may be hazardous depends on our having a complete description of the experiment and on our criteria of behavioral toxicity.

Absorption↗
PubMed1994

Instrumentation in neonatal research: commonly used statistics.

Nurse researchers share one common characteristic: They all use statistical tests to provide the answers they are seeking. For others to correctly interpret research, it is important to understand what choices of tests are available and why a test was used. As nursing becomes more sophisticated in the research arena, the ability to read, interpret, and critique reported research findings becomes an important component of professional practice. This month's column contains a description of commonly used statistical tests. Researchers are often interested in differences between groups and relationships between variables. Examples of these two types of research are provided to illustrate use of the various tests. One common part of statistical tests examining differences between groups is the number of degrees of freedom. Degrees of freedom are usually defined as the number of observations (number of subjects or categories) minus the number of limitations placed on those observations. Examples of this concept are provided throughout the pertinent tests.

Humans↗
PubMedDate not supplied

[Interobserver variation of the Global Assessment Scale. Study of 59 patients at admission to a general adult psychiatric unit].

UNLABELLED: In France, an analysis of the evaluation of psychiatric activity was done by a work group representing thirteen hospitals spread over the entire country. The group just recently published their final report in the form of an experimentation protocol for the description of psychiatric activity. The proposed methodology leads to some modifications of the existing data collection based on individual patient information sheets "fiche par patient", more particularly concerning new items such as the Global Assessment Scale (GAS or Axis V of DSM III-R): our first impression was that this new type of evaluation seemed to us somewhat subjective. We therefore decided to analyze the reliability of the score established by psychiatrists not familiar with its use. In the beginning the GAS score was evaluated in clinical cases (patients seen at their admission by two or three psychiatrists and scored afterwards independently), then in theoretical cases (34 cases types taken from the Health-Sickness Rating Scale of Luborsky) with the objective to improve the consensus between clinicians. RESULTS: The clinical case studies made in an adult psychiatry pavilion permitted evaluating 59 patients at admission, of which 25 by three judges and respectively 40, 28 and 41 by pairs. The global accuracy of the score obtained with the clinical cases seems satisfactory for a discipline such as psychiatry (Kappa of Cohen's coefficient = 0.51, p < 0.001 for 25 patients by three judges--Kappa = 0.45, p < 0.001 for the 109 pairs of evaluations). The more detailed study of the classes obtained a satisfactory consensus for the scores below 40 and above 60 (K = 0.46 to 0.59) but not entirely satisfactory for the scores in the mid range of the scale between 40 and 60 (K = 0.22 to 0.29) which represents 39% of the patients in the study; this is improved by grouping into larger classes this part of the scale and it is therefore advisable to use it that way. For the 34 theoretical cases taken from the Luborsky HSRS evaluated independently by three judges the results obtained are clearly not as good (global Kappa = 0.29, p < 0.01). That is perhaps due to the fact that these "case types" don't use the descriptive patient models generally used in France. Keeping in mind that the mid range of the scale should be interpreted prudently, the GAS scale can nevertheless be credited with a certain global objectivity in the case of neutral study. Would it be the same if the GAS study could influence the allocation of resources? Taking into account all the clinical practices in mental health, the question of how all the data of this type evaluation could be recorded and updated should also examined.

Adult↗
PubMedDate not supplied

How to design an effective research study.

The previous paper in this series (March 13) examined three methodological issues: sample selection, treatment and/or intervention and observation and measurement. Here, aspects of research design and procedures will be considered. Research design is important in helping to ensure that the results can be correctly interpreted and that observed changes can be attributed to the planned intervention rather than to other intervening factors. The description of the procedure explains how the selected methods were combined and describes the practical details of how the study was carried out.

Confounding Factors, Epidemiologic↗
PubMed1996

An interactive decision support system for breast fine needle aspiration cytology.

