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Fast computation of full density matrix of multispin systems for spatially localized in vivo magnetic resonance spectroscopy.

ABSTRACT: PURPOSE:Numerical simulations of three-dimensionally localized MRS spectra have been very time consuming for multispin systems because the current state-of-the-art method requires computation of a large ensemble of spins pixel-by-pixel in three dimensional space. This paper describes a highly accelerated technique for computing spatially localized MRS spectra using the full solution to the Liouville-von Neumann equation. METHODS:The time evolution of spatially localized multispin density matrix as the full solution to the Liouville-von Neumann equation was analyzed. A new technique based on one dimensional spatial projection of the full density matrix was proposed. This method was implemented using a computer program written in Java language. RESULTS:The MRS spectra calculated using the new method were found to be identical to conventional three-dimensional simulation for the same digitization of the voxel while the new method reduced computation time by orders of magnitude and led to not only improved speed but also accuracy. Applications of the new method to phantom studies of multispin systems and quantification of in vivo MRS spectra of brain were demonstrated. CONCLUSION:The dramatically enhanced computational efficiency makes accurate simulation of localized MRS spectra highly accessible for calculating basis sets for spectral quantification and for optimizing pulse sequences.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC5578626 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Fast computation of full density matrix of multispin systems for spatially localized in vivo magnetic resonance spectroscopy.

Zhang Yan Y An Li L Shen Jun J

Medical physics 20170710 8

<h4>Purpose</h4>Numerical simulations of three-dimensionally localized MRS spectra have been very time consuming for multispin systems because the current state-of-the-art method requires computation of a large ensemble of spins pixel-by-pixel in three dimensional space. This paper describes a highly accelerated technique for computing spatially localized MRS spectra using the full solution to the Liouville-von Neumann equation.<h4>Methods</h4>The time evolution of spatially localized multispin ...[more]

PMID: 28548302

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Project description:Medulloblastoma (MB) is the most common malignant brain tumor occurring in childhood and rarely found in adult. Based on transcriptome profile MB are currently classified into four major molecular groups reflecting a considerable biological heterogeneity: WNT-activated, SHH-activated, group 3 and group 4. Recently, DNA methylation profiling allowed the identification of additional subgroups within the four major molecular groups associated with different clinic-pathological and molecular features. Isocitrate Dehydrogenase-1 (IDH1) mutations have been described in several tumours, including gliomas, while in MB are exceptionally reported and not routinely investigated. By mean of magnetic resonance spectroscopy (MRS) we unequivocally assessed the presence the oncometabolite D-2-Hydroxyglutarate (2HG), a marker of IDH1 and IDH2 mutation, in a case of adult MB. Immunophenotypical work-up and methylation profiling assigned the diagnosis of MB, subclass SHH-A, and molecular testing revealed the presence of the non-canonical somatic IDH1(p.R132C) mutation and an additional GNAS mutation, also exceptionally described in MB. To our knowledge this is the first reported case of MB harboring both mutations together. Of note, tumour exhibited a heterogeneous phenotype with a tumour component displaying glial differentiation, with robust GFAP expression, and a component with conventional MB features and selective presence of GNAS mutation, suggesting coexistence of two different major tumour clones. These findings draw attention to the need of a deeper genetic characterization of MB in order to get insights into their biology and improve stratification and clinical management of the patients. Moreover, reported data underling the importance of performing MRS for the identification of IDH mutations in non-glial tumours. The use of throughput molecular profiling analysis and advanced medical imaging technology will certainly increase the frequency with which rare tumour entities will be identified. Whether they have any particular therapeutic implications or prognostic relevance requires further investigations.

Dataset Information

Fast computation of full density matrix of multispin systems for spatially localized in vivo magnetic resonance spectroscopy.

Publications

Fast computation of full density matrix of multispin systems for spatially localized in vivo magnetic resonance spectroscopy.

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