Development and performance evaluation of an upright dedicated cone-beam breast CT system

Dedicated breast CT is an emerging breast X-ray imaging modality. While current commercial breast CT systems use prone-patient, pendant-breast geometry, the system described here uses upright patient geometry with the uncompressed breast supported by a cup.

The purpose of this work is to describe the development of a newly designed, upright geometry, dedicated cone-beam breast CT system and to evaluate its imaging performance using objective metrics.

The prototype system uses a tungsten-target, mammography-format, X-ray tube operating at 60 kV with 0.25 mm Cu and 1 mm Al added filtration, and a complementary metal-oxide semiconductor (CMOS) detector with 0.152 mm pixel pitch coupled to 500 microns thick CsI:Tl scintillator. During short scan acquisition, the X-ray source moves inferior to the breast, and 210 projections are acquired over an angular range of 210 degrees. The projections are reconstructed to an isotropic voxel pitch of 0.22 mm using Feldkamp-Davis-Kress (FDK) algorithm with Parker weights. Quantitative performance measures including linearity, modulation transfer function (MTF), and noise power spectrum (NPS) were evaluated. Phantom studies were conducted at various X-ray tube current (mA) and pulse-width (ms) combinations with the objective of determining the minimum detectable size of low-contrast targets and calcium carbonate spheres representing soft tissue lesions and microcalcification clusters, respectively.

The measured 1st HVL was 4.23 ± 0.01 mm of Al. The limiting resolution (10% MTF) was 2.18 mm^-1 in the coronal (cross-sectional) plane near the axis of rotation. In the coronal plane, the peak of the NPS occurred at 0.5 mm^-1. Phantom studies at a mean glandular dose of 3-5.7 mGy showed the ability to visualize 2-3 mm low-contrast targets and 0.27-0.29 mm calcium carbonate spheres.

The developed upright breast CT system showed the ability to achieve high spatial resolution and low contrast resolution. The excellent technical performance of the breast CT system reported here suggests that further investigations using patient imaging are warranted.