Rexford L. Hill

Progressive Coding and Transmission of Digital Diagnostic Pictures

In radiology, as a result of the increased utilization of digital imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), over a third of the images produced in a typical radiology department are currently in digital form, and this percentage is steadily increasing. Image compression provides a means for the economical storage and efficient transmission of these diagnostic pictures. The level of coding distortion that can be accepted for clinical diagnosis purposes is not yet well-defined. In this paper we introduce some constraints on the design of existing transform codes in order to achieve progressive image transmission efficiently. The design constraints allow the image quality to be asymptotically improved such that the proper clinical diagnoses are always possible. The modified transform code outperforms simple spatial-domain codes by providing higher quality of the intermediately reconstructed images. The improvement is 10 dB for a compression factor of 256:1, and it is as high as 17.5 dB for a factor of 8:1. A novel progressive quantization scheme is developed for optimal progressive transmission of transformed diagnostic images. Combined with a discrete cosine transform, the new approach delivers intermediately reconstructed images of comparable quality twice as fast as the more usual zig-zag sampled approach. The quantization procedure is suitable for hardware implementation.

Regional ventilation-perfusion relationships.

Regional ventilation-perfusion ratios have been determined in 12 healthy subjects, 16 patients with pulmonary embolism, and 22 patients with chronic obstructive lung disease. The ventilation-perfusion ratios were determined from xenon-133 ventilation studies and 99-tc-m-labeled particle perfusion scans, using either the fractional exchange of air or the relative distribution of tidal volume per unit volume as the numerator of the ratio. A comparison of these two methods showed comparable distributions of regional ventilation-perfusion relationships in the healthy subjects and patients with pulmonary embolism. However, in the patients with chronic obstructive pulmonary disease, the fractional exchange method clearly separated this group of patients from the others.

Image Transmission Studies

Radiological PACS image sizes and desired retrieval response times demand high-bandwidth communication networks. Local area network technology at speeds higher that 10 Megabits/second (IEEE 802.3) have not achieved standardization nor production volume. Our current PACS experiments are based on a three-level subnet approach using 10 Mb/s Ethernet channels. An Ethernet channel is shown to support image transfers at an average throughput of 3 Mb/s. Preliminary measurements and simulation results suggest that traffic from as many as two-to-three archives can be supported on the same channel.

PACS Experience As A Motivation For A Campus-Wide Picture Network

Picture archiving and communication systems (PACS) have so far been studied primarily as a tool to address the problems of electronic radiology. Certainly the trends toward digital imaging within radiology provide strong ecomomic and medical incentives for the development of medical picture networks, but we believe that the applications for picture networks extend far beyond the field of radiology. Architects, engineers, biologists - practicioners of virtually every academic and commercial pursuit - deal with picture information every day, and increasingly these pictures are finding their way into digital form. We believe that industries and universities of the future will utilize sophisticated workstations serving a variety of scientific and commercial needs, and that these workstations will be linked by wideband networks capable of supporting not only text but high-resolution picture transmission as well.

The Application of Computer Simulation Modeling to the Radiology Film Library

The radiology film storage and retrieval system (film library) of the Mallinckrodt Institute of Radiology was studied by means of a computer simulation model. The current operation of the film library was studied and a model of the library was used to demonstrate which functions might be most susceptible to overloading and insufficiency. This is a valid technique for systematic study of a radiological film library and is also useful for many other complex administrative problems.

A digital data acquisition system for nuclear medicine

Abstract A Nuclear Medicine data acquisition system has been developed which interfaces directly with a digital computer and thus affords the opportunity for multiple forms of clinical Nuclear Medicine data to be computer analysed. The versatility of this approach is demonstrated by two examples. Data recorded from multiple head probes following an intracarotid injection of Xenon 133 is used in a computer program for the rapid calculation of regional cerebral blood flow using standard washout techniques. A second example is the application of computer analysis to dual label rectilinear scanning using subtraction techniques. These examples substantiate the opinion that this data acquisition system can provide a valuable adjunct for a clinical Nuclear Medicine laboratory using both kinetic and static data acquisition systems.

