1
|
Sveinsson B, Koonjoo N, Zhu B, Witzel T, Rosen MS. Detection of nanotesla AC magnetic fields using steady-state SIRS and ultra-low field MRI. J Neural Eng 2020; 17:034001. [PMID: 32268305 DOI: 10.1088/1741-2552/ab87fe] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Functional magnetic resonance imaging (fMRI) is commonly used to measure brain activity through the blood oxygen level dependent (BOLD) signal mechanism, but this only provides an indirect proxy signal to neuronal activity. Magnetoencephalography (MEG) provides a more direct measurement of the magnetic fields created by neuronal currents in the brain, but requires very specialized hardware and only measures these fields at the scalp. Recently, progress has been made to directly detect neuronal fields with MRI using the stimulus-induced rotary saturation (SIRS) effect, but interference from the BOLD response complicates such measurements. Here, we describe an approach to detect nanotesla-level, low-frequency alternating magnetic fields with an ultra-low field (ULF) MRI scanner, unaffected by the BOLD signal. APPROACH A steady-state implementation of the stimulus-induced rotary saturation (SIRS) method is developed. The method is designed to generate a strong signal at ultra-low magnetic field as well as allowing for efficient signal averaging, giving a high contrast-to-noise ratio (CNR). The method is tested in computer simulations and in phantom scans. MAIN RESULTS The simulations and phantom scans demonstrated the ability of the method to measure magnetic fields at different frequencies at ULF with a stronger contrast than non-steady-state approaches. Furthermore, the rapid imaging functionality of the method reduced noise efficiently. The results demonstrated sufficient CNR down to 7 nT, but the sensitivity will depend on the imaging parameters. SIGNIFICANCE A steady-state SIRS method is able to detect low-frequency alternating magnetic fields at ultra-low main magnetic field strengths with a large signal response and contrast-to-noise, presenting an important step in sensing biological fields with ULF MRI.
Collapse
Affiliation(s)
- Bragi Sveinsson
- A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States of America. Department of Radiology, Harvard Medical School, Boston, MA, United States of America. Author to whom any correspondence should be addressed
| | | | | | | | | |
Collapse
|
2
|
Ito Y, Ueno M, Kobayashi T. Neural magnetic field dependent fMRI toward direct functional connectivity measurements: A phantom study. Sci Rep 2020; 10:5463. [PMID: 32214147 PMCID: PMC7096527 DOI: 10.1038/s41598-020-62277-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 03/10/2020] [Indexed: 11/16/2022] Open
Abstract
Recently, the main issue in neuroscience has been the imaging of the functional connectivity in the brain. No modality that can measure functional connectivity directly, however, has been developed yet. Here, we show the novel MRI sequence, called the partial spinlock sequence toward direct measurements of functional connectivity. This study investigates a probable measurement of phase differences directly associated with functional connectivity. By employing partial spinlock imaging, the neural magnetic field might influence the magnetic resonance signals. Using simulation and phantom studies to model the neural magnetic fields, we showed that magnetic resonance signals vary depending on the phase of an externally applied oscillating magnetic field with non-right flip angles. These results suggest that the partial spinlock sequence is a promising modality for functional connectivity measurements.
Collapse
Affiliation(s)
- Yosuke Ito
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan.
