Lowell D. Harris

Display and visualization of three-dimensional reconstructed anatomic morphology: Experience with the thorax, heart, and coronary vasculature of dogs

A new method, termed reprojection, is used to visualize anatomic morphology contained within three-dimensional reconstructions made up of images of multiple parallel cross sections. This method involves the projection, either orthographically onto a plane or radially onto a cylinder, of the volume picture elements (voxels) of the reconstruction. Orthographic reprojection images, formed by mathematically summing the magnitudes of the voxels along selected parallel paths through the reconstructed volume, are analagous to conventional radiographs formed by the passage of an X-ray beam through the volume. The reprojection image is a two-dimensional array of picture elements that is displayed on a television monitor using a digital-to-video scan converter. Also described are the techniques of noninvasive selective tissue dissolution and numerical dissection, whereby obscuring portions of the reconstructed volume are either partially “dissolved” or totally eliminated before reprojection. Utilizing these methods, anatomic information present in a three-dimensional reconstruction but not clearly seen in a reprojection image is rendered visible after removal of superposed structures. The usefulness of these methods is demonstrated utilizing three-dimensional reconstructions of the thorax, heart, and coronary arteries of dogs.

Three-dimensional spatial, density, and temporal resolution of the dynamic spatial reconstructor

Spatial, density, and temporal resolution of the dynamic spatial reconstructor (DSR), a multiple X-ray source, high speed, computed tomography scanning system, are evaluated. Hole-pair resolution was evaluated in a stationary phantom surrounded with air, 15 cm of water, or 20 cm of water. Temporal resolution was evaluated by rotation of one of the resolution phantoms during the scan, and with a balloon inflated to a known volume and at a known rate to approximate a typical left ventricular chamber volume and filling rate. These studies confirmed that the spatial resolution is essentially the same in the transverse and axial directions, and that retrospective manipulation of the image data is important for maximization of spatial and density resolution in any structure under examination by obtaining a tradeoff with partial-volume and motion-blurring effects. Maximum spatial resolution in the scanned volume was shown, under ideal conditions, to be greater than five hole pairs per centimeter. Under conditions of intravenous injection of contrast agent, the resolution of blood vessels in an experimental animal approximately 25 kg in weight is expected to be on the order of three hole pairs per centimeter; and in an adult human weighing approximately 60 kg, a resolution of about two hole pairs per centimeter is to be expected.

Quantitative analysis of a vascular tree model with the Dynamic Spatial Reconstructor

The accuracy in determining the three-dimensional anatomy of a vessel network by computed tomography (CT) is evaluated using a glass model of a pulmonary artery. The dynamic spatial reconstructor (DSR), a high temporal resolution, volumetric, roentgenographic, CT scanner, was used to scan the model. The glass of the model had a roentgen attenuation coefficient μ, = 0.55 cm-1, which is approximately equivalent to the 20% dilution of contrast medium to be expected in the pulmonary arterial tree following a contrast agent bolus injection of 2 ml/kg in the right atrium. The model was scanned inside a 20 cm diameter Plexiglas cylinder with a 1 cm thick wall (μ = 0.2 cm-1) to simulate the chest wall of a 20 kg dog, and it was filled with potato flakes to simulate lung parenchyma (μ = 0.06 cm-1)- In one 0.011 s scan, information for reconstruction of a stack of images of transaxial sections was recorded. Sequential scans were performed to obtain data for either maximum transaxial resolution (14 angles of view every 0.0167 s, 120 parallel slices each 1.8 mm thick) or maximum axial resolution (eight angles of view every 0.0167 s, 240 parallel slices each 0.9 mm thick) reconstructions. Estimated detectable “vessel” size, cross-sectional area, branching angle, and interbranch segment length were determined as a function of imaged slice thickness, orientation of section image, and number of angles of view (i.e., scan duration) used to make images. Retrospective selection of 0.05 s duration scan apertures at sequential 0.5 s intervals was used to simulate a typical, retrospectively gated reconstruction from a DSR scan. Using these reconstructed images, 2 mm diameter “vessels” could be readily detected and their structure quantitated. Comparing direct measurements and DSR estimates, cross-sectional area (SEE = 3 mm2), branching angles (SEE = 2°), and segment length (SEE = 1 mm) all had a correlation coefficient greater than 0.99, and the regression lines showed no significant differences from the lines of identity (p > 0.05). Index Terms: Image reconstruction—In vivo studies, vascular macroanatomy—Dynamic spatial reconstructor—Computed tomography.

The DSR: A High-Speed Three-Dimensional X-Ray Computed Tomography System for Dynamic Spatial Reconstruction of the Heart and Circulation

High temporal resolution, full three-dimensional imaging of the heart and circulation is required for accurate basic physiological studies of the structural-to-functional relationships of these organ systems, and for improved diagnostic evaluation and treatment of patients with cardiovascular disorders. A new generation, fully electronic and very rapid whole-body computed tomography system called the Dynamic Spatial Reconstructor (DSR) will provide stop-action (0.01 sec), rapidly sequential (60-per-second), synchronous volume (240 simultaneous transaxial sections) reconstructions and display of the full anatomic extent of the heart throughout successive cardiac cycles, and will permit visualization of the three-dimensional vascular anatomy and circulatory functions in all regions of the body of patients with cardiovascular and other pathological disabilities. The feasibility and potential of a DSR system has been demonstrated by studies using a currently operational single source prototype assembly, the SSDSR, from which full three-dimensional dynamic reconstructions of the thorax and its contents have been obtained.

