Most assessments of display performance are limited to studying the display quality for static images. However,
dynamic scenes constitute a large fraction of medical images and are becoming more widespread due to the
increase in the number of images to be interpreted. The image quality of a dynamic scene is affected by
the display's temporal characteristics and the human visual system's temporal response. We propose to use a
computational observer to understand the effect of image browsing speed in medical displays. We use a 3D cluster
lumpy background to study the effect of different browsing speeds using liquid crystal display (LCD) temporal
response measurements reported in our previous work. The image set is then analyzed by the computational
observer. This allows us to quantify the effect of slow temporal response of medical LCDs on the performance of
the anthropomorphic observer. Slow temporal response of the display device affects the lesion contrast and the
observer performance. Human visual system also adds to the complexity of image perception of dynamic scenes.
A human observer study was used to validate the computational observer results.
We report on the characterization of two novel probes for measuring display color without contamination from
other screen areas or off-normal emissions. The probes are characterized with a scanning slit method and a
moving laser and LED arrangement. The tails of the scans indicate the spread in signal due to light from
areas outside the intended measuring spot. A dual-laser setup suggests that color purity of the reading can be
maintained up to a few tens of millimeters outside of the measurement spot, and a dual-LED setup shows the
effects of secondary light emissions in the readings. The first design, color probe A, is then used to quantify
display color, maximum color difference, luminance uniformity, graylevel tracking, and angular color shifts of
medical liquid crystal displays and mobile displays.
We compare the image quality characteristics of state-of-the-art mobile display systems based on different types of
liquid crystal and organic light-emitting materials with respect to luminance and color, viewing angle, resolution,
temporal response, and reflectance. The results for a reflective liquid crystal display suggest that the changes
in angular contrast and color shifts are more severe than for other LCDs, particularly for medical LCDs, where
no color or grayscale inversion is present within the entire hemisphere of viewing directions. A prototype light-emitting
device showed a wide viewing angle and large small-spot contrast. Display reflectance and resolution
were affected by the additional touch-screen coatings. The methodology developed provides a framework for the
comparison of alternative technologies for display of diagnostic images in small portable devices.
Active-matrix liquid crystal displays (LCDs) are becoming widely used in medical imaging applications. With
the increasing volume of CT images to be interpreted per day, the ability of showing a fast sequence of images
in stack mode is preferable for a medical display. Slow temporal response of LCD display can compromise the
image quality/fidelity when the images are browsed in a fast sequence. In this paper, we report on the effect
of the LCD response time at different image browsing speeds based on the performance of a contrast-sensitive
channelized-Hotelling observer. A correlated stack of simulated cluster lumpy background images with a signal
present in some of the images was used. The effect of different browsing speeds is calculated with LCD temporal
response measurements established in our previous work. The image set is then analyzed by the model observer,
which has been shown to predict human detection performance in non-Gaussian lumpy backgrounds. This allows
us to quantify the effect of slow temporal response of medical liquid crystal displays on the performance of the
anthropomorphic observer. Slow temporal response of the display device greatly affects the lesion contrast and
observer performance. This methodology, after validation with human observers, could be used to set limits for
the rendering speed of large volumetric image datasets (from CT, MR, or tomosynthesis) read in stack-mode.
Liquid crystal displays (LCDs) are fast gaining ground over the cathode ray tube (CRT) displays in the medical display market. High performing LCDs are considered to have comparable or better performance than CRTs in displaying static images. However, LCDs are inferior to CRTs in displaying moving scenes due to their slow response. The response time provided by display manufacturers is typically measured while switching the LCD from black to white and white to black. This is usually not the longest response time. In reality, the transition time between different gray scales can be many times longer. In this paper we report preliminary work on measuring the gray level response time of LCDs and simulating luminance errors caused by slow transition between some gray levels. We first characterized the measuring system using a fast light-emitting diode (LED) to explore the accuracy and noise-filtering capability of the system. A 256x256 matrix of response time between different gray levels was then measured. Nearly half of the gray level transitions are much longer than the frame time (16.67~ms) of LCD displays. The longest response time was above 100~ms. When driving a display between these gray levels, the targeted gray level can't be achieved until many frame times. To understand how the slow response may affect the display's ability to render the desired image values, we calculated the achieved luminance based on the measured matrix. The results simulate the visual effect of displaying a moving object on the LCD monitors, and providing a reference for determining LCD performance.
We report progress in the development of polymer waveguides and devices for photonic applications in three areas: non-photolithographic techniques for polymer waveguide fabrication, bistability in laterally-coupled polymer microring resonators, and ultrafast photoconductive switches fabricated from semiconducting polymers. The non-photolithographic techniques for waveguide fabrication under development include laser milling with an excimer laser and programmable automatic dispensing of multimode polymer waveguides using an Essemtech automatic dispenser. Asymmetric diffraction gratings fabricated using phase masks and the interference of two excimer laser beams have exhibited concentration of optical power into the 1st diffraction order. Polymer micro-ring resonators laterally coupled to a bus line were fabricated by lithography from benzocyclobutene with radii as small as 10 μm and free spectral ranges on the order of 20 nm. These devices exhibit bistability in the frequency domain which can arise from thermal or nonlinear optical changes in refractive index and that may have application for all-optical switching. Metal-polymer-metal switches fabricated with interdigitated electrodes in an inverted structure exhibited fast transient photoconductive pulsewidths under 20 ps in response to femtosecond pump laser pulses, but the measurement was bandwidth limited by the oscilloscope. Here we report pump-probe measurements that indicate carrier lifetimes on the order of 2 ps.