| | - Masahito Ueno
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan
| | - Tetsuo Kobayashi
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan
| |
Collapse
|
3
|
Feasibility of functional MRI at ultralow magnetic field via changes in cerebral blood volume. Neuroimage 2018; 186:185-191. [PMID: 30394329 DOI: 10.1016/j.neuroimage.2018.10.071] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Revised: 10/24/2018] [Accepted: 10/26/2018] [Indexed: 11/23/2022] Open
Abstract
We investigate the feasibility of performing functional MRI (fMRI) at ultralow field (ULF) with a Superconducting QUantum Interference Device (SQUID), as used for detecting magnetoencephalography (MEG) signals from the human head. While there is negligible magnetic susceptibility variation to produce blood oxygenation level-dependent (BOLD) contrast at ULF, changes in cerebral blood volume (CBV) may be a sensitive mechanism for fMRI given the five-fold spread in spin-lattice relaxation time (T1) values across the constituents of the human brain. We undertook simulations of functional signal strength for a simplified brain model involving activation of a primary cortical region in a manner consistent with a blocked task experiment. Our simulations involve measured values of T1 at ULF and experimental parameters for the performance of an upgraded ULFMRI scanner. Under ideal experimental conditions we predict a functional signal-to-noise ratio of between 3.1 and 7.1 for an imaging time of 30 min, or between 1.5 and 3.5 for a blocked task experiment lasting 7.5 min. Our simulations suggest it may be feasible to perform fMRI using a ULFMRI system designed to perform MRI and MEG in situ.
Collapse
|
4
|
Huang X, Dong H, Qiu Y, Li B, Tao Q, Zhang Y, Krause HJ, Offenhäusser A, Xie X. Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 286:52-59. [PMID: 29183004 DOI: 10.1016/j.jmr.2017.11.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 11/16/2017] [Accepted: 11/17/2017] [Indexed: 06/07/2023]
Abstract
Power-line harmonic interference and fixed-frequency noise peaks may cause stripe-artifacts in ultra-low field (ULF) magnetic resonance imaging (MRI) in an unshielded environment and in a conductively shielded room. In this paper we describe an adaptive suppression method to eliminate these artifacts in MRI images. This technique utilizes spatial correlation of the interference from different positions, and is realized by subtracting the outputs of the reference channel(s) from those of the signal channel(s) using wavelet analysis and the least squares method. The adaptive suppression method is first implemented to remove the image artifacts in simulation. We then experimentally demonstrate the feasibility of this technique by adding three orthogonal superconducting quantum interference device (SQUID) magnetometers as reference channels to compensate the output of one 2nd-order gradiometer. The experimental results show great improvement in the imaging quality in both 1D and 2D MRI images at two common imaging frequencies, 1.3 kHz and 4.8 kHz. At both frequencies, the effective compensation bandwidth is as high as 2 kHz. Furthermore, we examine the longitudinal relaxation times of the same sample before and after compensation, and show that the MRI properties of the sample did not change after applying adaptive suppression. This technique can effectively increase the imaging bandwidth and be applied to ULF MRI detected by either SQUIDs or Faraday coil in both an unshielded environment and a conductively shielded room.
Collapse
Affiliation(s)
- Xiaolei Huang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hui Dong
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany.
| | - Yang Qiu
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany; China Jiliang University, Hangzhou 310018, China
| | - Bo Li
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany; China Jiliang University, Hangzhou 310018, China
| | - Quan Tao
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Institute of Complex Systems (ICS-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany
| | - Yi Zhang
- Institute of Complex Systems (ICS-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany
| | - Hans-Joachim Krause
- Institute of Complex Systems (ICS-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany. h.-
| | - Andreas Offenhäusser
- Institute of Complex Systems (ICS-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany
| | - Xiaoming Xie
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, China; CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai 200050, China; Joint Research Institute on Functional Materials and Electronics, Collaboration between SIMIT and FZJ, Germany
| |
Collapse
|
5
|
Ahlfors SP, Wreh C. Modeling the effect of dendritic input location on MEG and EEG source dipoles. Med Biol Eng Comput 2015; 53:879-87. [PMID: 25863693 PMCID: PMC4573790 DOI: 10.1007/s11517-015-1296-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 04/02/2015] [Indexed: 12/18/2022]
Abstract
The cerebral sources of magneto- and electroencephalography (MEG, EEG) signals can be represented by current dipoles. We used computational modeling of realistically shaped passive-membrane dendritic trees of pyramidal cells from the human cerebral cortex to examine how the spatial distribution of the synaptic inputs affects the current dipole. The magnitude of the total dipole moment vector was found to be proportional to the vertical location of the synaptic input. The dipole moment had opposite directions for inputs above and below a reversal point located near the soma. Inclusion of shunting-type inhibition either suppressed or enhanced the current dipole, depending on whether the excitatory and inhibitory synapses were on the same or opposite side of the reversal point. Relating the properties of the macroscopic current dipoles to dendritic current distributions can help to provide means for interpreting MEG and EEG data in terms of synaptic connection patterns within cortical areas.
