Abstract
The aim of the SYRMA-CT collaboration is to set-up the first clinical trial of phase-contrast breast CT with synchrotron radiation (SR). In order to combine high image quality and low delivered dose a number of innovative elements are merged: a CdTe single photon counting detector, state-of-the-art CT reconstruction and phase retrieval algorithms. To facilitate an accurate exam optimization, a Monte Carlo model was developed for dose calculation using GEANT4. In this study, high isotropic spatial resolution (120 μm)3 CT scans of objects with dimensions and attenuation similar to a human breast were acquired, delivering mean glandular doses in the range of those delivered in clinical breast CT (5–25 mGy). Due to the spatial coherence of the SR beam and the long distance between sample and detector, the images contain, not only absorption, but also phase information from the samples. The application of a phase-retrieval procedure increases the contrast-to-noise ratio of the tomographic images, while the contrast remains almost constant. After applying the simultaneous algebraic reconstruction technique to low-dose phase-retrieved data sets (about 5 mGy) with a reduced number of projections, the spatial resolution was found to be equal to filtered back projection utilizing a four fold higher dose, while the contrast-to-noise ratio was reduced by 30%. These first results indicate the feasibility of clinical breast CT with SR.
Highlights
In x-ray breast imaging the challenge is to match high image quality and acceptable delivered dose
The phase sensitive technique exploited in the clinical studies at the SYRMEP beamline is the so called propagation-based phase-contrast and it is based on the high coherence of the synchrotron radiation (SR) beam and on the long propagation distance between patient and detector (~2 m); to detect the edge-enhancement effect associated to this PhC technique the spatial resolution of the detector has to be adequately high (Arfelli et al 1998), since no optical elements are present in the beam path and the transverse diffraction pattern in the near field has to be very finely sampled in space
Monoenergetic CT scans of objects with dimensions and attenuation similar to human breast were acquired, delivering mean glandular dose (MGD) in the irradiated volume (MGDv) in the range of MGD delivered in clinical breast CT (5 − 25 mGy) (Zhao et al 2015)
Summary
In x-ray breast imaging the challenge is to match high image quality and acceptable delivered dose. In propagation-based PhC tomography the phase information can be decoupled from absorption when a phase retrieval algorithm is applied to the projections before tomographic reconstruction (with suitable approximations on the sample properties) This procedure increases the contrast resolution in the reconstructed images (Cloetens et al 1999, Paganin et al 2002, Chen et al 2013). The aim of the SYRMA-CT (SYnchrotron Radiation MAmmography-Computed Tomography) collaboration is to set-up the first clinical trial of PhC breast CT with SR at the SYRMEP (SYnchrotron Radiation for MEdical Physics) beamline of Elettra, the synchrotron radiation laboratory in Trieste (Italy) Pursuing both high image quality and low delivered dose, a number of innovative elements will be merged: a novel CdTe single photon counting detector (PIXIRAD-8, Bellazzini et al 2013), state-of-the-art CT reconstruction techniques, phase retrieval algorithm. In this paper we present the key elements of the project and discuss the first images of a mammographic test object and of two breast tissue specimens
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