Alek S. Hayrapetian

Three-dimensional transform compression of images from dynamic studies

Transform based compression methods achieve their effect by taking advantage of the correlations between adjacent pLtels in an image. The increasing use of three-dimensional imaging studies in radiology requires new techniques for image compression. For time-sequenced studies such as digital subtraction angiography, pixels are correlated between images, as well as within an image. By using three-dimensional cosine transforms, correlations in time as well as space can be exploited for image compression. Sequences of up to eight 512 x 512 x 8-bit images were compressed using a single full volume three-dimensional cosine transform, followed by quantization and bit-allocation. The quantization process is a uniform thresholding type and an adaptive three-dimensional bit-allocation table is used. The resultant image fidelity vs. compression ratio was shown to be superior to that achieved by compressing each image individually.

Assessment of asynchronous transfer mode (ATM) networks for regional teleradiology

The purpose of this study was to assess the effect of ATM network capabilities on the clinical practice of regional teleradiology, by providing immediate interactive radiology consultations between subspecialists and general radiologists at affiliated academic institutions. PACS installed at three affiliated hospitals (UCLA Medical Center, West LA VAMC and UCLA Olive-View Medical Centers) were connected via an ATM network. Two commercial PACS (Agfa) systems, one at the VAMC and one in an ultrasound outpatient clinic at UCLA were connected via ATM switches (Newbridge, Inc.) and a Santa Monica GTE central office switch. We evaluated this initial system configuration and measured image transfer performance, including memory-to-memory, disk-to-disk, disk-to-archive with and without DICOM protocols. Although the memory-to-memory data rate was 25 Mbps, the average remote disk-to-disk image transfer performance, using DICOM 3.0 communications protocols on SUN SPARCstation 10 servers, was 3 to 5 Mbps. Using these capabilities, timely interactive subspecialty consultations between radiologists was successfully performed while both were at different physical locations. We present the use of ATM technology in a realistic clinical environment and evaluate its impact on patient care and clinical teaching within the radiology departments of 2 institutions. Image communications over a regional PACS using an ATM network can allow interactive consultations between different subspecialist and general radiologists or other specialized radiologist spread over three different medical centers.

X-window-based 2K display workstation

A high-definition, high-performance display station for reading and review of digital radiological images is introduced. The station is based on a Sun SPARC Station 4 and employs X window system for display and manipulation of images. A mouse-operated graphic user interface is implemented utilizing Motif-style tools. The system supports up to four MegaScan gray-scale 2560 X 2048 monitors. A special configuration of frame and video buffer yields a data transfer of 50 M pixels/s. A magnetic disk array supplies a storage capacity of 2 GB with a data transfer rate of 4-6 MB/s. The system has access to the central archive through an ultrahigh-speed fiber-optic network and patient studies are automatically transferred to the local disk. The available image processing functions include change of lookup table, zoom and pan, and cine. Future enhancements will provide for manual contour tracing, length, area, and density measurements, text and graphic overlay, as well as composition of selected images. Additional preprocessing procedures under development will optimize the initial lookup table and adjust the images to a standard orientation.

Acquisition Interface for Computed Radiography

Digital interface to the Philips Computed Radiography (PCR) units 701 and 9000 is not available as a standard component. Custom interfaces have been constructed using hardware and software techniques to achieve automatic data link without affecting the operational procedure or or slowing down the PCR. A complete acquisition interface design includes polling text patient information, image reformatting to the UCLA standard, and software interface to the network and database. Finally, an ethernet interface to the Luminsys computed radiograph plate reader is also reported.

Display conditions and lesion detectability: effect of background light

We assessed the effect of high background light on observer performance for the detection of a variety of chest radiographic abnormalities. Five observers reviewed 66 digital hard copy chest images formatted to 1 1 x 14 inch size under two display conditions: 1) on a specially prepared 1 1 x 14 inch illuminated panel with no peripheral light and 2) on a standard viewing panel designed for 14 x 17 inch radiographs. The images contained one - or more of the following conditions: pneumothorax, interstitial disease, nodules, alveolar process, or no abnormality. The results of receiver operator characteristic analysis show that extraneous light does reduce observer performance and the detectability of nodules, interstitial disease.