The dynamic spatial reconstructor: Investigating congenital heart disease in four dimensions

The Dynamic Spatial Reconstructor (DSR) is a high-temporal resolution, three-dimensional (3-D) X-ray scanning device based on computed tomography (CT) principles. It was designed for investigation of some problems inherent in current diagnostic imaging techniques, and to allow quantitative studies of cardiovascular structure and function. One of the research protocols in which DSR is currently used involves studying selected pediatric patients with complex congenital heart disease. Initial results show that 3-D dynamic images can be obtained from these patients with minimal invasiveness and that these images may provide useful diagnostic information.

Three-Dimensional Cardiac Anatomy and Function in Heart Disease in Adults: Initial Results With the Dynamic Spatial Reconstructor

The dynamic spatial reconstructor, or DSR, is a unique high-speed volume-imaging x-ray scanner based on computed tomographic principles. In this report, we present data obtained from the first feasibility DSR studies of adult patients with heart disease. Information from three patients--one with hypertrophic obstructive cardiomyopathy, one with calcific aortic valvular disease, and one with a left ventricular aneurysm--is described in detail. The mean DSR scanning time for each patient was 20 seconds, and the mean total irradiation to the sternum was 15.3 R. Transverse cross sections were reconstructed and then retrospectively reformatted to provide operator-selected oblique sections in space (for example, long-axis and short-axis sections of the left ventricle), to follow these sections through time (such as from end-diastole through end-systole), and to create three-dimensional displays (for instance, of the left ventricular chamber). Unique quantitative measurements of structure and function were made by using these images. For generation of most imaging data, only one injection of contrast material into the right side of the heart is necessary. Clinically useful three-dimensional dynamic imaging data can be acquired from adult patients with heart disease by using the DSR. Compared with conventional angiocardiography, DSR studies can provide information with less x-ray exposure and fewer angiographic injections.

Computerized x-ray reconstruction tomography in stereometric analysis of cardiovascular dynamics

The basic determinants required for accurate estimation of the functional status of the intact heart, lungs and other organs; namely, their true dynamic changes in regional shape and dimensions, the temporal and regional distribution of blood flow to, within, and from these organs, and their internal and transmural pressures, can be obtained by application of dynamic spatial reconstruction techniques to simultaneous and synchronous recordings of multiplanar x-ray images and multiple associated physiological variables. This paper describes a computerized method for obtaining cross-sectional images of the dynamic spatial distribution of x-ray attenuation covering the entire anatomic extent of the thorax and its contents in living dogs with 1 mm resolution and at 1/60th second intervals in time. Operator-interactive computer programs for display of the dynamic sequences of these reconstructed cross sections, for display of any desired single or spatially related set of coronal, sagittal or obliquely oriented section(s) calculated from these reconstructed cross sections, and for display of the three-dimensional surface of the entire organ structure are operational for viewing the temporal and spatial distribution of contraction, expansion, and perfusion of the heart, lungs, and other organs over their full anatomic extent from various aspects and in variable time-base modes ranging from stop-action to real-time. The results achieved with this computerized system for three-dimensional reconstruction and display of the heart, lungs, and circulation demonstrate the potential for providing greatly improved techniques for investigation of the relationships of the dynamic three-dimensional structure of these and other organ systems of the body to their regional and integrated function.

DISPLAY OF 3-D ULTRASONIC IMAGES

Three-dimensional (3-D) ultrasonic images made up of a “stack” of adjacent digitized B-scans are displayed as a volume image using the method of numerical projection. This display method involves the generation by a computer, of two-dimensional digital projection images of the display volume viewed from any desired direction. They are formed by summing the “intensity” values of the individual volume picture elements (voxels) of the 3-D B-scan along the set of paths which project the 3-D image array onto a plane. Stereo-pair projection images generated at two angles of “view” differing by 2° to 8° are utilized to visualize the volume image in three dimensions. The 3-D display of a “stack” of B-scans may result in the obscuring of some portions of the image due to superposed “bright” structures unless this undesirable effect is overcome by selective enhancement of features of interest in the 3-D B-scan. These enhancement methods are selective “tissue dissolution” and “numerical dissection” whereby portions of the 3-D B-scan are either partially “dissolved” or totally eliminated from the volume before projection to enhance the visibility of desired structure. Because they operate on the 3-D image array before projection and not on the resulting projection image, they are both effective and highly selective as visual enhancement methods.

Physics And Technical Considerations In The Design Of The Dynamic Spatial Reconstructor (DSR)-A High Temporal Resolution Volume Scanner

A. multiple x-ray source high-speed transaxial scanner system (DSR) is about to undergo evaluation. studies. The capH.bility for programmable scanning modes and operator interactive retrospective reconfiguration of scan data makes the DSR a very powerful research tool. The physics and technological basis for system design and selection of several major components of the DSR scanner are discussed.

High temporal resolution synchronous volumetric scanning tomography: Potential roles in clinical evaluation of ischemic heart disease

Abstract A new quantitative imaging device, the Dynamic Spatial Reconstructor (DSR), is described. Because, unlike commercially available computed tomography scanners, it obtains stop-action (0.01 second) images of a volume rather than a slice at a repetition rate of 60 volumetric scans per second, the DSR is particularly well suited for the study of ischemic heart disease. Its capabilities for recording the transit and dilution of contrast media within the coronary vasculature and all regions of the myocardium simultaneously with regional and global myocardial mechanics are being evaluated as a research tool for physiologic and ultimately clinical investigations.