Scattered radiation is inevitably generated in the object. The distribution of the scattered radiation is influenced by
object thickness, filed size, object-to-detector distance, and primary energy. One of the investigations to measure scatter
intensities involves measuring the signal detected under the shadow of the lead discs of a beam-stop array (BSA). The
measured scatter by BSA includes not only the scattered radiation within the object (object scatter), but also the external
scatter source. The components of external scatter source include the X-ray tube, detector, collimator, x-ray filter, and
BSA. Excluding background scattered radiation can be applied to different scanner geometry by simple parameter
adjustments without prior knowledge of the scanned object.
In this study, a method using BSA to differentiate scatter in phantom (object scatter) from external background was
used. Furthermore, this method was applied to BSA algorithm to correct the object scatter. In order to confirm
background scattered radiation, we obtained the scatter profiles and scatter fraction (SF) profiles in the directions
perpendicular to the chest wall edge (CWE) with and without scattering material. The scatter profiles with and without
the scattering material were similar in the region between 127 mm and 228 mm from chest wall. This result indicated
that the measured scatter by BSA included background scatter. Moreover, the BSA algorithm with the proposed method
could correct the object scatter because the total radiation profiles of object scatter correction corresponded to original
image in the region between 127 mm and 228 mm from chest wall. As a result, the BSA method to measure object scatter
could be used to remove background scatter. This method could apply for different scanner geometry after background
scatter correction. In conclusion, the BSA algorithm with the proposed method is effective to correct object scatter.
Digital breast tomosynthesis (DBT) is a technique developed to overcome the limitations of conventional digital
mammography by reconstructing slices through the breast from projections acquired at different angles. In developing
and optimizing DBT, the x-ray scatter reduction technique remains a significant challenge due to projection geometry
and radiation dose limitations. The most common approach for scatter reduction technique is a beam-stop-array (BSA)
algorithm while this method has a concern of additional exposure to acquire the scatter distribution. The compressed
breast is roughly symmetry and the scatter profiles from projection acquired at axially opposite angle are similar to
mirror image from each other. The purpose of this study was to apply the BSA algorithm acquiring only two scans with a
beam stop array, which estimates scatter distribution with minimum additional exposure. The results of scatter correction
with angular interpolation were comparable to those of scatter correction with all scatter distributions at each angle and
exposure increase was less than 13%. This study demonstrated the influence of scatter correction by BSA algorithm with
minimum exposure which indicates the practical application in clinical situations.
The purpose of this study was to investigate the effect of different acquisition parameters and to characterize their
relationships in order to improve the detection of microcalcifications using digital breast tomosynthesis (DBT). DBT
imaging parameters were optimized using 32 different acquisition sets with six angular ranges (±5°, ±10°, ±13°, ±17°, ±21°, and ±25°) and eight projection views (5, 11, 15, 21, 25, 31, 41, and 51 projections). To investigate the effects of
variable angular dose distribution, the acquisition sets were evaluated with delivering more dose toward the central
views. Our results show that a wide angular range improved the reconstructed image quality in the z-direction. If a large
number of projections are acquired, then electronic noise may dominate the contrast-to-noise ratio (CNR) due to reduced
radiation dose per projection. With delivering more dose toward the central views, it was found that the vertical
resolution was reduced with increasing dose in the central PVs. On the other hand, the CNR clearly increased with
increasing concentration of dose distribution in central views. Although it was found that increasing angular range
improved the vertical resolution, it was also found that the image quality of microcalcifications in the in-focus plane did
not improve by increasing the noise due to greater effective breast thickness. Angular dose distributions, with more dose
delivered to the central views, generally yielded a higher quality factor (QF) than uniform dose distributions.
The rapid development and clinical use of digital mammography in the past decade has made possible the development
of digital breast tomosynthesis (DBT), which can overcome the limitation of conventional mammography and improve
the specificity of mammography with improved marginal visibility of lesion and early breast cancer detection, especially
for women with dense breast. The purpose of this study is to characterize the physical properties of DBT system and to
optimize the exposure condition using effective modulation transfer function (eMTF), effective noise power spectrum
(eNPS), and effective detective quantum efficiency (eDQE). The first generation KERI prototype digital tomosyntesis
system for breast imaging using CMOS flat panel detector was used in this study. It was found that the spatial frequency
dependent metrics depend on both the inherent properties of the detector and imaging geometry including breast
thickness. For thicker breast, eDQE decreases as scatter fraction increases at fixed tube voltage. Moreover, eMTF shows
no significant difference as changing tube voltage while eDQE at 27 kVp is relatively degraded. Consequently, the
quantitative evaluation of the DBT system with different exposure condition and breast thickness should be fully
considered before building the system and application in clinical hospital.
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