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Biomedical subjects

C E Metz

Publications and source records attributed to C E Metz.

17 recordsLinked to original sources
PubMed1992

The use of continuous and discrete confidence judgments in receiver operating characteristic studies of diagnostic imaging techniques.

Virtually all receiver operating characteristic (ROC) studies of medical imaging methods have involved data collected on a discrete confidence-rating scale, though in principle ROC studies can be conducted with either discrete or continuous scales. Continuous scales provide potential advantages in medical applications of ROC analysis, but the possible dependence of ROC results on the kind of scale used in an observer-performance experiment has not been investigated empirically. The authors conducted a multi-observer ROC study in which radiologists read abdominal computed tomography (CT) examination results displayed on a workstation with a high-resolution video monitor. Ninety-five examinations were evaluated by five radiologists who reported their confidence concerning the presence of abdominal masses on a conventional five-category discrete scale and, in a separate reading session, on a continuous subjective-probability scale. ROC analysis showed no statistically significant difference between the detection accuracies (Az) achieved with the two scales by any reader. Accuracies averaged over all readers were identical with the two scales. The results of this study suggest that discrete or continuous scales often can be used interchangeably in image-evaluation studies. However, the authors recommend continuous scales for routine use in radiologic ROC studies because of their potential advantages in some situations.

Confidence Intervals↗
PubMed1978

Basic principles of ROC analysis.

The limitations of diagnostic "accuracy" as a measure of decision performance require introduction of the concepts of the "sensitivity" and "specificity" of a diagnostic test. These measures and the related indices, "true positive fraction" and "false positive fraction," are more meaningful than "accuracy," yet do not provide a unique description of diagnostic performance because they depend on the arbitrary selection of a decision threshold. The receiver operating characteristic (ROC) curve is shown to be a simple yet complete empirical description of this decision threshold effect, indicating all possible combinations of the relative frequencies of the various kinds of correct and incorrect decisions. Practical experimental techniques for measuring ROC curves are described, and the issues of case selection and curve-fitting are discussed briefly. Possible generalizations of conventional ROC analysis to account for decision performance in complex diagnostic tasks are indicated. ROC analysis is shown to be related in a direct and natural way to cost/benefit analysis of diagnostic decision making. The concepts of "average diagnostic cost" and "average net benefit" are developed and used to identify the optimal compromise among various kinds of diagnostic error. Finally, the way in which ROC analysis can be employed to optimize diagnostic strategies is suggested.

Cost-Benefit Analysis↗
PubMed1978

A comparison of optimum detector spatial resolution in nuclear imaging based on statistical theory and on observer performance.

An expression for the expected image of a spherical tumour in a uniform background was derived in terms of background thickness and concentration of radioactivity, the tumour size, depth and uptake ratio, the gamma-ray energy and the detector response function. Three models of human observer performance for tumour detection were developed from different signal-to-noise ratio measures based on the statistical theory of detection. The optimum detector spatial resolution predicted by each model was then compared to that obtained from an observer performance study in which the subjects viewed computer-simulated scintigrams. The predictions from two of these models seem to be consistent with the results of the observer performance study. Model II involves a comparison of the counts integrated over the tumour region with the counts integrated over a background region of the same area. Model III compares the count density estimates of signal-plus-background and background obtained from application of non-uniform weighting functions to the image data.

Gamma Rays↗
PubMed1977

Determination of X-ray spectra incident on and transmitted through breast tissue.

X-ray spectra incident on and transmitted through breast tissue were measured using a fresh whole excised breast. These spectra and corresponding radiographs show that hardening of the beam from a molybdenum-anoda x-ray tube by a 0.5-mm AI filter instead of the conventional 0.03-mm Mo filter allows shorter exposure times and reduces patient exposure. Acceptable image contrast is preserved in mammography of thick or dense breasts.

Female↗
PubMed1977

Image quality in mammography.

Image quality in mammography is affected by the shape, size, and x-ray absorption properties of the anatomic part or lesion to be radiographed in addition to x-ray beam quality, geometric unsharpness, and the resolution, characteristic curve, and noise properties of the recording system. The authors review x-ray energy spectra, modulation transfer functions. Wiener spectra, characteristic and gradient curves, and radiographs of a breast phantom and a resected breast specimen containing microcalcifications; these factors, and the complex relationship between them, affect image quality and patient radiation exposure. Evaluation of the best system or technique for obtaining a breast image is discussed in terms of the compromise between diagnostic certainty and cost or risk.

Breast Neoplasms↗
PubMed1977

Screen/film system speed: its dependence on x-ray energy.

