Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

Purpose: Within the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility (Trieste, Italy) the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis. Methods: Test objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and Noise Power Spectrum (NPS). Phase-contrast CT images as well as images obtained after the application of a phase-retrieval algorithm were evaluated. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were explored. Results: For a voxel size of (60 \u3bcm)3, phase-contrast images showed higher spatial resolution (6.7 mm-1 at 10% MTF) than corresponding phase retrieval images (2.5 mm-1). Phase retrieval produced a reduction of the noise level as well as an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. CaCO3 microcalcifications with a diameter down to 130 \u3bcm were detected both in phase-contrast and in phase retrieval images of the test object. Conclusions: The investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Phase-retrieved images showed the best performance in the trade-off between spatial resolution and image noise

Dose and image quality in X-ray phase contrast breast imaging

Nowadays, mammographic examination is the gold standard technique for detecting breast cancer in asymptomatic women. However, it presents some limitations, mainly due to the superimposition of the tissues in the 2D mammograms, which may hide tumor lesions. Partially (digital breast tomosynthesis) and fully (CT dedicated to the breast) 3D breast imaging techniques have been developed in order to have a better tissues separation and to overcome such a limitation. Along with 3D breast imaging, the use of the X-ray beam phase shift, via so-called phase-contrast imaging techniques, has been shown to be a promising method in order to increase the image contrast between glandular tissue and tumor lesions. Indeed, in phase-contrast the image contrast is due to the X-ray wave phase-shift between different imaged materials, while in conventional imaging the image contrast arises from the different attenuation they introduce. Among all phase-contrast techniques, propagation based phase-contrast imaging does not need any special optical elements in the beam path, but only an X-ray beam with a certain degree of coherence and enough distance between imaged object and detector. It can be implemented either with synchrotron radiation source or with a compact X-ray tube. The 3D propagation based phase-contrast breast imaging devices are not yet employed in the routine clinical exams but they are available only at experimental level, and appropriate evaluations of image quality and dose are necessary. This is needed in order to optimize the various techniques and to understand the corresponding dose limitations. In this thesis, the dose paradigms in X-ray breast imaging are revisited and specific Monte Carlo simulation codes have been developed. A part of this work focuses on the breast dose aiming at studying the adopted breast models and the effects of the breast partial irradiation on the dose estimates, as occurs in 2D spot mammography clinical examinations as well as by adopting a narrow beam produced via synchrotron radiation. The second part of this work focuses on the image quality obtainable in 3D images of the breast by adopting propagation based phase-contrast imaging. We present the CT scanner dedicated to the breast developed within the SYRMA-CT project at Elettra synchrotron radiation facility. We evaluate its imaging performance in terms of spatial resolution, image noise properties and capability of showing breast lesions and microcalcification clusters. Finally, the CT scanner dedicated to the breast, developed at the University of Naples, which relies on compact X-ray source with a 7-μm focal spot is presented and its image performance at dose comparable to that adopted in two-view digital mammography is explored together with its capability of producing phase-contrast effects. This scanner was developed and studied in order to compare a scanner which is clinical feasible in terms of cost, setup dimension and scan time to the results obtainable via the high flux and monochromatic X-ray beam synchrotron based experimental scanner

Breast cancer: imaging and radiotherapy with synchrotron radiation

The breast cancer is the most common cancer in woman worldwide. In this scenario, two aspects are very important: the early diagnosis and the efficacy of the care. The gold standard for the screening of breast cancer is the two-view mammography and the standard care includes surgery, usually coupled with chemotherapy or radiotherapy with 6-MV X-ray tangential beams from a linear accelerator. The problem of superimposition of tissue along the direction of the beam, which can make difficult the task of lesion detection in mammography, has led to the development of 3D techniques – such as Digital Breast Tomosynthesis (DBT) and Breast Computed Tomography (BCT) – which resolve the breast anatomy also in the longitudinal direction. In addition, in the last decades the use of phase-contrast (PhC) imaging techniques (which permit to detect the phase-shift of the X-ray beam in tissue) produced improvements in the detection of breast cancer. As regards adjuvant radiotherapy of breast cancer, an effective treatment has to guarantee the maximum sparing to the healty tissues, in particular to the skin. For this purpose, new techniques – such as IMRT, helical tomotherapy, VMAT – are under clinical investigation. Moreover, new kilovoltage rotational radiotherapy techniques with X-ray beam from orthovoltage X-ray tube as well as linear accelerator have been proposed. In this work, we investigated the use of the synchrotron radiation (SR) for both low-dose phase-contrast breast computed tomography (PhC-BCT) and breast rotational radiotherapy, via Monte Carlo simulations and measurements. Experiments were conducted at three different synchrotron radiation facilities: ELETTRA (Trieste, Italy), ESRF (Granoble, France), Australian Synchrotron (Melbourne, Australia). Phase contrast mammography on a cohort of patients was pioneered at ELETTRA in the last decade, showing the advantage of propagation based PhC imaging in producing higher conspicuity of breast masses; the ongoing projects at ELETTRA aim at devising a setup and a protocol for future computed tomography (CT) scans of the breast. The first part of the work, carried out in the framework of the SYRMA-CT/3D projects funded by INFN (National Institute for Nuclear Physics, Italy), showed the dosimetry measurements as well as the first imaging test of PhC-BCT at ELETTRA, carried out at 38 keV or lower energies. New dose metrics were introduced to take into account the partial breast irradiation envisaged for the exam; in addition, we carried out a characterization of dosimeters (TLD GR-200A and radiochromic film XR-QA2) to be employed for beam and phantom dosimetry. Finally, we showed the results of the first imaging test with a breast tissue specimen.In the second part of this PhD work, we demonstrated the feasibility of rotational breast radiotherapy with synchrotron radiation laying the foundations for the study of a new image-guided radiotherapy technique for breast cancer. This technique employs the same setup used for BCT but uses higher energies (60–120 keV) and higher intensity SR beams. The use of such low photon energies (with respect to megavoltage photon energies used in conventional radiotherapy) would provide a higher dose-enhancement when a radiosensitizing (e.g. gold nanoparticles) is used for breast radiotherapy. Possible applications of this technique could be the treatment of the small lesion and hypo-fractionated radiotherapy