Collapse
Affiliation(s)
- Seppo P Ahlfors
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Medical School, 149 13th Street, Rm 2301, Charlestown, MA, 02129, USA.
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, 02135, USA.
| | - Christopher Wreh
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Medical School, 149 13th Street, Rm 2301, Charlestown, MA, 02129, USA
| |
Collapse
|
6
|
Current density imaging sequence for monitoring current distribution during delivery of electric pulses in irreversible electroporation. Biomed Eng Online 2015; 14 Suppl 3:S6. [PMID: 26356233 PMCID: PMC4565567 DOI: 10.1186/1475-925x-14-s3-s6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Background Electroporation is gaining its importance in everyday clinical practice of cancer treatment. For its success it is extremely important that coverage of the target tissue, i.e. treated tumor, with electric field is within the specified range. Therefore, an efficient tool for the electric field monitoring in the tumor during delivery of electroporation pulses is needed. The electric field can be reconstructed by the magnetic resonance electric impedance tomography method from current density distribution data. In this study, the use of current density imaging with MRI for monitoring current density distribution during delivery of irreversible electroporation pulses was demonstrated. Methods Using a modified single-shot RARE sequence, where four 3000 V and 100 μs long pulses were included at the start, current distribution between a pair of electrodes inserted in a liver tissue sample was imaged. Two repetitions of the sequence with phases of refocusing radiofrequency pulses 90° apart were needed to acquire one current density image. For each sample in total 45 current density images were acquired to follow a standard protocol for irreversible electroporation where 90 electric pulses are delivered at 1 Hz. Results Acquired current density images showed that the current density in the middle of the sample increased from first to last electric pulses by 60%, i.e. from 8 kA/m2 to 13 kA/m2 and that direction of the current path did not change with repeated electric pulses significantly. Conclusions The presented single-shot RARE-based current density imaging sequence was used successfully to image current distribution during delivery of short high-voltage electric pulses. The method has a potential to enable monitoring of tumor coverage by electric field during irreversible electroporation tissue ablation.
Collapse
|
7
|
Balasubramanian M, Mulkern RV, Wells WM, Sundaram P, Orbach DB. Magnetic resonance imaging of ionic currents in solution: the effect of magnetohydrodynamic flow. Magn Reson Med 2014; 74:1145-55. [PMID: 25273917 DOI: 10.1002/mrm.25445] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 07/25/2014] [Accepted: 08/15/2014] [Indexed: 11/06/2022]
Abstract
PURPOSE Reliably detecting MRI signals in the brain that are more tightly coupled to neural activity than blood-oxygen-level-dependent fMRI signals could not only prove valuable for basic scientific research but could also enhance clinical applications such as epilepsy presurgical mapping. This endeavor will likely benefit from an improved understanding of the behavior of ionic currents, the mediators of neural activity, in the presence of the strong magnetic fields that are typical of modern-day MRI scanners. THEORY Of the various mechanisms that have been proposed to explain the behavior of ionic volume currents in a magnetic field, only one-magnetohydrodynamic flow-predicts a slow evolution of signals, on the order of a minute for normal saline in a typical MRI scanner. METHODS This prediction was tested by scanning a volume-current phantom containing normal saline with gradient-echo-planar imaging at 3 T. RESULTS Greater signal changes were observed in the phase of the images than in the magnitude, with the changes evolving on the order of a minute. CONCLUSION These results provide experimental support for the MHD flow hypothesis. Furthermore, MHD-driven cerebrospinal fluid flow could provide a novel fMRI contrast mechanism.
