Enhanced SPH modeling of free-surface flows with large deformations

The subject of the present thesis is the development of a numerical solver to study the violent interaction of marine flows with rigid structures. Among the many numerical models available, the Smoothed Particle Hydrodynamics (SPH) has been chosen as it proved appropriate in dealing with violent free-surface flows. Due to its Lagrangian and meshless character it can naturally handle breaking waves and fragmentation that generally are not easily treated by standard methods. On the other hand, some consolidated features of mesh-based methods, such as the solid boundary treatment, still remain unsolved issues in the SPH context. In the present work a great part of the research activity has been devoted to tackle some of the bottlenecks of the method. Firstly, an enhanced SPH model, called delta-SPH, has been proposed. In this model, a proper numerical diffusive term has been added in the continuity equation in order to remove the spurious numerical noise in the pressure field which typically affects the weakly-compressible SPH models. Then, particular attention has been paid to the development of suitable techniques for the enforcement of the boundary conditions. As for the free-surface, a specific algorithm has been designed to detect free-surface particles and to define a related level-set function with two main targets: to allow the imposition of peculiar conditions on the free-surface and to analyse and visualize more easily the simulation outcome (especially in 3D cases). Concerning the solid boundary treatment, much effort has been spent to devise new techniques for handling generic body geometries with an adequate accuracy in both 2D and 3D problems. Two different techniques have been described: in the first one the standard ghost fluid method has been extended in order to treat complex solid geometries. Both free-slip and no-slip boundary conditions have been implemented, the latter being a quite complex matter in the SPH context. The proposed boundary treatment proved to be robust and accurate in evaluating local and global loads, though it is not easy to extend to generic 3D surfaces. The second technique has been adopted for these cases. Such a technique has been developed in the context of Riemann-SPH methods and in the present work is reformulated in the context of the standard SPH scheme. The method proved to be robust in treating complex 3D solid surfaces though less accurate than the former. Finally, an algorithm to correctly initialize the SPH simulation in the case of generic geometries has been described. It forces a resettlement of the fluid particles to achieve a regular and uniform spacing even in complex configurations. This pre-processing procedure avoids the generation of spurious currents due to local defects in the particle distribution at the beginning of the simulation. The delta-SPH model has been validated against several problems concerning fluid-structure interactions. Firstly, the capability of the solver in dealing with water impacts has been tested by simulating a jet impinging on a flat plate and a dam-break flow against a vertical wall. In this cases, the accuracy in the prediction of local loads and of the pressure field have been the main focus. Then, the viscous flow around a cylinder, in both steady and unsteady conditions, has been simulated comparing the results with reference solutions. Finally, the generation and propagation of 2D gravity waves has been simulated. Several regimes of propagation have been tested and the results compared against a potential flow solver. The developed numerical solver has been applied to several cases of free-surface flows striking rigid structures and to the problem of the generation and evolution of ship generated waves. In the former case, the robustness of the solver has been challenged by simulating 2D and 3D water impacts against complex solid surfaces. The numerical outcome have been compared with analytical solutions, experimental data and other numerical results and the limits of the model have been discussed. As for the ship generated waves, the problem has been firstly studied within the 2D+t approximation, focusing on the occurrence and features of the breaking bow waves. Then, a dedicated 3D SPH parallel solver has been developed to tackle the simulation of the entire ship in constant forward motion. This simulation is quite demanding in terms of complexities of the boundary geometry and computational resources required. The wave pattern obtained has been compared against experimental data and results from other numerical methods, showing in both the cases a fair and promising agreement

Relationship between mild to moderate renal dysfunction and obstructive sleep apnea: Data from the European sleep apnea database

The relationship between severity of obstructive sleep apnea (OSA) and kidney function was investigated in the European Sleep Apnea Database (ESADA), where clinical, sleep, and biochemical data of patients studied for suspected OSA in 24 sleep centres of 17 European countries are stored. After excluding patients with missing data or extremely high/low creatinine values, data from 8112 subjects (2328 female) with creatinine values ranging between 0.5 and 2.0 mg% were analyzed. Estimated glomerular filtration rate (eGFR) was obtained with the Modified Diet in Renal Disease (MDRD) equation. Patients were subdivided into two groups: group 1 (n = 3709) studied by full polysomnography; group 2 (n = 4403) studied by nocturnal cardiorespiratory monitoring. Altogether, 8.5% subjects had an eGFR<60 ml/min/1.73m2. At univariate analysis, eGFR correlated to age, comorbidities and severity of OSA in both groups. At logistic regression analysis, risk factors for eGFR<60 were in group 1: diabetes, female gender, age, body mass index, and lowest nocturnal SaO2 (r2=0.086); in group 2: hypertension, female gender, age, and lowest nocturnal SaO2 (r2=0.087). In conclusion, as expected, comorbidities, female gender and advanced age are significant risk factors for low eGFR in subjects with OSA. While traditional severity measures of OSA (apnea/hypopnea index, oxygen desaturation index) did not contribute to low eGFR, more severe nocturnal hypoxia captured by lowest nocturnal SaO2 appeared as a significant predictor in this large patient cohort. The ESADA study is supported by ResMed and Philips Respironics

