Functional Magnetic Resonance Imaging in Follow-up of Cerebral Glial Tumors. Summary of the Doctoral Thesis

Abstract

The doctoral thesis “Functional magnetic resonance imaging in follow-up of cerebral glial tumors” is devoted to the two most topical yet insufficiently explored glial tumors problems: glioma cell invasion real border in vivo and distinction between brain glioma recurrence and treatment related injury. The use of conventional or structural magnetic resonance imaging (MRI) sequences in detection of glial tumor real spread before operation is limited. Pathological macro- and microscopic studies showed that the actual glial tumor cell invasion exists outside the border visible on conventional MRI. Thus, the planned amount of tumor resection and irradiation or planned chemotherapy chosen only from the structural MRI data may be insufficient. Another important, unresolved issue is the clinical and radiological distinction of glial tumor recurrence and radiation/chemotherapy induced injury, which is essential for the patient's treatment plan and prognosis. The objective of the study was to assess the usefulness of new, functional brain information-bearing MRI sequences - magnetic resonance spectroscopy and diffusion tensor imaging – firstly, in glial brain tumor specified primary radiological diagnosis, secondly, in differentiation between glial tumor recurrence and radiation/chemotherapyinduced changes in the brain. To achieve the objective, we analyzed 73 MRI scans of patients with typical glial brain tumors and 77 MRI scans of patients in clinical and radiological remission period after brain glioma treatment. The quantitative parameter of diffusion tensor imaging (fractional anisotropy - FA) was measured in selected brain areas. Metabolic ratios were calculated from choline, N-acetylaspartate, lactate/lipids, myo-inositol, and creatine spectroscopic values within identical brain areas. The brain white matter tracts were reconstructed in damaged hemisphere and compared with the opposite normal hemisphere pathways using diffusion tensor imaging 3-dimensional tractography method, color coded FA maps and color coded fiber orientation maps. This is the first study evaluating the repeatability index of FA and magnetic resonance spectroscopy measures in the tumor, zone of perifocal edema, as well as the distant and the contralateral symmetrical normal-appearing white matter. Magnetic resonance spectroscopy and diffusion tensor imaging quantitative measurements from glioma peritumoral area revealed pathological changes, despite the normal signal intensity in structural MRI. Magnetic resonance spectroscopy and diffusion tensor imaging in combination with structural magnetic resonance examination sequences enhanced vital glial tumor cells areas and infiltration border. We suggest that increased LL/Cr ratios and decreased FA values may have the superior implications in the detecting of glial tumors extent along the white matter tracts. NAA/Cr reduction and Cho/Cr increase may provide additional diagnostic value. Our study indicates that LL/Cr ratio in distal normal signal intensity area could be used as a radiation/chemotherapy effectiveness criteria, as this will reduce after the received treatment and in remission period. Using a combination of structural MRI, diffusion tensor imaging tractography, color coded fiber orientation and FA maps, it was possible to differentiate between different white matter tract lesions and appreciate the efficacy of treatment.