OBJECTIVE: To develop a computerized system to assist in the diagnosis of malignancy in breast fine needle aspiration cytology. STUDY DESIGN: A Bayesian belief network was designed to control uncertainty and allow a diagnostic decision to be reached based on the sequential collection of cytologic information. Ten cytologic features were defined as clues that contribute to the diagnostic discrimination of benign and malignant aspirates. The impact of each feature on the diagnostic decision was quantified by a conditional probability matrix. RESULTS: For the assessment of a new case, the computer guides the user through the diagnosis, prompting him or her for information on each of the diagnostic features in turn. For each feature, the user is presented with a series of digitally stored color microscopic images that have been selected to represent good examples of the different feature grades-e.g., pleomorphism: none, mild, moderate and severe. Each image is mapped to an overlapping curve, and by positioning a line on the spectrum where the user feels the case lies, a membership function vector is calculated and entered as evidence into the network. This results in an update in the belief in the diagnostic alternatives. After all the clues have been assessed, a final diagnostic probability is reported. In addition, a cumulative belief curve can be drawn that maps the change in the diagnostic probabilities after each piece of evidence has been submitted, providing unique insight into the diagnostic process. CONCLUSION: Systems like this represent an important step forward in the use of descriptive classifiers. They impose consistency in terminology, improve reproducibility in the grading of cellular abnormalities and remove subjectivity in interpreting the significance of pvisual clues to diagnosis. As such, they represent a necessary tool in pathologic decision making.

Biopsy, Needle↗
PubMed2002

A minimum description length approach to statistical shape modeling.

We describe a method for automatically building statistical shape models from a training set of example boundaries/surfaces. These models show considerable promise as a basis for segmenting and interpreting images. One of the drawbacks of the approach is, however, the need to establish a set of dense correspondences between all members of a set of training shapes. Often this is achieved by locating a set of "landmarks" manually on each training image, which is time consuming and subjective in two dimensions and almost impossible in three dimensions. We describe how shape models can be built automatically by posing the correspondence problem as one of finding the parameterization for each shape in the training set. We select the set of parameterizations that build the "best" model. We define "best" as that which minimizes the description length of the training set, arguing that this leads to models with good compactness, specificity and generalization ability. We show how a set of shape parameterizations can be represented and manipulated in order to build a minimum description length model. Results are given for several different training sets of two-dimensional boundaries, showing that the proposed method constructs better models than other approaches including manual landmarking-the current gold standard. We also show that the method can be extended straightforwardly to three dimensions.

Algorithms↗
PubMed2003

Correlations between small aperture skin suction parameters: statistical analysis and mechanical model.

BACKGROUND/AIMS: Skin suction experiments are widely used in order to evaluate the effects of skin treatments, both for cosmetic and for dermatological purposes. Classically, the elevation of the skin is measured at different discrete time instances after the pressure has been changed. Relations between the classical parameters - Uv, Ur, Ue and Uf - have been investigated and used in order to develop a new model for interpreting the mechanical properties of the skin. METHODS: Within a group of 68 female subjects - aged between 37 and 68 - a Cutometer has been used in order to determine classical skin suction parameters on the female facial skin. Each skin suction measurement consists of three consecutive underpressure cycles. Within the resulting parameter set, a statistical analysis has been performed to investigate interparameter relations. RESULTS: Strong interparameter correlations have been found within a set of 12 classical skin suction parameters. The set contains three independent groups of interrelated parameters. Based on this observation, a one-dimensional mechanical model - consisting of springs and dampers - is constructed. When two extra independent parameters are included in the model, the elevation versus time curves as recorded during three consecutive underpressure cycles can be fully described. The model reveals that typical skin suction data can be described in terms of a quick and a slow deformation process. The two characteristic time scales are 0.1 and 7 s approximately. The 0.1 s-value matches the response time of the device used. In reality, the quick deformation process in the skin may have a shorter time scale. CONCLUSIONS: In skin suction data, each underpressure cycle is usually characterized by four classical parameters - Uv, Ur, Ue and Uf. Within the 12 parameters of a three-cycle measurement, three independent groups of interrelated parameters have been found. These groups can be represented by the parameters Uv1, Ur1 and Uf1 of the first underpressure cycle. A model that is based on these three independent groups and two other independent parameters is proposed. The model provides an accurate description of the skin deformation as recorded during a measurement involving three underpressure cycles. The model is an improvement over classical interpretations of skin suction data where interrelated parameters are used. Moreover, the five-parameter model accounts for well-known mechanical characteristics of the skin such as preconditioning and visco-elastic behavior.

Adaptation, Physiological↗
PubMed2006

Positive interpretation training: effects of mental imagery versus verbal training on positive mood.

