Computer screening of xeromammograms: a technique for defining suspicious areas of the breast.
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Breast Diseases↗
Biomedical subjects
J L Semmlow
Publications and source records attributed to J L Semmlow.
Accommodative and fusional components of fixation disparity.
Traditional measurements of fixation disparity, like other binocular measurements, confound influences from both blur-driven and disparity-driven components. Measuring fixation disparity with accommodation open-loop eliminates accommodative interactions, and results show fixation disparity is reduced to about half the value observed normally for high levels of forced vergence. Thus fixation disparity curves are shaped by both accommodative and fusional vergence processes.
Accommodation, Ocular↗
The role of accommodative convergence at the limits of fusional vergence.
Two possible explanations are presented for the mechanism which limits the maximum fusional vergence response. An experimental paradigm is developed to differentiate between these alternatives. Experimental results indicate that the blur generally associated with strong fusional effort is due to convergence accommodation "overdrive." Th important theoretical and clinical implications of this finding are presented.
Accommodation, Ocular↗
Accommodative convergence response to off-foveal retinal images.
A special stimulus device was designed and developed to present blur stimulation through off-foveal retinal images. An infrared reflecting eye movement monitor was used to measure the dynamic accommodative convergence response to both foveal and off-foveal blur stimulation. In most subjects studies a substantial off-foveal accommodative vergence response was found; however, this response diminished rapidly as image distance from the fovea increased. Considerable variation in the response was noted between subjects, and, to a lesser extent, in the same subject for left-versus-right off-foveal image positions.
Adaptation, Ocular↗
Utility of the injury severity score: a confirmation.
Independent results obtained from Illinois Trauma Registry data confirm an earlier finding of a fixed, monotonic relationship between expected mortality and the Injury Severity Score (ISS) value of injuries sustained in both vehicular and nonvehicular incidents. Further results show the ISS measure to be a good indicator of hospitalization demand from accident victims and suggest that this variable can be used to control for variations in injury severity in comparative evaluations of EMS systems.
Accidents, Traffic↗
Frequency characteristics of the saccadic eye movement.
Using a piecewise linear approach, individual saccadic eye movements have been Fourier decomposed in an attempt to determine the effect of saccadic amplitude on frequency characteristics. These characteristics were plotted in the traditional Bode plot form, showing gain and phase as a function of frequency for various eye movement amplitudes. Up to about one octave beyond the -3 db gain frequency, the limiting system dynamics represented by the saccadic trajectory of a given amplitude may be considered linear and second order. The -3 db gain frequency was used as a measure of bandwidth, and the -90 degrees phase crossover frequency was used as a measure of undamped natural frequency. These two quantities were used to calculate the damping factor. Both bandwidth and undamped natural frequency decrease with increasing saccadic eye movement amplitude. The damping factor shows no trend with amplitude and indicates approximate critical damping. When compared with the normal variation of characteristics for a given movement, the frequency characteristics of fixed-amplitude saccades showed no generalized trends with changes in direction or DC operating level of movement.
Analog-Digital Conversion↗
Noninvasive characterization of the sound pattern caused by coronary artery stenosis using FTF/FAEST zero tracking filters: normal/abnormal study.
In this article, a new approach has been proposed to investigate the extraction of useful information from diastolic heart sounds caused by partially occluded coronary arteries. This method, which estimates and tracks the zeros (poles) of the diastolic heart sounds directly, takes advantage of the FTF/FAEST (Fast Transversal Filters/Fast a Posteriori Error Sequential) technique which possesses the fast convergence property of the Recursive Least Square (RLS) method and the computational simplicity of the Least Mean Square (LMS) method. In previous studies, the main assumption was that the diastolic heart sounds were a stationary process. Since the production of the heart sounds were a stationary process. Since the production of the heart sounds is not a stationary process, a new approach that performs well not only for stationary but also for nonstationary processes can be required. This requirement can be satisfied by the adaptive FTF/FAEST zero tracking method which provides fast and stable convergence as well as computational efficiency since the adaptive FTF/FAEST zero tracking method is based on the exact minimization of least squares criteria and the filter weights of this method are optimal at each time instant. The zero trajectories of the diastolic heart sounds were used to diagnose patients as diseased or normal. Results showed that the normal and abnormal records were incorrectly distinguished in only 6 of 35 cases using a blind protocol where analysis was done without knowledge of the actual disease states of the patients. The most discriminant time region of the zero trajectories of the diastolic heart sounds associated with coronary artery disease was between 200 and 300 msec after the second heart sound during the diastolic period.
