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Photon counting detectors (PCDs) with energy discrimination capabilities provide numerous benefits over conventional energy integrating detectors (EIDs). PCDs enable higher spatial resolution, improved contrast-to-noise ratio, reduced beam hardening artifact, and quantitative material-selective imaging. However, the increased spatial resolution and multiple energy bins (e.g., 8 bins for a prototype photon counting CT using silicon-based PCDs) greatly increase the amount of data generated. As a consequence, projection data transmission from the detector to the processing computer becomes more challenging due to the limited bandwidth of the slip ring. In this work, we compare the performance of four projection-domain energy bin compression strategies: conventional bins, summed bins, binary weights, and continuous weights, using the raw projection data from a prototype photon counting CT using silicon-based PCDs.
We reduce the 8 energy bins of the projection data from the prototype silicon-based PCDs to 2 or 3 virtual measurements using the phantom independent and globally applicable bin compression strategies, which were each optimized by minimizing the Cramér–Rao lower bound (CRLB) of the virtual measurements using only material decomposition calibration data over a predefined material space, and no other a priori knowledge. We evaluate the performance of the above 4 bin compression strategies in reconstructed images of a Catphan700 phantom. The results show that the 2 measurements generated with continuous weights can provide comparable material decomposition (MD) and virtual monoenergetic images (VMI) that exhibit low bias- and near zero variance-penalty, to that of the original binned counts, with a data reduction of 75%. On the other hand, neither conventional bins, summed bins, nor binary weights can provide comparable results versus continuous weights, even if we use 3 virtual measurements. We also conclude that to achieve low bias and variance in MD and VMI images with only two measurements, it is necessary to first measure as many energy bins as possible, then use continuous weights to compress the binned data.
Effects of window width and window level adjustment on detection tasks in computed tomography images
This course provides you with a basic working knowledge of color and color calibration. The course concentrates on consistent color and consistent grayscale presentation for the increasingly used color displays in medical imaging replacing the traditional monochrome displays. There will be four main subject areas:
• The science of color and color measurements.
Here you will learn about the tri-chromatic theory, the color-matching functions, the tristimulus values, the chromaticity coordinates and the various color spaces. Of particular importance for the measurement of color are the colorimeter and the spectro-photometer.
• Computational tools for calibration and color reproduction.
In this section you will be exposed to a typical system consisting of a colorimeter and a color display with an image for measuring color coordinates of that image, or a color camera for capturing the image of a color display like a color LCD. You learn that you need to do an input calibration, processing and an output calibration.
• Assessment of display performance for medical imaging systems.
In this section you will be reminded of the AAPM Task Group 18 and its efforts to establish performance criteria recommending minimum performance requirements for safe utilization of electronic monochrome displays in medical applications. You will learn that such efforts will also be required for color displays.
• Visual thresholds and the effect of color on the correct diagnosis.
In this section you will hear about some of the areas in medical imaging in which the importance of color images and color displays have been explored. Emphasis will be on radiologic imaging, but examples from other areas such as pathology and dermatology where true color images are used will also be referenced.
Ultimately the objective of this course is to familiarize you with the elements of consistent color presentation as well as consistent grayscale presentation of medical images on digital color displays for medical image interpretation.
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