One of the advantages of digital mammography is to display mammograms on softcopy (electronic displays). Softcopy display of mammography is challenging because of the spatial and contrast resolution demands present in mammograms. We have designed and developed a softcopy mammography display application, Mammoview, which is capable of allowing radiologists to read mammograms as quickly and as accurately as they can on film alternators. We review the studies using Mammoview to elucidate the requirements of a successful softcopy display state. The design and development of the Mammoview softcopy display station are described. Results of several studies using Mammoview are reviewed, including subjective feedback from RSNA demonstrations, and clinical studies measuring performance in terms of speed and accuracy. Additional analysis of user interactions and user feedback is used to study the successes and shortcomings of mammography display stations like Mammoview.
Recent standards and upcoming guidelines are beginning to address the issue of image display quality, and image representation consistency. The DICOM standard has recently been extended to address the consistency of the grayscale presentation of images (DICOM part 14, Grayscale Standard Display Function), and it also addresses the consistency of presentation of associated information (text, graphics, annotation, zoom, rotation) with the recently approved addition of the Softcopy Presentation State, i.e. DICOM Supplement 33). These two new standards provide image consistency between viewing stations and printers independent of the manufacturer, brand and/or type. These services have been demonstrated at ECR, RSNA, and are also part of the continuing IHE demonstrations. In addition to the DICOM standards, work is being done by AAPM Task Group 18 to address the issue of Quality Control and Quality Assurance for electronic displays.
KEYWORDS: Image processing, Mammography, Digital mammography, Breast, Digital image processing, Printing, Image enhancement, Algorithm development, Digital imaging, Standards development
One of the advantages of digital mammography is the ability to acquire a mammography image with a larger contrast range. With this advantage comes the tradeoff of how to display this larger contrast range. Laser printed film, and video display both have smaller dynamic ranges than standard mammography film-screen systems. This work examines performance and preference studies for display processing methods for digital mammograms.
ACR/NEMA has released for public comment the display function standard document. This standard, produced by ACR/NEMA Working Group XI, has been developed in order to solve the problem of standardizing the response of grey scale display systems. This paper presents a methodology proposed in the display function standard for quantitatively calculating the conformance of a display device to the standard display function based on statistical measures, which are referred to as the linearization uniformity measures (LUM). There are two LUM measures, R2, or global uniformity, and root mean square error, or local uniformity. The derivation of both measures is described. Two additional measures that provide a better description of the achievable dynamic range of a display device than simply its luminance range are also described, the theoretical number of just noticeable differences (JNDS) of the display, and the realized number of JNDS of the display. Currently available medical image display systems are analyzed using each of these measures, to examine their shortcomings, and suggest what changes might be desirable in the design of medical image display systems in the future.
The purpose of this study was to determine the interaction of the luminance range of the display system with the feature detection rate for detecting simulated masses in mammograms. Simulated masses were embedded in cropped 512 by 512 portions of mammograms digitized at 50 micron pixels, 12 bits deep. The masses were embedded in one of four quadrants in the image. An observer experiment was conducted where the observer's task was to determine in which quadrant the mass is located. The key variables involved in each trial included the exposition of the mass, the contrast level of the mass, and the luminance of the display. The contrast of the mass with respect to the background was fixed to one of four selected contrast levels. The digital images were printed to film, and displayed on a mammography lightbox. The display luminance was controlled by the placing neutral density films between the laser printed films of mammogrpahic backgrounds and the lightbox. The resulting luminances examined in this study ranged from a maximum of 10 ftL to 600 ftL. Twenty observers viewed 20 different combinations of the 5 neutral density filters with the 4 contrast levels, for a total of 400 observations per observer, and 8000 observations overall. An ANOVA analysis showed that there was no statistically significant correlation between the luminance range of the display and the feature detection rate of the simulated masses in mammograms. None of the luminance display ranges performed better than any of the others.
Perceptual linearization has been advocated for medical image presentation, both for the faithful reproduction of images, and for standardizing the appearance across different display devices. It is currently being proposed as the standard display function for medical image presentation by ACR/NEMA working group 11 (display function standard). At this time, studies have not been made to evaluate how close existing display systems are to being perceptually linearized. This paper presents a methodology for quantitatively calculating the perceptual linearity of a display device based on a statistical measure, the linearization uniformity measure (LUM), of standard deviation of the ratio of contrast thresholds of the display system versus the contrast thresholds of the human observer. Currently available medical image display systems are analyzed using LUM metric, and their pre-linearization and post-linearization results are compared with that of the desired human observer response curve. We also provide a better description of the achievable dynamic range of a display device, based on the three quantitative measures: the standard deviation of the contrast threshold ratios, the mean of the contrast threshold ratios, and the number of DDL steps used.
