Antagonist EMG temporal patterns during rapid voluntary movement.

This study of 10 normal college-aged women was designed to clarify possible antagonist control mechanisms during the silent period of the agonist in rapid elbow extension tasks. Antagonist electromyographic temporal patterns were observed after agonist silence under various conditions to determine if antagonist activity in the rapid movement was controlled supraspinally (preprogrammed), spinally (reflexively), or by a combination of the two mechanisms. The subjects followed a velocity-controlled dot displayed on an oscilloscope. The antagonist latencies remained constant during intentionally and unintentionally terminated movements, but were altered by load conditions. This was seen as an automatic deceleration response, elucidating differences between antagonist control during ballistic and rapid movements.

Quantification of thallium-201 scintigrams in acute myocardial infarction.

A method has been developed for measurement of myocardial infarct size from thallium-201 scintigrams that depends on computer measurement of levels of radioactivity in the myocardium. In 16 dogs, thallium-201 scintigrams were obtained in the left lateral and left anterior oblique projections 48 hours after ligation of the left anterior descending coronary artery. Scintigraphic results were obtained by two independent observers and were compared with tissue measurements of infarct volume calculated from thallium autoradiograms and nitro-blue tetrazolium (NBT)-stained tissue slices. Infarct volumes derived from tissue measurements were used to develop criteria for the computer scintigraphic technique. There was no significant difference in the scintigraphic measurements made by the two observers. Scintigraphic infarct size in the left lateral and left anterior oblique projections correlated with tissue infarct size with r values of 0.88 and 0.75, respectively, for thallium autoradiography and 0.71 and 0.70, respectively, for NBT tissue staining. The range of infarct volume was 3.3 to 14.8 percent of the left ventricular mass. Results of this study suggest that scintigraphic quantitation of infarct size is feasible in this dog model.

Automatic detection of inter-frame motion in echocardiographic images.

Signal averaging of echocardiographic frames acquired over multiple cardiac cycles has been used to improve image quality. However, misalignment of frames from respiration, transducer or patient movement, and irregular cardiac contraction affects the quality of the resultant averaged image. A motion detection system has been developed using inter-frame subtraction and statistical pattern recognition techniques. Automatic selection of frames exhibiting significant motion in a canine cardiac model compare favorably to manual selection by cardiologists (phi = 0.94) in a test set of 103 images. This method, combined with signal averaging, has resulted in an improvement in image quality.

Quantification of myocardial ischemia and infarction with 201thallium scintigraphy.

A quantitative method for the analysis of 201thallium myocardial scintigrams, developed in an experimental infarcted dog heart model, has been compared with two nonquantitative methods for interpretation of stress myocardial scintigrams in two groups of patients studied with coronary angiography: 11 with normal coronary arteries and 14 with coronary artery disease. Three independent observers interpreted scintigrams which were 1) not computer processed; 2) corrected for background activity in lungs and chest wall; and 3) processed by a computer method which uses a uniform threshold of counts determined from the dog model to define perfusion defects. Interobserver variability as well as sensitivity and specificity of detecting coronary disease were examined. In patients with coronary artery disease interobserver variability was improved by using the computer technique: observers agreed as to the existence of a perfusion defect in 93% of the scintigrams as compared to 55% and 81% for the unprocessed and background-subtracted images respectively. No false positive indications of coronary disease were obtained by any of the three techniques. Use of the computer method did not improve the sensitivity of detecting coronary disease, however--71% compared to 64% for unprocessed images and 79% for background-substracted images. The advantages of this quantitative computer method are increased consistency of interpretation and lack of false positive diagnoses of coronary disease. An improved sensitivity of detection may be gained by varying thallium count thresholds according to anatomic location in the heart.

Cardiology education using hypermedia and digital imagery.

