Edward A. Geiser

Using Prior Shapes in Geometric Active Contours in a Variational Framework

In this paper, we report an active contour algorithm that is capable of using prior shapes. The energy functional of the contour is modified so that the energy depends on the image gradient as well as the prior shape. The model provides the segmentation and the transformation that maps the segmented contour to the prior shape. The active contour is able to find boundaries that are similar in shape to the prior, even when the entire boundary is not visible in the image (i.e., when the boundary has gaps). A level set formulation of the active contour is presented. The existence of the solution to the energy minimization is also established.We also report experimental results of the use of this contour on 2d synthetic images, ultrasound images and fMRI images. Classical active contours cannot be used in many of these images.

Speckle reduction and contrast enhancement of echocardiograms via multiscale nonlinear processing

This paper presents an algorithm for speckle reduction and contrast enhancement of echocardiographic images. Within a framework of multiscale wavelet analysis, the authors apply wavelet shrinkage techniques to eliminate noise while preserving the sharpness of salient features. In addition, nonlinear processing of feature energy is carried out to enhance contrast within local structures and along object boundaries. The authors show that the algorithm is capable of not only reducing speckle, but also enhancing features of diagnostic importance, such as myocardial walls in two-dimensional echocardiograms obtained from the parasternal short-axis view. Shrinkage of wavelet coefficients via soft thresholding within finer levels of scale is carried out on coefficients of logarithmically transformed echocardiograms. Enhancement of echocardiographic features is accomplished via nonlinear stretching followed by hard thresholding of wavelet coefficients within selected (midrange) spatial-frequency levels of analysis. The authors formulate the denoising and enhancement problem, introduce a class of dyadic wavelets, and describe their implementation of a dyadic wavelet transform. Their approach for speckle reduction and contrast enhancement was shown to be less affected by pseudo-Gibbs phenomena. The authors show experimentally that this technique produced superior results both qualitatively and quantitatively when compared to results obtained from existing denoising methods alone. A study using a database of clinical echocardiographic images suggests that such denoising and enhancement may improve the overall consistency of expert observers to manually defined borders.

Effects of carbon dioxide, Nd-YAG, and argon laser radiation on coronary atheromatous plaques☆

Laser radiation has been successfully applied in several areas of medical practice. However, its use in cardiology and specifically its effects on obstructive atherosclerosis have largely been unexplored. To evaluate effects of laser radiation on atherosclerotic plaques 25 fresh necropsy atherosclerotic coronary artery segments were exposed to laser radiation with either a carbon dioxide, Nd-YAG, or argon laser. Split or intact segments were prepared under dry conditions or while immersed in saline solution or blood and exposed to laser radiation as power and duration of exposure varied. All 3 lasers were capable of creating controlled injury to atherosclerotic plaques. In general, the magnitude of injury varied according to the total energy delivered (that is, power times duration of exposure. Calcified and noncalcified plaques were penetrated with similar levels of injury. Histologic examination demonstrated that laser radiation produced a wedge incision in the atherosclerotic plaque which was surrounded by zones of thermal and acoustic injury.

On the incorporation of shape priors into geometric active contours

A novel model for boundary determination that incorporates prior shape information into geometric active contours is presented. The basic idea of this model is to minimize the energy functional depending on the information of the image gradient and the shape of interest, so that the boundary of the object can be captured either by higher magnitude of the image gradient or by the prior knowledge of its shape. The level set form of the proposed model is also provided. We present our experimental results on some synthetic images, functional MR brain images, and ultrasound images for which the existing active contour methods are not applicable. The existence of the solution to the proposed minimization problem is also discussed.

An Effective Algorithm for Extracting Serial Endocardial Borders from 2-Dimensional Echocardiograms

An effective image processing algorithm for extracting the endocardial border from a series of 2-dimensional echocardiograms (2D echo) is proposed. The main steps involved in this algorithm are coordinate transformation, regional co-occurrence matrix thresholding, search region limiting, border detecting, and spatial and temporal smoothing. Using these steps, some major difficulties related to 2D echo image processing including low signal-to-noise ratio, echo drop out, and gray level intensity variability have been dramatically reduced. All endocardial borders in an entire cardiac cycle are computed. This is done automatically on the basis of observer-drawn outlines at end systole and end diastole. These outlines facilitate the quantitative analysis by defining a range in which both boundary dimension and shape changes should occur. Image processing is restricted to this range. The validation studies have been perfonned on test balloons where both image quality has been changed and complex motion abnormalities have been experimentally produced. Good results have also been obtained in patient studies.

Infective endocarditis and echocardiography

15. Behar VS, Whalen RE, McIntosh HD: The ballooning mitral valve in patients with “precordial honk” and “whoop.” Am J Cardiol 20:789. 1967. Leon DE, Leonard JJ, Kroelz FW, Page WL, Shaver JA. Lancaster JF: Late systolic murmurs, clicks and whoops arising from the mitral valve. AM HEART J 72:325, 1966. Felner JM, Harwood S, Mond H, Planth W, Brinsfield D, Schlant RC: Systolic honks in young children. Am J Cardiol 40:206, 1977. Rizzon P, Biasco G, Maselli CP: The precordial honk. Br Heart J 33:707, 1971. Keenan TJ, Schwartz MJ: Tricuspid whoop. Am J Cardiol 31:642, 1973. Upshaw CB: Precordial honk due to tricuspid regurgitation. Am J Cardiol 35:85, 1975. Venkatarman K, Seigel R, Kim SJ, Allen JW: Musical murmurs: And echo phonocardiographic study. Am ,J Cardiol 41:952, 1978. Sheikh MU, Ali N: Systolic honk in heart failure: Its origin and mechanism of production. Clin Cardiol 2~52, 1979. Tei C, Shah PM, Tanake H: Phonocardiographic-echocardiographic documentation of systolic honk in tricuspid prolapse. AM HEART J 103:294, 1982. Bellet S, Gouley B, Nichols CF, McMillan TM: Loud musical diastolic murmurs of aortic insufficiency, AM HEART ,J l&483, 1939. Nichols CF: A study of syphilis of the aorta and aortic valve area. Ann Intern Med 14:960, 1940. Gelfand D, Bellet S: The musical murmurs of aortic insufficiency, clinical manifestations; based on a study of 18 cases. Am J Med Sci 221:644, 1951. 16.

