Aloysius Chu

Digital Computer Simulation Study of a Real-Time Collection, Post-Processing Synthetic Focusing Ultrasound Cardiac Camera

High resolution ultrasound images (90% of Rayleigh limit at all depths) were obtained by computer analysis of digitized (at 10 and 20 points per microsecond, 8 bits per point) signals detected with a 32 element lead zirconium titanate 3.0 MHz array. Every sixth element was used as a transmitter and pulsed 31 times while the signals from the remaining 31 elements were addressed sequentially by an analog switch and their signals digitized and recorded. Each pixel in the cross-sectional image was produced by calculating the inner product of a specific window function and the ensemble of digitized signals. Thus the array is mathematically focused optimally for each pixel in the image. The acquisition and storage of all received signals allows subsequent approximate calculation of spatial distributions of such parameters as reflection, index of refraction, attenuation, etc. The extension of these techniques through the use of a fast analog and digital computer interface to obtain realtime and stop-action imaging is treated. Examples of images produced by these algorithms, the time requirements of various algorithms as determined by the computation speeds of present and anticipated digital and analog processing hardware is presented. Supported in part by NIH research grants HT-4-2904, RR-7, and HL-04664. Also supported in part by a contract from the Office of Naval Research to E. M. Eyring, with whom S. A. Johnson was a part-time research associate.

Ultra high speed transaxial image reconstruction of the heart, lungs, and circulation via numerical approximation methods and optimized processor architecture.

Abstract A high temporal resolution scanning multiaxial tomography unit, the Dynamic Spatial Reconstructor (DSR), presently under development will be capable of recording multiangular X-ray projection data of sufficient axial range to reconstruct a cylindrical volume consisting of up to 240 contiguous 1-mm thick cross sections encompassing the intact thorax. At repetition rates of up to 60 sets of cross sections per second, the DSR will thus record projection data sufficient to reconstruct as many as 14 400 cross-sectional images during each second of operation. Use of this system in a clinical setting will be dependent upon the development of software and hardware techniques for carrying out X-ray reconstructions at the rate of hundreds of cross sections per second. A conceptual design, with several variations, is proposed for a special purpose hardware reconstruction processor capable of completing a single cross section reconstruction within 1 to 2 msec. In addition, it is suggested that the amount of computation required to execute the filtered back-projection algorithm may be decreased significantly by the utilization of approximation equations, formulated as recursions, for the generation of internal constants required by the algorithm. The effects on reconstructed image quality of several different approximation methods are investigated by reconstruction of density projections generated from a mathematically simulated model of the human thorax, assuming the same source-detector geometry and X-ray flux density as will be employed by the DSR. These studies have indicated that the prudent application of numerical approximations for the generation of internal constants will not cause significant degradation in reconstructed image quality and will in fact require substantially less auxiliary memory and computational capacity than required by direct execution of mathematically exact formulations of the reconstruction algorithm.

Validation of a new UNIX‐based quantitative coronary angiographic system for the measurement of coronary artery lesions

We describe a method of validation of computerized quantitative coronary arteriography and report the results of a new UNIX-based quantitative coronary arteriography software program developed for rapid on-line (digital) and off-line (digital or cinefilm) analysis. The UNIX operating system is widely available in computer systems using very fast processors and has excellent graphics capabilities. The system is potentially compatible with any cardiac digital x-ray system for on-line analysis and has been designed to incorporate an integrated database, have on-line and immediate recall capabilities, and provide digital access to all data. The accuracy (mean signed differences of the observed minus the true dimensions) and precision (pooled standard deviations of the measurements) of the program were determined x-ray vessel phantoms. Intra- and interobserver variabilities were assessed from in vivo studies during routine clinical coronary arteriography. Precision from the x-ray phantom studies (6-In. field of view) for digital images was 0.066 mm and for digitized cine images was 0.060 mm. Accuracy was 0.076 mm (overestimation) for digital images compared to 0.008 mm for digitized cine images. Diagnostic coronary catheters were also used for calibration; accuracy.varied according to size of catheter and whether or not they were filled with iodinated contrast. Intra- and interobserver variabilities were excellent and indicated that coronary lesion measurements were relatively user-independent. Thus, this easy to use and very fast UNIX based program appears to be robust with optimal accuracy and precision for clinical and research applications.

