1,721,003 research outputs found
A Unified Framework For Blood Data Modeling In Dynamic Positron Emission Tomography Studies
Full text linkQuantification of dynamic PET images requires the measurement of radioligand concentrations in the arterial plasma. In general, this cannot be derived from PET images directly but it must be measured from blood samples taken from the subject’s radial artery.
The aim of this thesis was to develop and validate a unified framework for the blood data modeling, which was both biologically and experimentally informed, in order to achieve a better description of the blood data
Modelling arterial input functions in positron emission tomography dynamic studies
No full textThe quantification of dynamic positron emission tomography (PET) images often requires the invasive measures of the arterial plasma tracer concentration to be used as arterial input function (AIF). In several situations, a mathematical model is fit to the hematic data to obtain a continuous and noise-free description of the AIF. In common practice, the tri-exponential and Feng's models are generally adopted. Despite their general applicability, often these approximations of blood tracer activity do not properly describe the complex behavior of the AIF (e.g. different clearance rates of the tracers) as well as they do not account for the length of the radiotracer injection. Here we propose two models able to include the injection duration as additional information in the AIF modeling and we compare their performances in eight different datasets acquired from different PET facilities.</p
Bayesian Quantification of Contrast-Enhanced Ultrasound Images with Adaptive Inclusion of an Irreversible Component
No full textContrast Enhanced Ultrasound (CEUS) is a sensitive imaging technique to assess tissue vascularity and it can be particularly useful in early detection and grading of arthritis. In a recent study we have shown that a Gamma-variate can accurately quantify synovial perfusion and it is flexible enough to describe many heterogeneous patterns. However, in some cases the heterogeneity of the kinetics can be such that even the Gamma model does not properly describe the curve, with a high number of outliers
Periventricular remyelination failure in multiple sclerosis: a substrate for neurodegeneration
No full textIn multiple sclerosis, spontaneous remyelination is generally incomplete and heterogenous across patients. A high heterogeneity in remyelination may also exist across lesions within the same individual, suggesting the presence of local factors interfering with myelin regeneration. In this study we explored in-vivo the regional distribution of myelin repair and investigated its relationship with neurodegeneration. We first took advantage of the myelin binding property of the amyloid radiotracer [11C]PiB to conduct a longitudinal [11C]PiB positron emission tomography study in an original cohort of 19 participants with a relapsing-remitting form of multiple sclerosis, followed-up over a period of 1-4 months. We then replicated our results on an independent cohort of 40 people with multiple sclerosis followed-up over one year with magnetization transfer imaging, an MRI metrics sensitive to myelin content. For each imaging method, voxel-wise maps of myelin content changes were generated according to modality-specific thresholds. We demonstrated a selective failure of remyelination in periventricular white matter lesions of people with multiple sclerosis in both cohorts. In both the original and the replication cohort, we estimated that the probability of demyelinated voxels to remyelinate over the follow-up increased significantly as a function of the distance from ventricular cerebro-spinal fluid. Enlarged choroid plexus, a recently discovered biomarker linked to neuroinflammation, was found to be associated with the periventricular failure of remyelination in the two cohorts (r=-0.79, p = 0.0018; r=-0.40, p = 0.045 respectively), suggesting a role of the brain-cerebrospinal fluid barrier in affecting myelin repair in surrounding tissues. In both cohorts, the failure of remyelination in periventricular white matter lesions was associated with lower thalamic volume (r = 0.86, p < 0.0001; r = 0.33; p = 0.069 respectively) an imaging marker of neurodegeneration. Interestingly, we also showed an association between the periventricular failure of remyelination and regional cortical atrophy that was mediated by the number of cortex-derived tracts passing through periventricular white matter lesions, especially in patients at the relapsing-remitting stage. Our findings demonstrate that lesion proximity to ventricles is associated with a failure of myelin repair and support the hypothesis that a selective periventricular remyelination failure in combination with the large number of tracts connecting periventricular lesions with cortical areas is a key mechanism contributing to cortical damage in multiple sclerosis
A new modelling approach for quantification of [11C]PBR28 brain PET data including a vascular component
No full textUse of a Variational Bayesian inference approach for the quantification of brain PET data at the voxel level
No full textEffective connectivity of the Default Mode Network in MS patients: increased self-inhibition of the Posterior Cingulate Cortex
No full textA unified framework for plasma data modelling in dynamic Positron Emission Tomography studies
No full textKinetic modeling using a two-tissue compartment model and an additional irreversible vascular component improves the quantification of [11C]PBR28 brain PET data
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