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Biomedical subjects

D Gur

Publications and source records attributed to D Gur.

At least 19 recordsLinked to original sources
PubMed1992

Comparison of three different techniques for dual-energy subtraction imaging in digital radiography: a signal-to-noise analysis.

Dual-energy subtraction imaging techniques allow the tissue and bone structures in the patient to be visualized and studied in two separate images, thus removing the obscurity associated with overlapping of the two structures. In addition, they allow the subtraction image signals to be used for quantifying the tissue and bone thicknesses. Thus, capability for dual-energy subtraction imaging is often incorporated with new digital radiography systems. There are three different approaches to dual-energy image subtraction imaging techniques. Among them, the dual-kilovolt (peak) [kV(p)] and sandwich detector techniques have been two widely used approaches. A third approach is the single-kV(p) dual-filter technique, which allows some flexible control of the spectra while avoiding the technical complexity of kV(p) value switching in slit-scan imaging. In this report, the noise properties associated with these three techniques are studied and compared by computing the noise variances in the subtraction image signals as a function of the kV(p) values and filter thicknesses. It was found that the dual-kVp technique results in the least noisy subtraction images, whereas the dual-filter technique results in slightly less noisy subtraction images than the sandwich detector technique. Following optimization of the kV(p) value and filter thicknesses, the dual-filter and sandwich detector techniques result in a noise level of approximately three and four times higher than that resulted from the dual-kV(p) technique, respectively.

Algorithms↗
PubMed1992

Dynamic heterogeneity of cerebral hypoperfusion after prolonged cardiac arrest in dogs measured by the stable xenon/CT technique: a preliminary study.

After prolonged cardiac arrest and reperfusion, global cerebral blood flow (gCBF) is decreased to about 50% normal for many hours. Measurement of gCBF does not reveal regional variation of flow or permit testing of hypotheses involving multifocal no-flow or low-flow areas. We employed the noninvasive stable Xenon-enhanced Computerized Tomography (Xe/CT) local CBF (LCBF) method for use in dogs before and after ventricular fibrillation (VF) cardiac arrest of 10 min. This was followed by external cardiopulmonary resuscitation (CPR) and control of cardiovascular pulmonary variables to 7 h postarrest. In a sham (no arrest) experiment, the three CT levels studied showed normal regional heterogeneity of LCBF values, all between 10 and 75 ml/100 cm3 per min for white matter and 20 and 130 ml/100 cm3 per min for gray matter. In four preliminary CPR experiments, the expected global hyperemia at 15 min after arrest, was followed by hypoperfusion with gCBF reduced to about 50% control and increased heterogeneity of LCBF. Trickle flow areas (LCBF less than 10 ml/100 cm3 per min) not present prearrest, were interspersed among regions of low, normal, or even high flow. Regions of 125-500 mm3 with trickle flow or higher flows, in different areas at different times, involving deep and superficial structures migrated and persisted to 6 h, with gCBF remaining low. These preliminary results suggest: no initial no-reflow foci (less than 10 ml/100 cm3 per min) larger than 125 mm3 persisting through the initial global hyperemic phase; delayed multifocal hypoperfusion more severe than suggested by gCBF measurements; and trickle flow areas caused by dynamic factors.

Animals↗
PubMed1992

Survey of the prevalence of beta-lactamases amongst 1000 gram-negative bacilli isolated consecutively at the Royal London Hospital.

beta-Lactamase expression was examined in 1000 consecutive Gram-negative bacilli isolated from urine, wound swab, sputum or blood specimens received at the Microbiology Laboratory of the Royal London Hospital. This survey, performed between January and April, 1991, followed a similar study undertaken in early 1982. The distribution of species was similar in the two surveys, except that the proportion of Pseudomonas aeruginosa isolates had increased from 11% in 1982 to 17.5% in the present study. This increase was balanced by a decreased proportion of enterobacteria. Amongst plasmid-mediated beta-lactamases, TEM-1 (especially), TEM-2, SHV-1 and OXA types continued to predominate in enterobacteria. Their frequency in Escherichia coli was unchanged (46% in 1991 compared with 43% in 1982), but had increased from 5 to 22% amongst Proteus mirabilis isolates. An apparent decrease in their frequency amongst Enterobacter cloacae isolates, from 48% in 1982 to 17% in 1991, probably reflected changes to strain prevalence rather than enzyme prevalence. Plasmid type beta-lactamases were present in fewer than 2% of P. aeruginosa isolates in both surveys. In the present study, chromosomal beta-lactamase derepression (constitutive hyperproduction) was detected in 10/76 isolates of E. cloacae, Enterobacter aerogenes, Citrobacter freundii, Serratia spp. and Morganella morganii, and in 2/170 P. aeruginosa isolates. These proportions were increased, compared with those seen the 1982 survey, though the significance was borderline (P approximately 0.05; chi 2 test). Extended-spectrum plasmid mediated beta-lactamases, unknown in 1982, were found in 11/70 Klebsiellae pneumoniae isolates in the present study. Ten of these organisms, representing at least five distinct strains, produced TEM-10 enzyme, encoded by a plasmid of c. 90 kb; the remaining organism had an unidentified SHV-derived enzyme.

