Evaluation of a Computer-Aided Diagnosis System in the Classification of Lesions in Breast Strain Elastography Imaging

Purpose: Evaluation of the performance of a computer-aided diagnosis (CAD) system based on the quantified color distribution in strain elastography imaging to evaluate the malignancy of breast tumors. Methods: The database consisted of 31 malignant and 52 benign lesions. A radiologist who was blinded to the diagnosis performed the visual analysis of the lesions. After six months with no eye contact on the breast images, the same radiologist and other two radiologists manually drew the contour of the lesions in B-mode ultrasound, which was masked in the elastography image. In order to measure the amount of hard tissue in a lesion, we developed a CAD system able to identify the amount of hard tissue, represented by red color, and quantify its predominance in a lesion, allowing classification as soft, intermediate, or hard. The data obtained with the CAD system were compared with the visual analysis. We calculated the sensitivity, specificity, and area under the curve (AUC) for the classification using the CAD system from the manual delineation of the contour by each radiologist. Results: The performance of the CAD system for the most experienced radiologist achieved sensitivity of 70.97%, specificity of 88.46%, and AUC of 0.853. The system presented better performance compared with his visual diagnosis, whose sensitivity, specificity, and AUC were 61.29%, 88.46%, and 0.829, respectively. The system obtained sensitivity, specificity, and AUC of 67.70%, 84.60%, and 0.783, respectively, for images segmented by Radiologist 2, and 51.60%, 92.30%, and 0.771, respectively, for those segmented by the Resident. The intra-class correlation coefficient was 0.748. The inter-observer agreement of the CAD system with the different contours was good in all comparisons. Conclusions: The proposed CAD system can improve the radiologist performance for classifying breast masses, with excellent inter-observer agreement. It could be a promising tool for clinical use

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

Uso di un software automatico per la valutazione della qualità tecnica delle immagini mammografiche per ottimizzare le performance del singolo tecnico di radiologia

Introduzione: La corretta esecuzione delle immagini mammografiche è fondamentale per aumentare la probabilità di identificare precocemente eventuali lesioni cancerose, soprattutto in ambito di screening. Il metodo anglosassone PGMI è uno tra i metodi maggiormente utilizzati per definire la correttezza del posizionamento e della compressione in mammografia. Questo elaborato ha come obiettivo principale quello di verificare se l’utilizzo da parte dei Tecnici Sanitari di Radiologia Medica (TSRM) di un software automatico di analisi delle immagini acquisite, basato sul metodo PGMI, associato ad una formazione continua, può essere considerato utile nella pratica quotidiana per migliorare la qualità tecnica di esecuzione degli esami mammografici. Materiali e metodi: Per questo studio sono stati raccolti i dati elaborati dal Software automatico Volpara Analytics, relativi alla compressione e al posizionamento delle immagini mammografiche del Progetto Screening Giovani Donne, eseguite dai TSRM presso l’UOC Radiologia Senologica dell’Istituto Oncologico Veneto di Padova. Dei 6 TSRM considerati, 1 si è unito al team a Marzo 2022. Sono stati selezionati i dati afferenti a due periodi diversi, aventi circa lo stesso numero di immagini e intervallati da un periodo di formazione: il primo pre-formazione comprende i dati tra Settembre 2021 e Dicembre 2021; il secondo, definito periodo di controllo, include i dati acquisiti successivamente alla formazione (Marzo 2022-Settembre 2022). I valori di queste due fasi differenti sono stati successivamente analizzati e confrontati tra di loro con metodo statistico per valutare eventuali progressi. Discussione e risultati: Dalle analisi eseguite confrontando i dati pre-formazione con i dati post-formazione è emerso che in media 3 criteri segnalati su 5 (61,3%) hanno visto un miglioramento in termini di percentuali e valori numerici. Si possono notare dei progressi sia nei parametri meno rispettati, sia in altri parametri, non definiti errori, ma con ampio margine di miglioramento. Conclusioni: L’utilizzo costante di un metodo di valutazione automatica, come il software Volpara Analytics, ha contribuito ad una ottimizzazione delle performance dei singoli TSRM nell’esecuzione delle immagini mammografiche, fornendo a ciascuno le conoscenze e le basi per capire gli errori e gli strumenti per poter risolvere la maggior parte di essi

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