Dependence of the speed of various screen/film systems on x-ray energy was studied using the nearly monoenergetic x rays emitted by a filtered fluorescent source. The results show that response depends on screen phosphor composition and thickness. Barium and rare earth screens having K absorption energies lower than that of calcium tungstate are relatively more sensitive to x rays in the 40-70-keV region.

Technology, Radiologic↗
PubMed1976

The effect of x-ray spectra from molybdenum and tungsten target tubes on image quality in mammography.

The measured x-ray spectra from a molybdenum anode Senographe mammography unit and a tungsten anode unit were used to calculate the x-ray energy spectra transmitted through various thicknesses of fat and water (breast-equivalent materials). The dependence of subject contrast and patient exposure on (a) x-ray spectra, (b) attenuation properties of two breast-equivalent materials, and (c) thickness of breast-equivalent material was predicted. Radiographs of resected breast tissue confirmed these predictions and demonstrated the general relative effects of x-ray beam quality on image contrast in mammography.

Adipose Tissue↗
PubMed1976

Observer performance in detecting multiple radiographic signals. Prediction and analysis using a generalized ROC approach.

The theories of decision processes and signal detection provide a framework for evaluation of observer performance. Some radiological procedures involve a search for multiple similar lesions, e.g., plain radiographic examinations for gallstones or pneumoconiosis. Presuming knowledge of the conventional ROC curve for detection of a single radiographic signal, a model is presented which is used to predict observer performance in an experiment requiring detection of more than one such signal. An experiment tests the validity of this model for detecting radiographically the presence of zero, one, or two low-contrast, 2-mm diameter, Lucite beads. Results confirm the validity of the model and suggest that observer performance in relatively complex detection tasks can be predicted from simpler experiments.

Decision Making↗
PubMed1975

A mathematical model for the determination of cardiac regurgitant and ejection fractions from radioisotope angiocardiograms.

A mathematical model taking into account the pulsatile pumping action of the heart has been developed which describes, in terms of a set of four recursive equations, the activity in the atrium and in the ventricle of the left or right heart at successive end-systoles and end-diastoles after bolus injection. The resulting closed form solutions permit calculations of chamber forward ejection fractions and valvular regurgitant fractions from computerized radioisotope angiocardiogram data. The method has been applied to a series of over thirty clinical studies with encouraging results.

Angiocardiography↗
PubMed1975

Visual detection and localization of radiographic images.

In conventional receiver-operating-characteristic (ROC) curve analysis of visual detection performance, the observer is credited with a true-positive response if a visual signal is present somewhere in a radiograph called "positive" by the observer; however, the measured true-positive rate can be different for a given false-positive rate if the observer is required to identify the correct location of the visual signal in order to receive credit for a true-positive response. The authors describe and have confirmed experimentally a model which can be used to predict observer performance in an experiment requiring both detection and localization on the basis of the conventional ROC curve determined in a detection experiment. Implications for the use of signal detection theory in the assessment of radiographic image quality are discussed.

Humans↗
PubMedDate not supplied

A simple source of fluorescent x rays for the study of radiographic imaging systems.

The properties of a simple source of fluorescent x rays were investigated with regard to its suitability for the study of radiographic imaging systems. The source, consisting of a diagnostic x-ray tube, fluorescent targets, and filters, was found to yield highly monoenergetic x-ray fluxes with intensity sufficient to allow the speed of medium- and high-speed screen-film systems to be studied as a function of x-ray energy.

Spectrometry, X-Ray Emission↗
PubMedDate not supplied

Linearizing mechanisms in conventional tomographic imaging.

Implicit in the concept of conventional tomography and in any attempt to characterize the tomographic process by a modulation transfer function is the assumption that the tomographic process is linear. A Fourier decomposition approach and an analysis of nonlinear contributions to the integrated tomographic image intensity are used in this paper to establish the validity of this assumption and to determine the mechanisms by which the tomographic process is effectively linearized.

Energy Transfer↗
PubMedDate not supplied

Gains in accuracy from replicated readings of diagnostic images: prediction and assessment in terms of ROC analysis.

From the perspective of signal detection theory, human variation in image reading degrades diagnostic accuracy by broadening the statistical distributions of perceived evidence upon which decisions were based. A new multivariate "random-effects" model formulates the total variation in a diagnostic decision variable as a sum of three uncorrelated components that represent differences among cases, readers, and repeated readings by a given reader. This model provides a basis for quantitative predictions concerning the amount by which diagnostic accuracy, as specified by ROC analysis, can be enhanced by the replication of image readings. Although these predictions apply exactly only to the hypothetical situation in which normally distributed decision variables from equivalent readers are averaged, computer-simulation studies and an analysis of mammographic image-reading data from five radiologists show that similar gains in accuracy can be achieved by averaging discrete confidence ratings.

Decision Support Techniques↗