Objective. To introduce the optimization of a customized GPU-based simultaneous algebraic reconstruction technique (cSART) in the field of phase-contrast breast computed tomography (bCT). The presented algorithm features a 3D bilateral regularization filter that can be tuned to yield optimal performance for clinical image visualization and tissues segmentation. Approach. Acquisitions of a dedicated test object and a breast specimen were performed at Elettra, the Italian synchrotron radiation (SR) facility (Trieste, Italy) using a large area CdTe single-photon counting detector. Tomographic images were obtained at 5 mGy of mean glandular dose, with a 32 keV monochromatic x-ray beam in the free-space propagation mode. Three independent algorithms parameters were optimized by using contrast-to-noise ratio (CNR), spatial resolution, and noise texture metrics. The results obtained with the cSART algorithm were compared with conventional SART and filtered back projection (FBP) reconstructions. Image segmentation was performed both with gray scale-based and supervised machine-learning approaches. Main results. Compared to conventional FBP reconstructions, results indicate that the proposed algorithm can yield images with a higher CNR (by 35% or more), retaining a high spatial resolution while preserving their textural properties. Alternatively, at the cost of an increased image ‘patchiness’, the cSART can be tuned to achieve a high-quality tissue segmentation, suggesting the possibility of performing an accurate glandularity estimation potentially of use in the realization of realistic 3D breast models starting from low radiation dose images. Significance. The study indicates that dedicated iterative reconstruction techniques could provide significant advantages in phase-contrast bCT imaging. The proposed algorithm offers great flexibility in terms of image reconstruction optimization, either toward diagnostic evaluation or image segmentation.

Optimization of a customized simultaneous algebraic reconstruction technique algorithm for phase-contrast breast computed tomography

PURPOSE The SYRMA-3D collaboration is setting up a breast computed tomography (bCT) clinical program at the Elettra synchrotron radiation facility in Trieste, Italy. Unlike the few dedicated scanners available at hospitals, synchrotron radiation bCT requires the patient's rotation, which in turn implies a long scan duration (from tens of seconds to few minutes). At the same time, it allows the achievement of high spatial resolution. These features make synchrotron radiation bCT prone to motion artifacts. This article aims at assessing and compensating for motion artifacts through an optical tracking approach. METHODS In this study, patients' movements due to breathing have been first assessed on seven volunteers and then simulated during the CT scans of a breast phantom and a surgical specimen, by adding a periodic oscillatory motion (constant speed, 1 mm amplitude, 12 cycles/minute). CT scans were carried out at 28 keV with a mean glandular dose of 5 mGy. Motion artifacts were evaluated and a correction algorithm based on the optical tracking of fiducial marks was introduced. A quantitative analysis based on the structural similarity (SSIM) index and the normalized mean square error (nMSE) was performed on the reconstructed CT images. RESULTS CT images reconstructed through the optical tracking procedure were found to be as good as the motionless reference image. Moreover, the analysis of SSIM and nMSE demonstrated that an uncorrected motion of the order of the system's point spread function (around 0.1 mm in the present case) can be tolerated. CONCLUSIONS Results suggest that a motion correction procedure based on an optical tracking system would be beneficial in synchrotron radiation bCT.

Motion artifacts assessment and correction using optical tracking in synchrotron radiation breast CT.

OBJECTIVES
To design a device that can support the breast during phase-contrast tomography, and characterise its fit parameterisation and comfort rating.


METHODS
Twenty-seven participants were recruited to trial a system for breast support during simulated Phase contrast imaging, including being positioned on a prone imaging table while wearing the device. Participants underwent a photogrammetry analysis to establish the geometric parameterisations. All participants trialled a single-cup design while 14 participants also trialled a double-cup with suction holder and all completed a series of questionnaires to understand subjective comfort.


RESULTS
Photogrammetry revealed significant positive correlations between bra cup volume and measured prone volume (p < 0.001), and between "best fit" single-cup holder volume and measured prone volume (p < 0.005). Both holders were suitable devices in terms of subjective comfort and immobilisation while stationary. However, some re-engineering to allow for quick, easy fitting in future trials where rotation through the radiation beam will occur is necessary. Light suction was well-tolerated when required.


CONCLUSIONS
All participants indicated the table and breast support devices were comfortable, and they would continue in the trial.


