Digital Radiography Image Quality Image Presentation, Processing Considerations, and Reading Environment
Display workstations used for the official interpretation of large-matrix systems should be capable of the following: bringing an image up on the workstation in 3 seconds or less; selection of image sequence and display format; flexible hanging protocols tailored to user preferences, with proper labeling and orientation of images; fast and easy navigation between new and old studies; rotating or flipping the images, provided that the labeling of patient orientation is preserved; and accurately associating the patient and study demographic information with the images of the study.
The total number of images acquired in a study needs to be accessible during interpretation. Although they need not all be displayed simultaneously, the use of dual monitors to display as many as possible is desirable. Clinically relevant technical parameters of the acquired image data should be accessible (eg, milliamperes, kilovolts, bit depth, exposure time, and matrix size). It is imperative that the exposure value be displayed on the picture archiving and communication system image to assess technique for dose, quality, and feedback to technologists.
Window and level adjustment tools must be available, because the full dynamic range of most images cannot be viewed on display devices with optimal contrast in all regions. Preset window and level settings (eg, bone or lung windows using set lookup-table transformations) are recommended to increase the speed of user interaction with the display device. It is recommended that the prior application of an irreversible compression ratio, processing, or cropping be noted in the image record.
Zoom (magnification) and pan (roaming) functions capable of meeting guidelines for display at the originally acquired spatial resolutions should be used rather than the user moving closer to the display. Calculating and displaying accurate linear measurements and pixel value determinations (mean and standard deviation) in values appropriate for the modality (eg, Hounsfield units for computed tomographic [CT] images) should be calculated and displayed if those data are available and can be calibrated to the acquisition device.
Most manufacturers apply processing algorithms (which are often proprietary) to optimize image quality, so it is necessary that the nature of these processing steps be made clear to users. It also is necessary to define what is considered for-processing (ie, raw image data before proprietary processing) vs for-presentation (ie, after some processing has been applied) data. Once the image data are transferred to the viewing workstation, they can be further processed using such tools as edge enhancement, histogram equalization, and other grayscale adjustments. Whether these tools actually improve diagnostic accuracy or simply improve the subjective appearance of images deserves further study.
Computer-aided detection (CAD) and computer-aided diagnostic tools for a variety of images and modalities (eg, nodule detection in computed radiographic and CT chest images, polyp detection in CT colonoscopy) are increasingly being approved by the Food and Drug Administration for routine clinical use. In general, these tools have been shown to enhance the performance of radiologists, although the effect may be lower for more experienced and specialized radiologists than for generalists. It is recommended that all CAD and computer-aided diagnostic algorithms begin with the for-processing data rather than the for-presentation data, because many of the algorithms already do a significant amount of image processing. The for-presentation data may alter the effectiveness of the CAD algorithms. It is recommended that radiologists using CAD understand what the CAD and computer-aided diagnostic tools are capable of doing, particularly with reference to their sensitivity and specificity, so that they can better judge the validity of the CAD prompts.
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The design of the digital reading room can generally influence not only the comfort and fatigue levels of radiologists but also interpretation accuracy. Viewing conditions should be optimized by controlling reading room lighting to eliminate reflections on the monitor and lowering the ambient lighting level as much as feasible. Ambient lights should not be turned off completely nor turned up completely. About 25 to 40 lux is generally sufficient to avoid most reflections and still provide sufficient light for the visual system to adapt to the surrounding environment and the displays. Incandescent lights with dimmer switches are recommended, especially those with natural filters. Fluorescent lights are not recommended. A combination of backlighting with desk side lighting with focused or shielded light (eg, for taking notes) is recommended. If view boxes and film are still being used in the room with soft-copy displays, it is recommended that partitions be put up between them to minimize reflections and glare. If this is not possible, the soft-copy displays should be positioned at 90° angles from the view boxes whenever possible.
With digital displays and their associated computers, it is necessary to ensure adequate airflow, optimal temperature, and humidity controls. It may be necessary, depending on the particular environment, to have direct ventilation for each workstation that is controllable by each user for personal comfort. Water-cooled computers should be considered. Avoid placing monitors in the same area as light boxes or alternators. If necessary, place them at 90° rather that 180° to avoid reflections. Separate each display workstation from others with partitions that can be moved or reconfigured depending on consultation needs.
Noise considerations (computers, fans, etc.) are also important to minimize with digital workstations. Water-cooled computers should be considered because they are quieter than fan-cooled computers.
Proper shielding (eg, via movable walls) should be considered, especially to isolate dictation systems from each other.Proper chairs with lumbar support and adjustable height controls (including armrests) are recommended to avoid injuries and excessive fatigue. The workstation table should be height adjustable, and the keyboard, mouse, and monitors should be designed to maximize comfort and efficiency. Dictation tools, Internet access, and other reference tools should be readily accessible and easy to use during image interpretation. Consider ergonomically designed input devices and alternatives to the more traditional mouse and trackball interfaces.