A Multimodal Knowledge-Based Deep Learning Approach for MGMT Promoter Methylation Identification

Glioblastoma Multiforme (GBM) is considered one of the most aggressive malignant tumors, characterized by a tremendously low survival rate. Despite alkylating chemotherapy being typically adopted to fight this tumor, it is known that O(6)-methylguanine-DNA methyltransferase (MGMT) enzyme repair abilities can antagonize the cytotoxic effects of alkylating agents, strongly limiting tumor cell destruction. However, it has been observed that MGMT promoter regions may be subject to methylation, a biological process preventing MGMT enzymes from removing the alkyl agents. As a consequence, the presence of the methylation process in GBM patients can be considered a predictive biomarker of response to therapy and a prognosis factor. Unfortunately, identifying signs of methylation is a non-trivial matter, often requiring expensive, time-consuming, and invasive procedures. In this work, we propose to face MGMT promoter methylation identification analyzing Magnetic Resonance Imaging (MRI) data using a Deep Learning (DL) based approach. In particular, we propose a Convolutional Neural Network (CNN) operating on suspicious regions on the FLAIR series, pre-selected through an unsupervised Knowledge-Based filter leveraging both FLAIR and T1-weighted series. The experiments, run on two different publicly available datasets, show that the proposed approach can obtain results comparable to (and in some cases better than) the considered competitor approach while consisting of less than 0.29% of its parameters. Finally, we perform an eXplainable AI (XAI) analysis to take a little step further toward the clinical usability of a DL-based approach for MGMT promoter detection in brain MRI

A negative expiratory pressure test during wakefulness for evaluating the risk of obstructive sleep apnea in patients referred for sleep studies

OBJECTIVE: Obstructive sleep apnea is characterized by increased upper airway collapsibility during sleep. The present study investigated the use of the negative expiratory pressure test as a method to rule out obstructive sleep apnea. METHODS: Flow limitation was evaluated in 155 subjects. All subjects underwent a diurnal negative expiratory pressure test and a nocturnal sleep study. The severity of sleep apnea was determined based on the apneahypopnea index. Flow limitation was assessed by computing the exhaled volume at 0.2, 0.5, and 1.0 s (V0.2, V0.5, and V1.0, respectively) during the application of a negative expiratory pressure and expressed as a percentage of the previous exhaled volume. Receiver-operating characteristic curves were constructed to identify the optimal threshold volume at 0.2, 0.5, and 1.0 s for obstructive sleep apnea detection. RESULTS: Mean expiratory volumes at 0.2 and 0.5 s were statistically higher (p <0.01) in healthy subjects than in all obstructive sleep apneic groups. Increasing disease severity was associated with lower expiratory volumes. The V0.2 (%) predictive parameters for the detection of sleep apnea were sensitivity (81.1%), specificity (93.1%), PPV (98.1%), and NPV (52.9%). Sensitivity and NPV were 96.9% and 93.2%, respectively, for moderate-to-severe obstructive sleep apnea, and both were 100% for severe obstructive sleep apnea. CONCLUSION: Flow limitation measurement by V 0.2 (%) during wakefulness may be a very reliable method to identify obstructive sleep apnea when the test is positive and could reliably exclude moderate and severe obstructive sleep apnea when the test is negative. The negative expiratory pressure test appears to be a useful screening test for suspected obstructive sleep apnea

Indocyanine green clearance test in liver transplantation: defining cut-off levels for graft viability assessment during organ retrieval and for the prediction of post-transplant graft function recovery - the Liver Indocyanine Green (LivInG) Trial Study Protocol

Introduction Viability assessment of the graft is essential to lower the risk of liver transplantation (LT) failure and need for emergency retransplantation, however, this still relies mainly on surgeon's experience. Post-LT graft function recovery assessment is also essential to aid physicians in the management of LT recipients and guide them through challenging decision making. This study aims to trial the use of indocyanine green clearance test (IGT) in the donor as an objective tool to assess graft viability and in the recipient to assess graft function recovery after LT.Methods and analysis This is an observational prospective single-centre study on consecutive liver transplant donors and recipients.Primary objective To determine the capability of IGT of predicting graft viability at the time of organ retrieval. Indocyanine green will be administered to the donor and the plasma disappearance rate (PDR) measured using the pulsidensitometric method. Some 162 IGT donor procedures will be required (alpha, 5%; beta, 20%) using an IGT-PDR cut-off value of 13% to achieve a significant discrimination between viable and non-viable grafts.Secondary objective IGT-PDR will be measured at different time-points in the LT recipient: during the anhepatic phase, after graft reperfusion, at 24 hours, on day 3 and day 7 after LT. The slope of IGT values from the donor to the recipient will be evaluated for correlation with the development of early allograft dysfunction.Ethics and dissemination This research protocol was approved by Fondazione Policlinico Universitario Agostino Gemelli IRCCS Ethics Committee (reference number: 0048466/20, study ID: 3656) and by the Italian National Transplant Center (CNT) (reference number: Prot.11/ CNT2021). Liver recipients will be required to provide written informed consent. Results will be published in international peer-reviewed scientific journals and presented in congresses