VOICE RECORDING MODULE FOR PACS

This paper describes the integration of a voice recording module in our existing PACS system at the UCLA Department of Radiology. This module consists of a personnal computer, speech signal digitizer, and a hard disk with appropriate amount of memory storage to handle a given number of reports. The system has the ability to record and store spoken reports in digitized form and play back an existing dictated report. Moreover, the voice module can be activated locally from its own keyboard or by receiving appropriate commands from two remote mini-computers which are used as review and diagnostic display workstations respectively.

ROC comparison of compressed images to original analog film and digital hardcopy

A receiver operating characteristic (ROC) experiment is used to compare the diagnostic performance of analog film to digital hardcopy and compressed hardcopy. The compression is done using a full-frame bit-allocation algorithm carried through on a custom designed board residing on a SUN computer bus. Image set included thirthy-one radiographs with septal lines (n=18) and/or parenchymal nodules (n=14), with six radiographs that had neither abnormality. Six radiologists viewed the image set under each modality. There is no statistically significant difference between the three modalities.

Teleradiology for Veterans Integrated Service Networks

Veterans Affairs Health Care has become more decentralized with the creation of local Veteran Integrated Service Networks (VISN). The purpose of this study was to analyze the design and cost of a wide-area-network (WAN) for teleradiology in a local VISN. The Southern California VISN includes 4 large and 3 small medical centers. Only one of the 7 medical centers has an operational PACS. Data were collected on the radiologist workloads and patient and image flow within and between the 7 medical centers. This was used to estimate the size and cost of local PACS at each medical center and the need for teleradiology services. A simplified cost-analysis model was used to estimate potential cost- savings by gong filmless. Asynchronous transfer mode (ATM) technology was selected for the WAN between the medical centers. A realistic cost-savings model was developed. Cost- effectiveness of a PACS/Teleradiology system was established. Based on this model, a PACS/Teleradiology configuration for the VISN was successfully designed and partially implemented. The ATM-based WAN provides instantaneous access to PACS at each centers. Cost-analysis of the design and implementation of a PACS/teleradiology network in a VISN is possible and important when planning such system. The experience gained will serve a model for future similar projects nationwide.

Workstation and network needs for very large PACS implementations

Large hospitals require many viewing stations for image access by referring doctors and personnel from the operating rooms and emergency room. We propose to discuss our experience in providing such review stations with inexpensive PC-based workstations, fast switched Ethernet and a client-server architecture within a large hospital. The bulk of computing processes overhead such as data acquisition, formatting, archiving, database management, routing was performed by large servers and 2 Ethernet giga- switches which are part of our PACS. PC-based workstations performed data retrieval and display functions with user configurable software. Ultrasound, MRI, CT, Angiography and digitized x-ray images were available on the servers. Referring doctors in ICU, CCU were very receptive to this technology. Film use decreased somewhat for hose services using this new technology. PC-based workstations can provide an economically viable solution for image data access by referring physicians and other staff.

Neural network based segmentation system

A neural network is used to segment double echo MR images. Images are acquired using an interleaved acquisition protocol that results in registered proton density and T2 weighted images. For each tissue class, a user selects approximately 15 - 20 points representative of the double echo signature of that tissue. This set of intensities and tissue classes are used as a pattern-target set for training a feed forward neural network using back propagation. The trained network is then used to classify all of the points in the dataset. Statistical testing of the network using pattern-target pairs distinct from those used in training showed roughly 90% correct classification for the selected tissues. The bulk of the error was due to ambiguities in classifying based solely on MR intensities. The resultant classified images can be further processed using special software that allows manual correction and interactive 2D or 3D connectivity analysis based on selection of seed points.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.