CONE BEAM COMPUTED TOMOGRAPHY: Preliminary studies on novel detector schemes

Background: Cone beam computed tomography ( CBCT) offers a comfortable breast examination accompanied by 3D breast representation, at the same or lower dose levels in comparison to classical mammography and its derivative tomosynthesis. In the case of dense breast, it provides specialists a reliable anatomical representation towards an accurate diagnosis of breast pathologies. CBCT system detector configuration usually is based on a CsI:Tl scintillator.

Materials and Methods: The purpose of this study was to instigate novel detector schemes applied to a simulated micro-CBCT system, with a view to designing future experimental setups. The energy spectrum of the CBCT system X-ray source ranged from 10 to 40 keV. The system relied on a 360° rotating table. Different detector materials, of the same size and shape, were simulated and investigated: LSO:Ce, LYSO:Ce, LuAG:Ce, GAGG:Ce, LaBr₃:Ce, LaCl₃:Ce, and CZT. A bone tissue capillary was used in order to investigate possible differences in the system’s spatial resolution. Further, a breast phantom was simulated in order to evaluate image quality, as it is derived from contrast-to noise ratios (CNRs) of specific ROIs (regions-of-interest). System simulation was based on GATE software. Images were reconstructed with FBP and OSEM. The evaluation was performed in conjunction to the standard CsI:Tl detector setup. All schemes were simulated with the same front-end electronic configuration.

Results: Image quality assessment depicted a dependence on detector material. LYSO:Ce, LuAG:Ce, GAGG:Ce, LaBr₃:Ce, and LaCl₃:Ce presented high CNRs for materials of different composition. CZT is a promising semiconductor energy converter in the case of a low-density bone tissue. Spatial resolution depends only on the reconstruction algorithm.

Conclusion: The aforementioned examined materials with increased CNRs could be an efficient alternative in a future CBCT system that will overcome further dense breast imaging limitations.