Dobutamine stress echocardiography in patients undergoing liver transplantation evaluation.

BACKGROUND Coronary artery disease has an important impact on perioperative morbidity and mortality in patients undergoing liver transplantation. To assess the role of dobutamine stress echocardiography (DSE) in these patients, DSE was included in the preoperative evaluation. METHODS Patients under consideration for liver transplantation underwent detailed clinical history, electrocardiography, and echocardiography. Patients with documented coronary disease or symptoms of myocardial ischemia underwent angiography. The remaining patients with cardiac risk factors, atypical chest pain, or age > or = 60 years underwent DSE. RESULTS These 121 patients (77 men and 44 women) ranged in age from 34 to 73 years (mean 53). Among the 61 patients who underwent liver transplantation, DSE was normal in 25, nondiagnostic in 34 because of inadequate heart rate response, and abnormal in two patients. Major perioperative events occurred in eight patients, all with normal or nondiagnostic DSE studies (negative predictive value 86%). CONCLUSIONS In patients with low to moderate risk of cardiac disease, DSE performed as part of an evaluation for liver transplantation is a poor predictor of major perioperative events.

Computer-assisted edge detection in two-dimensional echocardiography: Comparison with anatomic data☆

Four methods of computer-based edge detection were evaluated for identification of endocardial and epicardial borders on 2-dimensional echocardiograms of excised hearts. A method was also evaluated for observer identification of cardiac borders in the same hearts. The accuracy of computer-derived borders and of observer-derived borders were determined by comparison to anatomic borders measured from photographs of slices of the excised hearts. Echocardiographic borders were compared with anatomic borders by calculation of segmental cavity areas and wall thickness. Each of the methods tested (computer and observer) identified endocardial borders accurately, resulting in cavity segment areas that correlated well with the corresponding anatomic data (r = 0.90 to 0.92). Regional wall thicknesses correlated less well with anatomic data (r = 0.74 to 0.80), suggesting that endocardial borders were identified more accurately than were epicardial borders. Thus, the methods of computer-assisted echocardiographic border detection tested identified the endocardium and epicardium as accurately as a trained observer evaluating unprocessed echocardiograms. Computer-based methods of border detection may be useful in the automated analysis of clinical echocardiograms.

Transesophageal echocardiographic guidance of transseptal left heart catheterization during radiofrequency ablation of left-sided accessory pathways in humans.

Radiofrequency ablation (RFA) of left‐sided accessory pathways can be achieved using catheters introduced by a retrograde or transseptal approach. Transesophageal echocardiography (TEE) has previously been demonstrated to be safe and efficacious in guiding transseptal puncture in patients during mitral valvuloplasty (MV). This study was undertaken to assess the feasibility, safety, and clinical utility of TEE during transsepta! puncture and RFA of left‐sided accessory pathways. Methods: TEE was performed during transseptal puncture in 30 patients (41 ± 12 years, 19 females), 15 patients during attempted RFA of a left‐sided accessory pathway and 15 patients during attempted balloon MV. Results: There was no difference in age, sex distribution, or procedural complications when MV patients were compared to RFA patients. At baseline, left atrial dimension was increased and congestive heart failure was more common when MV patients were compared to RFA patients (P < 0.05) Adequate baseline two‐dimensional and Doppler TEE images were obtained in all patients. One patient sustained mild esophageal bleeding during the TEE, Positioning of the transseptal catheter in the fossa ovalis was facilitated and confirmed by TEE in 29 of 30 cases. One case of cardiac perforation occurred and was associated with inadequate TEE localization of the fossa ovalis. Thrombus was detected on the transseptal catheter by TEE in two cases prior to systemic heparinization. In both cases, thrombus was removed without embolic event. Conclusions: TEE safely guides transseptal puncture in patients undergoing RFA of left‐sided accessory pathways. TEE markers of the fossa ovalis facilitate puncture and may reduce the risk of cardiac perforation particularly in patients with a normal size left atrium. TEE may be especially valuable for identifying thrombus during transseptal puncture.

A framework for three-dimensional time-varying reconstruction of the human left ventricle: sources of error and estimation of their magnitude.

Abstract This report summarizes development of a computer/ultrasound system to graphically reconstruct the contracting human left ventricle in three dimensions and calculate indices of cardiac performance. The three-dimensional reconstruction is performed by realignment of five cross-sectional two-dimensional echograms along a single longitudinal section. The spatial position of the cross sections is recorded by a specially developed indexing arm. Cross sections are then realigned perpendicular to the long axis and parallel to each other by the computer. Points at 30° intervals are chosen from the inner and outer muscle boundaries of a cross section and connected by straight lines. Thus areas can be calculated simply by summation of triangular areas with vertices at the origin. Volumes can then be calculated using a modified Simpsons rule. To test these computer programs three hypothetical time-varying computer-generated left ventricular models were developed. Effects of six major anticipated sources of error were determined by systemic introduction of simulated measurement errors into data for these hypothetical models. These results demonstrate that this system is practical for the three-dimensional reconstruction of the left ventricle, that volumes and derived indices of ventricular performance can be calculated, and that anticipated sources of error result in relatively small deviations from true values.