A distributed approach to integrated inquiry and display for radiology.

Picture archive and communications (PACS) systems should be flexible and modular in design so that new advances in storage, computation, and display technology can be introduced into the system without a significant redesign of existing software. The acquisition, storage, and management of radiologic images must be carefully integrated with a radiology information system. Our architecture is based on a four-level data model: (1) patient information, (2) examination information and reports, (3) image information, and (4) instances of images. The PACS being developed at the Mallinckrodt Institute of Radiology within the Electronic Radiology Laboratory consists of three primary components: application clients, database servers and image servers. One type of application client is an image-capable workstation that supports a radiology image viewing application. The application client queries the database server for information regarding patient and examination data in response to user-level requests. The database server responds to the request by retrieving the appropriate patient demographics and examination information, along with a pointer to the image/instance data from a central database. The client then uses the image data pointer to query the image server for the actual pixel data. The image server responds by transmitting the pixel data to the requesting application client or a designated auxiliary display device. Other clients act as image data acquisition nodes. Queries to the database servers are made via a library of callable subroutines. Software integrity is maintained throughout the system by dynamically loading software from a code-control database. Inquiry and display transactions, supported on a local-area network (Ethernet), have been measured and analyzed. Results and observations are presented.

A core-conductor model of the cardiac Purkinje fibre based on structural analysis.

1. Structural analysis of voltage clamp preparations of sheep cardiac Purkinje fibres was carried out using methods based on light and electron microscopic observations. Results demonstrate the marked structural variability in preparations that appear, outwardly, simple.2. The length of the cell aggregate was measured in vitro, and the mean area of cross-section, by light microscopic methods in serially sampled transverse sections. The number of intercellular clefts and path lengths of cell profiles distributed at the lateral surface and along clefts were determined from photomicrographs. Accuracy of these estimates was improved by obtaining, electron microscopically, values representing the degree of membrane folding in longitudinal and transverse planes.3. Cleft width was evaluated from electron micrographs. Measurements made on sections that there tilted through wide arcs with a goniometer indicate that cleft width is quite variable and, on average, somewhat greater than 400 A.4. A three-dimensional core-conductor model is presented to aid in quantitative interpretation of electrophysiological experiments. Application of the model to individual preparations requires evaluation of the length and perimeter of cross-section of cell aggregates and of the mean number, width and depth of intercellular clefts, with appropriate corrections for fine sarcolemmal folding. Methods are given for estimating these structural parameter values from measurements of external dimensions of cell aggregates.5. The core-conductor model is applied in an accompanying analysis of the linear electrical characteristics of Purkinje membrane.

Linear analysis of membrane conductance and capacitance in cardiac Purkinje fibres.

1. The membrane capacitance and slope conductance of sheep cardiac Purkinje tissue were examined under conditions of constant and slowly changing voltage within the potential range: -70 to -100 mV. Data were secured by applying constant current pulses, or by imposing ramp commands or small changes in holding potential under voltage clamp control.2. The electrical measurements, combined with light and electron microscopic data on preparation structure, were interpreted with the aid of a core-conductor model that permits quantitative representation of cleft- and lateral surface membranes for individual preparations (Hellam & Studt, 1974).3. The analysis led to the following conclusions. The slope conductance of unit membrane area (G(m)) is quite low in the normal resting potential range; at -80 mV the value is 0.09 mmho/cm(2). G(m) exhibits a marked decline with depolarization in the region positive to -88 mV, but only slight voltage-dependence at more negative potentials within the range of present observations. The capacitance of unit membrane area (C(m)), from voltage ramp data collected near -90 mV, is 0.9 muF/cm(2).4. Comparison with results of earlier studies indicates that the differences between present and previous experimental estimates of these membrane characteristics result from differences in modelling and structural analysis of tissue preparations.