The SYRMA-CT project for breast computed tomography with synchrotron radiation: image quality and dose evaluation

Introduction: The SYRMA-CT project (INFN, ELETTRA Synchrotron Radiation Facility, Trieste University Hospital) is a pilot study for 3D breast imaging with Synchrotron Radiation (SR) monochromatic X-rays, via propagation based phase-contrast X-ray CT of the pendant breast. This project aims at producing the first high-resolution phase-contrast in vivo images of the breast, for improved visualization of breast cancer lesions, at dose levels comparable to that of two-view mammography. Materials and Methods: In SR breast CT the patient is in prone position with her breast freely pending without compression from a hole in the bed. The SR beam is incident horizontally and irradiates a thin section of the breast. For acquiring multiple views, the patient bed rotates around a horizontal axis: for a scan of a thick section of the breast the bed translates vertically. The SR laminar beam has a size of 210 × 3 mm2 and the photon energy was 38 keV. The detector is at about 2 m away from the isocenter. The single-photon counting detector is PIXIRAD-8, a 0.65-mm thick CdTe hybrid detector (25 × 2.5 cm2 sensitive area) with 60-µm pixel pitch on a hexagonal 2D arrangement. A breast specimen of about 9 cm diameter was imaged, as well as test objects for image quality evaluation. CT slices were reconstructed via FBP or iteratively both in attenuation and after phase retrieval using the homogeneous transport-of-intensity algorithm. Discussion and Conclusion: First CT attenuation images and phase images have been produced of the breast specimen, at glandular dose levels in the irradiated slice of 5–20 mGy. Phase retrieval increased the signal-to-noise ratio with respect to attenuation CT; iterative reconstruction allowed to reduce significantly the dose with a limited reduction of the contrast-to-noise ratio. The limiting spatial resolution was over 2.5 mm-1 after phase retrieval. SR phase-contrast breast CT is technically feasible at dose levels comparable to two-view mammograph