Perceived fidelity of compressed and reconstructed radiological images: a preliminary exploration of compression, luminance, and viewing distance.

The authors' goal was to explore the impact of image compression algorithm and ratio, image luminance, and viewing distance on radiologists' perception of reconstructed image fidelity. Five radiologists viewed 16 sets of four hard-copy chest radiographs prepared for secondary interpretation. Each set included one uncompressed, and three compressed and reconstructed images prepared using three different algorithms but the same compression ratio. The sets were prepared using two subjects, four compression ratios (10:1, 20:1, 30:1, 40:1), and two luminance levels (2,400 cd/m2, standard lightbox illumination, and 200 cd/m2, simulating a typical CRT display). Readers ranked image quality and evaluated obviousness and clinical importance of differences. Viewing distances for image screening, inspection, and comparison were recorded. At 10:1 compression, the compressed and uncompressed images were nearly indistinguishable; the three algorithms were very similar, and differences were rated "not obvious" and "not important." At higher compression, readers consistently preferred uncompressed images, with notable differences between algorithms. The obviousness and clinical importance of differences were rated higher at lightbox luminance. Viewing distances appeared to be idiosyncratic.

Soft-copy versus hard-copy cranial sonography: intraobserver agreement and workstation efficiency.

OBJECTIVE: The objective of the study was to determine the intraobserver agreement, confidence level, and efficiency in interpretation of soft-copy (workstation) versus hard-copy (laser-printed film) sonograms of the cranium. MATERIALS AND METHODS: Cranial sonograms of 100 premature infants were randomly reviewed twice on both soft-copy and hard-copy images by three observers and were graded for hemorrhage using a five-level scale. The kappa statistic was calculated to measure intraobserver agreement. Differences in agreement were tested for statistical significance with a test for marginal homogeneity. Observers rated their confidence in interpretation using a six-point ordinal scale. Total viewing time was recorded, and videotaped sessions were analyzed for image handling time (opening each case, closing each case, and selecting the next case) and interpretation time. RESULTS: For soft copy versus hard copy, the mean kappa value was .73; for hard-copy 1 versus hard-copy 2, .71; and for soft-copy 1 versus soft-copy 2, .65. None of these differences was statistically significant (p > .05). The mean confidence score was the same for soft copy (5.3) and hard copy (5.3). On average, the observers needed 24 min longer to review 100 studies on soft copy than on hard copy. Opening and closing times for soft copy were significantly faster than for hard copy (p = .0001); however, case selection for soft copy, which was not needed for hard copy, took 4.69-9.09 sec per case. Extrapolated to 100 cases, case selection accounted for 8-15 min of viewing time. CONCLUSION: Radiologist agreement and confidence in the interpretation of cranial sonograms for hemorrhage was the same for soft copy and hard copy. However, viewing times were longer for soft copy. Elimination of inefficiency in case selection could improve image-handling time.

Networks for electronic radiology.

Next-generation health care systems must successfully integrate hospital information, laboratory automation, and medical-image management to provide a seamless view of the complete medical record to the primary care physician across a distributed medical enterprise. Broadband networks are an important component of the systems required to achieve this goal. This article provides a brief tutorial on relevant network principles and products, a perspective on the evolution of the field, and a simple view of the network requirements posed by electronic radiology.

Teleradiology via narrow-band integrated services digital network (N-ISDN) and Joint Photographic Experts Group (JPEG) image compression.

The importance of remote access to both radiological images and medical information has stimulated many demonstration projects that use a variety of telecommunications providers' offerings. Teleradiology, through modest cost channels, can achieve adequate response times using a combination of narrow-band integrated services digital network (N-ISDN) and data compression. A demonstration project, developed in collaboration with Southwestern Bell Technology Resources, Inc, uses the aggregate bandwidth of two B channels (achieving a rate of 120 kilobits per second) and a block-oriented discrete cosine transform compression/decompression implementation based on the Joint Photographic Experts Group Standard for Still Image Compression. System response measurements for an Inquiry and Display Station accessing the Mallinckrodt Institute of Radiology's Radiology Image and Information Management Testbed via the N-ISDN connection show response times to be within 20 seconds. Viewing applications have been shown at sites within St Louis and at Radiological Society of North America, 1990, in Chicago.