Anti-Bacterial Agents↗
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↗
PubMed1992

Clinicians' access to diagnostic imaging information at an academic center: perceived impact on patient management.

We studied the efficiency with which clinicians were able to obtain the results of radiologic studies during visits to the radiology department in an effort to determine how often delays occurred and, if so, how they were perceived to have influenced patient care. We monitored 322 physician's visits to four locations within the radiology department in search of imaging information or consultative services. The average duration of these visits was 6.2 min (range, 38 sec-55 min). Two hundred forty-three visits (75%) were completed successfully, and 10 additional visits were for consultation purposes only. In 43% of the 69 unsuccessful visits, physicians indicated that lack of access to imaging information would definitely (38%) or possibly (6%) result in delays in diagnosis and/or therapy. In 17% of the unsuccessful visits, physicians indicated that the inability to access imaging information would definitely (13%) or possibly (4%) extend the patient's length of stay in the hospital. Our study suggests that better access to imaging information may prevent delays in patient management decisions, thereby substantially reducing costs and potentially improving patient care.

Hospitals, University↗
PubMed1991

Primary CT diagnosis of abdominal masses in a PACS environment.

Whether the display medium--film versus cathode ray tube (CRT)--affects observer performance during interpretation of computed tomographic (CT) images is an important research issue in these times of implementation and growth of picture archiving and communications systems in radiology. The authors performed a multiobserver receiver operating characteristic (ROC) study to determine the performance of radiologists who read abdominal CT studies displayed on film, as well as on a high-resolution workstation (video monitor) that made use of three different display modes. A total of 166 examinations were evaluated by eight radiologists, who recorded their ordinal confidence ratings of the demonstration of presence or absence of abdominal masses. ROC analysis showed small differences in the confidence ratings assigned by individual readers for the detection and interpretation tasks. Results for the group as a whole showed no significant reduction or improvement in observer performance when ratings for any one of the workstation display modes were analyzed. The results of this study demonstrate that current CRT display technology is adequate for enabling the primary detection of abdominal masses with CT examinations.

Abdominal Neoplasms↗
PubMed1990

Autoregulation remains intact during stable xenon inhalation in the baboon.

To test the possible effect of 32% end-tidal Xe concentration upon autoregulation, 5 baboons, Papio anubis/cynocephalus, were anesthetized/paralyzed with propranolol 0.02, diazepam 0.1, morphine sulfate 0.1, and pancuronium 0.2 (mg/(h.kg)). The animals were subjected to a servocontrolled blood infusion-withdrawal program to control central aortic blood pressure (CAP). PaCO2 was held to 30 to 35 torr, with individual variation less than 3 torr by control of ventilation and by including CO2 in the Xe/O2 mixture. Three to six CBF measurements were made in each subject over the above range. In four animals the CAP was varied between 18 and 150 torr, with corresponding CBF measurements. The CAP range was extended to 196 torr in the 5th animal by IV administration of phenylephrine. Significant lowering of global blood flow did not occur above 40 torr mean CAP. While regulated flow persists to about 150 torr at the high end, there is a breakaway between 150 and 190 torr where flow increased 90%. A 4th order polynomial fit of the data has the characteristic appearance of the familiar autoregulation curve. We conclude that autoregulation is preserved even in the presence of FIXe of 32% in the breathing mixture.

Animals↗
PubMed1990

Effect of two rating formats in multi-disease ROC study of chest images.