Collapse
Affiliation(s)
- Mukund Balasubramanian
- Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Robert V Mulkern
- Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - William M Wells
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Padmavathi Sundaram
- Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Darren B Orbach
- Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| |
Collapse
|
8
|
Kim K, Lee SJ, Kang CS, Hwang SM, Lee YH, Yu KK. Toward a brain functional connectivity mapping modality by simultaneous imaging of coherent brainwaves. Neuroimage 2014; 91:63-9. [PMID: 24473099 DOI: 10.1016/j.neuroimage.2014.01.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 12/18/2013] [Accepted: 01/18/2014] [Indexed: 10/25/2022] Open
Abstract
Matching the proton-magnetic-resonance frequency to the frequency of a periodic neural oscillation (e.g., alpha or gamma band waves) by magnetic resonance imaging techniques, enables direct visualization of brain functional connectivity. Functional connectivity has been studied by analyzing the correlation between coherent neural oscillations in different areas of the brain. In electro- or magneto-encephalography, coherent source reconstruction in a source-space is very tricky due to power leaking from the correlation among the sources. For this reason, most studies have been limited to sensor-space analyses, which give doubtful results because of volume current mixing. The direct visualization of coherent brain oscillations can circumvent this problem. The feasibility of this idea was demonstrated by conducting phantom experiments with a SQUID-based, micro-Tesla NMR/MRI system. We introduce an experimental trick, an effective step-up of the measurement B-field in a pulse sequence, to decouple the magnetic resonance signal from the strong magneto-encephalographic signal at the same frequency.
Collapse
Affiliation(s)
- Kiwoong Kim
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea.
| | - Seong-Joo Lee
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea
| | - Chan Seok Kang
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea
| | - Seong-Min Hwang
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea
| | - Yong-Ho Lee
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea
| | - Kwon-Kyu Yu
- Center for Brain and Cognition Measurement, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340, Republic of Korea
| |
Collapse
|
9
|
Körber R, Nieminen JO, Höfner N, Jazbinšek V, Scheer HJ, Kim K, Burghoff M. An advanced phantom study assessing the feasibility of neuronal current imaging by ultra-low-field NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 237:182-190. [PMID: 24252245 DOI: 10.1016/j.jmr.2013.10.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 10/17/2013] [Accepted: 10/19/2013] [Indexed: 06/02/2023]
Abstract
In ultra-low-field (ULF) NMR/MRI, a common scheme is to magnetize the sample by a polarizing field of up to hundreds of mT, after which the NMR signal, precessing in a field on the order of several μT, is detected with superconducting quantum interference devices (SQUIDs). In our ULF-NMR system, we polarize with up to 50mT and deploy a single-stage DC-SQUID current sensor with an integrated input coil which is connected to a wire-wound Nb gradiometer. We developed this system (white noise 0.50fT/√Hz) for assessing the feasibility of imaging neuronal currents by detecting their effect on the ULF-NMR signal. Magnetoencephalography investigations of evoked brain activity showed neuronal dipole moments below 50nAm. With our instrumentation, we have studied two different approaches for neuronal current imaging. In the so-called DC effect, long-lived neuronal activity shifts the Larmor frequency of the surrounding protons. An alternative strategy is to exploit fast neuronal activity as a tipping pulse. This so-called AC effect requires the proton Larmor frequency to match the frequency of the neuronal activity, which ranges from near-DC to ∼kHz. We emulated neuronal activity by means of a single dipolar source in a physical phantom, consisting of a hollow sphere filled with an aqueous solution of CuSO4 and NaCl. In these phantom studies, with physiologically relevant dipole depths, we determined resolution limits for our set-up for the AC and the DC effect of ∼10μAm and ∼50nAm, respectively. Hence, the DC effect appears to be detectable in vivo by current ULF-NMR technology.