Real-time volume rendering of medical image datasets on commercial hardware became possible in 1993. We have developed an application, SeeThru, that allows real-time volume visualization under the interactive control of the physician. This ability enables the physician to look inside of the patient's body to visually comprehend the information from radiological procedures, resulting in improved treatment planning. We report on preliminary results from two areas: (1) cardiothoracic surgical planning from spiral computed tomography (CT) and (2) staging of breast cancer from magnetic resonance imaging (MRI). We compared different rendering methods (projection, maximum intensity projection, opacity blended, and opacity combined with gradient blended) and chose opacity blending as the most effective for both applications. In cardiothoracic surgical planning experiment we found the ability to interactively control and view 3D direct volume visualizations resulted in improvements in surgical plans and in the surgeon's confidence in the plan. In the MR breast experiment we found that 3D visualization of the subtraction images improved comprehension and identification of tumor lesions difficult to appreciate on mammograms. Overall, we believe that interactive, real-time volume rendering significantly adds to clinical understanding and improves treatment planning for the patient.
KEYWORDS: Image segmentation, Visualization, 3D image processing, 3D visualizations, Surgery, Image processing, Medical imaging, Radiation oncology, 3D displays, Kidney
Object definition is an increasingly important area of medical image research. Accurate and fairly rapid object definition is essential for measuring the size and, perhaps more importantly, the change in size of anatomical objects such as kidneys and tumors. Rapid and fairly accurate object definition is essential for 3D real-time visualization including both surgery planning and Radiation oncology treatment planning. One approach to object definition involves the use of 3D image hierarchies, such as Eberly's Ridge Flow. However, the image hierarchy segmentation approach requires user interaction in selecting regions and subtrees. Further, visualizing and comprehending the anatomy and the selected portions of the hierarchy can be problematic. In this paper we will describe the Magic Crayon tool which allows a user to define rapidly and accurately various anatomical objects by interacting with image hierarchies such as those generated with Eberly's Ridge Flow algorithm as well as other 3D image hierarchies. Preliminary results suggest that fairly complex anatomical objects can be segmented in under a minute with sufficient accuracy for 3D surgery planning, 3D radiation oncology treatment planning, and similar applications. Potential modifications to the approach for improved accuracy are summarized.
The perceptual linearization of video display monitors plays a significant role in medical image presentation. First, it allows the maximum transfer of information to the human observer. Second, for an image to be perceived as similarly as possible when seen on different displays, the two displays must be standardized. Third, perceptual linearization allows us to calculate the perceived dynamic range of the display device, which allows comparison of the maximum inherent contrast resolution of different devices. This paper provides insight into the process of perceptual linearization by decomposing it into the digital driving level to monitor luminance relationship, the monitor luminance to human brightness perception relationship, and the construction of a linearization function derived from these two relationships. We compare and contrast the results of previous work with recent experiments in our laboratory and related work in vision and computer science. Based on these analyses we give recommendations for using existing methods when appropriate, and propose new methods or suggest additional work where the current methods fall sort. Finally, we summarize the significant issues from all three component areas.
In this paper, we consider the nature of mental workload and how one might determine whether mental workload effects the potential accuracy of a particular medical image display method. Then we detail observer experiments we have conducted evaluating electronic display of CT images. While detailing these results, we will focus on the evidence we have accumulated which suggests that mental workload has a significant influence on workstation accuracy and interpretation speed. These results suggest that experiments involving interpretation tasks that are very similar to those in the clinic are needed in addition to conventional ROC analysis when evaluating the effectiveness of a new display device or method.
KEYWORDS: Visualization, RGB color model, Associative arrays, Medical imaging, Displays, Data modeling, Magnetic resonance imaging, Roentgenium, Image visualization, Computed tomography
We have developed a technique for visualizing medical image data sets that have multiple values at each physical location. These data sets are increasingly common as physicians attempt to correlate between modalities (for instance, CT and nuclear medicine, MR and PET, CT and MR) as well as within modalities (for instance, MR metabolic and anatomical scans). Our technique, termed 'isoluminance', is designed primarily for displaying sets that have two scalar values associated with each physical (x,y) location on a two dimensional scan. A perceptually uniform luminance scale is used to encode one dimension. At each step of the luminance scale a set of isoluminant hue steps are used to encode the other dimension. The hue scale is chosen to be perceptually uniform and as 'natural' as possible. The resulting data set can then be displayed as a single image on a color display. We have found observers using our technique are able to comprehend both of the data sets, to understand relationships between the data sets, and, when using interactive manipulation techniques, are able to select or label specific features of the data set.