ROC methodology has been expanded in recent years to include multi-disease experiments. To accommodate these changes, different rating formats, general or disease specific, can be used. No experimental data are available concerning the possible effects of the rating format on the results of these studies. We performed a multi-observer, multi-disease study in which 196 chest images were rated using a format where each disease was evaluated individually and one in which the cases were evaluated without scoring a specific disease. The results indicate that for our data set, the overall assessment of accuracy was not significantly affected by the study format used. Thus, in spite of the difficulties in selecting appropriate controls and the necessity of reassessing sample size considerations, the disease-specific format appears to produce an assessment of accuracy equivalent to that produced by the general format. This equivalence permits the use of the disease-specific approach since it more closely simulates the readers' true environment and is more appropriate for comparing imaging systems that may have a relative accuracy that is disease specific.

Diagnosis, Differential↗
PubMed1990

Effect of observer instruction on ROC study of chest images.

Receiver-operating characteristic (ROC) analysis has been used in many medical imaging applications during the past decade. In order to ensure that reader-confidence ratings are analyzable (well distributed to meet convergence requirements of curve-fitting algorithms) and meaningful (limit extrapolation of the data), many investigators train readers specifically for this purpose. No experimental data are available concerning the possible effects of such training on the results of ROC studies. We performed a multi-observer, multi-disease study in which 300 chest images were rated by four radiologists before and after they were trained to provide well-distributed confidence ratings. The results indicate that for our data set, reader and disease-specific accuracy was not significantly affected by the training process for interstitial disease and pneumothoraces. However, the accuracy of two readers was significantly affected for the detection of nodules (P less than 0.05), and the overall accuracy of one reader was significantly affected for the classification of normal versus abnormal images (P less than 0.01). Thus, in spite of the difficulties associated with the performance of ROC studies in a free-reading environment, one should carefully consider the possible effects of any intervention on the results prior to conducting ROC studies.

Humans↗
PubMed1990

Practical issues of experimental ROC analysis. Selection of controls.

Receiver operating characteristics (ROC) analysis has been used in many medical imaging applications during the past decade. With the recent expansion of the ROC methodology to multi-disease studies, several reports have begun to address both the theoretical and experimental design issues associated with such studies. While the appropriate selection, classification, and verification of actually positive cases is carefully addressed in the literature, similar considerations are rarely given to the selection of actually negative controls for these studies. In this paper, theoretical considerations and experimental data are provided to demonstrate the significance of this very issue.

Case-Control Studies↗
PubMed1990

Nonparametric estimation of degenerate ROC data sets used for comparison of imaging systems.

Maximum likelihood estimation, assuming a binormal model, has been used extensively to estimate the area under receiver operating characteristic (ROC) curves and thus provide an index of diagnostic accuracy for the comparison of two imaging systems. However, in some instances, a degenerate data set results in a fitted ROC curve of inappropriate shape. In those instances, a nonparametric Wilcoxon statistic may be used to compare the areas under two ROC curves. Simulation of this approach indicates that the procedure has relatively high statistical power and its use in specific degenerate data sets shows its applications potential.

Data Interpretation, Statistical↗
PubMed1990

The effect of image processing on chest radiograph interpretations in a PACS environment.

The question of whether image processing affects a radiologist's diagnostic performance is becoming more important as the digital modalities proliferate. In the multi-observer study reported, the performance of radiologists who interpret a series of posteroanterior digitized chest images displayed on a high-resolution workstation, with and without a set of image processing options, is determined. These include brightness, contrast, reverse look-up tables (black-bone), and two edge enhancement options. Three hundred images were evaluated twice (once in each mode) by each of seven board-certified radiologists, who recorded their confidence ratings for the presence or absence of one or more of the following abnormalities: interstitial disease, nodule, and pneumothorax. The original, unprocessed digital image was available for reference for those sessions in which the processing options were available. With the exception of one reader, receiver operating characteristic (ROC) analysis showed no statistically significant difference between the two modes (with and without processing) for the detection of any of the different abnormalities by individual readers. Likewise, the group as a whole showed no significant difference (P less than .05) for detection of any of the three abnormalities between the two reading modes.

Hospital Information Systems↗
PubMed1990

High-resolution digital imaging with storage phosphors.

