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PubMed1997

A pilot study of eye movement during mammography interpretation: eyetracker results and workstation design implications.

Digital mammography can potentially improve mammography image and interpretation quality. On-line interpretation from a workstation may improve interpretation logistics and increase availability of comparison images. Interpretation of eight 4k- x 5k-pixel mammograms on two to four 2k- x 2.5k-pixel monitors is problematic because of the time spent in choosing which images display on which monitors, and zooming and roaming on individual images that are too large to display completely at full resolution. The authors used an eyetracker to measure radiologists viewing behavior during mammography interpretation with film on a viewbox. It was observed that a significant portion of the mammographers' time is spent viewing "comparison pairs" (typically two or more comparisons per case), such as the left mediolateral and craniocaudal images or old and new images. From the eyetracker measurements, we estimated that the number of image display, roam, and zoom operations decreases from an average of 64 for one monitor to 31 for four monitors, with the largest change going from one to two monitors. We also show that fewer monitors with a faster response time is superior to more monitors with a slower response time. Finally, the authors demonstrate the applicability of time-motion analysis to mammographic workstation design.

Adult↗
PubMed1995

The health care professional multimedia workstation: development and integration issues.

Workstations for health care professionals provide access to distributed healthcare information systems. They are complex systems that have to manage, in a unified framework, the distributed and multimedia information needed for optimal patient care. The objective is to provide the end-user with a virtual and unified device that conceals the complexity of the underlying information system. Integration and reuse of modular software components are important in the development of such a workstation. A reference set of evaluation criteria is proposed that includes functional, technical, organizational, medical, cultural and ethical, economic and industrial components.

Computer Communication Networks↗
PubMed2002

Calibrated LCD/TFT stimulus presentation for visual psychophysics in fMRI.

Standard projection techniques using liquid crystal (LCD) or thin-film transistor (TFT) technology show drastic distortions in luminance and contrast characteristics across the screen and across grey levels. Common luminance measurement and calibration techniques are not applicable in the vicinity of MRI scanners. With the aid of a fibre optic, we measured screen luminances for the full space of screen position and image grey values and on that basis developed a compensation technique that involves both luminance homogenisation and position-dependent gamma correction. By the technique described, images displayed to a subject in functional MRI can be specified with high precision by a matrix of desired luminance values rather than by local grey value.

Brain Mapping↗
PubMed1999

Detection of caries with conventional digital imaging and tuned aperture computed tomography using CRT monitor and laptop displays.

OBJECTIVE: The purpose of this study was to compare the diagnostic performance of conventional digital images and tuned aperture computed tomography (TACT) slices in caries detection through use of cathode-ray tube monitor and laptop displays. STUDY DESIGN: Forty-two extracted posterior teeth were mounted and imaged with a direct digital radiography system. Conventional digital bitewing projections and TACT slices were acquired. Images were viewed on a high-resolution cathode-ray tube monitor and on an active-matrix laptop display. Eight observers assessed caries status of occlusal and proximal surfaces of the teeth using all combinations of image and display modality. Observers' assessments were compared with the results of histologic examination of tooth sections. Possible differences in receiver operating characteristic curve areas among displays, image modalities, observers, and surfaces were analyzed by means of analysis of variance. RESULTS: There was no statistically significant difference between the diagnostic performances provided by the cathode-ray tube monitor and laptop displays in caries detection (P = .588). In addition, the performances of digital images and TACT slices were not significantly different (P = .843). CONCLUSIONS: Modern active-matrix laptop displays provide diagnostic quality for caries detection comparable to that obtainable with cathode-ray tube monitors.

Analysis of Variance↗
PubMed2002

Evaluation of accuracy of computer-aided intraoperative positioning of endosseous oral implants in the edentulous mandible.

The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96 +/- 0.72 mm (range 0.0-3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.

Cadaver↗
PubMed1992

Visual increment and decrement threshold curves as a function of luminance range and noise in simulated computed tomographic scans.

OBJECTIVES: The effect of luminance range compression on the visual threshold of a target in a computed tomographic (CT) scan was investigated in eight experiments. METHODS: Both visual increment thresholds of a hot target and visual decrement thresholds of a cold target were obtained. Realistic noisy CT images simulating a scan reconstruction and partial volume blurring were tested as representative of complex medical images. Negative versions, high luminance versions, and noise-free versions of these CT images also were tested. RESULTS AND CONCLUSIONS: In all the noisy images, as the luminance range of the image was compressed, proportionately smaller physical luminance differences between the target and its local background were needed to reach visual threshold. However, the thresholds were the same in terms of the difference in CT numbers between target and background. Noise in terms of CT numbers sets the threshold for a wide range of display conditions. In the noise-free CTs, as the luminance range was compressed, the luminance differences between the target and background needed to reach threshold also decreased, but only marginally. However, in terms of CT numbers, the thresholds were increased.

