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This study aims to investigate the impact of external filtration on image quality and exposure time of an in-line phase-contrast x-ray breast imaging prototype.
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.
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