Coexistence of mastoid, frontal and vertebral hemangiomas in a patient with diabetic neuropathy: Possible correlation between diabetic angiopathy and intraosseous neoangiogenesis

: Bony hemangiomas are benign vascular lesions with an expansive growth; usually they tend to obliterate the entire bony cavity. They are typical lesion of the spinal bones, but they can rarely arise within other bones of the neurocranium. Diabetic microangiopathy is a condition characterized by the development of aberrant vessel tangles anastomosed to each other due to dysregulated neoangiogenesis. We report the case of a 56-year-old woman, suffering from type 2 diabetes mellitus, admitted to the neurology department due to a reported worsening of paresthesias and dysesthesias of the upper and lower limbs. She performed a contrast-enhanced brain CT scan that showed the presence, at the level of the right mastoid process, of an hypervascular angioma. A subsequent MRI study of the brain and spine showed the presence of multiple bone angiomas, at the level of the right frontal theca and C7, Th3, and Th7 vertebral bodies. Due to the absence of further symptoms and clinical and radiological signs of intracranial compression, the patient did not perform surgery. A radiological follow-up was advised. Although possible pathophysiological correlations between diabetes and vertebral hemangiomas are mentioned in literature, vascular lesions of this type involving vertebrae and skull base simultaneously can be discovered in a patient with chronic diabetic disease. As long as these lesions remain asymptomatic, surgical treatment is not indicated, and the patient is followed over time with radiological follow-up

Imaging of hepatocellular carcinoma recurrence after liver transplantation

Liver transplantation (LT) provides the highest survival benefit to patients with unresectable hepatocellular carcinoma (HCC). The Milan criteria have been developed for the selection of LT candidates with the goal of improving survival and maintaining an acceptable risk of HCC recurrence. Despite this, recurrence of HCC after LT occurs in up to 20% of cases and represents a major concern due to the poor prognosis of these patients. Furthermore, several extended criteria for the selection of LT candidates have been proposed to account for the growing demand for organs and the resultant increase in the risk of HCC recurrence. Radiologists should be aware that HCC can recur after LT with multiple organ involvement. Knowledge of the location and radiologic appearance of recurrent HCC is necessary to ensure the choice of the most appropriate therapy. This paper aims to comprehensively summarize the spectrum of HCC recurrence after LT and to examine and discuss the imaging features of these lesions. CRITICAL RELEVANCE STATEMENT: This paper aims to share a review of imaging findings of HCC recurrence after LT and to make radiologists familiar with the spectrum of this disease

Safeness and efficacy of 2-µm handheld thulium laser during microsurgical resection of supratentorial and infratentorial meningiomas: Experience of a single center

AimsWe performed a retrospective nonrandomized study to analyze the results of a microsurgery of intracranial meningiomas using 2-μm thulium flexible handheld laser fiber (Revolix jr).MethodsFrom February 2014 to December 2021, 75 nonconsecutive patients suffering from intracranial meningiomas, admitted in our department, have been operated on with microsurgical technique assisted by 2-μm thulium flexible handheld laser. We have reviewed demographic and clinical data to evaluate safety and efficacy of the technique.ResultsThere were no complications related to the use of the 2-μm thulium laser. We operated on a high percentage of cranial base and tentorial and posterior fossa meningioma in our series. The neurological outcome and degree of resection did not differ from previous series. The neurosurgical team found the laser easy to use and practical for avoiding bleeding and traction.ConclusionThe use of 2-μm thulium fiber handheld flexible laser in microsurgery of intracranial meningiomas seems to be safe and to facilitate tumor resection, especially in “difficult” conditions (e.g., deep seated, highly vascularized, and hard tumors). Even if in this limited retrospective trial the good functional outcome following conventional microsurgery had not further improved, nor the surgical time was reduced by laser, focusing its use on “difficult” (large and vascularized) cases may lead to different results in the future

Modelling Environmental Niche for the Endangered Crayfish Austropotamobius pallipesComplex in Northern and Central Italy

The potential distribution of endangered species is a necessary step to assess species conservation status and manage reintroduction plans. In the context of a EU project on the endangered Austropotamobius pallipescomplex, we modelled the environmental niche of the species in two large areas of Northern (Lombardy, 43 records) and Central Italy (Abruzzo, Province of Isernia, Gran Sasso e Monti della Laga National Park; 69 records). Ecological niche models (ENMs) were built by using the maximum entropy approach as implemented in the MaxEnt software, which predicts the occurrence of a species using presence-only data. The environmental niche was modelled using six variables: altitude, slope, aspect, human disturbance, mean temperature of warmest quarter and distance from stream. Each study area was modelled independently. Both ENMs obtained high performance scores as measured by the AUC index (Northern Italy: 0.854; Central Italy: 0.817). Slope in Northern Italy and the mean temperature of warmest quarter in Central Italy achieved the greatest predictive power. Our results clearly show that the endangered white-clawed crayfish has a narrow range of habitat selection in the two study areas. Our findings may help researchers to select the best sites for future reintroductions in conservation projects