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Biomedical subjects

D Gur

Publications and source records attributed to D Gur.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1990

Stable xenon-enhanced CT measurement of cerebral blood flow in reversible focal ischemia in baboons.

When the lateral striate arteries of the baboon are temporarily occluded for either 20 or 60 minutes, a near-cessation of blood flow is followed by a dramatic, transient local increase in blood flow values. These findings are evident from serial xenon (Xe)-computerized tomography (CT) measurement of cerebral blood flow (CBF). In this study, 20 minutes of vessel occlusion resulted in brief (less than 1 hour) hyperemia, with no subsequent CT alteration and minimal random neuronal injury. Sixty minutes of occlusion resulted in a more prolonged hyperemia, a low-density area on CT images within 3 hours of reperfusion, and infarction of all cellular elements within the anterior lentiform nucleus. The Xe-CT method provides a sensitive, noninvasive technique for examining sequential alterations of CBF in small regions deep within the brain. This method of recording CBF also permits correlative studies of cerebral infarction, both clinically and experimentally, and allows reasonable inference about the probabilities of neuronal tissue damage with or without reperfusion.

Animals↗
PubMed1989

Verification of electron beam therapy with conventional and storage phosphor images: preliminary experience.

Portal verification images were generated by the photon contamination in electron beams produced by a linear accelerator during treatment of patients receiving high-energy electron radiation therapy. Both conventional and storage phosphor methods yielded projection radiographs in which anatomy of the irradiated and surrounding tissue was demonstrated. Exposed phantoms were used to confirm that the images represent a true projection of the radiation field. A preliminary series of 22 cases was evaluated by two radiotherapists and judged subjectively to be of clinical value. Geometric error, or more importantly, the lack thereof, during high-energy electron treatments was easily confirmed with this method. In three cases, the treatment protocol was corrected based on the images obtained. Because the readout process of storage phosphor images allows for gain adjustments and post-processing, the images obtained with this method were found to delineate anatomy in the treated and surrounding tissues somewhat more consistently than could conventional images.

Electrons↗
PubMed1989

Cerebral blood flow determination within the first 8 hours of cerebral infarction using stable xenon-enhanced computed tomography.

Cerebral blood flow mapping with stable xenon-enhanced computed tomography (Xe/CT) was performed in conjunction with conventional computed tomography (CT) within the first 8 hours after the onset of symptoms in seven patients with cerebral infarction. Six patients had hemispheric infarctions, and one had a progressive brainstem infarction. Three patients with very low (less than 10 ml/100 g/min) blood flow in an anatomic area appropriate for the neurologic deficit had no clinical improvement by the time of discharge from the hospital; follow-up CT scans of these three patients confirmed infarction in the area of very low blood flow. Three patients with moderate blood flow reductions (15-45 ml/100 g/min) in the appropriate anatomic area had significant clinical improvement from their initial deficits and had normal follow-up CT scans. One patient studied 8 hours after stroke had increased blood flow (hyperemia) in the appropriate anatomic area and made no clinical recovery.

Aged↗
PubMed1989

Determination of irreversible ischemia by xenon-enhanced computed tomographic monitoring of cerebral blood flow in patients with symptomatic vasospasm.

In patients with subarachnoid hemorrhage, delayed neurological deficits, often followed by infarction, are believed to result from ischemia caused by vasospasm. Cerebral blood flow (CBF) data have been useful in predicting the risk of vasospasm in these patients and in distinguishing those deficits caused by vasospasm. Although CBF thresholds for infarction have been established in animals, few clinical studies have correlated CBF values with neurological symptoms and infarction. To assess the sensitivity to ischemia provided by xenon-enhanced computed tomography (Xe/CT) of CBF and to define the clinical significance of specific values that it measures, we compared the clinical, CT, and Xe/CT findings on CBF in 51 patients with subarachnoid hemorrhage caused by ruptured aneurysms. Each patient had 1 to 6 Xe/CT studies. Fourteen patients had symptomatic vasospasm. In all 14, the first post deficit Xe/CT study found abruptly reduced CBF, either regionally or globally. In 9 of these 14 patients, flow values fell below 15 ml/100 g/min in 2 or more adjacent 2-cm cortical regions of interest, and in all 9, concurrent follow-up CT scans showed infarction in these regions. Eight of the 9 had paralysis and a severe sensory deficit. No patient whose CBF remained above 18 ml/100 g/min developed infarction. The blood flow studies caused neither significant complications nor neurological deterioration. The Xe/CT CBF method appears very sensitive to the early detection of symptomatic vasospasm. In most patients with subarachnoid hemorrhage, this noninvasive technique can replace angiography to delineate the location and severity of vasospasm, and may be useful in predicting the development of infarction.