Collapse
Affiliation(s)
- Rainer Körber
- Physikalisch-Technische Bundesanstalt (PTB), Abbestrasse 2-12, 10587 Berlin, Germany.
| | - Jaakko O Nieminen
- Physikalisch-Technische Bundesanstalt (PTB), Abbestrasse 2-12, 10587 Berlin, Germany; Department of Biomedical Engineering and Computational Science, Aalto University School of Science, P.O. Box 12200, FI-00076 AALTO, Finland
| | - Nora Höfner
- Physikalisch-Technische Bundesanstalt (PTB), Abbestrasse 2-12, 10587 Berlin, Germany
| | - Vojko Jazbinšek
- Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana, Slovenia
| | - Hans-Jürgen Scheer
- Physikalisch-Technische Bundesanstalt (PTB), Abbestrasse 2-12, 10587 Berlin, Germany
| | - Kiwoong Kim
- Korea Research Institute of Standards and Science, Daejeon 305-340, South Korea
| | - Martin Burghoff
- Physikalisch-Technische Bundesanstalt (PTB), Abbestrasse 2-12, 10587 Berlin, Germany
| |
Collapse
|
10
|
Abstract
We present in vivo images of the human brain acquired with an ultralow field MRI (ULFMRI) system operating at a magnetic field B0 ~ 130 μT. The system features prepolarization of the proton spins at Bp ~ 80 mT and detection of the NMR signals with a superconducting, second-derivative gradiometer inductively coupled to a superconducting quantum interference device (SQUID). We report measurements of the longitudinal relaxation time T1 of brain tissue, blood, and scalp fat at B0 and Bp, and cerebrospinal fluid at B0. We use these T1 values to construct inversion recovery sequences that we combine with Carr-Purcell-Meiboom-Gill echo trains to obtain images in which one species can be nulled and another species emphasized. In particular, we show an image in which only blood is visible. Such techniques greatly enhance the already high intrinsic T1 contrast obtainable at ULF. We further present 2D images of T1 and the transverse relaxation time T2 of the brain and show that, as expected at ULF, they exhibit similar contrast. Applications of brain ULFMRI include integration with systems for magnetoencephalography. More generally, these techniques may be applicable, for example, to the imaging of tumors without the need for a contrast agent and to modalities recently demonstrated with T1ρ contrast imaging (T1 in the rotating frame) at fields of 1.5 T and above.
Collapse
|
11
|
Nagahara S, Kobayashi T. Bloch simulations towards direct detection of oscillating magnetic fields using MRI with spin-lock sequence. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2013:1061-1064. [PMID: 24109874 DOI: 10.1109/embc.2013.6609687] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A new MRI method using the spin-lock sequence has attracted wide attention because of its potential for detecting small oscillating magnetic fields. However, as the mechanism involved is complicated, we visualized the magnetization performance during the spin-lock sequence in order to better understand interaction of the spin-lock pulse and the externally applied oscillating magnetic fields by means of a fast-and-simple method using matrix operations to solve a time-dependent Bloch equation. To improve spin-lock imaging in the detection of small magnetic fields (in an fMRI experiment that modeled neural magnetic fields), we observed that the phenomenon decreases MR signals, which led us to investigate how spin-lock parameters cause the MR signal to decrease; based on this, we determined that MR signals decrease in oscillating magnetic fields that are resonant with the spin-lock pulse. We also determined that MR signals decrease is directly proportional to spin-lock duration. Our results suggest that MRI can feasibly detect oscillating magnetic fields directly by using of the spin-lock sequence.
