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Yen YF, Takahashi AM, Ackerman JL. X-nuclear MRS and MRI on a standard clinical proton-only MRI scanner. JOURNAL OF MAGNETIC RESONANCE OPEN 2023; 16-17:100118. [PMID: 38046796 PMCID: PMC10691785 DOI: 10.1016/j.jmro.2023.100118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
In light of the growing interest in-vivo deuterium metabolic imaging, hyperpolarized 13C, 15N, 3He, and 129Xe imaging, as well as 31P spectroscopy and imaging in large animals on clinical MR scanners, we demonstrate the use of a (radio)frequency converter system to allow X-nuclear MR spectroscopy (MRS) and MR imaging (MRI) on standard clinical MRI scanners without multinuclear capability. This is not only an economical alternative to the multinuclear system (MNS) provided by the scanner vendors, but also overcomes the frequency bandwidth problem of some vendor-provided MNSs that prohibit users from applications with X-nuclei of low magnetogyric ratio, such as deuterium (6.536 MHz/Tesla) and 15N (-4.316 MHz/Tesla). Here we illustrate the design of the frequency converter system and demonstrate its feasibility for 31P (17.235 MHz/Tesla), 13C (10.708 MHz/Tesla), and 15N MRS and MRI on a clinical MRI scanner without vendor-provided multinuclear hardware.
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Affiliation(s)
- Yi-Fen Yen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
| | - Atsushi M. Takahashi
- Department of Brain and Cognitive Sciences, McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - Jerome L. Ackerman
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
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Bhat S, Lührs M, Goebel R, Senden M. Extremely fast pRF mapping for real-time applications. Neuroimage 2021; 245:118671. [PMID: 34710584 DOI: 10.1016/j.neuroimage.2021.118671] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 09/28/2021] [Accepted: 10/20/2021] [Indexed: 11/28/2022] Open
Abstract
Population receptive field (pRF) mapping is a popular tool in computational neuroimaging that allows for the investigation of receptive field properties, their topography and interrelations in health and disease. Furthermore, the possibility to invert population receptive fields provides a decoding model for constructing stimuli from observed cortical activation patterns. This has been suggested to pave the road towards pRF-based brain-computer interface (BCI) communication systems, which would be able to directly decode internally visualized letters from topographically organized brain activity. A major stumbling block for such an application is, however, that the pRF mapping procedure is computationally heavy and time consuming. To address this, we propose a novel and fast pRF mapping procedure that is suitable for real-time applications. The method is built upon hashed-Gaussian encoding of the stimulus, which tremendously reduces computational resources. After the stimulus is encoded, mapping can be performed using either ridge regression for fast offline analyses or gradient descent for real-time applications. We validate our model-agnostic approach in silico, as well as on empirical fMRI data obtained from 3T and 7T MRI scanners. Our approach is capable of estimating receptive fields and their parameters for millions of voxels in mere seconds. This method thus facilitates real-time applications of population receptive field mapping.
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Affiliation(s)
- Salil Bhat
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Maastricht Brain Imaging Centre, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
| | - Michael Lührs
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Department of Research and Development, Brain Innovation B.V., Maastricht, the Netherlands
| | - Rainer Goebel
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Maastricht Brain Imaging Centre, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Department of Research and Development, Brain Innovation B.V., Maastricht, the Netherlands; Department of Neuroimaging and Neuromodeling, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, the Netherlands
| | - Mario Senden
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Maastricht Brain Imaging Centre, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
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Balasubramanian M, Polimeni JR, Schwartz EL. Exact geodesics and shortest paths on polyhedral surfaces. IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 2009; 31:1006-1016. [PMID: 19372606 DOI: 10.1109/tpami.2008.213] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We present two algorithms for computing distances along convex and non-convex polyhedral surfaces. The first algorithm computes exact minimal-geodesic distances and the second algorithm combines these distances to compute exact shortest-path distances along the surface. Both algorithms have been extended to compute the exact minimal-geodesic paths and shortest paths. These algorithms have been implemented and validated on surfaces for which the correct solutions are known, in order to verify the accuracy and to measure the run-time performance, which is cubic or less for each algorithm. The exact-distance computations carried out by these algorithms are feasible for large-scale surfaces containing tens of thousands of vertices, and are a necessary component of near-isometric surface flattening methods that accurately transform curved manifolds into flat representations.
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Affiliation(s)
- Mukund Balasubramanian
- Department of Cognitive and Neural Systems, Boston University, 677 Beacon Street, Boston, MA 02215, USA.
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