Biomedical subjects

E Muka

Publications and source records attributed to E Muka.

5 recordsLinked to original sources

PubMed2000

Assessment of visually lossless irreversible image compression: comparison of three methods by using an image-comparison workstation.

PURPOSE: To determine the degree of irreversible image compression detectable in conservative viewing conditions. MATERIALS AND METHODS: An image-comparison workstation, which alternately displayed two registered and magnified versions of an image, was used to study observer detection of image degradation introduced by irreversible compression. Five observers evaluated 20 16-bit posteroanterior digital chest radiographs compressed with Joint Photographic Experts Group (JPEG) or wavelet-based trellis-coded quantization (WTCQ) algorithms at compression ratios of 8:1-128:1 and x2 magnification by using (a) traditional two-alternative forced choice; (b) original-revealed two-alternative forced choice, in which the noncompressed image is identified to the observer; and (c) a resolution-metric method of matching test images to degraded reference images. RESULTS: The visually lossless threshold was between 8:1 and 16:1 for four observers. JPEG compression resulted in performance as good as that with WTCQ compression at these ratios. The original-revealed forced-choice method was faster and as sensitive as the two-alternative forced-choice method. The resolution-metric results were robust and provided information on performance above visually lossless levels. CONCLUSION: The image-comparison workstation is a versatile tool for comparative assessment of image quality. At x2 magnification, images compressed with either JPEG or WTCQ algorithms were indistinguishable from unaltered original images for most observers at compression ratios between 8:1 and 16:1, indicating that 10:1 compression is acceptable for primary image interpretation.

Algorithms↗

PubMed1998

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.

Adolescent↗

PubMed1996

Effect of exposure variation on the clinical utility of chest radiographs.

PURPOSE: To study the effects of exposure error on the clinical utility of chest radiographs. MATERIALS AND METHODS: Under- and overexposed screen-film images were simulated by adding exposure offsets to the normalized CR log(10) exposure data from a computed radiography (CR) system and printed by using the sensitometric response of a medium-latitude system. The clinical utility of the overall image, lung, and soft tissue in 48 images were independently graded by eight radiologists. RESULTS: Most variability in image scores was due to differences in exposure. About 95% of the lung regions and 75% of the soft-tissue regions were rated as having good or ideal clinical utility at the nominal exposure. About 80% of the overall images were rated as good or better for exposures within 40% [0.15 log(10) exposure] of the nominal. The overall image scores were heavily influenced by the lung region, and reader tolerance for exposure error was greater for soft tissue than for lung. The optimal exposure for soft tissue was about 60% [0.25 log(10) exposure] greater than for lung; therefore, no single exposure was optimal for the entire image. CONCLUSION: Conventional medium-latitude screen-film systems have intrinsic limitations for capturing and displaying the wide transmittance differences in the thorax. The clinical utility of chest radiographs may be improved by developing better image capture and display techniques.

Adult↗

PubMed1994

New techniques in chest radiography.

Advances in film-screen radiography (e.g., InSight) and beam equalization radiography (e.g., AMBER) have improved the quality of standard chest radiographs. Despite the improved visibility of the mediastinum and retrocardiac and retrodiaphragmatic lung with AMBER, it is debatable whether this advantage outweighs its disadvantages, especially the increased cost of the unit and decreased reliability. The benefits of storage phosphor systems have largely been in the area of bedside radiography, where consistent image quality over a wide range of exposures and image processing compensate for the lower spatial resolution. More routine application of this technology to standard chest radiography is likely, especially as image processing techniques improve and digital units become more cost effective. Storage phosphor digital imaging may be the most appropriate technique for entry of images into a picture archiving and communication system in which images stored in image management systems can be displayed on high-resolution monitors in local or distant sites. Such systems have the potential of improving patient care by providing more rapid access to radiographic images, especially if the image is accompanied by an immediate report. Because of the significant expense of a picture archiving and communication system, their introduction is likely to be gradual, via networks in specific areas such as between intensive care units and radiology departments.

Data Display↗

PubMed1992

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.

Computer Peripherals↗