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An ACR mammography phantom and three different Contrast Detail (CD) phantoms were used in experiments. Each phantom is 5cm in thickness and fabricated with materials simulating 50% glandular tissue and 50% adipose tissue. The phantoms were imaged by 59kV and 89kV with varying levels of external filtrations. The x-ray exposure was adjusted so that the average glandular dose was consistently to be 1.3 mGy throughout the imaging.
A noise reduction algorithm was applied to the images. The algorithm being evaluated is a state-of-the-art self-supervised single image denoising approach that can prioritize the preservation of fine-grained image structures while performing noise removal.
The contrast-to-noise (CNR) ratio was measured to conduct objective analysis. Additionally, an observer performance study was conducted in which observers were shown the images from each phantom in a randomized order before and after the denoising algorithm was applied. The observers rated the detectability of each image by identifying the minimum perceptible feature.
The results indicate some improvement from the objective studies; however, in the subjective observer studies, no improvement was observed in the detectability of the ACR images, and limited improvement was observed in the detectability of the CD phantom images.
A Contrast-Detail phantom is imaged by 59 kV and 89 kV systems with a CCD camera and varying filter thicknesses, ranging from 1.0 mm to 3.3 mm of aluminum. The average glandular radiation dose is set to 1.3 mGy throughout the experiment, regardless of imaging parameters. The Contrast-Detail (CD) curves are generated from the reading results of three experienced observers. The Contrast-to-Noise-Ratio (CNR) is calculated for objective comparisons. The results show that the beam hardening with 1.3 and 2.5 mm aluminum filters in the 59 kV system provides the most desirable CNRs and CD curves, whereas a 3.3 mm aluminum might be a preferable external filtration in the 89 kV system. It can be concluded that the 59 KV beam, filtered by a 1.3 mm aluminum, is a better choice, as it results in comparable image quality and a 35% shorter exposure time. On the other hand, the 89 KV beam filtered by 3.3 mm aluminum results in higher image quality at the expense of slightly increased acquisition time. The prolonged acquisition effect on the image blurring should be evaluated in patient studies where the object is not immobile like imaging phantoms.
First of all, an imaging prototype was demonstrated based on a high-energy in-line phase contrast system prototype. The DQE of this system is calculated through modulation transfer function (MTF), noise power spectrum (NPS) and input signal to noise ratio under a fixed radiation dose. The radiation dose was estimated by employing a 4-cm-thick BR12 phantom. In this research, the x-ray exposure conditions were modified by not only using different tube voltage but also different prime beam filtration. Aluminum, Molybdenum, Rhodium, and a combined filter were selected to acquire a variety of x-ray energy compositions with 100, 110 and 120 kVp exposures. The resultant curves are compared through the modes of different kVp/same filter and different filter/same kVp.
As a result, the curves obtained under a fixed radiation dose, indicate that the MTF performs similar behavior under different experimental mode; the NPS is majorly affected by the composition of x-ray photon energies; and the overall DQE decreases with the increasing portion of high-energy x-ray photons in the exposure.
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