Syfte: Att ta reda på hur lång livslängd en bildplatta har avseende slitage och bildkvalité.Material och metod: Tre fabriksnya bildplattor användes för att undersöka hur en enskild faktor i arbetsgången för bildgenerering påverkar bildkvalitén. Den första plattan exponerades och skannades 300 gånger. Platta nummer två användes för att undersöka effekten av totalt 300 av- och påtagningar i en frigolithållare, och platta tre användes för motsvarande test av en plasthållare. Exponering skedde utan patient och mot en neutral bakgrund. För samtliga plattor togs i initialskedet en referensbild, och resulterande bilder från testerna granskades i Planmeca Romexis 3.8 och bedömdes enligt en skala 0-3. Plattorna i sig granskades även okulärt, och test av uniformitet gjordes av referensbild och bild 300 i serie 1 med hjälp av ImageJ. Resultat: Samtliga bilder från samtliga plattor bedömdes vara likvärdiga med referensbild. Vid okulär granskning var reporna klart mer uttalade hos den platta som skannats 300 gånger, men reporna återfanns endast på den sida som ej är avsedd att exponeras. Test av uniformitet fann ingen skillnad mellan referensbild och bild nr 300 i serie 1. Slutsats: Studien visar att varken röntgenexponering, skanning eller av- och påtagning i hållare av två olika slag har någon inverkan på bildkvalité efter 300 upprepningar då momenten gjordes var för sig. Vi konkluderar att plattan sannolikt är som mest sårbar då den placeras intraoralt, och föreslår att alla moment gjorda i följd delvis kan svara för den reduktion av bildkvalité som observerats i andra studier. / Aim: To determine the longevity of photostimulable storage phosphor plates (PSPs) with respect to wear and image quality. Method: Three brand new PSPs were used to assess how a solitary factor in the picture generation process affects the picture quality. The first plate was exposed and scanned 300 times. Plate number two was used to assess the effect of mounting and demounting the plate 300 times onto a holder made of styrofoam, and the third plate was used for a corresponding test with a plastic holder. A flat surface was exposed and no patients were involved. A reference picture was taken initially for each plate, and the resulting pictures from the tests were viewed using Planmeca Romexis 3.8 and were evaluated on a scale from 0-3. The individual plates also underwent ocular inspection, and a uniformity test was performed on the first and last picture taken with plate 1, using ImageJ. Results: Each picture from each plate was deemed equivalent to the reference picture. The ocular inspection revealed a more distinct band of scratches on the plate that was scanned the most, although the scratches were only found on the side not meant to receive exposure. No difference in uniformity was found between the first and last picture taken using plate 1. Conclusion: X-ray exposure, scanning and mounting and demounting of PSPs onto holders of two different kinds do not affect the picture quality after 300 repetitions when done separately. We conclude that the plate is likely most susceptible to wear when placed intraorally, and suggest that all the steps made in succession can partly account for the reduction in picture quality observed in other studies.

The concept of "visual fatigue" has been studied for 70 years or more. In that time, no single metric of measuring visual fatigue nor one agreed-upon set of tasks to induce visual fatigue has been settled upon. Not even a robust definition of visual fatigue has been established. This research worked to solve some of those problems. This research first set out to develop an index of visual fatigue that could be used effectively in quantifying the subjective experience of visual fatigue. Then it sought to create a set of measurable tasks, representative of office work, that would induce visual fatigue. Taking these two developments, an experiment using human participants was conducted to validate these developments and work toward solving two issues in the visual fatigue field: how visual display technology and ambient illumination affect the onset of visual fatigue. A 4x4 within-subjects design was developed and executed to study how these two independent variables affected ratings of visual fatigue, performance on the task battery, subjective image quality judgments, and contrast sensitivity shifts. Two cathode ray tube (CRT) and two active-matrix LCD (AMLCD) monitors were used in this study. While many instances of the monitors as a whole caused significant differences in reports of visual fatigue, performance, subjective image quality, and contrast sensitivity loss, only a slight effect of display technology was found. Four of eleven visual fatigue and two of eight subjective image quality dimensions showed that the LCD monitors induced more visual fatigue and were rated poorer than the CRT monitors. Ambient illumination levels of 0, 300, 600, and 1200 lux affected all four groups of dependent variables. On the whole, lighting caused visual fatigue, with "watery eyes" and "glare from lights" being adversely affected by brighter lighting. The 0 and 1200 lux were associated with the worst performance, while 300 lux was associated with the best performance. Subjective image quality was affected by lighting, with increasing lighting causing bothersome screen reflections and more temporal (e.g., flicker and jitter) distortions; 600 lux induced more reports of image sizing anomalies. Finally, it caused significantly worse shifts at the 6.0 c/deg spatial frequency on the contrast sensitivity test. The data show that lighting of 300 lux is the best of these four illumination levels. The results of this study not only contribute to the body of research in the areas of display technology and ambient illumination, but several developments of this research are offered to the research community: a complete survey metric of visual fatigue, a standardized battery of tasks for studying visual fatigue and image quality, and a comprehensive subjective image quality survey. / Ph. D.