A computer-based educational system for the study of cardiovascular imaging is described. This system, based on HyperCard * and a standard Macintosh II, integrates hypertext retrieval, computer graphics, sound, and medical images into a single interactive environment stored on a standard hard disk. This 'hypermedia' approach allows arbitrary complexity coupled with direct, immediate, easy traversal of the images and related text, which provides the opportunity for students to move at their own pace, choose their own direction through the material and repeat as often as desired. Storage on magnetic medium allows for easy updating with new studies and material in order to keep pace with advances in medical imaging technology. The system could be mastered onto CD-ROM for ease of distribution if so desired. The system includes a tutorial on the basics of digital image representation and example studies from cineangiography, nuclear medicine, echocardiography and magnetic resonance imaging of the heart. Quantitative techniques for evaluation of left ventricular function are explained using computer graphics overlays on the original medical images. Color encoded functional images are also included as an aid to visualization of ventricular performance data. The system has proven useful as a primer for digital imaging in cardiology prior to specific case study in a traditional mentor relationship.

Regional sequential motion in the normal left ventricle: nonuniform apical motion.

Timing of the onset and sequence of systolic regional wall motion was examined in the digitized left ventricular cineangiograms of 13 patients with angiographically normal coronary arteries and left ventricular function. Distance--time curves for anterior and inferior wall segments, the aortic valve plane, and apex point were compared to the volume--time curve in each ventricle. No significant differences were found in the onset of motion for the wall segments or for descent of the aortic valve where the sequence of motion was generally uniform. At the apex point, however, the onset of motion was significantly delayed. In addition, reduced velocity of motion in the first half of systole was followed by high velocity motion in the latter half. This apparent nonuniform apical motion may be explained by a geometric relationship of normally contracting myocardial wall fibers adjacent to a thin apical point which has relatively little or no contractile motion of its own.

An expert system for diagnosis of coronary artery stenosis based on 201Tl scintigrams using the Dempster-Shafer theory of evidence.

An expert system for the diagnosis of stenoses in the three main coronary arteries (left anterior descending, right coronary artery and circumflex) is described. First, the knowledge base domain--201Tl scintigrams--is explained and the method of preprocessing the original heart images is given. Next, the method of dealing with the uncertainties present both in the cardiologist-specified rules and the data using the Dempster-Shafer theory of evidence is explained. Finally, the constructed expert system and the results are discussed and several graphical examples are shown.

Acute myocardial ischemia detected in dogs by temporal variation in two-dimensional ultrasound gray level.

This study tests the hypothesis that acute myocardial ischemia induces a characteristic temporal variation in regional ultrasound amplitudes. Myocardial ischemia was created by circumflex coronary artery occlusion in seven closed-chest mongrel dogs. Ultrasound images were acquired prior to occlusion and post-occlusion on a phased-array two-dimensional system. Unprocessed ultrasound data from end-diastolic images were taken digitally for quantitative gray level analysis. Temporal variation in ultrasonic gray level of a nonischemic control region was compared to the temporal variation in gray level of the ischemic area. In the ischemic area, the average gray level for all seven dogs increased from 39.2 +/- 4.2 prior to occlusion to 42.5 +/- 4.9 at 15 minutes after occlusion, and then to 44.4 +/- 5.9, 45.3 +/- 6.2, and 47.0 +/- 6.0 at 30, 60, and 120 minutes, respectively (p less than 0.05 for control vs 15 minutes and 15 minutes vs 120 minutes). No significant changes in the average gray level of all seven dogs occurred in the nonischemic area from pre-occlusion to 2 hours post-occlusion (38.8 +/- 8.8, 38.4 +/- 8.0, 37.7 +/- 8.4, 37.8 +/- 8.5, and 38.0 +/- 8.2 for control, 15, 30, 60, and 120 minutes, respectively. These data show that regions of acute myocardial ischemia can be characterized by temporal variation in intramyocardial ultrasonic gray level, not only from the time before coronary occlusion to 15 minutes after occlusion, but also between 15 and 120 minutes in the post-occlusion period. Gray level values in nonischemic regions of the left ventricle are remarkably constant over time.

A client/server approach to telemedicine.

This paper describes the Medical College of Ohio's efforts in developing a client/server telemedicine system. Telemedicine vastly improves the ability of a medical center physician or specialist to interactively consult with a physician at a remote health care facility. The patient receives attention more quickly, he and his family do not need to travel long distances to obtain specialists' services, and the primary care physician can be involved in diagnosis and developing a treatment program [1, 2]. Telemedicine consultations are designed to improve access to health services in underserved urban and rural communities and reduce isolation of rural practitioners [3].