Narrow beam breast CT: proof-of-concept

In breast CT, scattered photons form a large portion of the acquired signal, adversely impacting image quality throughout the frequency response of the imaging system. Prior studies provided evidence for a new image acquisition design, dubbed Narrow Beam Breast CT (NB-bCT), in preventing scatter acquisition.

Here, we report the design, implementation, and initial characterization of the first NB-bCT prototype.

The imaging system's apparatus is composed of two primary assemblies: a dynamic Fluence Modulator (collimator) and a photon-counting line detector. The design of the assemblies enables them to operate in lockstep during image acquisition, converting sourced x-rays into a moving narrow beam. During a projection, this narrow beam sweeps the entire fan angle coverage of the imaging system. The assemblies are each comprised of a metal housing, a sensory system, and a robotic system. A controller unit handles their relative movements. To study the impact of fluence modulation on the signal received in the detector, three physical breast phantoms, representative of small, average, and large size breasts, were developed and imaged, and acquired projections analyzed. The scatter acquisition in each projection as a function of breast phantom size was investigated. The imaging system's spatial resolution at the center and periphery of the field of view was measured.

Minimal acquisition of scattered rays occurs during image acquisition with NB-bCT; results in minimal scatter to primary ratios in small, average, and large breast phantoms imaged were 0.05, 0.07, and 0.9, respectively. System spatial resolution of 5.2 lp/mm at 10% max MTF and 2.9 lp/mm at 50% max MTF at the center of the field of view was achieved, with minimal loss with the shift toward the corner (5.0 lp/mm at 10% max MTF and 2.5 lp/mm at 50% max MTF).

The disclosed development, implementation, and characterization of a physical NB-bCT prototype system demonstrates a new method of CT-based image acquisition that yields high spatial resolution while minimizing scatter-components in acquired projections. This methodology holds promise for high-resolution CT-imaging applications in which reduction of scatter contamination is desirable.