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Experimental characterization of a direct conversion amorphous selenium detector with thicker conversion layer for dual‐energy contrast‐enhanced breast imaging
Author(s) -
Scaduto David A.,
Tousignant Olivier,
Zhao Wei
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12358
Subject(s) - detector , image resolution , materials science , optics , detective quantum efficiency , breast imaging , flat panel detector , mammography , medical imaging , image quality , physics , radiology , computer science , medicine , breast cancer , cancer , artificial intelligence , image (mathematics)
Purpose Dual‐energy contrast‐enhanced imaging is being investigated as a tool to identify and localize angiogenesis in the breast, a possible indicator of malignant tumors. This imaging technique requires that x‐ray images are acquired at energies above the k ‐shell binding energy of an appropriate radiocontrast agent. Iodinated contrast agents are commonly used for vascular imaging, and require x‐ray energies greater than 33 keV. Conventional direct conversion amorphous selenium ( a ‐Se) flat‐panel imagers for digital mammography show suboptimal absorption efficiencies at these higher energies. Methods We use spatial‐frequency domain image quality metrics to evaluate the performance of a prototype direct conversion flat‐panel imager with a thicker a ‐Se layer, specifically fabricated for dual‐energy contrast‐enhanced breast imaging. Imaging performance was evaluated in a prototype digital breast tomosynthesis (DBT) system. The spatial resolution, noise characteristics, detective quantum efficiency, and temporal performance of the detector were evaluated for dual‐energy imaging for both conventional full‐field digital mammography (FFDM) and DBT. Results The zero‐frequency detective quantum efficiency of the prototype detector is improved by approximately 20% over the conventional detector for higher energy beams required for imaging with iodinated contrast agents. The effect of oblique entry of x‐rays on spatial resolution does increase with increasing photoconductor thickness, specifically for the most oblique views of a DBT scan. Degradation of spatial resolution due to focal spot motion was also observed. Temporal performance was found to be comparable to conventional mammographic detectors. Conclusions Increasing the a ‐Se thickness in direct conversion flat‐panel imagers results in better performance for dual‐energy contrast‐enhanced breast imaging. The reduction in spatial resolution due to oblique entry of x‐rays is appreciable in the most extreme clinically relevant cases, but may not profoundly affect reconstructed images due to the algorithms and filters employed. Degradation to projection domain spatial resolution is thus outweighed by the improvement in detective quantum efficiency for high‐energy x‐rays.