Michael J. Potel

Methods for evaluating cardiac wall motion in three dimensions using bifurcation points of the coronary arterial tree.

An accurate three-dimensional (3D) representation of heart wall motion would be an important means of evaluating cardiac function. To accomplish this, we have developed an interactive computer graphics system designed to enter the time-dependent 3D positions of bifurcations of the coronary arterial tree. These bifurcations are precise markers of the epicardial surface, and their motions accurately represent the motion of the underlying heart wall. We demonstrate techniques for calculating local wall motion, including displacement and velocity, for determining a time-dependent center-of-contraction point towards which the epicardium tends to move and for tracking the mechanical contraction wave using cross-correlation methods. We have applied these techniques to study seven patients with normal left ventriculograms and coronary arteriograms. We have found these methods to be generally applicable and to provide information not obtainable without 3D analysis.

Graphics methods for tracking three-dimensional heart wall motion

Abstract An analysis of heart wall motion requires that specific points on the wall be identified and their movements tracked in three dimensions over several heart beats. A method to reconstruct time-dependent 3D coordinates from any two or more perspective views has been developed. We have used this method to determine accurately the 3D dynamics of bifurcation points of the coronary arteries or surgically implanted markers by tracking their projections in both views of a biplane coronary cineangiogram. The tracking operation is aided by a sophisticated interactive computer system which superimposes an animated graphics display onto the film image. This allows entries to be checked and corrected immediately. The most powerful tool provided by the graphics system is the ability to display the backprojections of positions from one view as auxiliary lines across the other view on which the projection of the point of interest must lie. We provide some examples of cardiac wall motion measures we have made using this system.

Quantitative analysis of cyclic AMP waves mediating aggregation in Dictyostelium discoideum

We have previously reported the detection of cAMP waves within monolayers of aggregating Dictyostelium discoideum cells (K. J. Tomchik and P.N. Devreotes, 1981, Science 212, 443-446). The computer-assisted analysis presented here of the fluorographic images of the cAMP waves reveals (1) all the waves have a consistent width and height; (2) cAMP concentrations within centers of concentric aggregation territories oscillate periodically while at spiral centers the concentration builds up to a plateau value within 2 mm; (3) cells within the region of intersection of two oppositely directed cAMP waves are stimulated to produce more cAMP than those responding to a single wave; (4) cells start to move when the cAMP level begins to increase and cease movement when the peak cAMP concentration reaches the cell.

Structural analysis of polymers of sickle cell hemoglobin. II. Sickle hemoglobin macrofibers.

We have examined the structure of hemoglobin S fibers, which are associated into large bundles, or fascicles. Electron micrographs of embedded and cross-sectioned fascicles provide an end-on view of the component fibers. The cross-sectional images are rotationally blurred as a result of the twist of the fiber within the finite thickness of the section. We have applied restoration techniques to recover a deblurred image of the fiber. The first step in this procedure involved correlation averaging images of cross-sections of individual fibers in order to improve the signal-to-noise ratio. The rotationally blurred image was then geometrically transformed to polar co-ordinates. In this space, the rotational blur is transformed into a linear blur. The linearly blurred image is the convolution of the unblurred image and a point spread function that can be closely approximated by a square pulse. Deconvolution in Fourier space, followed by remapping to Cartesian co-ordinates, produced a deblurred image of the original micrograph. The deblurred images indicate that the fiber is comprised of 14 strands of hemoglobin S. This result provides confirmation of the fiber structure determined using helical reconstruction techniques and indicates that the association of fibers into ordered arrays does not alter their molecular structure.

Structure and mechanisms of schooling intadpoles of the clawed frog, Xenopus laevis

Abstract The geometric structure and sensory bases of social aggregates in larvae of the clawed frog, Xenopus laevis, were studied using photographic data interpreted with the aid of a computerized image analyser. The system records positional data from photographs and uses this information to assess: (1) extent of parallel orientation between tadpoles that are nearest neighbours, (ii) distance over which significant parallel orientation is maintained (interactive distance), and (iii) extent of clumping or evenness of individuals. o (1) Under all density, size, and illumination conditions, tadpoles show a highly significant tendency to line up parallel (0° between neighbours) and, to a lesser extent, antiparallel (180° between neigh-bours) to their nearest neighbour. (2) Tadpoles in the light show a much greater tendency to orient parallel to nearest neighbours than in the dark. (3) The tendency to orient parallel to nearest neighbours increases slightly with increasing tadpole size and density. (4) In the light, tadpoles have an interactive distance of approximately two body lengths; in the dark, only approximately one body length. (5) Interactive distance shows a slight increase with decreasing tadpole density. (6) Interactive distance is proportional to tadpole size. (7) Spacing between tadpoles is random, but there is a weak tendency toward increased evenness with increasing tadpole size and density; tadpoles in the light position themselves more evenly than in the dark. We propose that Xenopus tadpoles use both visual and lateral line input to school. Lateral line input is presumably necessary for maintaining some degree of parallel orientation in the dark and is augmented by visual information in the light.