Quality monitoring of soft-copy displays for medical radiography.

As presentation of medical radiographic images on soft-copy displays (cathode ray tubes) becomes increasingly prevalent in electronic radiography, methods of quality assurance must be developed to ensure that radiologists can effectively transfer film-based reading skills. Luminance measurements provide the basis for evaluating the state of soft-copy displays. An integrated approach has been implemented at Mallinckrodt Institute of Radiology (MIR, Washington University, St Louis, MO) that facilitates measurement of geographically distributed soft-copy displays with centralized data logging, performance tracking, and calibration. MIR's central radiology image manager exercises the display station that drives the monitor, harvests the measurement data, stores the results, and submits the resulting data for additional processing. The luminance measurements are collected by a small, portable, photometric instrument designed at MIR that includes a serial port that is accessed via local area terminal service supported by the radiology image manager. The design details of the photometric instrument and example luminance characteristics of several soft-copy displays used at MIR are presented in this report.

Performance characteristics and image fidelity of gray-scale monitors.

Gray-scale monitors are an essential element of electronic radiology, and their ability to provide images that are perceived to be identical to those available on conventional or laser-printed film is crucial to success of electronic radiology. Image fidelity is measured in physical characteristics (luminance, dynamic range, distortion, resolution, and noise) and with psychophysical techniques, including receiver operator characteristics analysis with clinical images and testing with contrast-detail patterns to determine threshold contrast. Currently, laser-printed images facilitate greater information transfer than does a gray-scale monitor because of their higher absolute luminance (500 ft-L vs 60 ft-L), greater perceived dynamic range, and better spatial resolution. In the near future, the developments of gray-scale monitors with 150-200 ft-L luminance, a display standard based on just noticeable differences, and algorithms to improve similarities between gray-scale display images and laser-printed images will help increase the acceptability of monitors as a means to make primary diagnoses.

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 prototype of a high-resolution computerized radiology teaching file.

Computers provide an excellent tool for handling the task of organizing a radiology teaching file. Currently available computerized teaching files are either film-based, slide-based, or use laser-disc video technology for image display. There are obvious advantages to having the management of radiologic images under the control of a computer, and the need for a higher resolution alternative to video laser-disc technology becomes apparent when one tries to computerize a chest radiology teaching file. We describe the prototype of such a system, named MIRTLE, (the Mallinckrodt Institute of Radiology Teaching and Learning Environment) which was designed to integrate text under the control of a custom data base with high-resolution digital images from a Picture Archiving and Communications System. This system with its easy-to-use windows environment should allow a significant increase in the use of the radiology teaching file.

Hospital-wide distribution of nuclear medicine studies through a broadband digital network.

Nuclear medicine provides a good environment for the evaluation of picture archiving and communication systems (PACS) because of the relatively small quantity of digital data that are generated, leading to reduced requirements for storage, display, and transmission compared with those found in radiology. The PACS in nuclear medicine is characterized by use of a single computer as a central storage, display, and analysis node. Images are acquired with use of small, low-cost computers attached to each camera. This network configuration offers advantages of convenience, but with great reliance on a single computer. A campus-wide picture network is under development at Washington University employing broadband cable television technology supplemented by baseband Ethernet (Digital Equipment Corp, Maynard, MA) components. All areas of diagnostic radiology and nuclear medicine are connected via a PACS testbed project. A radiology information system, supporting over 250 terminals, provides digital tracking of patients and report generation and retrieval. A new image workstation is under development in conjunction with Digital Equipment Corp. This system will permit display in multiple windows of report information and images from various modalities. A lung scan demonstration project is now beginning that is designed to test the value of a PACS in nuclear medicine. Digitally acquired chest radiographs will be displayed on an image workstation in nuclear medicine along with digital ventilation and perfusion lung scans. It is hoped that time-consuming logistic bottlenecks now encountered in lung scan interpretation will be reduced.