The identification of bias in studies of the diagnostic performance of imaging modalities

The demand for evidence-based healthcare is increasing nationally and internationally and it is equally necessary in both diagnostic and therapeutic practice. Evidence may be collected and combined by means of a systematic literature review of published and unpublished data on a well-defined topic. The output of such reviews is then available to guide health policy, influence good practice or direct research. Published guidelines are available on the performance of systematic reviews, especially those of randomized controlled trials. Although there is an extensive literature base of research data in diagnostic imaging there are few such trials, but it is still possible to perform systematic reviews. With the alternative study designs encountered it is important to be aware of the main threats to study validity. In this paper the biases likely to be encountered in studies of diagnostic performance are reviewed, with particular reference to diagnostic imaging tests. The biases are sub-divided into three categories. The first category is patient selection and covers the validity of generalizing results beyond the study population. The other two, concerning study design and execution and the interpretation of results, affect the likely validity of the results of a study. An understanding of these factors is an essential prerequisite for those undertaking or using a systematic literature review in the field of diagnostic imaging. The definitions form the foundations of a defensible review protocol.     

Correction of partial volume effects in myocardial SPECT

BACKGROUND: Marked partial volume effects occur in myocardial single photon emission computed tomographic (SPECT) studies because of limited resolution in imaging the myocardial wall and contractile motion of the heart. Little work has been undertaken to develop correction techniques for SPECT except for efforts to improve the reconstructed resolution. Our purpose was to examine the extent of the problem and propose a correction method. METHODS AND RESULTS: A potential correction method, developed initially for positron emission tomography, involved estimation of extravascular density by means of subtracting vascular density derived in a blood pool study from total density derived from a transmission study. Provided partial volume errors are the same for transmission and emission data, activity per gram of extravascular tissue can be obtained by means of dividing the perfusion regional data by extravascular density for the same region. Simulations were designed to assess the importance of partial volume errors and the use of extravascular density to correct the errors. Recovery coefficients for the myocardium were estimated by means of simulation of the beating heart on the basis of published values for ventricular dimensions. Resolution for transmission with a scanning line source system was compared with emission resolution. The effect of spillover on measured partial volume losses was assessed, and a method for matching spillover for emission and extravascular density was demonstrated. Correction for partial volume effects was demonstrated for a phantom with variable wall thickness. Significant variation in recovery coefficient was demonstrated between posterior and septal walls for individual patients independent of heart size. Filtering was necessary to account for the difference in transmission resolution measured in the axial direction. Spillover effects had a significant influence on the measured recovery for small objects; however, for a specific reconstruction algorithm and defined region size, correction was implemented to match the spillover effects for emission and extravascular density. Use of extravascular density for correction of partial volume loss, for ordered subsets expectation maximization reconstruction with compensation for resolution, was demonstrated to be accurate to within 10%. CONCLUSIONS: The feasibility of correcting partial volume effects with extravascular density was demonstrated. Correction is effective provided care is taken to match both resolution and spillover for emission and extravascular density.     

International programs utilizing soy foods: The world food program

The World Food Program was set up 10 years ago by the United Nations and Food and Agriculture Organization as a multilateral agency to provide food aid where needed. Soy products in the form of corn-soy milk and wheat-soy blend are playing increasing roles in this program described in this paper.     

The pathophysiology of tension pneumothorax in ventilated swine

Patients with possible acute renal obstruction often undergo numerous types of radiological examinations. Renal Doppler ultrasound is a quick and noninvasive way to assess for physiological and hemodynamic changes that accompany acute obstruction. The renal Doppler study may provide unique data not available from conventional sonography. Most, but not all, clinical and laboratory studies regarding Doppler of acute renal obstruction have reported encouraging results. As limitations to the Doppler examination in this clinical setting are delineated, a proper role for renal Doppler will continue to emerge.     

Asymmetry of the lateral (sylvian) fissures in man

We compared the courses of right and left lateral (sylvian) fissures by superimposing left lateral and reversed right lateral photographic slide projections and tracing the sulci and fissures of each hemisphere in different colors. A characteristic pattern of divergence of posterior regions of the lateral fissures was noted in 25 of 36 adult brains. After pursuing similar courses, the right lateral fissure angulates sharply upward into the inferior parietal area while the left one continues posteriorly. As a consequence, on the right, there is a smaller parietal operculum, a shorter planum temporale, a higher sylvian point, and compensatory expansion of the inferior parietal region posterior to the lateral fissure.     