Collapse
|
12
|
NAGAHARA S, UENO M, KOBAYASHI T. Spin-Lock Imaging for Direct Detection of Oscillating Magnetic Fields with MRI: Simulations and Phantom Studies. ADVANCED BIOMEDICAL ENGINEERING 2013. [DOI: 10.14326/abe.2.63] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Affiliation(s)
- Shizue NAGAHARA
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University
- Research Fellow of the Japan Society for the Promotion of Science
| | - Masahito UENO
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University
| | - Tetsuo KOBAYASHI
- Department of Electrical Engineering, Graduate School of Engineering, Kyoto University
| |
Collapse
|
13
|
Magnetic resonance imaging at frequencies below 1 kHz. Magn Reson Imaging 2012; 31:171-7. [PMID: 22898690 DOI: 10.1016/j.mri.2012.06.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 05/31/2012] [Accepted: 06/16/2012] [Indexed: 11/23/2022]
Abstract
Within the magnetic resonance imaging (MRI) community the trend is going to higher and higher magnetic fields, ranging from 1.5 T to 7 T, corresponding to Larmor frequencies of 63.8-298 MHz. Since for high-field MRI the magnetization increases with the applied magnetic field, the signal-to-noise-ratio increases as well, thus enabling higher image resolutions. On the other hand, MRI is possible also at ultra-low magnetic fields, as was shown by different groups. The goal of our development was to reach a Larmor frequency range of the low-field MRI system corresponding to the frequency range of human brain activities ranging from near zero-frequency (near-DC) to over 1 kHz. Here, first 2D MRI images of phantoms taken at Larmor frequencies of 100 Hz and 731 Hz will be shown and discussed. These frequencies are examples of brain activity triggered by electrostimulation of the median nerve. The method will allow the magnetic fields of the brain currents to influence the magnetic resonance image, and thus lead to a direct functional imaging modality of neuronal currents.
Collapse
|
14
|
Vesanen PT, Nieminen JO, Zevenhoven KCJ, Dabek J, Parkkonen LT, Zhdanov AV, Luomahaara J, Hassel J, Penttilä J, Simola J, Ahonen AI, Mäkelä JP, Ilmoniemi RJ. Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer. Magn Reson Med 2012; 69:1795-804. [PMID: 22807201 DOI: 10.1002/mrm.24413] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 05/08/2012] [Accepted: 06/24/2012] [Indexed: 11/10/2022]
Abstract
Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device.
Collapse
Affiliation(s)
- Panu T Vesanen
- Department of Biomedical Engineering and Computational Science, Aalto University School of Science, Espoo, Finland.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Höfner N, Albrecht HH, Cassará AM, Curio G, Hartwig S, Haueisen J, Hilschenz I, Körber R, Martens S, Scheer HJ, Voigt J, Trahms L, Burghoff M. Are brain currents detectable by means of low-field NMR? A phantom study. Magn Reson Imaging 2011; 29:1365-73. [PMID: 21907519 DOI: 10.1016/j.mri.2011.07.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 05/16/2011] [Accepted: 07/06/2011] [Indexed: 11/30/2022]
Abstract
A number of different methods have been developed in order to detect the spreading of neuronal currents by means of noninvasive imaging techniques. However, all of these are subjected to limitations in the temporal or spatial resolution. A new approach of neuronal current detection is based on the use of low-field nuclear magnetic resonance (LF-NMR) that records brain activity directly. In the following, we describe a phantom study in order to assess the feasibility of neuronal current detection using LF-NMR. In addition to that, necessary preliminary subject studies examining somatosensory evoked neuronal currents are presented. During the phantom study, the influences of two different neuronal time signals on (1)H-NMR signals were observed. The measurements were carried out by using a head phantom with an integrated current dipole to simulate neuronal activity. Two LF-NMR methods based on a DC and an AC (resonant) mechanism were utilized to study the feasibility of detecting both types of magnetic brain signals. Measurements were made inside an extremely magnetically shielded room by using a superconducting quantum interference device magnetometer system. The measurement principles were validated applying currents of higher intensity than those typical of the neuronal currents. Through stepwise reduction of the amplitude of the current dipole strength, the resolution limits of the two measuring procedures were found. The results indicate that it is necessary to improve the signal-to-noise ratio of the measurement system by at least a factor of 38 in order to detect typical human neuronal activity directly by means of LF-NMR. In addition to that, ways of achieving this factor are discussed.
