C.A. Mitchell

A Comparative Study of Conventional Mammography Film Interpretations with Soft Copy Readings of the Same Examinations

An acceptable mammography film digitizer must provide high-quality images at a level of diagnostic accuracy comparable to reading conventional film examinations. The purpose of this study was to determine if there are significant differences between the interpretations of conventional film-screen mammography examinations and soft copy readings of the images produced by a mammography film digitizer. Eight radiologists interpreted 120 mammography examinations, half as original films and the other half as digital images on a soft copy work station. No radiologist read the same examination twice. The interpretations were recorded in accordance with the Breast Imaging Reporting and Data System and included other variables such as perceived image quality and diagnostic difficulty and confidence. The results provide support for the hypothesis that there are no significant differences between the interpretations of conventional film-screen mammography examinations and soft copy examinations produced by a mammography film digitizer.

SU‐FF‐I‐41: Effect of Room Setting On Object Dectectability for Two Different AMLCD Displays

Purpose: The purpose of this study was to estimate the effect of viewing room setup on the readers ability to detect subtle details in radiographicimages displayed on two different active matrix liquid crystal displays (AMLCD). Method and Materials: Two viewing rooms were used in the study: one of them having a standard setup with white ceiling, light walls and furniture, and other monitors. The other room was a specially designed with black walls and ceiling and no other equipment except the monitors under study. Two different monitors, a standard IBM flat panel T‐221 and an experimental high‐bright IBM flat panel T‐221 were used in this study. In order to evaluate the effect of the different viewing room setups on the results of image reading, a computer generated 11×11 test pattern with two circular objects in every square cell were used. Each object of the pattern is defined by two parameters: diameter (number of pixels used for its generation) and contrast (number of digital driving levels). Five medical physicists were requested to read these contrast‐detail patterns at three different room illuminances (0, 5 and 20 lux) and four different backgrounds surrounding the entire test pattern (0%, 5%, 20% and 50% of max luminance) on both monitors. Results: At all conditions (room illuminance and surround) and on both flat panels, reader performance was significantly better in the specially designed dark room than in the typical viewing room. Conclusion: Higher diagnostic quality is realized in the room specially designed to minimize reflections.

SU‐FF‐I‐73: Comparison of the Effects of Viewing Conditions and Viewing Angle On Object Dectectability for Different AMLCD Displays

Purpose: The ability to interpret images displayed on active matrix liquid crystal displays (AMLCD) can be influenced by factors such as display luminance, surrounding background, room illuminance and viewing angle. We have been investigating how these parameters influence reader scores with images featuring both small objects and low contrast as typically seen in mammography. We are in a position to make some comparisons between the results obtained with displays from two different manufacturers. Method and Materials: Reader studies were conducted using a computer generated contrast detail phantom alternately presented against a display background of selected luminance levels. Luminance was also measured at different viewing angles and at four selected room illuminance levels. Image scoring was performed at each combination of background level, viewing angle and room illuminance level. Results:Image scoring performance was interpreted using k values, which reflect the contrast and diameter of the objects detected in the images. The best image scoring results were obtained when viewing angles were kept small, and also when room illuminance was at the level of 5 – 10 lux. Better scoring results were also obtained when the image background luminance was adjusted to 5 – 20 % of maximum. These results differ from what had previously been found when evaluating displays from a different manufacturer. In this case the best scoring results were obtained at zero background and the room illuminance did not seem to have a significant effect on the results obtained when kept in the range of 0 – 20 lux. Conclusion: The results support the view that while it is advisable to keep the viewing angle to a minimum, it may be advisable also to adjust the room illuminance and monitor background luminance to specific levels which may be best suited for a particular AMLCD display.

Optimization of Reading Conditions for Flat Panel Displays

Task Group 18 (TG 18) of the American Association of Physicists in Medicine has developed guidelines for Assessment of Display Performance for Medical Imaging Systems. In this document, a method for determination of the maximum room lighting for displays is suggested. It is based on luminance measurements of a black target displayed on each display device at different room illuminance levels. Linear extrapolation of the above luminance measurements vs. room illuminance allows one to determine diffuse and specular reflection coefficients. TG 18 guidelines have established recommended maximum room lighting. It is based on the characterization of the display by its minimum and maximum luminance and the description of room by diffuse and specular coefficients. We carried out these luminance measurements for three selected displays to determine their optimum viewing conditions: one cathode ray tube and two flat panels. We found some problems with the applicationof the TG 18 guidelines to optimize viewing conditions for IBM T221 flat panels. Introduction of the requirement for minimum room illuminance allows a more accurate determination of the optimal viewing conditions (maximum and minimum room illuminance) for IBM flat panels. It also addresses the possible loss of contrast in medical images on flat panel displays because of the effect of nonlinearity in the dependence of luminance on room illuminance at low room lighting.