This article describes the current status and potential applications of high-resolution storage phosphor for imaging of the chest. Digital imaging that uses storage phosphor technology is easily adaptable to existing x-ray--generating equipment and can also be used with mobile equipment. The wide latitude of the storage phosphor technique permits satisfactory imaging in situations in which exposure factors cannot be accurately estimated or easily controlled. Early experience with an experimental Kodak high-resolution (4K x 4K) storage phosphor system suggests that standard and portal chest images of excellent quality can be obtained. Many issues must be resolved, however, before digital radiology with a storage phosphor can be advocated as being preferable to conventional film-screen systems. These issues, which include display modalities (film or television monitor), resolution requirements, and the effects of image processing, can only be resolved by further large-scale accuracy studies. The change to a digital imaging system will involve major expenditures for equipment and computers. Cost will be related largely to the level of spatial resolution required for primary radiographic diagnosis.

Humans↗
PubMed1990

Receiver operating characteristic analysis of chest image interpretation with conventional, laser-printed, and high-resolution workstation images.

The differences among radiologists in interpreting conventional and digitized images obtained with different radiologic procedures is an important research issue in these times of implementation and growth of the digital modalities. The authors performed a multiobserver study to determine the performance of radiologists reading posteroanterior conventional radiographs, digitized radiographs laser printed onto film, and images displayed on a high-resolution workstation (video monitor). A total of 300 images were evaluated by seven radiologists who recorded their ordinal confidence rating of the presence or absence of one or more of the following abnormalities: interstitial disease, nodule, and pneumothorax. Receiver operating characteristic analysis showed statistically significant differences for the detection of different abnormalities by individual readers. The group as a whole showed a significant reduction in observer performance for the detection of interstitial disease and pneumothorax when the laser-printed radiographs or the workstation was used rather than conventional radiographs.

Computer Systems↗
PubMed1990

Verification of electron beam therapy with storage phosphor images: precision of field placement.

Portal verification images were generated from the photon contamination in electron beams produced by a linear accelerator during treatment of patients receiving high-energy electron radiation therapy (8-14 MeV). An experimental storage phosphor system was used to record the images and display them on laser-printed film. Images were obtained from four or more treatment fractions from 21 cases of head and neck cancer. Precision in field placement was estimated by determining the position of a selected anatomic landmark relative to the center of the field for each series of images. The average standard deviation in the field-position measurements was 3.8 mm. Several procedural problems were also detected and corrected after review of the verification images. The results indicate that the emphasis placed on monitoring and control of field-positioning error in high-energy electron treatments should be similar to the emphasis placed on this aspect of error in photon treatment.

Electrons↗
PubMed1990

Xenon-enhanced computed tomography compared with [14C]iodoantipyrine for normal and low cerebral blood flow states in baboons.

The correlation between the acute, invasive diffusible [14C]iodoantipyrine technique for cerebral blood flow and the noninvasive xenon-enhanced computed tomographic method has been assessed by simultaneous measurements in the baboon. Blood flows in small tissue volumes (about 0.125 cm3) were directly compared in normal and low flow states. These studies demonstrate a statistically significant association between the two methods (p less than 0.001). Similar correlations were obtained by both the Kendall (tau) and the Spearman (r) methods (r = 0.67 to 0.92, n greater than or equal to 19 for each study). The problems and limitations of such correlations are discussed.

Animals↗
PubMed1990

Does knowledge of the clinical history affect the accuracy of chest radiograph interpretation?

To examine the effect that a concise, objective, and potentially computer-extractable history would have on diagnostic accuracy in the interpretation of chest radiographs, we designed and tested a computerized patient-history form that could be integrated realistically into the clinical environment. We performed a series of studies in which 247 posteroanterior normal (79) and abnormal (168) chest radiographs were interpreted by four board-certified radiologists, both with and without accompanying clinical histories. The radiologists recorded their confidence rating of the presence or absence of one or more of the following abnormalities: interstitial disease, nodule, and pneumothorax. Analysis of receiver operating characteristics showed that, with the exception of interpretation of one abnormality by one radiologist, there were no statistically significant differences (p less than .05) between cases interpreted with and without the history form for any of the radiologists. The results of our study suggest that knowledge of clinical history does not affect the accuracy of chest radiograph interpretations for the detection of interstitial disease, nodules, and pneumothoraces. These results may not be applicable to other clinical situations.

Humans↗