Therapists often assume a special association between mental imagery and emotion, though empirical evidence has been lacking. Using an interpretation training paradigm, we previously found that imagery had a greater impact on anxiety than did verbal processing of the same material (Holmes & Mathews, 2005). Although the finding of a differential impact of imagery versus verbal processing of negative material was replicated, findings did not extend to benign material. Results therefore left open the question of whether there may be a special association between imagery and positive emotion. The current experiment examined positive interpretation training. Numerous scenarios were presented with initial ambiguity as to positive outcome or not, with final information then yielding consistently positive resolutions. Participants were asked to either imagine these positive events or to listen to the same descriptions while thinking about their verbal meaning. Those participants in the imagery condition reported greater increases in positive affect and rated new descriptions as being more positive than did those in the verbal condition. Results suggest that positive training can be enhanced through imagery as opposed to verbal processing. This study also provides the first test of a standardized intervention using an "interpretive bias training" paradigm to improve positive mood.

Adult↗
PubMed2003

Pieter Pauw's tumor oculorum: reappraisal of the presumed first description of retinoblastoma in 1597.

Cancer in a young child is unusual and has always aroused curiosity. Proptosis and an enormous, rapidly growing unilateral tumor in a 3-year-old boy prompted Pieter Pauw (1564-1617), a 16th-century anatomist, to perform an autopsy. His published notes from the autopsy were rediscovered in the 19th century, first by the German ophthalmologist and historian Julius Hirschberg and then by Edwin B. Dunphy, from Boston, Mass, who suggested that the child suffered from retinoblastoma, an interpretation that has held sway. Critical translation of the original Latin text suggests that an orbital tumor, such as embryonal rhabdomyosarcoma, would equally well explain Pauw's observations. His description also gives insight into the concept of a mole as a congenital as well as an intrauterine tumor in Renaissance medicine.

History, 16th Century↗
PubMed2005

Nonrigid shape correspondence using landmark sliding, insertion and deletion.

The growing usage of statistical shape analysis in medical imaging calls for effective methods for highly accurate shape correspondence. This paper presents a novel landmark-based method to correspond a set of 2D shape instances in a nonrigid fashion. Different from prior methods, the proposed method combines three important factors in measuring the shape-correspondence error: landmark-correspondence error, shape-representation error, and shape-representation compactness. In this method, these three important factors are explicitly handled by the landmark sliding, insertion, and deletion operations, respectively. The proposed method is tested on several sets of structural shape instances extracted from medical images. We also conduct an empirical study to compare the developed method to the popular Minimum Description Length method.

Algorithms↗
PubMed2003

Potential for improving description of bovine udder health status by combined analysis of milk parameters.

The objective of this study was to assess the potential of a stepwise multivariate procedure to quantify cow-level udder health based on eight milk parameters: milk yield, protein percentage, fat percentage, lactose percentage, citrate percentage, somatic cell count (SCC), and two electrical conductivity parameters. The data were collected in one research herd and included 821 cow-level observations. In addition to milk parameters, disease recordings and bacteriology on quarter milk samples every eighth week throughout lactation were included. A multivariate mixed model was applied to the milk parameters in a healthy subset to adjust for the following systematic factors: total mixed ration (TMR) energy density, breed-line combination, parity, stage of lactation, and season. The proportion of variance accounted for by the mixed model ranged from 0.14 to 0.82 depending on milk parameter. The adjustments estimated in the healthy subset were applied to the whole dataset, including observations pertaining to nonhealthy cows. Combined description of the adjusted variation in the milk parameters was performed with a principal component analysis. The first principal component (Prin1) described 30% of the adjusted variation and was interpreted as being the main consequences of mastitis. Finally, cluster analysis based on Prin1 separated the observations into nine clusters, which were strongly associated with udder health in terms of increasing clinical and subclinical mastitis with increasing level of Prin1. It was concluded that a multivariate approach to assess udder health from milk parameters has the potential to substantially improve description of udder health.

Analysis of Variance↗
PubMed2006

Can a checklist reduce SOS errors in chest radiography?