Within the home environment there exits a host of digital color imaging (DCI) system configurations. The combination of devices and software at the consumer's desktop with devices and services at a remote location (e.g., Print at Kodak), creates a complex interaction of device, contextual, and observer characteristics. In particular, the cathode-ray tube (CRT) display has the potential to influence consumers' perceptions of image quality and their subsequent image manipulation activities. Depending on the inherent color bias and apparent contrast of the CRT, extensive image manipulation may occur, significantly altering the digital values of the image. Output generated by a remote printer will reflect any image manipulation undertaken by the consumer. If manipulation was extensive, what the consumer receives from a remote printer will appear quite different from the softcopy version and thus, may be deemed unacceptable. This research was designed to address the softcopy-hardcopy matching issues that arise from the home DCI system configuration just described. The primary study examined how the CRT display influenced perceived color quality of photographs generated at two points in a DCI system; on-screen photographs (softcopy) and photographic quality prints (hardcopy). CRT gamma, color temperature, and excitation purity were manipulated using an orthogonal, blocked, central composite design. Twenty-two Eastman Kodak Company employees viewed 6 photographs under each of the 15 CRT conditions. Participants rated the color quality of each softcopy photograph, then were given an opportunity to edit color balance, brightness, and contrast for each photograph. The edited photos were printed and rated once again for color quality and acceptability. Results indicated that monitor calibration influenced perceived softcopy color quality, softcopy editing behavior, and subsequent perceived hardcopy color quality. Perception of softcopy color quality ratings was determined predominantly by the CRT gamma level. Participants responded to CRT color balance differences through their editing behavior. In some cases, edits were large enough to significantly and negatively impact perceived hardcopy color quality. Gamma in particular, was the most significant predictor of hardcopy color quality ratings and rejection rates. Additional differences were observed between first- and third-party photographs. Results from this research may be applied to the development of monitor calibration tools, scene balancing algorithms, and software, for the purpose of accommodating consumer image manipulation behavior, in the context of the home DCI system presented herein. / Ph. D.

The objectives of this research were (1) to develop scales of preferred image sharpness for thermal dye transfer prints and (2) to relate these scales to an objective measurement of image quality. Interval scales were developed using two different indirect scaling techniques, paired comparison and rank ordering, for three groups of participants (novice photographers, advanced amateur photographers, and Kodak image quality experts). Differences between scales developed through the separate scaling procedures were minor, suggesting that either procedure would produce a reliable and valid interval scale. Given the time required to perform the method of paired comparisons, the method of rank ordering would likely be the preferred procedure. The results from multiple range tests of the interval scales found that higher levels of image sharpening (filter levels 1.5x to 2.5x) were generally preferred. However, for some conditions, particularly the portrait, lower levels of sharpening were generally preferred. While it appears that the preferred level of image sharpness may be somewhat dependent upon scene content, participants always preferred a small amount of sharpening to none at all. For all conditions examined, stimuli that received no sharpening were the least preferred. In relating interval scales to an objective measure of image quality, scale values developed from within a level of addressability were highly correlated with values of modified MTFA for all participant groups. These correlations show that a strong relationship exists between preferred levels of image sharpness and increasing levels of luminance modulation for edges in thermal prints. However, values of modified MTFA were not well correlated with interval scale values developed from experts participants for the between levels of addressability portion of the experiment. Values of MTFA were considered modified due to limits that were imposed on the bounds of integration. These results suggest that the preferences of experts may not represent those of the average consumer for desired levels of thermal print sharpness. / Ph. D.