Collapse
Affiliation(s)
- Nora Höfner
- Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, D-10587 Berlin, Germany.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Körber R, Curio G, Hartwig S, Hilschenz I, Höfner N, Scheer HJ, Trahms L, Voigt J, Burghoff M. Simultaneous measurements of somatosensory evoked AC and near-DC MEG signals. ACTA ACUST UNITED AC 2011; 56:91-7. [DOI: 10.1515/bmt.2011.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
17
|
Biosignalverarbeitung - Zentrales Nervensystem. BIOMED ENG-BIOMED TE 2011. [DOI: 10.1515/bmt.2011.817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
18
|
Sersa I. Enhanced sensitivity current density imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 204:219-224. [PMID: 20303307 DOI: 10.1016/j.jmr.2010.02.025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 02/24/2010] [Accepted: 02/24/2010] [Indexed: 05/29/2023]
Abstract
One of the major weaknesses of current density imaging (CDI) is its poor sensitivity and therefore a need for the use of high voltage in CDI. In this work, a new CDI technique with enhanced sensitivity (ES-CDI) is presented. The ES-CDI sequence overcomes the sensitivity problem in samples with a long T(2) relaxation time that allows the use of a long current encoding period. As successful CDI detection is conditioned by a sufficiently large product of current and its application time a longer current encoding period enables the use of lower current and also lower voltage therefore significantly reducing any sample damage. In addition, the ES-CDI sequence also uses fast image signal acquisition and so enables heavy signal averaging and with it associated additional CDI sensitivity increase within the experiment time of the conventional CDI experiment. The feasibility of the ES-CDI sequence was tested on a model sample filled with physiological solution. Voltage of just 1 V and current application time of 800 ms were sufficient to detect current density of 20A/m(2) with a detection limit of 0.7A/m(2).
Collapse
Affiliation(s)
- Igor Sersa
- Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
| |
Collapse
|
19
|
Abstract
Functional MRI has become an important tool of researchers and clinicians who seek to understand patterns of neuronal activation that accompany sensory and cognitive processes. However, the interpretation of fMRI images rests on assumptions about the relationship between neuronal firing and hemodynamic response that are not firmly grounded in rigorous theory or experimental evidence. Further, the blood-oxygen-level-dependent effect, which correlates an MRI observable to neuronal firing, evolves over a period that is 2 orders of magnitude longer than the underlying processes that are thought to cause it. Here, we instead demonstrate experiments to directly image oscillating currents by MRI. The approach rests on a resonant interaction between an applied rf field and an oscillating magnetic field in the sample and, as such, permits quantitative, frequency-selective measurements of current density without spatial or temporal cancellation. We apply this method in a current loop phantom, mapping its magnetic field and achieving a detection sensitivity near the threshold required for the detection of neuronal currents. Because the contrast mechanism is under spectroscopic control, we are able to demonstrate how ramped and phase-modulated spin-lock radiation can enhance the sensitivity and robustness of the experiment. We further demonstrate the combination of these methods with remote detection, a technique in which the encoding and detection of an MRI experiment are separated by sample flow or translation. We illustrate that remotely detected MRI permits the measurement of currents in small volumes of flowing water with high sensitivity and spatial resolution.
Collapse
|
20
|
Trahms L, Burghoff M. NMR at very low fields. Magn Reson Imaging 2010; 28:1244-50. [PMID: 20409667 DOI: 10.1016/j.mri.2010.02.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Revised: 12/15/2009] [Accepted: 02/08/2010] [Indexed: 11/19/2022]
Abstract
Although nuclear magnetic resonance in low fields around or below the Earth's magnetic field is almost as old as nuclear magnetic resonance itself, the recent years have experienced a revival of this technique that is opposed to the common trend towards higher and higher fields. The background of this development is the expectation that the low-field domain may open a new window for the study of molecular structure and dynamics. Here, we will give an overview on the specific features in the low-field domain, both from the technical and from the physical point of view. In addition, we present a short passage on the option of magnetic resonance imaging in fields of the micro-Tesla range.
Collapse
Affiliation(s)
- Lutz Trahms
- Physikalisch-Technische Bundesanstalt, Berlin, Germany.
| | | |
Collapse
|
21
|
Bildgebung und Bildverarbeitung. BIOMED ENG-BIOMED TE 2010. [DOI: 10.1515/bmt.2010.701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|