Cone Beam CT Breast Imaging Research Articles

WE‐E‐L100J‐01: Simulation of Tomosynthesis Mammograms with Cone Beam CT Images of Mastectomy Breast Specimens

Purpose: To describe and discuss about a technique to simulate digital mammograms and tomosynthesis images with cone beam CT images of mastectomy breast specimens. Method and Materials: To allow x‐ray images to be simulated, cone beam breast CT images of a mastectomy breast specimen were acquired at 80 kVp and used to generate a 3‐D map of linear attenuation coefficients for mammographic x‐rays. The map was then deformed to generate a new map for a compressed breast. A software re‐projector was developed and used to compute projection images for a stationary detector and a linearly shifted x‐ray source. A special re‐projector was developed to preserve the contrast of microcalcifications (MCs). The resulting images were then used to reconstruct tomosynthesis mammograms using various reconstruction algorithms. Results: We have successively used cone beam CT images of mastectomy breast specimens to generate 3‐D maps of attenuation coefficients to model compressed breasts and to use them to simulate digital mammograms and tomosynthesis images. It was found that MCs clearly visible in cone beam CT images were not visible in regular mammograms but faintly visible in tomosynthesis images. The MCs were clearly visible in both MC enhanced mammograms and the tomosynthesis images reconstructed from them. Conclusions: Cone beam CT images may be used to model a compressed breast for simulating mammograms and tomosynthesis images. Cone beam CT images are superior to regular or tomosynthesis mammograms in depicting MCs within their resolution limit. MC enhanced re‐projection, however, could be useful in displaying the cone beam CT images with the more conventional appearances of regular and tomosynthesis mammograms while maintaining the contrast and visibility of MCs in the CT images.This work was supported in part by a research grant EB00117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI.

Tilted angle CZT detector for photon counting/energy weighting x-ray and CT imaging

X-ray imaging with a photon counting/energy weighting detector can provide the highest signal to noise ratio (SNR). Scanning slit/multi-slit x-ray image acquisition can provide a dose-efficient scatter rejection, which increases SNR. Use of a photon counting/energy weighting detector in a scanning slit/multi-slit acquisition geometry could provide highest possible dose efficiency in x-ray and CT imaging. Currently, the most advanced photon counting detector is the cadmium zinc telluride (CZT) detector, which, however, is suboptimal for energy resolved x-ray imaging. A tilted angle CZT detector is proposed in this work for applications in photon counting/energy weighting x-ray and CT imaging. In tilted angle configuration, the x-ray beam hits the surface of the linear array of CZT crystals at a small angle. This allows the use of CZT crystals of a small thickness while maintaining the high photon absorption. Small thickness CZT detectors allow for a significant decrease in the polarization effect in the CZT volume and an increase in count rate. The tilted angle CZT with a small thickness also provides higher spatial and energy resolution, and shorter charge collection time, which potentially enables fast energy resolving x-ray image acquisition. In this work, the major performance parameters of the tilted angle CZT detector, including its count rate, spatial resolution and energy resolution, were evaluated. It was shown that for a CZT detector with a 0.7 mm thickness and 13° tilting angle, the maximum count rate can be increased by 10.7 times, while photon absorption remains >90% at photon energies up to 120 keV. Photon counting/energy weighting x-ray imaging using a tilted angle CZT detector was simulated. SNR improvement due to optimal photon energy weighting was 23% and 14% when adipose contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for the adipose. SNR improvement was 42% and 31% when CaCO3 contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for CaCO3. The SNRs of the photon counting single-kVp dual-energy subtracted images of CaCO3 and adipose were higher by 2.04 and 2.74 times, respectively, as compared to currently used dual-kVp dual-energy subtracted images. Experiments with a CZT crystal with 2 mm thickness have shown significant decrease in the tailing effect of the CZT pulse spectrum at 59 keV and 122 keV photon energies, when the tilting angle configuration was used. Finally, feasibility of the tilted angle CZT detector for photon counting cone beam breast CT imaging was demonstrated.

Why should breast tumour detection go three dimensional?

Although x-ray mammography is widely developed for breast tumour detection, it suffers from spatial superposition in its two-dimensional (2D) representation of a three-dimensional (3D) breast structure. Accordingly, 3D breast imaging, such as cone-beam computed tomography (CT), arises at the historic moment. In this paper, we theoretically elucidate the spatial superposition effect associated with x-ray mammography on breast tumour detection. This explanation is based on the line integral of x-ray traversing a composite breast model. As a result, we can characterize the difficulty of detecting small tumours in terms of local intensity contrast in x-ray images. In comparison, we also introduce cone-beam CT breast imaging for 3D breast volume representation, which offers advantages for breast mass segmentation and measurement. The discussion is demonstrated with an experiment with a breast surgical specimen. In conclusion, we strongly believe that 3D volumetric representation allows for more accurate breast tumour detection.