The late stage of serpiginous (geographic) choroiditis

Questionnaires rating twins' physical similarity and similarity of dress were obtained from the parents of 121 identical and 70 same-sex fraternal twin pairs. Within-pair difference scores on several behavioral measures (two intelligence tests, two perceptual tests, one reading test, one test of speech articulation, and one personality inventory) were correlated with the twins' scores for physical similarity and similarity of dress. The correlations revealed no systematic relation between the similarity of appearance and the similarity of behaviors for either the identical twin pairs or the same-sex fraternal twin pairs. The assumption that twins' behaviors are more alike because they are more similar in appearance does not seem warranted.     

Influence of client socioeconomic status on selected behaviors, attitudes, and decisions of counselors.

Seven male and 9 female graduate students in counseling psychology were asked to interview an actor and an actress whom they believed to be real clients. To half of the counselors, the players posed as well-to-do individuals, and to half they posed as working class individuals. They briefly mentioned their socioeconomic status at the beginning of the interview and then told the counselor about some of the problems they were experiencing. When the clients were presented as having lower status, a significant correlation coefficient existed between (a) the counselor's self-reported degree of personality similarity to the client and the counselor's self-reported liking for the client, and (b) the counselor's self-reported liking for the client and the counselor's estimate that the client would benefit from long-term counseling. No significant correlation coefficient existed for data collected during high-status interviews. These results suggest that counselors may unconsciously employ a different decision-making process for high- and low-status clients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ethics of medical research in developing countries: the role of international codes of conduct

Many statisticians work with informal codes of ethics, and are probably unaware of the existence or content of rules which have been drawn up to govern statistical practice. Medical statisticians will be aware of codes of conduct for medical research, and most codes of professional ethics have some dependence on evidence. Statisticians, therefore, have a valuable contribution to make to debates on ethics which concern scientific soundness, data and perceptions of risk. A lively debate on the revision of the widely respected Declaration of Helsinki, to reflect issues arising from research in developing countries, particularly HIV research, centres on questions of study design, data analysis and assessment of risk. Collectively owned multiprofessional work requires each of the various professions to take responsibility for the conduct of the research, and the impact that it might have. Statisticians share important responsibilities in maintaining ethical medical research in all countries.     

Optimized EPI for fMRI studies of the orbitofrontal cortex: compensation of susceptibility-induced gradients in the readout direction

Object Most functional magnetic resonance imaging (fMRI) studies record the blood oxygen leveldependent (BOLD) signal using gradient-echo echo-planar imaging (GE EPI). EPI can suffer from substantial BOLD sensitivity loss caused by magnetic field inhomogeneities. Here, BOLD sensitivity losses due to susceptibility- induced gradients in the readout (RO) direction are characterized and a compensation approach is developed. Materials and Methods Based on a theory describing the dropout mechanism, an EPI sequence was optimized for maximal BOLD sensitivity in the orbitofrontal cortex (OFC) using a specific combination of an increased spatial resolution in the RO direction and a reduced echo time. Using measured BOLD sensitivity maps and a breath hold experiment, the model and compensation approach were tested. Results Using typical fMRI EPI parameters, susceptibility-induced gradients in the RO direction caused dropouts in the OFC and the inferior temporal lobe. Optimizing the echo time and spatial resolution effectively reduced the dropout as predicted by the theory. Conclusion The model-based compensation approach effectively reduces BOLD sensitivity losses due to susceptibility-induced gradients in the RO direction. It retains the high temporal resolution of single-shot EPI and can be readily combined with methods for the compensation of susceptibility-induced field gradients in the phase-encoding and through-plane direction.     

亨尼斯多夫市政厅，亨尼斯多夫，德国

这个市政厅起到了连接的作用。它将历史上线性城市边缘的一个小公园和铁路另一边已经发展形成的新城市中心连接起来。这栋新建筑的高度，介于沿主路的农舍和其附近的5层居住建筑之间。柔和的几何形体和首层视觉的渗透性，使它很轻易就融入到新公园的流动空间当中。