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Biomedical subjects

C E Metz

Publications and source records attributed to C E Metz.

At least 73 records · Page 4Linked to original sources
PubMed1984

A comparison of physical image quality indices and observer performance in the radiographic detection of nylon beads.

Although various models have been proposed in an attempt to predict the usefulness of a radiographic image in terms of its physical characteristics, no previous work has shown whether a single physical image quality index, such as a signal-to-noise ratio, can reliably predict the performance of a human observer over a broad range of image characteristics. We studied the relationship between physical and visual image quality for the task of detecting nylon beads in radiographs. Thirty-seven imaging cases with different combinations of physical image characteristics were considered; these included variations in object size and magnification, X-ray beam quality, screen-film system, screen-film contact, film density and illumination, and viewing distance. For each imaging case, visual image quality was quantified in terms of observer performance in a 2AFC visual detection experiment. Physical image quality indices were calculated according to eight different models of the detection process; these indices combined data regarding object size and attenuation, screen-film system MTF, film gradient, noise Wiener spectrum, and visual system response. The results of this work indicate that, for the conditions studied, human observer detection performance most closely resembles that of a sub-optimal statistical decision process.

Form Perception↗
PubMed1984

Digital image processing: effect on detectability of simulated low-contrast radiographic patterns.

Detection studies of simulated low-contrast radiographic patterns were performed with a high-quality digital image processing system. The original images, prepared with conventional screen-film systems, were processed digitally to enhance contrast by a "windowing" technique. The detectability of simulated patterns was quantified in terms of the results of observer performance experiments by using the multiple-alternative forced-choice method. The processed images demonstrated a significant increase in observer detection performance over that for the original images. These results are related to the displayed and perceived signal-to-noise ratios derived from signal detection theory. The improvement in detectability is ascribed to a reduction in the relative magnitude of the human observer's "internal" noise after image processing. The measured dependence of threshold signal contrast on object size and noise level is accounted for by a statistical decision theory model that includes internal noise.

Computers↗
PubMed1983

Wiener spectral effects of spatial correlation between the sites of characteristic x-ray emission and reabsorption in radiographic screen-film systems.

When characteristic x-rays are generated and reabsorbed in the phosphor of a radiographic screen-film system, the positions at which light is emitted from the initial and secondary interactions are correlated. A simple statistical model is developed to account for the effect of this correlation on the Wiener spectrum of quantum mottle. Unlike previous models, which ignore spatial correlation, the new model predicts that not only noise magnitude but also noise texture is changed as the incident x-ray energy exceeds the phosphor K-edge.

Mathematics↗
PubMed1983

Optimum detector spatial resolution for discriminating between tumour uptake distributions in scintigraphy.

The optimum detector spatial resolution has been determined for a scintigraphic decision task in which the observer must discriminate between two different distributions of radioactivity in tumours. The two kinds of tumour used are: (i) a solid sphere of increased uptake relative to background, and (ii) a thin spherical shell with high uptake in the shell and no radioactivity within the shell. Both tumours are embedded at the same depth within a cylinder of tissue-equivalent material containing a uniform distribution of radioactivity. On the basis of statistical decision theory, the optimum detector spatial resolution for discriminating between the two tumour activity distributions is predicted. The result of an observer performance experiment substantially agreed with the theoretical prediction, though some discrepancy was found, apparently due to a decrease in observer efficiency at poorer spatial resolution. The experimental result suggests that the optimum FWHM of detector spatial response for the discrimination task considered is about 65% of the tumour radius.

Decision Theory↗
PubMed1982

Maximum likelihood estimation of dose-response parameters for therapeutic operating characteristic (TOC) analysis of carcinoma of the nasopharynx.

A Therapeutic Operating Characteristic (TOC) curve for radiation therapy plots, for all possible treatment doses, the probability of tumor ablation as a function of the probability of radiation-induced complication. Application of this analysis to actual therapeutic situations requires that dose-response curves for ablation and for complication be estimated from clinical data. We describe an approach in which "maximum likelihood estimates" of these dose-response curves are made, and we apply this approach to data collected on responses to radiotherapy for carcinoma of the nasopharynx. TOC curves constructed from the estimated dose-response curves are subject to moderately large uncertainties because of the limitations of available data. These TOC curves suggest, however, that treatment doses greater than 1800 ret may substantially increase the probability of tumor ablation with little increase in the risk of radiation-induced cervical myelopathy, especially for T1 and T2 tumors.

Dose-Response Relationship, Radiation↗
PubMed1982

The effect of a thigh tourniquet on the incidence of deep venous thrombosis after operations on the fore part of the foot.

We performed a prospective randomized clinical study to determine whether use of a thigh tourniquet influences the incidence of deep venous thrombosis. The lower limbs of patients who were scheduled for elective surgery on the fore part of the foot were randomized and assigned to one of three treatment categories: Group I, no tourniquet; Group II, exsanguination by an Esmarch bandage before tourniquet application; and Group III, exsanguination by elevation of the extremity prior to application of a tourniquet. The 117 limbs of seventy-one patients included in this study were evaluated preoperatively and twenty-four and seventy-two hours postoperatively with 125I-labeled fibrinogen, and preoperatively and seventy-two hours postoperatively with Doppler ultrasound studies and phleborheography. The findings in all of the Doppler ultrasound studies and all of the phleborheograms were normal. Two of the 125I-fibrinogen studies were positive, but subsequent contrast venography revealed that these were false-positive findings. We therefore concluded that the use of a thigh tourniquet does not increase the risk of deep venous thrombosis in patients who have had an operation on the fore part of the foot.

