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Identifier 000429560
Title Multiparametric semi-quantitative and quantitative study of soft tissue tumors with advanced Magnetic Resonance methods
Alternative Title Πολυμετρική ημιποσοτική και ποσοτική μελέτη όγκων μαλακών μορίων με νεότερες τεχνικές Μαγνητικού Συντονισμού
Author Νικηφοράκη, Κατερίνα
Thesis advisor Καραντάνας, Απόστολος
De Bree Eelco
Μαριάς, Κωνσταντίνος
Abstract Soft tissue tumors comprise a broad category of neoplasms with variable degree of malignancy. Accurate and early tissue characterization yields a vital role in patient management and disease prognosis. MRI is the imaging modality of choice for preoperative assessment of soft tissue tumors as it offers supreme soft tissue contrast, multi plane coverage and does not involve exposure to ionizing radiation. More importantly, multi modal MRI imaging offers insight into tissue pathology from a number of different contrast mechanisms each one highlighting a different aspect of tumor microenvironment. However, histopathologic correlation of MR findings is a necessary step for the validation of MR findings and definite tissue characterization. Contrast on MR images can indirectly characterise these properties by adjusting image contrast to be dependent on a sought-after property of tissue. Specifically, contrast on DW images is related to cell density and vascularity as derived from water mobility in tissue. DCE dynamic protocol highlights areas of increased vascular permeability through dynamic imaging during contrast medium administration. Since biomarkers related to vascularity can be derived by both DCE and DWI methods based on different theoretical assumptions, a study of agreement attracts great interest. As DWI is also indicative of tissue cellularity, which along with vascularity/permeability, is a very powerful metric of tumor aggressiveness. In paper III a correlation study is presented between the two different methodologies (DWI-DCE) in terms of statistical correlation and spatial agreement for increased tumor malignancy and conclude to a visual guide of areas within the tumor with MR findings indicative of increased malignancy. Paper IV is a study of the different DCE enhancement patterns that are indicative of viable necrotic and hypoxic tumor sites. Another robust quantitave MRI methodology dating from the early days of MR imaging is T2 and T2* relaxometry as it provides tissue specific metrics of magnetic properies, independent of acquisition parameters and thus indicative of tissue properties. For this part of the study benign lipoma patients were also enrolled and additionally phantoms were used for reference measurements. This study focused selectively on tumors of adipocytic origin as liposarcomas were the majority of soft tissue sarcomas in the patient cohort used in our study. Paper II and V inferred tissue identity and composition as manifested indirectly in multi echo T2 relaxometry measurements. Paper II introduces Spin Coupling ratio (SCratio) metric indicative of signal loss related to the spin coupling phenomenon which is a known phenomenon for healthy adipose tissue (bright fat phenomenon) but has not been studied for other tissues of lipomatous origin, such as lipomas or liposarcomas. This marker has the potential to be used for identification of areas of increased / decreased tissue differentiation within a heterogeneous neoplasm and can be a helpful tool for pre-operative tissue characterization for biopsy guiding. The study was supported by preliminary phantom results published in paper I. Paper V introduces a proposed methodology for multi exponential T2 relaxometry (Mexp) and validates the results also in comparison with the well-established ILT method on a phantom as a preliminary stage for the application of the proposed methodology to adipocytic tumors (paper VI). The proposed technique has the added advantage over the gold standard ILT method of producing voxel based parametric maps rather than ROI based T2 distributions, which is essential taking into account tissue heterogeneity. Lipomatous tumors with different degree of malignancy exhibit distinct behavior patterns as measured with Mexp, and thus the proposed method can be used along with conventional imaging methods for preoperative radiological assessment. An advanced oncologic protocol hosting all abovementioned imaging techniques was deployed in this study and resulting biomarkers were validated with histopathologic assessment in order to constitute a set of robust and clinically relevant biomarkers for the characterization of soft tissue neoplasms. Histopathologic analysis results were used for final tissue classification, necessary for the analysis of MR findings. The results presented in this thesis are useful for supporting radiological diagnosis and can also be a useful tool for optimizing imaging-driven biopsies.
Language English
Subject Biomarkers
Spin coupling ratio
Όγκοι λιπώδους αρχής
Issue date 2020-08-05
Collection   Faculty/Department--School of Medicine--Department of Medicine--Doctoral theses
  Type of Work--Doctoral theses
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