A Linear Systems Approach To Medical Image Capture And Display

ABSTRACT A picture archival and communications system has been under development at the Hospital of the University of Pennsylvania for the past two years. This system features a fiber optic network, high resolution display for Initial Interpretation, and a lower resolution display for review and comparison. A laser optical disk will be used for mass storage. A high resolution digital camera Is used to acquire Images from x-ray film.This manuscript addresses an analysis of the Image resolution, Intensity transformations, and noise associated with the digital scanning camera and the high resolution cathode ray tube displays. A I near systems approach is utllIzed for this analysis. INTRODUCTION The picture archival and communication system (PACS) for medical images under development at the Hospital of the University of Pennsylvania has been described previously (Arenson 1982a,b) Digital imaging systems allow the direct acquisition of images already In digital form. However, approximately 80? of the Images In the Department of Radiology are still captured on x-ray film. These images are converted Into digital form by an Eikonix high-resolution digital scanning camera. We operate this digital camera in a matrix of 1024 x 1024 pixels to match the storage requirements of our Imaging network. Twelve bits of Intensity levels are recorded.These Image acquisition systems transfer digital images over the fiber optic network to the storage and/or Image display systems. The token- passing content I on-handI ing ring architecture of our fiber optic network has been described previously as wel I (Arenson, 1983a).There are two types of display systems on the network. Our high resolution, 1024 x 1024 pixel matrix, RAMtek displays are located In the main radiology Interpretation area. The other, lower resolution, 512 x 512 pixel, displays for reviewand comparison purposes, are based on a Gould- DeAnza Image array processor and associated image memory planes and video channels. These lower resolution displays will be relocated to our Medical Intensive Care Unit (MICU) for a clinical trial starting this FalI.The laser optical disk from PhilIps Medical Systems, Inc. (PMSI) is expected to ful f II I the storage needs for our cl inical trial In the MICU. The most recent images will also be available on Winchester disks associated with the DeAnza system.As we have implemented portions of our PACS, many problems have been encountered. Implementation of the ISO OS I network protocol has been difficult and performance has not matched expectations. Our ten megabytes per second fiber optic network is adequate to handle the traffic, but the computer buses I imlt effective transmission to one-two megabytes per second.The Eikonix camera Is sensitive to fine adjustments and the distance from the lens to the film source cannot be altered without recalI bratI on. Furthermore, we encountered difficulties choosing the appropriate adjustments based on Image observation alone.Therefore, we decided to perform a more rigorous analysis of the effects of both digitizing camera and display systems on the Image resolution, intensity transformation, and noise. The following discussion deals with this linear systems analysis approach appl led to our PACS.