Biomedical subjects
H L Kundel
Publications and source records attributed to H L Kundel.
Sodium MRI with coated magnetite: measurement of extravascular lung water in rats.
This study was done to see if signal intensity in sodium images of edematous rat lungs made after iv administration of a negative intravascular contrast agent could serve as a measure of the edema fluid present. First, a method to produce a stable condition of hydrostatic pulmonary edema was developed and verified by CT. Second, dose-response curves for coated magnetite preparations were constructed by giving edematous rats varied doses of these preparations and measuring signal intensity changes of various organs by sodium MRI in a 31-cm-bore 1.9-T magnet. Third, rats were given varied levels of pulmonary edema followed by a constant dose of coated magnetite to eliminate the plasma sodium signal. Finally, coated magnetite particles of two sizes were administered to rats, and the differences in effects on signal from various organs were measured. Signal intensity of the lungs after magnetite correlated (r = 0.86) with extravascular lung water measured gravimetrically, suggesting that sodium MRI may be useful for measuring pulmonary edema fluid. Smaller particles appear to remain in the blood longer than larger particles.
Sodium nuclear magnetic resonance imaging of neuroblastoma in the nude mouse.
The average concentration of sodium is known to be elevated in some tumors relative to normal tissues, and necrosis is suspected of being a possible cause. We have performed in vivo sodium-23 magnetic resonance imaging (MRI) of IMR-5 neuroblastoma in the athymic nude mouse on a 1.9-Tesla, small-bore animal imaging system. We compared the sodium images with histologic analysis for necrosis and with proton images, chemical measurements of water and blood content, and sodium and potassium concentrations. We found that the sodium concentrations determined by MRI were proportional to the fraction of the tumor tissue that was necrotic. Correlation coefficients varied from 0.65 to 0.78, depending upon how the data were selected. With further refinement it is possible that the sodium concentration measurements determined noninvasively by MRI may have applications as part of clinical diagnosis and staging of soft tissue tumors.
Searching for lung nodules. The guidance of visual scanning.
Four subjects searched a chest image for lung nodules using an eye position-dependent display that presented the image of a nodule selectively to either the central or peripheral visual field, while preserving the appearance of the chest. The time required to scan the image and fixate the nodule was shortest for nodules that were both reported and accessible to the peripheral vision. A stepwise concentric reduction in the size of the peripheral field that could access the nodules only affected search performance when the field was less than 5 degrees. (A chest image subtends about 25 degrees.) These data support the hypothesis that the optimal scanning strategy for lung nodules consists of spacing fixation clusters 5 degrees apart, and that peripheral vision only acts as an adjunct in guiding the gaze to inconspicuous nodules.
Computer applications and digital imaging.
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The effect of verification on the assessment of imaging techniques 1983.
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Variability of myocardial signal on magnetic resonance images.
The diagnosis of myocardial disease by magnetic resonance (MR) imaging depends on accurate measurement of myocardial signal intensity. The authors performed 15 experiments in four rabbits at 1.9 T with spin-echo MR imaging to study the variability of myocardial signal intensity throughout the cardiac cycle and to measure myocardial T2 values. Variability in signal from the myocardium throughout the cardiac cycle was observed in all experiments. During systole, a significant increase in myocardial signal was noted, when data acquisition was performed with electrocardiogram (ECG)-gating and controlled ventilation (P = .02). An inverse relationship between myocardial signal and phase noise was found, indicating the motion-related nature of the variation of myocardial signal. A similar inverse relationship was observed in images obtained from a normal human volunteer. Ex vivo myocardial T2 values of rabbit myocardial tissue were significantly higher than the in vivo values (P = .003), reflecting residual motion despite cardiac gating and controlled ventilation.
Visual cues in the interpretation of medical images.
The use of the computer in imaging has provided great versatility for the display of medical image information. In order to be useful in a medical sense, the display must be perceptually acceptable to the human observer, who must be able to extract the relevant diagnostic information from the image. Diagnostic information is defined by the imaging task, and the concept of task-dependent image quality is, therefore, very important. Visualization and estimation tasks may require different visual cues for their performance. Visualization tasks require strong boundary cues, whereas intensity estimation tasks require texture cues. Both tasks can be aided by appropriate image displays. Color can be helpful in estimation tasks, and three-dimensional display can aid visualization tasks. No matter what the task or the image, as long as an observer is needed to read out the information, performance is the final arbiter of the goodness of the image.
The digital imaging workstation.
Picture archiving and communication systems (PACS) are expected to convert film-based radiology into a computer-based digital environment, with associated cost savings and improved physician communication. The digital workstation will be used by physicians to display these "soft-copy" images; however, difficult technical challenges must be met for the workstation to compete successfully with the familiar viewbox. Issues relating to image perception and the impact on physicians' practice must be carefully considered. The spatial and contrast resolutions required vary according to imaging modality, type of procedure, and class of user. Rule-based software allows simple physician interaction and speeds image display. A consensus appears to be emerging concerning the requirements for the PACS workstation. Standards such as the American College of Radiology/National Electrical Manufacturers' Association Digital Imaging and Communication Standard are facilitating commercial applications. Yet much careful study is needed before PACS workstations will be fully integrated into radiology departments.