Coronary Disease↗
Dynamical analysis of diastolic heart sounds associated with coronary artery disease.
In a new approach to noninvasively diagnose coronary artery disease (CAD), auditory correlates attributed to blood flow turbulence have been associated with stenosed coronary arteries. These auditory components have been detected in diseased subjects by spectral estimation of diastolic heart sound recordings made on the surface of the chest. In this study, we investigated the dynamics of the process that produces these sounds in diseased subjects by applying the techniques of dimensional analysis. Our results indicate a difference in the "correlation dimension" between heart sounds of diseased and normal subjects. In particular, diseased subjects show a fractal dimension, implying the presence of a strange attractor and the possible existence of low-dimensional chaos in sounds associated with coronary artery disease.
Algorithms↗
Lawrence Stark, M.D., biomedical engineer.
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Biomedical Engineering↗
Comparison of ischemic and reperfusion injury in canine bowel viability assessment.
The purpose of these experiments was to evaluate two methods of bowel viability assessment in two distinct models of intestinal ischemia. Bowel viability was assessed in 32 dogs by means of three methods: (1) a probe that quantified the intestinal electromyographic (EMG) measurements in millivolts (mV), (2) Doppler ultrasonography, and (3) perfusion fluorometry, which quantified serosal blood flow in indexed dye fluorescence units (dfi). Ischemia was created using one of two methods: (1) a chronic model in which the blood supply to 40 cm of ileum was ligated and viability assessed 24 hours later, or (2) an acute model in which the main superior mesenteric artery was occluded for 3 1/2 hours and then released. Viability parameters were assessed every 5 minutes for 30 minutes after release. After viability assessment was completed, the ischemic bowel was resected and anastomosed at the site where the EMG measurements approximated 50% of the values obtained in normal bowel. In the chronic group 3 of 20 dogs died of necrosis in contrast to none of 12 dogs in the acute reperfusion group. In the acute model EMG values steadily increased after reperfusion, stabilizing by 15 minutes after release. Mean EMG values at 15 through 30 minutes after release were significantly greater than the 5- and 10-minute postrelease and prerelease values, suggesting that the electromyogram is affected by reperfusion. Conversely, postrelease fluorometry measurements rapidly increased to levels that exceeded measurements obtained in normal bowel. There was a significant difference in the number of audible Doppler signals in the marginal artery of survivors of the acute vs. the chronic model. Fluorometry measurements in survivors of the acute model (99+/-9 dfi) were significantly greater than measurements in the chronic model (54+/-4 dfi, P<or=0.004). Conversely, intermodel differences in the EMG measurements were not significant. These results show significant differences in the magnitude of ischemic damage induced by reperfusion vs. mesenteric ligation, which had a significant impact on the objective blood flow measurements that were used to predict bowel viability. The results also suggest that intestinal reperfusion injury in dogs has a negligible impact on bowel survival.
Animals↗
Access performance in an emergency medical service system.
Data obtained from two different sources (the Illinois Trauma Registry and the Illinois Department of Transportation) are combined in an analysis of the relative performance of Emergency Medical Service (EMS) "access components". Access components are defined to include: discovery and notification; dispatch of help; and transportation. Results show that the majority of EMS incidents occurred near a care facility and encountered reasonable access delays. However, a number of "problem incidents" were identified which incurred long access delays despite close proximity to a care facility. Further results indicate the "problem incident" delays are due to the non-transportation components of the EMS access system.
Emergency Medical Services↗
EMS access performance: the relative cost of treatment delay.
A quantitatively defined relationship between in-system mortality and treatment delay (the total time delay between traumatic injury and initial care) is developed empirically from an emergency medical services data source. This relationship is described as an approximate indicator of the cost of treatment delay in the system studied which should be useful for resource allocation and planning.
Costs and Cost Analysis↗
Dynamic details of disparity convergence eye movements.
