Study of the thermal effects induced by magnetic resonance on endocardial leads: numerical models and experimental validation

Magnetic resonance imaging (MRI) is today precluded to patients bearing active implantable medical devices AIMDs). The great advantages related to this diagnostic modality, together with the increasing number of people benefiting from implantable devices, in particular pacemakers(PM)and carioverter/defibrillators (ICD), is prompting the scientific community the study the possibility to extend MRI also to implanted patients. The MRI induced specific absorption rate (SAR) and the consequent heating of biological tissues is one of the major concerns that makes patients bearing metallic structures contraindicated for MRI scans. To date, both in-vivo and in-vitro studies have demonstrated the potentially dangerous temperature increase caused by the radiofrequency (RF) field generated during MRI procedures in the tissues surrounding thin metallic implants. On the other side, the technical evolution of MRI scanners and of AIMDs together with published data on the lack of adverse events have reopened the interest in this field and suggest that, under given conditions, MRI can be safely performed also in implanted patients. With a better understanding of the hazards of performing MRI scans on implanted patients as well as the development of MRI safe devices, we may soon enter an era where the ability of this imaging modality may be more widely used to assist in the appropriate diagnosis of patients with devices. In this study both experimental measures and numerical analysis were performed. Aim of the study is to systematically investigate the effects of the MRI RF filed on implantable devices and to identify the elements that play a major role in the induced heating. Furthermore, we aimed at developing a realistic numerical model able to simulate the interactions between an RF coil for MRI and biological tissues implanted with a PM, and to predict the induced SAR as a function of the particular path of the PM lead. The methods developed and validated during the PhD program led to the design of an experimental framework for the accurate measure of PM lead heating induced by MRI systems. In addition, numerical models based on Finite-Differences Time-Domain (FDTD) simulations were validated to obtain a general tool for investigating the large number of parameters and factors involved in this complex phenomenon. The results obtained demonstrated that the MRI induced heating on metallic implants is a real risk that represents a contraindication in extending MRI scans also to patient bearing a PM, an ICD, or other thin metallic objects. On the other side, both experimental data and numerical results show that, under particular conditions, MRI procedures might be consider reasonably safe also for an implanted patient. The complexity and the large number of variables involved, make difficult to define a unique set of such conditions: when the benefits of a MRI investigation cannot be obtained using other imaging techniques, the possibility to perform the scan should not be immediately excluded, but some considerations are always needed.

Acquired and inherited cardiomyopathies: evaluation of cardiotoxic effects in preclinical models

Cardiomyopathies are a heterogeneous group of myocardial disorders defined by structural and functional alterations of the heart. These cardiac diseases can have both non-genetic and genetic origin. Nevertheless, a different etiology can trigger the same phenotype, as in the case of anthracycline-induced cardiotoxicity and desmin-related cardiomyopathy (DRM). Therefore, the aim of this study was to investigate the cellular mechanisms driving the development of these cardiotoxic conditions in in vitro models. Doxorubicin (DOX) is a commonly used antineoplastic drug for the treatment of a wide range of tumors. Besides, its clinical use is restricted because of dose-dependent cardiotoxicity. Our findings provided evidence that phospholipase C Beta 2 (PLCβ2) may have a critical role in DOX-induced cardiotoxicity in undifferentiated and differentiated H9c2 cell line. Interestingly, the results obtained revealed that cardiomyocytes are less sensitive to DOX, following the evaluation of cellular mechanisms such as: oxidative stress, apoptosis and cell proliferation. Nonetheless, the treatment induced a significant upregulation of PLCβ2 associated to morphological changes in both models, demonstrating the implication in a hypertrophic response. On the other hand, a hereditary DRM was associated to a missense mutation of aB crystallin (CRYAB), a chaperone protein involved in the regulation of the intermediate filament network. Since research has only been conducted on transgenic (TG) mice and neonatal rat cardiomyocytes, this study aimed at investigating cellular mechanisms triggered by CRYABR120G mutation in a hiPSC-derived DRM model. Our model confirmed the impairment of the cytoskeletal organization resulting in the formation of desmin and CRYAB aggregates and myofibril misalignment. Moreover, the missense mutation confirmed a hypertrophic cardiomyopathy phenotype, a feature of DRM patients, on cardiac engineered tissues. Lastly, these data obtained suggest that further research on PLCβ2 and CRYAB are needed to comprehend the molecular mechanisms behind the development of these 2 cardiac diseases.

Advanced studies on two animal models, murine and fish. RadKI21A626T mouse model: new insights into molecular mechanisms of enteric neuro-epithelial pathology. European sea bass: study of the effects of essential oils in different diets on the gastric system.

My PhD research period was focused on the anatomical, physiological and functional study of the gastrointestinal system on two different animal models. In two different contexts, the purpose of these two lines of research was contribute to understand how a specific genetic mutation or the adoption of a particular dietary supplement can affect gastrointestinal function. Functional gastrointestinal disorders are chronic conditions characterized by symptoms for which no organic cause can be found. Although symptoms are generally mild, a small subset of cases shows severe manifestations. This subset of patients may also have recurrent intestinal sub-occlusive episodes, but in absence of mechanical causes. This condition is referred to as chronic intestinal pseudo-obstruction, a rare, intractable chronic disease. Some mutations have been associated with CIPO. A novel causative RAD21 missense mutation was identified in a large consanguineous family, segregating a recessive form of CIPO. The present thesis was aimed to elucidate the mechanisms leading to neuropathy underlying CIPO via a recently developed conditional KI mouse carrying the RAD21 mutation. The experimental studies are based on the characterization and functional analysis of the conditional KI Rad21A626T mouse model. On the other hand aquaculture is increasing the global supply of foods. The species selected and feeds used affects the nutrients available from aquaculture, with a need to improve feed efficiency, both for economic and environmental reasons, but this will require novel innovative approaches. Nutritional strategies focused on the use of botanicals have attracted interest in animal production. Previous research indicates the positive results of using essential oils (EOs) as natural feed additives for several farmed animals. Therefore, the present study was designed to compare the effects of feed EO supplementation in two different forms (natural and composed of active ingredients obtained by synthesis) on the gastric mucosa in European sea bass.