Analysis of Variance↗
PubMed1992

A universal system for interactive image-directed neurosurgery.

Stereotactic methods confer great accuracy to intracranial target localization, but require strict adherence to a complex program of mechanical and computational maneuvers. A computerized, articulated, localizing 'arm' has been developed that frees the neurosurgeon of these constraints and provides a completely intuitive, 'user-friendly' interface. This universal system is independent of whatever localizing fiducial system is selected. The arm may be sterilized for intracranial use. A variety of intraoperative end effectors may be selected. The patient's CT/MR/PET scans are loaded into computer memory and a three-dimensional shaded surface wireframe diagram of the patient's head is displayed simultaneously with up to 3 independent sets of cross-referenced CT/MR/PET scan images on the intraoperative video screen. The arm's endpoint location and the directional vector are shown as cursors on the relevant scan slices, and change continuously as the surgeon moves the arm. Because the information is continuously updated, an unlimited number of targets and trajectories may be displayed throughout the operation. The arm has an ultimate design accuracy for end-point localization to within 0.1 mm throughout a target volume of 40 x 40 x 40 cm. The tested application accuracy of the first prototype model is 0.31 mm. In clinical use during 30 surgeries, its real-world application accuracy is 0.9 mm. This system provides stereotactic accuracy and universally compatible, intuitive, interactive operation.

Biopsy↗
PubMed1995

Image quality control for digital mammographic systems: initial experience and outlook.

This report presents (1) a broad topical review and a tutorial of the possibilities for image quality control (IQC) with digital systems, and (2) results and initial experience for IQC with two commercial digital imaging systems, but with limited discussion on any particular method. Digital imaging systems used for mammographically guided digital stereotactic breast biopsy were evaluated extensively at the University of Arizona. Measurements were made of linearity, sensitivity, signal-to-noise ratio, and square-wave modulation. Images of phantoms such as the American College of Radiology Accreditation Phantom and the contrast detail mammography Phantom were evaluated as well as images of the x-ray source's focal spot. The evaluation also included the cathode ray tubes for the imaging systems. The data collected show that digital imaging systems have an important advantage over film-screen systems because they provide a digital signal as output that can be used for quantitative analysis. As a result, IQC can become a much more quantitative discipline than presently practiced, providing more information on the imaging systems under evaluation, and providing better control over their properties during actual operation.

Computer Terminals↗
PubMed2001

Evaluation of a head-mounted display (HMD) in the performance of a simulated laparoscopic task.

BACKGROUND: Head-mounted display (HM) units are used in various industries, but they have been tried only recently in surgery. In this study, we evaluated whether a commercially available HMD would improve or impede a laparoscopic task-in this case, suturing. METHODS: Six participants performed a total of 120 laparoscopic suture knots in an experimental model. The Olympus FMD011 model with a two-dimensional image was used. The order of each task with or without the head display unit was random. The time to complete each knot was recorded, and the results were analyzed. RESULTS: The display unit prolonged the suturing times of the subjects by 10% (p < 0.04). CONCLUSIONS: In this experimental model, the HMD we utilized did not appear to improve laparoscopic suturing. More developments, such as improved depth perception and better resolution, may increase its usefulness for laparoscopic tasks.

Computer Simulation↗
PubMed1994

The effects of computer interface design on human postural dynamics.

The main objective of this study was to examine the effects of human-computer interface design on postural dynamics, i.e., changes in working postures and postural discomfort exhibited by operators of the computer-based remote bar coding (RBC) system. In addition, the effects of different work/rest schedules on postural dynamics were evaluated. Twelve subjects participated in the laboratory experiment, which consisted of twelve scenarios utilizing two cognitive task requirement factors, i.e., (1) information presentation mode, defined through the letter image preview on the computer screen (none or one preview image); and (2) the information processing mode, defined through the specific keying method (key all characters or key 5 digits only). The third experimental factor was the work/rest schedule (50 min work/10 min break, 2 h of work/15 min break, or flexible schedule). The results showed that requirements of human-computer interface design significantly affected the operators' postural dynamics. It was concluded that not only the physical, organizational, or psychosocial work environment characteristics, but also the cognitive task characteristics are important for assessment of postural effects in the VDT work. The relationship between interface design, mental workload and postural dynamics should be carefully considered in future studies aimed at optimizing the human-computer data entry tasks.

