Optimization of a Coded Aperture Coherent Scatter Spectral Imaging System for Classification of Breast Cancer

Coherent scatter spectral imaging has been demonstrated as an effective way to classify healthy and malignant breast tissues. Previously in our group, data acquired using sectioned, lumpectomy specimens obtained from surgical pathology have been used to demonstrate the efficacy of this imaging method. Although effective in its current state, the system has not been optimized for use with these types of specimens (i.e. tissue types and thicknesses). Specimens obtained from lumpectomies often vary in thickness (up to 3 mm). The current X-ray tube operating parameters have been considered excessive for these tissues based on heating of the tube’s anode and the unnecessary, high quality of resulting spectra. The purpose of this work was to optimize our spectral imaging system to maintain accurate and consistent results of sectioned lumpectomy specimens while simultaneously maximizing system throughput by reducing the power requirements of the imaging system.

Teflon, adipose breast tissue, and malignant breast tissue were scanned using different combinations of X-ray source parameters (70-125 kVp, 25-500 mAs) to obtain a coherent-scatter diffraction spectrum for each measurement. Cross correlation was performed on the measured spectra to compare their quality against known, ground truth spectra from literature. In addition, a classification algorithm was developed to classify our measured spectra as one of four tissue types (adipose, normal, fibroglandular, and cancer). The locations of the spectral peaks were used to distinguish cancer from adipose and normal (50/50 fibroglandular/adipose) tissue, followed by a weighted cross correlation method used to distinguish cancer from fibroglandular tissue. Classification performance was assessed across all acquisition protocols to evaluate accuracy.

The optimal setting was identified as the minimal power supplied to the X-ray tube that resulted in the highest correlation to the ground truth spectra. The optimal setting was identified at 115 kVp, 100 mAs when using the raw spectra and 95 kVp, 50 mAs after processing the spectra. These settings result in an increase in system efficiency of at least 400% (at 115kVp, 100 mAs) compared to our current system operating protocol. Finally, the optimized system was tested using a new, unknown tumor specimen obtained from a preserved lumpectomy section.

This study successfully demonstrates the optimization of a new coherent scatter spectral imaging system based on classification using cross correlation and a weighted cross correlation method. The efficiency improvement obtained through the work allows for higher system throughput, thereby allowing enhanced data collection with shorter scans or scanning the specimens at higher resolutions.