This dissertation research had three primary objectives. The first was to develop and evaluate a metric of image quality that incorporates a model of suprathreshold contrast and is based upon the perceived magnitude of suprathreshold contrast. The second objective was to determine the effects that common display characteristics, such as MTF shape, noise, and field of view, have on a display observer's ability to perceive egocentric motion from a display. The third and final objective was to provide a discussion of the use of image quality metrics for the evaluation of displays that are designed to facilitate motion perception. To meet these objectives, two experiments were conducted. The first experiment investigated the effects of the display Field of View, Dynamic Contrast Range, Noise Level, and Bandwidth on perceived image quality. The second study investigated the effects of these same display parameters as well as the effect of terrain type on observers’ sensitivity to changes in the speed of image motion. Existing visual psychophysical data were used to propose the two additional image quality metrics, the Perceived Contrast Magnitude (PCM) and the Weighted Perceived Contrast Magnitude (WPCM). Each of these metrics provides some additional model parameters to the Modulation Transfer Function Area (MTFA). However, based upon the studies that were conducted in this dissertation, it appears that the Integrated Contrast Sensitivity (ICS) and Square Root Integral (SQRI) provide significantly better estimates of perceived image quality than do MTFA, PCM, or WPCM. Results indicate that the display parameters of Bandwidth, Field of View, and Noise Level, plus several interactions significantly influenced the observers’ sensitivity to changes in the speed of images. One interaction indicated that observers were more sensitive to changes in the speed of images when the scene contained a lot of contextual information or when the scene was viewed through a display with reasonably high bandwidth and low noise level. However, when the bandwidth of the system was decreased, the noise level was increased, and the contextual information in the image was reduced, the observer's sensitivity to changes in motion was degraded when viewing the image through a small field of view display (20 deg) but it was not degraded when viewing the image through a larger field of view display (47 deg). Based upon the evidence collected in this dissertation, it appears that displays designed to support motion perception should have a relatively large field of view with partitions to facilitate relative motion perception. The factors of Dynamic Contrast Range and Field of View were shown to have different effects on the perception of image quality than they have on the perception of changes in the speed of an image. Therefore, the use of image quality metrics for the evaluation and design of displays that must support the veridical perception of motion should be questioned. Instead, it appears that a task specific evaluation technique should be developed for the evaluation of these displays. / Ph. D.

The effects of physical image quality on reading and on perceived image quality from CRT and hard copy were studied in this experiment. The results showed that as the image quality of a display increased, indicated by an increase in the value of the MTFA, the reading speed increased and subjective image quality V; ratings increased. This change in reading speed and perceived image quality occurred in the hard copy as well as in the soft copy condition. Image quality, therefore, is concluded to be the major determinant of subjects' performance with respect to displayed information. This implies that if the image quality the displayed text ls the same on the display techniques used, subjects will read from CRT displays as fast as from hard copy displays. / Master of Science

Image compression reduces the amount of space necessary to store digital images and allows quick transmission of images to other hospitals, departments, or clinics. However, the degradation of image quality due to compression may not be acceptable to radiologists or it may affect diagnostic results. A preliminary study was conducted using several chest images with common lung diseases and compressed with JPEG and wavelet techniques at various ratios. Twelve board-certified radiologists were recruited to perform two types of experiments. In the first part of the experiment, presence of lung disease, confidence of presence of lung disease, severity of lung disease, confidence of severity of lung disease, and difficulty of making a diagnosis were rated by radiologists. The six images presented were either uncompressed or compressed at 32:1 or 48:1 compression ratios. In the second part of the experiment, radiologists were asked to make subjective ratings by comparing the image quality of the uncompressed version of an image with the compressed version of the same image, and judging the acceptability of the compressed image for diagnosis. The second part examined a finer range of compression ratios (8:1, 16:1, 24:1, 32:1, 44:1, and 48:1). In all cases, radiologists were able to judge the presence of lung disease and experienced little difficulty diagnosing the images. Image degradation perceptibility increased as the compression ratio increased; however, among the levels of compression ratio tested, the quality of compressed images was judged to be only slightly worse than the original image. At higher compression ratios, JPEG images were judged to be less acceptable than wavelet-based images but radiologists believed that all the images were still acceptable for diagnosis. These results should be interpreted carefully because there were only six original images tested, but results indicate that compression ratios of up to 48:1 are acceptable using the two medically optimized compression methods, JPEG and wavelet techniques. / Master of Science