Adult↗
PubMed2001

Factors influencing optical 3D scanning of vinyl polysiloxane impression materials.

PURPOSE: Future growth in dental practice lies in digital imaging enhancing many chairside procedures and functions. This revolution requires the fast, accurate, and 3D digitizing of clinical records. One such clinical record is the chairside impression. This study investigated how surface angle and surface roughness affect the digitizing of vinyl polysiloxane impression materials. MATERIALS AND METHODS: Seventeen vinyl polysiloxane impression materials were digitized with a white light optical digitizing system. Each sample was digitized at 3 different angles: 0 degrees, 22.5 degrees, and 45 degrees, and 2 digitizer camera f-stops. The digitized images were rendered on a computer monitor using custom software developed under NIH/NIDCR grant DE12225. All the 3D images were rotated to the 0 degrees position, cropped using Corel Photo-Paint 8 (Corel Corp, Ottawa, Ontario, Canada), then saved in the TIFF file format. The impression material area that was successfully digitized was calculated as a percentage of the total sample area, using Optimas 5.22 image processing software (Media Cybernetics, LP, Silver Spring, MD). The dependent variable was a Performance Value calculated for each material by averaging the percentage of area that digitized over the 3 angles. New samples with smooth and rough surfaces were made using the 7 impression materials with the largest Performance Values. These samples were tested as before, but with the additional angle of 60 degrees. Silky-Rock die stone (Whip Mix Corp, Louisville, KY) was used as a control. RESULTS: The Performance Values for the 17 impression materials ranged from 0% to 100%. The Performance Values for the 7 best materials were equivalent to the control at f/11 out to a surface angle of 45 degrees; however, only Examix impression material (GC America Inc, Alsip, IL) was equivalent to the control at f/11/\16. At the 60 degrees surface angle with f/11/\16, the Performance Values were 0% for all the impression materials, whereas that for the control was 90%. The difference in the Performance Values for the smooth and rough surface textures was 7%, which was not significant. CONCLUSIONS: The digitizing performance of vinyl polysiloxane impression materials is highly material and surface angle-dependent and is significantly lower than the die stone control when angles to 60 degrees are included. It is affected to a lesser extent by surface texture.

Analysis of Variance↗
PubMed2002

The effect of typing posture on wrist extensor muscle loading.

High static loading of the forearm extensor musculature has been observed during keying tasks. To reduce the level of loading, one must first understand the contributing factors. A simulation of the human finger was used to determine muscle force contributions during a static index finger key press at several wrist postures. The planar model included active and passive muscle forces of the intrinsic and extrinsic finger muscles. The model was expanded to include the passive forces from the other fingers as well as the weight of the hand to determine the exertion required of the wrist extensor muscles to maintain the given wrist and finger postures. Model results indicated that greater than 25% of maximal exertion is required of the wrist extensors when the wrist is extended to 30. The increased moment contribution from passive forces of the extrinsic finger flexor muscles was responsible for the majority of the increased wrist extensor contribution as the wrist was extended. These findings are in relative agreement with previous electromyographic studies and may indicate a mechanism for forearm extensor pain in office workers. Potential applications of this research include ergonomic modeling of the upper limb to determine internal loads that may lead to work-related disorders.

Biomechanical Phenomena↗
PubMed2001

A mechanism for stop codon recognition by the ribosome: a bioinformatic approach.

Protein synthesis in ribosomes requires two kinds of tRNAs: initiation and elongation. The former initiates the process (formylmethionine tRNA in prokaryotes and special methionine tRNA in eukaryotes). The latter participates in the synthesis proper, recognizing the sense codons. Synthesis is also assisted by special proteins: initiation, elongation, and termination factors. The termination factors are necessary to recognize stop codons (UAG, UGA, and UAA) and to release the complete protein chain from the elongation tRNA preceding a stop codon. No termination tRNA capable of recognizing stop codons by their anticodons is known. The termination factors are thought to do this. In the large ribosomal RNA, we found two sites that, like tRNAs, contain the anticodon hairpin but with triplets complementary to stop codons. One site is hairpin 69 from domain IV; the other site is hairpin 89, domain V. By analogy, we call them termination tRNAs: Ter-tRNA1 and Ter-tRNA2, respectively, even though they transport no amino acids, and suggest that they directly pair to stop codons. The termination factors only aid in this recognition, making it specific and reliable. A strong argument in favor of our hypothesis comes from vertebrate mitochondria. They are known to acquire two new stop codons, AGA and AGG. In the standard code, these are two out of six arginine codons. We revealed that the corresponding anticodons, UCU and CCU, have evolved in Ter-tRNA1 of these mitochondria.

Base Sequence↗