Abstract
In this study we compared the image quality of a synchrotron radiation (SR) breast computed tomography (BCT) system with a clinical BCT in terms of contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), noise power spectrum (NPS), spatial resolution and detail visibility. A breast phantom consisting of several slabs of breast-adipose equivalent material with different embedded targets (i.e., masses, fibers and calcifications) was used. Phantom images were acquired using a dedicated BCT system installed at the Radboud University Medical Center (Nijmegen, The Netherlands) and the SR BCT system at the SYRMEP beamline of Elettra SR facility (Trieste, Italy) based on a photon-counting detector. Images with the SR setup were acquired mimicking the clinical BCT conditions (i.e., energy of 30 keV and radiation dose of 6.5 mGy). Images were reconstructed with an isotropic cubic voxel of 273 µm for the clinical BCT, while for the SR setup two phase-retrieval (PhR) kernels (referred to as “smooth” and “sharp”) were alternatively applied to each projection before tomographic reconstruction, with voxel size of 57 × 57 × 50 µm3. The CNR for the clinical BCT system can be up to 2-times higher than SR system, while the SNR can be 3-times lower than SR system, when the smooth PhR is used. The peak frequency of the NPS for the SR BCT is 2 to 4-times higher (0.9 mm−1 and 1.4 mm−1 with smooth and sharp PhR, respectively) than the clinical BCT (0.4 mm−1). The spatial resolution (MTF10%) was estimated to be 1.3 lp/mm for the clinical BCT, and 5.0 lp/mm and 6.7 lp/mm for the SR BCT with the smooth and sharp PhR, respectively. The smallest fiber visible in the SR BCT has a diameter of 0.15 mm, while for the clinical BCT is 0.41 mm. Calcification clusters with diameter of 0.13 mm are visible in the SR BCT, while the smallest diameter for the clinical BCT is 0.29 mm. As expected, the image quality of the SR BCT outperforms the clinical BCT system, providing images with higher spatial resolution and SNR, and with finer granularity. Nevertheless, this study assesses the image quality gap quantitatively, giving indications on the benefits associated with SR BCT and providing a benchmarking basis for its clinical implementation. In addition, SR-based studies can provide a gold-standard in terms of achievable image quality, constituting an upper-limit to the potential clinical development of a given technique.
Highlights
Breast cancer is the leading cause of cancer death in women worldwide[1]
synchrotron radiation (SR)-based studies can provide a gold-standard in terms of achievable image quality and they can constitute an upper-limit to the potential clinical development of a given technique
contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) are related to low-contrast detail visibility, the shape of noise power spectrum (NPS) reveals the image texture, and spatial resolution determines the ability to detect small details
Summary
Breast cancer is the leading cause of cancer death in women worldwide[1]. It is the most diagnosed cancer in women, accounting for one-third of all diagnosed cancers[2]. Digital breast tomosynthesis (DBT), a pseudo 3D breast imaging modality[3], has been developed to diminish the masking effect and the anatomical noise, showing potential applicability in the diagnostic domain and in the screening setting[4,5,6] Another recent major technological advance is dedicated breast computed tomography (BCT), a fully 3D mammographic technique in which multiple low-dose projections are acquired and reconstructed[7,8]. At the same time, assessing the difference with clinically available systems can provide a benchmark on the current level of behaviour of SR-based techniques, and establish its potential for clinical implementation, as well as providing information relevant to the translational research aimed at developing compact high-coherence x-ray sources[33] In this context, considering the lack of quantitative image-quality comparative studies, a comparison with the clinical domain is paramount. CNR and SNR are related to low-contrast detail visibility (e.g., glandular tissue embedded in an adipose background), the shape of NPS reveals the image texture (i.e., low-frequency-peaked NPS is related to coarse image graininess; high-frequency-peaked NPS results in a finer grain noise), and spatial resolution determines the ability to detect small (high-contrast) details (e.g., microcalcifications)
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