Images, image quality and observer performance: new horizons in radiology lecture.
Technical and diagnostic image quality are distinguished and the limitations of three methods currently used for assessing diagnostic image quality are discussed. They are evaluations based on individual clinical experience, measurement of diagnostic performance, and physical measurements made on images or imaging systems. Finally, a psychophysical approach to image quality evaluation is presented and its potential value discussed.
Psychophysical studies of detection errors in chest radiology.
In 62 of 124 cases analyzed, there occurred a failure to detect a pulmonary nodule which was retrospectively noted only after detection at a subsequent examination. The characteristics of the lesions and their surrounds were measured, and a computer analysis used, to identify that combination of parameters (the conspicuity, K) which was best capable of separating the group into populations of missed and detected lesions.
Lesion conspicuity, structured noise, and film reader error.
The concept of conspicuity is introduced in an attempt to objectively quantitate radiographic observational error. Defined as a ratio between lesion contrast and surround complexity, the measure correlates well with the probability of detecting faint nodular lesions in chest radiographs. The concept helps in understanding why abnormalities are missed by radiologists. It is also used to explain why image-processing techniques advocated in the past did not yield improvements in diagnostic accuracy and to outline directions for the future. Preliminary results are presented which show that photographic subtraction can increase the conspicuity of simulated early lung lesions and improve their detection.
Peripheral vision, structured noise and film reader error.
The ability of film readers to detect a nodular target abnormality with the peripheral vision was studied using a gray structureless background, chest radiographs with a bilateral pneumothorax and chest radiographs with pulmonary vasculature. Peripheral detection of the nodular abnormality was profoundly decreased by the presence of the normal structures even though the nodule properties such as size and contrast were not different and, in the case of the pneumothorax, the nodules did not overlap normal structures. Structured noise is an important and often neglected variable in studies of visual search, film reader error and image processing in radiology.
Interpreting chest radiographs without visual search.
Ten radiologists were shown a series of 10 normal and 10 abnormal chest films under two viewing conditions: a 0.2-second flash and unlimited viewing time. The results were compared in terms of verbal content, diagnostic accuracy, and level of confidence. The overall accuracy was surprisingly high (70% true positives) considering that no search was possible. Performance improved as expected with free search (97% true positives). These data support the hypothesis that visual search begins with a global response that establishes content, detects gross deviations from normal, and organizes subsequent foveal checking fixations to conduct a detailed examination of ambiguities. The total search strategy then consists of an ordered sequence of interspersed global and checking fixations.
Clinical experience with PACS at the University of Pennsylvania.
A Picture Archiving and Communication System (PACS) was installed in the Medical Intensive Care Unit of the Hospital of the University of Pennsylvania. For one year, 8 week periods of FILM ONLY usage were alternated with 8 week periods of PACS OR FILM usage. The time interval between obtaining portable chest images and taking image dependent actions decreased when the PACS was used, however, about 40% of the action decisions were made without a radiologist's consultation. Only 5% of action decisions were made without consultation during the FILM ONLY periods. A new clinical study for measuring diagnostic accuracy and efficiency as well as communication patterns is described.
The influence of film density on the radiologic detection of lung lesions.
Experiments were conducted on a series of chest radiographs to evaluate the effects of mean film density on reader performance. It was found that the false negative is not measurably affected, in agreement with earlier published data. It was also found, however, that the false positive rate increases with increasing film density. The causes and implications of these results are discussed.
Visual scanning, pattern recognition and decision-making in pulmonary nodule detection.
Eye movements were recorded while four subjects searched a set of 60 films, 24 normal and 36 abnormal for pulmonary nodules. Error rates, scanning patterns and the dwell time of fixation clusters on normal and nodule-containing areas of the film were studied. Using the assumption that prolonged dwell time indicates intensive processing of visual data, a model was developed for nodule detection that includes four steps: orientation, scanning, pattern recognition and decision-making. False-negative errors were divided into three classes: scanning errors, recognition errors and decision-making errors. Of 20 false-negative errors, 30% were considered scanning, 25% recognition and 45% decision-making.
Contrast gradient and the detection of lung nodules.
The effects of edge gradient and blur on the detection pulmonary nodules were studied, using a test series of 175 artificial nodules on 30 chest films. The nodules were of homogeneous texture, about 1 cm in diameter and had a mean contrast of .12. Six observers viewed the film set, scoring both location and confidence. The sensitivity or the probability of a true-positive response was linearly related to the blur and a modified ROC analysis resulted in a family of ROC curves with the index of detectability monotonically decreasing with increased blur.