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The feasibility of using the dual-resolution cone beam breast CT technique to obtain high-resolution images inside
a selected volume-of-interest (VOI). The spatial resolution improvement, dose saving and scatter reduction with this
technique are studied and demonstrated with simulations. With the dual-resolution cone beam CT technique, the breast is
first scanned with a low resolution detector at a lower exposure level. A selected volume-of-interest (VOI) in the breast
is then scanned with a small field, high-resolution detector at a higher exposure level. The two image sets are then
combined together to reconstruct high-resolution 3-D images for the VOI. The spatial resolution that can be achieved
was estimated by obtaining 3-D images of point objects and use them to compute the MTFs for evaluation as a function
of the geometric magnification, detector blurring function and focal spot size. Monte Carlo simulation based on the
Geant4 package was used to estimate the degree of dose saving and scatter reduction for a cylinder shaped breast
phantom. The VOI images generated with the dual-resolution cone beam CT technique demonstrated the same visibility
of micro-calcifications as those generated with the full-breast, high resolution image acquisition. It has been shown that
the spatial resolution can be increased by factor of 1.2 with smaller focal spot size and larger magnification. With the
exposure level outside the VOI reduced by a factor of 15, scatter components can be reduced by a factor of 5.5 or greater
in and outside the VOI. Dose can be reduced by a factor of 5.5 inside the VOI and up to 20 outside the VOI. We have
demonstrated that high spatial resolution inside the VOI may be achieved with a high-resolution detector (e.g. CCD/CsI),
reduced focal spot size (0.3 mm), and optimized geometrical magnification (e.g.1.63). Exposure reduction outside the
VOI has been shown to reduce the scatter components in the high-resolution projection image data for the VOI. This has
also led to significantly lowered doses inside and outside the VOI.
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