Diana Sima

Quantification of in vivo Magnetic Resonance Spectroscopy signals with baseline and lineshape corrections

Quantification of Magnetic Resonance Spectroscopy (MRS) signals is a method to estimate metabolite concentrations of the tissue under investigation. Estimation of these concentrations provides information about the biochemical characteristics of the tissue and are finally used as a complementary information in the diagnosis of cancer, epilepsy and metabolic diseases. Obtaining reliable metabolite concentrations is still a challenge due to the experimental conditions affecting the spectral quality. The decay of MRS signals (lineshape of MR spectra), for instance, is affected by inhomogeneities in the magnetic field caused by shimming problems and tissue heterogeneities. To handle this type of distortions, we study a method where the unsuppressed water is used to correct lineshape distortions, an inversion recovery signal is used to account for macromolecules and lipids present in the tissue and splines are used to correct additional baseline distortions. In this study, we consider rat brain in vivo signals and quantify them taking into account both lineshape distortions and the background signal.

Measurement of Whole-Brain and Gray Matter Atrophy in Multiple Sclerosis: Assessment with MR Imaging

Purpose To compare available methods for whole-brain and gray matter (GM) atrophy estimation in multiple sclerosis (MS) in terms of repeatability (same magnetic resonance [MR] imaging unit) and reproducibility (different system/field strength) for their potential clinical applications. Materials and Methods The softwares ANTs-v1.9, CIVET-v2.1, FSL-SIENAX/SIENA-5.0.1, Icometrix-MSmetrix-1.7, and SPM-v12 were compared. This retrospective study, performed between March 2015 and March 2017, collected data from (a) eight simulated MR images and longitudinal data (2 weeks) from 10 healthy control subjects to assess the cross-sectional and longitudinal accuracy of atrophy measures, (b) test-retest MR images in 29 patients with MS acquired within the same day at different imaging unit field strengths/manufacturers to evaluate precision, and (c) longitudinal data (1 year) in 24 patients with MS for the agreement between methods. Tissue segmentation, image registration, and white matter (WM) lesion filling were also evaluated. Multiple paired t tests were used for comparisons. Results High values of accuracy (0.87-0.97) for whole-brain and GM volumes were found, with the lowest values for MSmetrix. ANTs showed the lowest mean error (0.02%) for whole-brain atrophy in healthy control subjects, with a coefficient of variation of 0.5%. SPM showed the smallest mean error (0.07%) and coefficient of variation (0.08%) for GM atrophy. Globally, good repeatability (P > .05) but poor reproducibility (P < .05) were found for all methods. WM lesion filling technique mainly affected ANTs, MSmetrix, and SPM results (P < .05). Conclusion From this comparison, it would be possible to select a software for atrophy measurement, depending on the requirements of the application (research center, clinical trial) and its goal (accuracy and repeatability or reproducibility). An improved reproducibility is required for clinical application.