Blood Flow Velocity↗
PubMed1989

Local cerebral blood flow by xenon-enhanced CT: current status, potential improvements, and future directions.

A noninvasive technique for measuring local cerebral blood flow (CBF) by xenon-enhanced x-ray transmission computed tomography (CT) was developed and reported on extensively in recent years. In this method, nonradioactive xenon gas in inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computed tomography. Time-dependent xenon concentration within various tissue segments in the brain is used to derive both the local partition coefficient (lambda) and CBF in each tissue volume (voxel) of the CT image. A comprehensive assessment of this method reveals that although it provides functional mapping of blood flow with excellent anatomic specificity and has several other significant advantages, there are distinct and important limitations. The assumptions underlying this methodology are examined and the advantages as well as the problems associated with applications of this technique are reviewed. Laboratory and clinical observations that have been made using this technique in recent years are summarized, and potential improvements as well as possible future directions are discussed.

Cerebrovascular Circulation↗
PubMed1988

Stable xenon enhanced computed tomography in the study of clinical and pathologic correlates of focal ischemia in baboons.

When the lateral striate arteries of baboons are occluded, an immediate cessation of blood flow followed by a transient, minimal restitution of flow occurs in that vascular distribution. These findings are evident from serial xenon/computed tomography cerebral blood flow imaging. In our study, infarction consistently accompanied arterial occlusion for 6 hours or more. The xenon/computed tomography method provides a sensitive, noninvasive technique for examining sequential alterations of cerebral blood flow in small regions deep within the brain. This methodology for recording cerebral blood flow permits correlative studies of cerebral infarction, clinically and experimentally, and allows reasonable inferences about the probabilities of neural tissue damage.

Animals↗
PubMed1988

Storage phosphor radiographs vs conventional films: interpreters' perceptions of diagnostic quality.

We compared storage phosphor images with high-quality conventional film-screen images by evaluating physicians' perceptions of image quality and their levels of confidence in making diagnostic interpretations. Eight physicians each examined 11 posteroanterior storage phosphor chest images (obtained with an experimental high-resolution storage phosphor system) side by side with conventional film images of the same patients. The storage phosphor images were obtained only minutes after the conventional radiographs were obtained. Storage phosphor images were digitally printed onto films in two different formats: a full-size (12 X 14 in. [30.5 X 35.6 cm]) and a half-size format of four computer-processed, minified images (6 X 7 in. [15.2 X 17.8 cm] each). Most of the responses rated the quality and resolution/sharpness of conventional images, as well as their ability to display the complete lung field, as either "excellent" or "good"; however, the storage phosphor images received significantly better ratings (p less than .05). Computer-processed minified versions of the storage phosphor images also received better ratings than did the conventional images. When the physicians were asked to rate their confidence level in making diagnoses with each of the two techniques, in 74 of 88 cases they indicated that their level of confidence would be at least as high when using the storage phosphor images as when using the conventional images.

Humans↗
PubMed1987

Xenon-enhanced computed tomography in brain death.

The absence of cerebral blood flow is a valuable adjunct confirming clinical criteria of brain death. However, current methods to confirm absent cerebral blood flow have problems that limit their clinical use. We reviewed cerebral blood flow data obtained with xenon-enhanced computed tomography in nine patients who were being evaluated for brain death. In eight patients who met clinical criteria for brain death, mean cerebral blood flow was 1.6 +/- 2.0 mL X 100 g X min. This value was within the range of error inherent in the method, and therefore represented absent flow. In a patient with persistent respiratory efforts, flow values compatible with absent flow were obtained in the supratentorial compartment, while mean flows as high as 24 mL X 100 g X min were measured in selected regions of interest in the infratentorial compartment, correlating with the clinical evidence of residual function of the brain stem. Xenon-enhanced computed tomography may be a useful test to confirm the absence of cerebral blood flow in patients being evaluated for brain death.

Adult↗