NASA/DARPA advanced communications technology satellite project for evaluation of telemedicine outreach using next-generation communications satellite technology: Mayo Foundation participation.

OBJECTIVE: To describe the development of telemedicine capabilities-application of remote consultation and diagnostic techniques-and to evaluate the feasibility and practicality of such clinical outreach to rural and underserved communities with limited telecommunications infrastructures. MATERIAL AND METHODS: In 1992, Mayo Foundation (Rochester, Minn, Jacksonville, Fla, and Scottsdale, Ariz), the National Aeronautics and Space Administration, and the Defense Advanced Research Projects Agency collaborated to create a complex network of fiberoptic landlines, video recording systems, satellite terminals, and specially developed data translators linking Mayo sites with other locations in the continental United States on an on-demand basis. The purpose was to transmit data via the asynchronous transfer mode (ATM) digital communications protocol over the Advanced Communications Technology Satellite. The links were intended to provide a conduit for transmission of data for patient-specific consultations between physicians, evaluation of medical imagery, and medical education for clinical staffs at remote sites. RESULTS: Low-data-rate (LDR) experiments went live late in 1993. Mayo Clinic Rochester successfully provided medical consultation and services to 2 small regional medical facilities. High-data-rate (HDR) experiments included studies of remote digital echocardiography, store-and-forward telemedicine, cardiac catheterization, and teleconsultation for congenital heart disease. These studies combined landline data transmission with use of the satellite. The complexity of the routing paths and network components, immaturity of available software, and inexperience with existing telecommunications caused significant study delays. CONCLUSIONS: These experiments demonstrated that next-generation satellite technology can provide batch and real-time imagery for telemedicine. The first-generation of the ATM and satellite network technology used in these experiments created several technical problems and inconveniences that should be overcome as the network infrastructure matures.

Optimization of wide-area ATM and local-area ethernet/FDDI network configurations for high-speed telemedicine communications employing NASA's ACTS.

A high data rate terrestrial and satellite network was implemented to transfer medical images and data. This article describes the a optimization of the workstations and switching equipment incorporated into the network. Topics discussed in this article include tuning of the network software, the configuration of the Sun Microsystems workstations, the FORE Systems asynchronous transfer mode switches, as well as the throughput results of two telemedicine experiments undertaken by Mayo's physician staff. The technical staff was successful in achieving the data throughput needed by the telemedicine software; particularly important was the proper determination of peak throughput and TCP window sizes to ensure optimum use of the resources available on the Sun Microsystems and Hewlett Packard workstations.

Mayo Clinic and Medical School Biodynamics Research Unit.

The facilities that make up the Mayo Biodynamics Research Unit include the dynamic spatial reconstructor (DSR), which when fully operational will generate raw data at 200 million samples per second. Processing of these data will require a computer capable of several billion arithmetic operations per second.

Three-dimensional imaging of heart, lungs, and circulation.

A new imaging device, the dynamic spatial reconstructor (DSR), is described. It differs from commercially available computed tomography scanners in several ways. It images a volume rather than a slice; it images the volume in stop-action to minimize blurring due to motion; and it repeats the scan 60 times per second so that the functional movements of heart muscle and lung tissue and the distribution of roentgen contrast medium in blood can be quantitated in any portion of the body, especially in the heart, great vessels, and lungs. The system is under evaluation as a research tool for physiologic and, ultimately, clinical investigations.

Physics and technical considerations in the design of the 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 capability 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.

The dynamic spatial reconstructor: a computed tomography system for high-speed simultaneous scanning of multiple cross sections of the heart.

A new generation whole-body computed tomography system has been developed to provide accurate visualization and measurement of the vital functions of the heart, lungs, and circulation. This dynamic spatial reconstructor system (DSR) provides stop-action (.01-sec), rapidly sequential (60-per-second), synchronous volume (240 simultaneous adjacent 1-mm-thick transaxial sections) reconstructions and display of the full anatomic extents of the internal and external surfaces 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 circulatory disabilities.

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.

Quantitative imaging of the structure and function of the heart, lungs, and circulation.

A 28-x-ray-source, cylindrical-scanning, transaxial tomographic x-ray-imaging system is in the process of being fabricated. This system will scan synchronously up to 250 parallel transverse cross sections of the human body over an axial range of 25 cm within 0.01 second at a maximum rate of 60 scans per second. The system will provide numerous variations of scanning configurations to permit quantitative assessment of the relative importance of transverse section thickness, image contrast, spatial and temporal resolution, and related computerized algorithms and display techniques. Synchronous imaging at high temporal resolution of a three-dimensional volume--for example, the heart--eliminates the need for successive periods of breath-holding and gated imaging techniques and is essential for quantitation of cardiovascular and pulmonary function and structure in intact animals or humans. Initial clinical applications are expected to be in the early detection of lung cancer and the diagnosis of the nature and degree of congenital and acquired cardiovascular disabilities.

Continuous determination of beat to beat stroke volume from aortic pressure pulses in the dog.

Present methods for measurement of stroke volume from the aortic pressure pulse are not suitable for beat-to-beat determinations during non-steady state conditions because these methods assume that each systolic ejection is equal to the peripheral runoff during the same beat. We have tested a new method which allows determination of an aortic pressure-volume conversion factor over a wide range of pressures during transient changes in stroke volume and infusions of vasoactive drugs in 6 dogs with chronically implanted aortic electromagnetic flowmeters. Each aortic diastolic pressure decay is approximated by an exponential the time constant of which is used to calculate the pressure loss during systole due to blood flow into the periphery. The total increment in aortic pressure due to systolic ejection, if there were no flow from the aorta during systole, then is calculated. The total systolic increment (delta PSV) is assumed to describe the pressure-volume characteristics during systole and is related to stroke volume by a constant multiplier that is derived from the indicator-dilution measurements of cardiac output. The values for beat-to-beat variations that were determined by use of the aortic electromagnetic flowmeter and by this aortic pressure pulse method were found to be within the range of measurement errors of stroke volume determined from individual aortic electromagnetic flow pulses.

A charge coupled transversal filter for biomedical signal conditioning.

The analysis and processing of biological signals is often hampered by the contamination of these low frequency, often low amplitude waveforms by motion artifact in fluid-filled catheter systems and skin electrodes, power line hum, and so on. Although noise suppression techniques have relied upon low pass filtration of the analog signals with active or passive RLC filters, even the most recent active RLC filter implementations display operational characteristics not entirely satisfactory for low frequency applications.