ADVANCES IN KNOWLEDGE
Phase contrast tomography is an emerging breast imaging modality and clinical trials are commencing internationally. This paper describes the biomedical engineering designs, in parallel with optimal imaging, that are necessary to measure breast volume so that adequate breast support can be achieved. Breast support devices have implications for comfort, motion correction and maximising breast tissue visualisation.

Designing a breast support device for phase contrast tomographic imaging: getting ready for a clinical trial.

Rationale and objectives: Breast cancer represents the leading cause of death from cancer in women worldwide. Early detection of breast tumours improves the prognosis and survival rate. Propagation-based phase-contrast computed tomography (PB-CT) is a technique that uses refraction and absorption of the X-ray to produce images for clinical applications. This study compared the performance of photon-counting and flat panel X-ray detectors in PB-CT breast imaging using synchrotron radiation. Materials and methods: Mastectomy specimens underwent PB-CT imaging using the Hamamatsu C10900D Flat Panel and PIXIRAD-8 CdTe single-photon-counting detectors. PB-CT images generated at different imaging conditions were compared to absorption-based CT (AB-CT) reference images acquired with the same detectors to investigate the image quality improvement delivered by PB-CT relative to AB-CT. The image quality of the different image sets was assessed by eleven readers in a visual grading characteristics (VGC) study. Results: The intraclass correlation coefficient showed a moderate/good interobserver agreement for the image set analysed (ICC = 0.626, p = <0.001). The area under the curve showed that the image quality improvement in PB-CT images obtained by the PIXIRAD-8 CdTe single-photon counting detector were consistently higher than the one for flat-panel Hamamatsu detector. The level of improvement in image quality was more substantial at lower radiation doses. Conclusion: In this study, the PIXIRAD-8 photon-counting detector was associated with higher image quality scores at all tested radiation dose levels, which was likely a result of the combined effect of the absence of dark current noise and better spatial resolution, compared to the flat-panel detector.

/pdf/propagation-based-phase-contrast-breast-computed-tomography-25zftyn3.pdf

Propagation-based phase-contrast breast computed tomography: a visual grading assessment of the performance of photon-counting and flat-panel X-ray detectors

Computational techniques allow breaking the limits of traditional imaging methods, such as time restrictions, resolution, and optics flaws. While simple computational methods can be enough for highly controlled microscope setups or just for previews, an increased level of complexity is instead required for advanced setups, acquisition modalities or where uncertainty is high; the need for complex computational methods clashes with rapid design and execution. In all these cases, Automatic Differentiation, one of the subtopics of Artificial Intelligence, may offer a functional solution, but only if a GPU implementation is available. In this paper, we show how a framework built to solve just one optimisation problem can be employed for many different X-ray imaging inverse problems.

/pdf/automatic-differentiation-for-inverse-problems-in-x-ray-2fwpetbi.pdf

Automatic Differentiation for Inverse Problems in X-ray Imaging and Microscopy

Aim: In recent years Phase Contrast Tomography (PCT) has been rapidly progressing towards clinical translation as an advanced imaging technology for breast cancer diagnosis. Recent optimization of PCT with mastectomy samples has refined imaging protocols and biomedical-engineering prowess is now required to formalize patient table and breast immobilisation requirements. PCT imaging requires women to lie in prone position similar to conventional breast CT, however the imaging couch rotates above the beam allowing exposure of the breast beneath. Motion artefact through involuntary movement of the breast through the rotation cycle has the potential to reduce diagnostic quality of the results. Methods: This paper details the biomedical engineering cycle of breast holder development alongside medical physics considerations. Breast immobilisation via a plastic or silicone supporting material which is sufficiently transparent for X-rays in the targeted energy range is explained, including the two step process of considering single cup versus double cup solutions and how mild-suction to the breast can be implemented in order to maximum breast tissue visualization and assist with dose uniformity. Results: Considering patient comfort, breast positioning and implications upon attenuation and phase shift, a number of models were developed in Australia and Italy. Early prototypes are described here with some preliminary imaging. Considerable work is taking place over the next three months as models undergo imaging with mastectomy samples at the Imaging and Medical Beamline at the Australian Synchrotron and the ELETTRA Synchrotron Italy. Consumer representatives will be rating the immobilisation device for comfort prior to the start of clinical trials in 2020.

Lucia Mariel Arana Pena

Papers

Motion artifacts assessment and correction using optical tracking in synchrotron radiation breast CT.

Getting a-breast of immobilisation needs for the implementation of phase contrast tomography