RATIONALE AND OBJECTIVES: A previous study demonstrated unexpected protection from satisfaction of search (SOS) effects when observers verbalized the focus of their attention during visual search and interpretation of chest radiographs. We suggested that protection from SOS might have occurred if each observer developed an informal checklist to help generate the verbal descriptions. The objective of this study is to determine whether a formal checklist reduces SOS effects in chest radiology. MATERIALS AND METHODS: Fifty-seven chest radiographs, half of which demonstrated diverse, native abnormalities were read twice by 20 observers, once with and once without the addition of a simulated pulmonary nodule. Area under the receiver operating characteristic (ROC) curve for detecting the native abnormalities was estimated for each observer in each treatment condition using the contaminated binormal ROC model. Radiologists in the current experiment used a checklist during the interpretation, rather than describing their visual search. Results were compared with those of the verbalization study, which used the same set of radiographs. RESULTS: Although no SOS effect was found when the checklist was used, ROC performance was, on average, much poorer with the checklist than when ongoing search was reported verbally (0.68 versus 0.75, F(1, 37) = 17.26, P < .001). CONCLUSIONS: Our results indicate that the recommendation to use a self-prompting checklist to counteract SOS is not warranted. The relative superiority of verbalizing search over using an imposed checklist may be based on the consistency of each of these interventions with the observer's internal strategy for searching radiographs.

Humans↗
PubMed2005

Computed tomography to visualize and quantify the plantar aponeurosis and flexor hallucis longus tendon in the diabetic foot.

BACKGROUND: The purposes of this report were to describe a three-dimensional computed tomography based method to visualize and quantify the thickness of the plantar aponeurosis and flexor hallucis longus tendon and determine the reliability of thickness measures. Given reliable measures, a secondary purpose was to compare plantar aponeurosis and flexor hallucis longus thickness in subjects with diabetes mellitus and peripheral neuropathy to an age and weight matched group without diabetes. METHODS: CT data from 16 people with diabetes mellitus and peripheral neuropathy (mean age 55.2 (SD 10.5), 4 female, 12 male, body mass index 31.7 (SD 7.6)) and 10 people without diabetes mellitus (mean age 53.8 (SD 9.1), 2 female, 8 male, body mass index 37.0 (SD 8.6)) were analyzed. Length and thickness of the plantar aponeurosis and flexor hallucis longus tendon were measured twice for five subjects from each group in a blinded single observer reliability study. FINDINGS: The average mean difference of the linear measurements was 0.12 mm (average SD=1.00 mm). Significant differences for measures of plantar aponeurosis thickness (p=0.044) were found between diabetic, 4.2 mm (SD 0.9), and control groups, 3.6 mm (SD 0.8), and approached significance for tendon thickness measured at the midfoot (diabetic group 4.8 mm (SD 0.8), control group 4.3 mm (SD 0.8), p=0.051). INTERPRETATION: CT was shown to be a reliable imaging technique for visualizing and quantifying soft tissue structures in diabetic feet. The methods and the quantitative description of the plantar aponeurosis and tendon thickness reported in this paper may be useful to those developing three-dimensional computational models of the foot.

Diabetic Foot↗
PubMedDate not supplied

Gout arthropathy: description of an atypical case.

The authors describe a case of gout localized in the knee, the clinical and radiographic signs of which may lead to numerous diagnostic interpretations. Other affections with which differential diagnosis is difficult are reported, and principal diagnostic tests are described.

Adult↗
PubMed1998

[Anatomic MRI study of commissural agenesis and dysplasia of the Telencephalon (Agenesis of the corpus callosum and related anomalies). Clinical correlations and morphogenetic interpretation].

A series of 78 patients presenting with agenesis of the cerebral commissures and properly investigated with MR imaging, was reviewed and analyzed morphologically. Results were compared with descriptive data from the literature, and with the developmental models proposed. From this, a model of a-commissural brain is described: the lamina terminalis would be homologous to a telencephalic anterior medullary velum of which the commissure would be the anterior commissure, and the lamina of white matter described as the Probst's and the fornical bundles, would be homologous to a posterior medullary velum having become a medial medullary velum due to the division of the prosecephalon into two cerebral hemispheres, and of which the commissure would be the (posterior) calloso-hippocampal commissure. Also, the comparison with the model establishes that in the actual malformations, defects of the cingulum and of at least some of the intralobaroccipital association bundles are observed beside the commissural defect. Such a model would reclassify these disorders, distinguishing the "simple" commissural defects, complete or segmental, global or dissociated, without or with a ventricular expansion, from more complex forms with multicystic defects, adding major dysplastic lesions of the dura mater, leptomeninges and parenchyma, to the commissural defects. Paradoxically, the latter group seems to be clinically less severe than the "simple agenesis" group, of which prognosis (including the neurologic and intellectual disorders as well as the associated pathologies) is generally very poor; this should be seriously considered since the antenatal diagnosis of these malformations is made routinely with ultrasonography and MRI.

Agenesis of Corpus Callosum↗