Design considerations for a picture archive and communication system (PACS) display station

The design of a system to manage digital images, a picture archive and communication system (PACS), is complex. A PACS development environment has been implemented that is built up from functionally distinct and independent blocks. It allows rapid modification and evaluation of various schemes for automatic image acquisition, reprocessing, display, and archiving from several imaging modalities. The authors focus on the image display block and some of the issues that were identified during its design.<<ETX>>

Transmission scanning in the measurement of regional ventilation: a comparison with xenon-133

Regional changes in gamma-ray transmission were measured in 23 subjects during natural and deep breathing using a disc source of technetium-99m and a gamma camera and spirometer interfaced to a small digital computer. Changes were measured as the logarithm of the difference in transmission between end-inspiration and end-expiration, and also as the rate of change of transmission during inspiration and expiration. Results were compared to figures for regional ventilation obtained from studies with xenon-133. Good correlation of this method and xenon-133 studies was found in normal subjects but in patients with delayed clearance of xenon-133, correlations were weaker and frequently not significant. This method is no substitute for xenon-133 studies in assessing patients with obstructive airways disease.

PACS Experience as a Motivation for a Campus-wide Picture Network

PICTURE ARCHIVING AND COMMUNICATION SYSTEMS (PACS) have so far been studied primarily as a tool to address the problems of electronic radiology. Certainly the trends toward digital imaging within radiology provide strong economic and medical incentives for the development of medical picture networks, but we believe that the applications for picture networks extend far beyond the field of radiology. Architects, engineers, biologists—practitioners of virtually every academic and commercial pursuit—deal with picture information every day, and increasingly these pictures are finding their way into digital form. We believe that industries and universities of the future will utilize sophisticated workstations serving a variety of scientific and commercial needs, and that these workstations will be linked by wideband networks capable of supporting not only text but high-resolution picture transmission as well. The technical problems are similar both within and outside the field of radiology. In order to develop an electronic picture network, it is necessary to develop high-performance, low-cost components which will serve each of the three major elements of a PACS—archive, network, and display. The high data rates required for picture transmission will stretch performance requirements far beyond those of a typical local area network, and require state-of-the-art technology for many elements of the system design. We continue to find that it is difficult to define and develop the basic PACS elements independently or without the application area context. Decisions regarding network configuration, for example, affect design decisions for the organization of a display. A comprehensive approach is required and, consequently, prototype PACS networks serve a useful purpose as a test bed for the evolution and evaluation of system concepts and component design. Washington University has made a significant committment to the development of a prototype PACS network. Initially, in 1981, modeling experiments were carried out to define the requirements of a picture network suitable for radiology.1 A prototype broadband network was designed, built, and installed in the medical center in 1983. Comprising approximately 1.5 miles of cable, the network served as an experimental laboratory for the transmission of video as well as low- and high-speed digital data.2 In 1984, links were established within the Mallinckrodt Institute of Radiology (MIR is the radiology department of Washington University) between the prototype image management system and the comprehensive patient information system developed at MIR, making it possible, at prototype workstations throughout the department, to retrieve image data stored in a prototype central image archive.3 In 1985, the scope of the prototype broadband network was increased as the Institute for Biomedical Computing at Washington University established an image presentation, analysis, and quantification (IPAQ) facility. The goal of this major project is to provide additional network connectivity supported by a center capable of providing tools and computational assistance required for the processing of medical images. In 1985, based on earlier PACS work at the medical center, a three-year project was begun to design and develop a campus-wide picture network capable of spanning the University from the medical center campus to the hilltop campus, three miles away. The objective of this fifteen-million-dollar project, undertaken in cooperation with Digital Equipment Corporation, was to develop a state-of-the-art wideband network capable of manipulating and transmitting pictures in addition to symbols and graphs. This picture network will cover all schools and departments of the University and will eventually extend outward into the community served by the University. Throughout this period of aggressive expansion of PACS research at Washington University, the enduring objective has been to establish a “workbench” for PACS development—to provide the tools, the resources, and the environment where experiments can be carried out to evaluate various alternatives for the design of the components required for network, archive, and display. Our goal at this time is not to build the ideal PACS network, but rather, in an ambitious time frame, to design and construct, in cooperation with industry, a large scale PACS prototype that will serve as a proving ground for picture networks of the future.

PACS Workbench at Mallinckrodt Institute of Radiology (MIR)

Initial components of a Picture Archive and Communication System (PACS) workbench have been installed at the Mallinckrodt Institute of Radiology (MIR) providing a set of basic “utilities” which facilitate comprehensive design studies and experiments. Each of the primary areas of picture acquisition, transport, processing, archiving and viewing are addressed by the PACS workbench.