Adult↗
PubMed1982

Critical evaluation of stress testing in the diagnosis of peripheral vascular disease.

We studied 218 patients (372 limbs) and 25 normal subjects (50 limbs) with resting ankle index (RAI), treadmill exercise (TE), and postocclusive reactive hyperemia (PORH) to determine whether diagnostic accuracy is improved through the use of stress testing. In addition, we studied 10 patients with stable claudication (20 limbs) to determine the reproducibility of the three measures. RAI was the most reproducible measure, with the smallest variance between testing days (P less than 0.001). RAI differentiated between arteriographically diseased and normal limbs with a sensitivity of 97% and a specificity of 100%, whereas the corresponding values for TE were 97% and 96% and for PORH 89% and 96%. Recovery to baseline index was prolonged in the diseased group compared with normal (p less than 0.001 for both TE and PORH), but this was of limited discriminative value. Receiver-operating characteristic curve analysis documented that RAI was as diagnostically useful as TE and that both were more valuable than PORH (P less than 0.02). However, the routine addition of stress testing increased diagnostic yield by only 1.6% and cost $1100 for each limb correctly diagnosed through the addition of stress testing. RAI is a simple, accurate, and reproducible test. Routine stress testing is not cost effective, adding little diagnostic information to RAI, and it should be reserved for the small subset of symptomatic patients with normal RAI.

Adult↗
PubMed1981

Analysis of recorded image noise in nuclear medicine.

The concepts of autocovariance function and Wiener spectrum have been applied to describe the recorded image noise in nuclear medicine. They were derived as functions of the expected detected count density and the detector and exposure point spread functions. It was shown that the detector system affects only the noise magnitude, whereas the recorder system affects both noise magnitude and texture. In experimental studies, the autocovariance function and Wiener spectrum of recorded image noise were measured by one-dimensional time-series analysis. Due to the non-linearity of the recording film, the best agreement between the theoretical predictions and the experimental results is found when the detected count density is sufficiently high and the size of the exposure spot is sufficiently large for the density fluctuations in the recorded noise image to be relatively low.

Models, Theoretical↗
PubMed1981

Operability of nuclear instruments for medical use in developing countries. A decision-analytic approach.

Nuclear technology in diagnostic medicine has become a world-wide phenomenon. One of the problems encountered in implementing this technology in developing countries is predicting the operability of nuclear instruments under local conditions of maintenance and use. Our approach to this problem employs an analytic method often applied in medical decision making, and which can be incorporated into schemes for evaluating the total diagnostic process which utilizes nuclear technology. A recent survey of nine types of nuclear instruments in medical use in eight countries in Southeast Asia provided comprehensive information on the application and maintenance of these instruments, as well as a detailed record of actual operability and use of these instruments over a six-month period. A multivariate statistical analysis for predicting the operability of these instruments was carried out with some of the survey data. Responses to a set of 14 potentially important attributes of instrument use and maintenance obtained from the survey data were used to estimate the posterior probabilities of an instrument being inoperable for more than a given total number of hours in the six-month period during which operability was required. The posterior probabilities were determined by means of both Bayesian and discriminant analysis and summarized in the form of receiver operating characteristic (ROC) curves. Among a number of possible interpretations of the results, the analysis suggests that attributes generally involving installation, documentation, environment, and personnel training appear to be particularly important in predicting the operability of the instruments surveyed.

Decision Making↗
PubMed1980

The geometric transfer function component for scintillation camera collimators with straight parallel holes.

A theoretical approach has been developed that allows the geometric transfer function component for conventional scintillation camera collimators to be predicted in closed form. If transfer function analysis is to be useful in describing imaging system performance, the image of a point source must not depend on source position in a plane parallel to the detection plane. This shift invariance can be achieved by analysis of system response in terms of an effective point spread function, defined as the normalised image of a point source that would be obtained if the camera collimator were uniformly translated (but not rotated) during image formation. The geometric component of the corresponding effective transfer function is shown to be expressed simply by the absolute square of the two-dimensional Fourier transform of a collimator hole aperture, with the spatial frequency plane scaled by a factor which depends on collimator length, source-to-collimator distance, and collimator-to-detection plane distance. Closed form algebraic expressions of the geometric transfer function have been obtained for all four common hold shapes (circular, hexagonal, square and triangular). Monte Carlo simulations and experimental measurements have shown these theoretical expressions to be highly accurate.

Fourier Analysis↗
PubMed1980

Relative efficiencies of energy to photographic density conversions in typical screen-film systems.

This study compared the speeds of six typical screen-film systems and the energy absorbed by their screen pairs as a function of incident x-ray energy. Three of the screen-film systems studied had calcium fungstate phosphors, one contained barium strontium sulfate, and two were composed of a mixture of lanthanum oxysulfide with larger amounts of gadolinium oxysulfide. A source of monoenergetic radiation was used for measurement of the relationship between these two quantities as a function of keV. With certain exceptions, the speeds of screen-film systems act in a manner similar to that which would be predicted if only the energy absorption properties of their screens were considered.

Models, Theoretical↗
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↗