Classically, the primary tool for quantifying the dynamics of vergence and other eye movements has been the main sequence. The main sequence is a plot of peak velocity versus response amplitude and is particularly useful for comparing the dynamics of a large number of eye movements over a range of response amplitudes. However, the main sequence represents only the equivalent first-order behavior of a response and does not describe its dynamics in detail. Since the main sequence is based on only two points on the dynamic trajectory, it is sensitive to measurement artifacts and noise. A new methodology is presented which quantifies the equivalent second-order dynamics of eye movements using a larger region of the transient response. These new indexes were applied to vergence eye movements and were found to differentiate between subtle, but important differences in movement dynamics.
Biomedical Engineering↗
Intraoperative assessment of bowel viability.
Viability of ischemic bowel was assessed in 30 dogs after mesenteric arterial ligation in a 40-cm length of ileum. Viability was evaluated using two gross features, color and peristalsis, and four objective methods including bowel wall surface oximetry (pO2), Doppler ultrasound, quantitative fluorescein fluorimetry, and myoelectric activity measured by a strain gauge probe. Each parameter was measured at 2-cm intervals within the 40-cm ischemic segment before resection and anastomosis was performed. There were seven fatal anastomotic leaks, all due to further bowel necrosis. Survival did not correlate with bowel color, presence of peristalsis, bowel wall pO2 Doppler ultrasound, or the myoelectric parameters. However, fluorescein fluorimetry was predictive of long-term viability. These results suggest that quantitative fluorescein fluorimetry may be a useful adjunct in intraoperative bowel viability assessment.
Animals↗
Bacterial translocation after mesenteric ligation in dogs.
These experiments were designed to determine the relationship between translocation of Escherichia coli and viability of ischemic small bowel. Twenty beagles were gavaged with 14C-labeled E. coli at two time intervals (3 and 24 h) prior to ligation of the blood supply to a 40-cm segment of ileum. Mesenteric lymph node (MLN) biopsies and bacterial cultures of the peritoneal fluid, peripheral arterial blood, and splanchnic venous blood were taken immediately prior to ligation and 24 h later both before and after the ischemic bowel was resected and anastomosed. Biopsies of each resection margin were taken to measure translocation of E. coli into the bowel wall. Several hemodynamic hemodynamic parameters were also measured before and 24 h after ligation. Seven of the 20 dogs died of further bowel necrosis. In survivors A-alpha DO2 was significantly decreased 24 h after mesenteric ligation vs. preligation, whereas in dogs that died DO2 was significantly increased after ligation vs. preligation. The incidence of mesenteric venous cultures positive for E. coli was significantly higher 24 h after ligation vs. preligation. However, there was no correlation between survival and the incidence of positive E. coli cultures in the blood or peritoneal fluid. Mean MLN counts were significantly higher in dogs gavaged at 3 h vs. those gavaged 24 h prior to laparotomy. However, there was no correlation between survival and translocation into either the bowel wall or MLN at either time interval. Viability of ischemic small bowel in this canine model was not affected by translocation of E. coli. Hemodynamic parameters that are altered during the course of sepsis also did not correlate with survival.
Animals↗
High resolution MRI study of circumlental space in the aging eye.
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Adult↗
Evaluation of quantitative approaches to assessment of bowel viability.
Predicting the survivability of intestine that has been made ischemic by impairment of blood flow is a major unsolved problem in gastrointestinal surgery. Currently, the surgeon must rely on qualitative, often subjective assessments that are known to have marginal reliability. This review describes various approaches to quantitatively assess the survivability of intestine compromised by ischemic disease. Much of the review centers on work done in the authors' laboratory to evaluate various approaches to predicting long-term survival and to develop new assessment parameters. Towards that end the authors have designed and developed techniques based on intestinal contractility and myoelectric activity (the intestinal EMG). Their evaluations of these and other methods of viability assessment utilize a highly representative canine model of intestinal ischemia that closely follows the development and treatment of ischemic intestinal disease in humans. Results to date suggest that the myoelectric measurements are more reliable than parameters based on blood flow or visual evaluation in terms of predicting bowel survival. However, improvements in instrumentation and technique are needed before this approach is suitable for clinical use.
Angiography↗