Application of optimized parallel processing digital computers and numerical approximation methods to the ultra high-speed three-dimensional reconstruction of the intact thorax

In order to achieve the computational capability to carry out many thousands of cross-sectional reconstructions, necessary to support a prototype high temporal and spatial resolution cylindrical scanning multiaxial tomographic unit, a series of design, software simulation, and fabrication studies is underway to develop a special-purpose high-speed reconstruction computer. This processor will rely upon integrated circuit arithmetic components of advanced design, and highly parallel architecture to execute X-ray based transaxial reconstruction algorithms at the rate of hundreds of cross sections/sec.

Rapid Computer Generation Of Three-Dimensional Phantoms And Their Cone-Beam X-Ray Projections

We describe a program that allows a user to generate 3-D phantoms and the corresponding radiographic data that might be expected for an arrangement of cone-beam x-ray sources and 2-D detector arrays. The software described is the firgt part of a project (GOLEM) to include in a single framework: the generation of 3-D phantoms and test data, fully 3-D reconstruction algorithms for cone-beam x-ray sources, and (fully-3D) algorithm evaluation.

Multifrequency Diffraction Tomography

In an attempt to obtain quantitative images of two-dimensional distributions of basic mechanical properties of tissue in a noninvasive manner, ultrasonic computer-assisted tomography has been developed1,2,3. Current techniques for applying ultrasonic com- puter-assisted tomography rely on mathematical methods of solution which require straight-line assumptions for the traversing trajectories of the ultrasonic rays4. Several authors have suggested more accurate methods of reconstructing distributions of parameters representing material properties such as attenuation and speed within tissue, using methods such as ray tracing5, miniature profiles6, ghase insensitive apertures7, and inverse scattering techniques.8,9,10,11 The promise of such methods is to obtain images having higher fidelity than those obtained using simple straight-ray assumptions.

Vascular Cell Proliferation Dynamics: Implications for Gene Transfer and Restenosis

Pharmacologic treatment of restenosis following coronary angioplasty has completely failed. The most widely accepted cause is formation of neointimal hyperplasia, considered a result of uncontrolled medial smooth muscle cell proliferation [1–5]. Studies in the rat carotid artery injury model has been the basis of this paradigm, having been documented in many studies [6, 7]. Therapies aimed at inhibiting proliferation have been quite successful in rat arterial injury [8, 9]. Yet when applied to large scale patient trials, these therapies have failed to exhibit any effect whatsoever on the loss of minimal lumen diameter (MLD) [10]. Reasons for these failures are unclear, but may relate in part to an incomplete understanding of cell kinetics in the growth of human neointimal hyperplasia. The literature is conflicting regarding the role of proliferation in human restenosis. Two studies of human restenotic lesions obtained using directional atherectomy demonstrated opposite conclusions. Pickering and colleagues [11] found peak cellular proliferation rates of about 20%, while in a similar study, O’Brien [12] reported a proliferation rate of less than 1%. Much debate has surfaced about the reasons for these divergent results, but centers on questions of technical factors such as tissue fixation methods and visual interpretation of positive cells by proliferating cell nuclear antigen (PCNA) staining.

Mathematical Generation Of Three-Dimensional Phantoms And Corresponding Cone-Beam X-Ray Projections

We describe the mathematical procedures needed to generate three-dimensional phantoms and corresponding simulated radiographic data for an arrangement of cone-beam x-ray sources and two-dimensional detector arrays. The techniques described here are being used to test fully three-dimensional cone-beam reconstruction algorithms for application to dynamic spatial reconstructor type machines.