In this study we theoretically investigated the minimum scan time of an inverse-geometry dedicated breast CT
system that provides sufficient sampling and dose equivalent to mammography without exceeding the limits
of source power or detector count rate. The inverse geometry, which utilizes a large-area scanned source and
a narrower photon-counting detector, is expected to have improved dose efficiency compared to cone-beam
methods due to reduced scatter effects and improved detector efficiency. The analysis assumed the specifications
of available inverse-geometry source and detector hardware (SBDX, NovaRay, Inc, Newark CA). The scan time
was calculated for a 10, 14, and 18-cm diameter breast composed of 50% glandular / 50% adipose tissue. The
results demonstrate a minimum scan time of 6.5, 14.3, and 14.7 seconds for a 10, 14, and 18-cm-diameter breast,
respectively. The scan times are comparable to those of proposed cone-beam systems. For all three breast sizes,
the scan time was limited by the detector count rate. For example, for the 14-cm-diameter breast, the minimum
scan time that met the source power limitation was 1.1 seconds, and the minimum scan time that achieved
sufficient sampling was 0.8 seconds. The scan time can be reduced by increasing the detector count rate or area.
Effective bowtie filters will be required to prevent detector saturation at the object edges. Overall, the results
support preliminary feasibility of dedicated breast CT with an inverse geometry.