Three-dimensional left ventricular wall motion in man. Coordinate systems for representing wall movement direction.

We have studied the three-dimensional (3D) motion of left ventricular (LV) epicardial points by tracking one to three dozen coronary artery bifurcations in eleven human subjects. Wall motion was analyzed using several different coordinate systems: (1) cylindrical centered about the LV long axis, (2) spherical with origin at the LV center-of-gravity (COG), and (3) spherical with origin at the LV center-of-contraction (COC), the best-fit 3D point toward which the wall moves. The coordinate systems were studied both fixed and moving with time. Three-dimensional motions were decomposed into three directional components, with high radial (in and out) percentages being regarded as the figure-of-merit of a given coordinate system. Average percentage radial motions were fixed cylindrical 16%, fixed spherical COG 35%, fixed spherical COC 47%, moving cylindrical 17%, moving spherical COG 30%, moving spherical COC 91%. Spherical systems were generally better than cylindrical systems, with the COC representing a better origin than the COG. Moving systems were appreciably better than fixed only for the COC model, indicating that the COC, which traverses up and down the LV midline, moves significantly while the other systems are more stationary. At each instant in time, almost all (91%) of the 3D motion of the entire heart wall is directed toward a single moving 3D point, the COC. Thus, there exists in principle a near-perfect 3D heart wall motion model. Approximately 25% of 3D wall motion is unseen in conventional monoplane views. Also, any model that represents 3D wall motion only along fixed straight 3D lines (eg, end-diastole to end-systole) necessarily ignores 27% of the true 3D heart wall motion.

An analysis of school structure for tadpoles (Anura: Amphibia)

SummaryThe spatial relationships of Bufo woodhousei larvae were examined in the laboratory and field and compared with laboratory data for Xenopus laevis larvae.1.Tadpoles of both species avoid positions directly in front of or behind neighbors. Bufo larvae demonstrate particularly strong preference for being directly lateral to conspecifics. Bearing relationships are different in light than in dark for Xenopus, but not for Bufo.2.In the absence of other cues, Bufo and Xenopus tadpoles orient parallel to nearest neighbors under a variety of conditions of density, size, and in both the light and dark, although more strongly in the light. Bufo larvae show little tendency to orient antiparallel in contrast to Xenopus. Bufo typically parallelorient over greater distances than Xenopus, whether interactive distance is measured in number of nearest neighbors, centimeters, or tadpole body lengths.3.Schooling tadpoles, in contrast to fish, tend to be relatively stationary and at random distances from their nearest neighbors.

Periodic movements of Dictyostelium discoideum sorocarps

We report periodic movements during erection of Dictyostelium discoideum (Dd) sorocarps. Our observations lead to the working hypothesis that Dd sorocarp erection occurs by two superimposed processes: one periodic, with a modal period of 6 1/2 min, and one continuous. We tentatively identify the periodic process with cell movement into the apex of the Dd stalk, and the continuous process with cell vacuolation, together with stalk sheath extension.

Macrofiber structure and the dynamics of sickle cell hemoglobin crystallization

Fibers of deoxyhemoglobin S undergo spontaneous crystallization by a mechanism involving a variety of intermediate structures. These intermediate structures, in common with the fiber and crystal, consist of Wishner-Love double strands of hemoglobin S molecules arranged in different configurations. The structure of one of the key intermediates linking the fiber and crystal, called a macrofiber, has been studied by a variety of analytical procedures. The results of the analysis indicate that the intermediates involved in the fiber to crystal transition have many common structural features. Fourier analysis of electron micrographs of macrofibers confirms that they are composed of Wishner-Love double strands of hemoglobin molecules. Electron micrographs of macrofiber cross-sections reveal that the arrangement of the double strands in macrofibers resembles that seen in micrographs of the a axis projection of the crystal. This orientation provides an end-on view of the double strands which appear as paired dumb-bell-like masses. The structural detail becomes progressively less distinct towards the edge of the particle due to twisting of the double strands about the particle axis. Serial sections of macrofibers confirm that these particles do indeed rotate about their axes. The twist of the particle is right handed and its average pitch is 10,000 A. The effect of rotation on the appearance of macrofiber cross-sections 300 to 400 A thick can be simulated by a 15 degrees rotation of an a axis crystal projection. The relative polarity of the double strands in macrofibers and crystals can be determined easily by direct inspection of the micrographs. In both macrofibers and crystals they are in an anti-parallel array. On the basis of these observations we conclude that crystallization of macrofibers involves untwisting and alignment of the double strands.

Interacting with the GALATEA film analysis system

GALATEA is an interactive animated graphics system providing a tool for the man-machine analysis of moving images recorded on film. The system relies on the users recognition of phenomena of interest and his manipulation of simple graphical objects to build up a kinegram, an animated representationof the film. Display of the kinegram superimposed on the original film facilitates the entry and refinement of the animation. The net result is an analysis by synthesis. In this paper we describe the current production version of GALATEA from the standpoint of the user. Included are a functional description of the constituent hardware, demonstration of various aspects of system behavior, and some examples of interactions common in user applications.