KEYWORDS: Radiology, Mica, Medicine, Image quality, Image processing, Sun, Visualization, Information visualization, Telecommunications, Control systems
As hospitals geographically spread and radiologic services are required in remote locations, the radiologist increasingly must conduct a remote practice. Rapid image transmission from the remote site to the radiologist is important but only half the problem. First, the radiologist may need to view and discuss the images with the technologist to verify image quality or to specify the location of follow-up images. Second, the radiologist may need to discuss the case with another radiologist for a second opinion or for the advice of a sub-specialist. Third, and most importantly, the radiologist may need to discuss the case with the referring physician to better understand the text data, clinical history, and referring physician's clinical questions and concerns, and to better convey the location and extent of the clinical findings. In this paper we detail the requirements for a remote consultation workstation, present previous work on remote computer interaction, and describe the FilmPlane remote consultation workstation in detail. We then discuss the MICA medical communications project in which FilmPlane will be used for a remote consultation study between the UNC family medicine clinic and the main hospital 1/2 mile away.
We are investigating how radiologists's readings of standard intensity windowed (IW) chest computed tomography (CT) films compare with readings of the same images processed with contrast limited adaptive histogram equalization (CLAHE). Previously reported studies where CLAHE has been tested have involved detection of computer generated targets in medical images. Our study is designed to evaluate CLAHE when applied to clinical material and to compare the diagnostic information perceived by the radiologists from CLAHE processed images to that from the conventional IW images. Our initial experiment with two radiologists did not yield conclusive results, due in part, to inadequate observer training prior to the experiment. The initial experimental protocol was redesigned to include more in-depth training. Three new radiologist observers were recruited for the follow-up study. Results from the initial study are reviewed and the follow-up study is presented. In the new study we find that while CLAHE and IW are not statistically significantly different overall, there are specific clinical findings where the radiologists were less comfortable reading CLAHE presentations. Advantages and disadvantages of using CLAHE as a replacement or as an adjunct to IW are discussed.
KEYWORDS: Mammography, Breast, Radiology, Image resolution, Medical imaging, Picture Archiving and Communication System, Computed tomography, Breast cancer, Tissues, Cancer
For the last four years, the UNC FilmPlane project has focused on constructing a radiology workstation facilitating CT interpretations equivalent to those with film and viewbox. Interpretation of multiple CT studies was originally chosen because handling such large numbers of images was considered to be one of the most difficult tasks that could be performed with a workstation. The authors extend the FilmPlane design to address mammography. The high resolution and contrast demands coupled with the number of images often cross- compared make mammography a difficult challenge for the workstation designer. This paper presents the results of preliminary work with workstation interpretation of mammography. Background material is presented to justify why the authors believe electronic mammographic workstations could improve health care delivery. The results of several observation sessions and a preliminary eyetracker study of multiple-study mammography interpretations are described. Finally, tentative conclusions of what a mammographic workstation might look like and how it would meet clinical demand to be effective are presented.
An interpretation report, generated with an electronic viewbox, is affected by two factors: image quality, which encompasses what can be seen on the display, and computer human interaction (CHI), which accounts for the cognitive load effect of locating, moving, and manipulating images with the workstation controls. While a number of subject experiments have considered image quality, only recently has the affect of CHI on total interpretation quality been measured. This paper presents the results of a pilot study conducted to evaluate the total interpretation quality of the FilmPlane2.2 radiology workstation for patient folders containing single forty-slice CT studies. First, radiologists interpreted cases and dictated reports using FilmPlane2.2. Requisition forms were provided. Film interpretation was provided by the original clinical report and interpretation forms generated from a previous experiment. Second, an evaluator developed a list of findings for each case based on those listed in all the reports for each case and then evaluated each report for its response on each finding. Third, the reports were compared to determine how well they agreed with one another. Interpretation speed and observation data was also gathered.
Image Perception, Observer Performance, and Technology Assessment
16 February 2005 | San Diego, California, United States
Image Perception, Observer Performance, and Technology Assessment
18 February 2004 | San Diego, California, United States
Image Perception, Observer Performance, and Technology Assessment
19 February 2003 | San Diego, California, United States
Course Instructor
SC096: Image Quality Clinic
This one-day clinic discusses the details of image quality in a soft and hardcopy environment. The theory and background of the components that impact image presentation and quality are discussed. It shows how to implement a QA/QC program in your facility while providing test images and tools. This is a hands-on class and bringing a laptop is highly recommended. All of the course materials, related documents, and demonstrations are provided on CD-ROM. Several of the demonstrations are for the attendees to do on their laptops. There are a couple of high quality viewing systems available to get hands-on experience with the impact of calibration and adjustment.
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