Abstract
A rigorous 2D analysis of signal and noise transfer applied to reconstructed planes in digital breast tomosynthesis (DBT) is necessary for system characterization and optimization. This work proposes a method for assessing technical image quality and system detective quantum efficiency (DQEsys) for reconstructed planes in DBT. Measurements of 2D in-plane modulation transfer function (MTF) and noise power spectrum (NPS) were made on five DBT systems using different acquisition parameters, reconstruction algorithms and plane spacing. This work develops the noise equivalent quanta (NEQ), DQEsys and detectability index (d’) calculated using a non-prewhitening model observer with eye filter (NPWE) for reconstructed DBT planes. The images required for this implementation were acquired using a homogeneous test object of thickness 40 mm poly(methyl) methacrylate plus 0.5 mm Al; 2D MTF was calculated from an Al disc of thickness 0.2 mm and diameter 50 mm positioned within the phantom. The radiant contrast of the MTF disc and the air kerma at the system input were used as normalization factors. The NPWE detectability index was then compared to the in-plane contrast-detail (c-d) threshold measured using the CDMAM phantom.The MTF and NPS measured on the different systems showed a strong anisotropy, consistent with the cascaded models developed in the literature for DBT. Detectability indices calculated from the measured MTF and NPS successfully predicted changes in c-d detectability for details between 0.1 mm and 2.0 mm, for DBT plane spacings between 0.5 mm and 10 mm, and for air kerma values at the system input between 157 µGy and 1170 μGy. The linear Pearson correlation between the detectability index and threshold gold thickness of the CDMAM phantom was −0.996. The method implements a parametric means of assessing the technical image quality of reconstructed DBT planes, providing valuable information for optimization of DBT systems.
Highlights
The development of digital breast tomosynthesis (DBT) has opened the way to various implementations of plane-based quasi-volumetric imaging in mammography
The automatic exposure control (AEC) settings obtained for the homogenous phantom for the different mammography units, the photon fluence per unit air kerma and the relative radiant contrast measured for the 0.2 mm aluminium thickness are given in table 2
The radiant contrast for the 0.2 mm Al disc varied between 10.7 % and 13.2 % for the different systems and was considered small enough such that the Impulse response function (IRF) was acquired on a linear region of the response for the different systems
Summary
The development of digital breast tomosynthesis (DBT) has opened the way to various implementations of plane-based quasi-volumetric imaging in mammography. As with all medical imaging equipment, quality control (QC) and routine performance testing is required at various stages of the equipment lifecycle (European Commission 2006). Guidance on QC testing suitable for DBT system is available from the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF). In the form of version 1.03 of the DBT protocol (EUREF 2019). The protocol covers a range of technical tests that give some insight equipment factors that can be tracked over time and that influence system imaging performance. The works of Rodriguez-Ruiz et al (2015) and Marshall and Bosmans (2012).
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