No / Neonatal chest radiography is a frequently performed diagnostic examination, particularly in preterm infants where anatomical and/or biochemical immaturity impacts on respiratory function. However, the quality of neonatal radiographic images has been criticized internationally and a prevailing concern has been that radiographers (radiologic technologists) fail to appreciate the unique nature of neonatal and infant anatomical proportions. The aim of this study was to undertake a retrospective evaluation of neonatal chest radiography image acquisition techniques against key technical criteria. Methods Hundred neonatal chest radiographs, randomly selected from all those acquired in 2014, were retrospectively evaluated. Inclusion criteria for radiographs acquisition were as follows: anterior-posterior supine; within 30 days of birth; and with all preprocessed collimation boundaries visible. Image evaluation was systematically undertaken using an image assessment tool. To test for statistical significance, Student's t-test, χ2 test, and logistic regression were undertaken. Results Only 47% of the radiographs were considered straight in both upper and lower thoraces. The cranial collimation border extended beyond the upper border of the third cervical vertebra in 30% of cases, and the caudal border extended below the lower border of the first lumbar vertebra in 20% of cases, suggesting high possibility of neonatal overirradiation. Upper thorax rotation was significantly associated with head position (χ2 = 10.907; P < .001) as has been stated in many published textbooks internationally, but arm position had no apparent influence on rotation of the upper thorax (χ2 = 5.1260; P = .275). Birth weight was associated with accurate midline centering of central ray (logistic regression; OR = 1.0005; P = .009; CI, 1.00139–1.000957) with greater accuracy observed in images of neonates with higher birth weight. Conclusion This study has highlighted areas for neonatal chest radiography improvement. Importantly, the findings bring into question commonly advocated radiographic techniques relating to arm positioning and assessment of rotation while confirming the importance of other technical factors. These findings begin the work toward developing the evidence base to underpin neonatal chest radiograph acquisition, but further prospective work and multicenter/multinational data comparison are required to confirm the findings.

Yes / Objectives: This study aimed to determine the impact on radiation dose and image quality of a new cardiac interventional X-ray system for trans-catheter aortic valve implantation (TAVI) patients compared to the previously-used cardiac X-ray system. Methods: Patient dose and image data were retrospectively collected from a Philips AlluraClarity (new) and Siemens Axion Artis (reference) X-ray system. Patient dose area product (DAP) and fluoroscopy duration of 41 patient cases from each X-ray system were compared using a Wilcoxon test. Ten patient aortograms from each X-ray system were scored by 32 observers on a continuous scale to assess the clinical image quality at the given phase of the TAVI procedure. Scores were dichotomised by acceptability and analysed using a Chi-squared test. Results: Significant reductions in patient dose (p<<0.001) were found for the new system with no significant change in fluoroscopy duration (p=0.052); procedure DAP reduced by 55%, fluoroscopy DAP by 48% and “cine” acquisition DAP by 61%. There was no significant difference between image quality scores of the two X-ray systems (p=0.06). Conclusions: The new cardiac X-ray system demonstrated a very significant reduction in patient dose with no loss of clinical image quality. Advances in Knowledge: The huge growth of TAVI may impact on the radiation exposure of cardiac patients and particularly on operators including anaesthetists; cumulative exposure of interventional cardiologists performing high volume TAVI over 30-40 years may be harmful. The Phillips Clarity upgrade including improved image enhancement and optimised X-ray settings significantly reduced radiation without reducing clinically acceptable image quality.

Yes / This study aimed to determine whether a reduction in radiation dose was found for percutaneous coronary interventional (PCI) patients using a cardiac interventional x-ray system with state-of-the-art image enhancement and x-ray optimization, compared to the current generation x-ray system, and to determine the corresponding impact on clinical image quality. Patient procedure dose area product (DAP) and fluoroscopy duration of 131 PCI patient cases from each x-ray system were compared using a Wilcoxon test on median values. Significant reductions in patient dose (p ≪ 0.001) were found for the new system with no significant change in fluoroscopy duration (p ¼ 0.2); procedure DAP reduced by 64%, fluoroscopy DAP by 51%, and “cine” acquisition DAP by 76%. The image quality of 15 patient angiograms from each x-ray system (30 total) was scored by 75 clinical professionals on a continuous scale for the ability to determine the presence and severity of stenotic lesions; image quality scores were analyzed using a two-sample t -test. Image quality was reduced by 9% (p ≪ 0.01) for the new x-ray system. This demonstrates a substantial reduction in patient dose, from acquisition more than fluoroscopy imaging, with slightly reduced image quality, for the new x-ray system compared to the current generation system. / Philips Healthcare (the Netherlands)