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Selvaganesan K, Wan Y, Ha Y, Wu B, Hancock K, Galiana G, Constable RT. Magnetic resonance imaging using a nonuniform Bo (NuBo) field-cycling magnet. PLoS One 2023; 18:e0287344. [PMID: 37319289 PMCID: PMC10270621 DOI: 10.1371/journal.pone.0287344] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 06/02/2023] [Indexed: 06/17/2023] Open
Abstract
Magnetic resonance imaging (MRI) is a powerful noninvasive diagnostic tool with superior soft tissue contrast. However, access to MRI is limited since current systems depend on homogeneous, high field strength main magnets (B0-fields), with strong switchable gradients which are expensive to install and maintain. In this work we propose a new approach to MRI where imaging is performed in an inhomogeneous field using radiofrequency spatial encoding, thereby eliminating the need for uniform B0-fields and conventional cylindrical gradient coils. The proposed technology uses an innovative data acquisition and reconstruction approach by integrating developments in field cycling, parallel imaging and non-Fourier based algebraic reconstruction. The scanner uses field cycling to image in an inhomogeneous B0-field; in this way magnetization is maximized during the high field polarization phase, and B0 inhomogeneity effects are minimized by using a low field during image acquisition. In addition to presenting the concept, this work provides experimental verification of a long-lived spin echo signal, spatially varying resolution, as well as both simulated and experimental 2D images. Our initial design creates an open MR system that can be installed in a patient examination table for body imaging (e.g., breast or liver) or built into a wall for weighted-spine imaging. The proposed system introduces a new class of inexpensive, open, silent MRIs that could be housed in doctor's offices much like ultrasound is today, making MRI more widely accessible.
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Affiliation(s)
- Kartiga Selvaganesan
- Department of Biomedical Engineering, Yale University, New Haven, CT, United States of America
| | - Yuqing Wan
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States of America
| | - Yonghyun Ha
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States of America
| | - Baosong Wu
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States of America
| | - Kasey Hancock
- Department of Electrical Engineering, Yale University, New Haven, CT, United States of America
| | - Gigi Galiana
- Department of Biomedical Engineering, Yale University, New Haven, CT, United States of America
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States of America
| | - R. Todd Constable
- Department of Biomedical Engineering, Yale University, New Haven, CT, United States of America
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States of America
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Wang H, Tam L, Kopanoglu E, Peters DC, Constable RT, Galiana G. O-space with high resolution readouts outperforms radial imaging. Magn Reson Imaging 2016; 37:107-115. [PMID: 27876569 DOI: 10.1016/j.mri.2016.11.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 11/17/2016] [Accepted: 11/17/2016] [Indexed: 11/25/2022]
Abstract
PURPOSE While O-Space imaging is well known to accelerate image acquisition beyond traditional Cartesian sampling, its advantages compared to undersampled radial imaging, the linear trajectory most akin to O-Space imaging, have not been detailed. In addition, previous studies have focused on ultrafast imaging with very high acceleration factors and relatively low resolution. The purpose of this work is to directly compare O-Space and radial imaging in their potential to deliver highly undersampled images of high resolution and minimal artifacts, as needed for diagnostic applications. We report that the greatest advantages to O-Space imaging are observed with extended data acquisition readouts. THEORY AND METHODS A sampling strategy that uses high resolution readouts is presented and applied to compare the potential of radial and O-Space sequences to generate high resolution images at high undersampling factors. Simulations and phantom studies were performed to investigate whether use of extended readout windows in O-Space imaging would increase k-space sampling and improve image quality, compared to radial imaging. RESULTS Experimental O-Space images acquired with high resolution readouts show fewer artifacts and greater sharpness than radial imaging with equivalent scan parameters. Radial images taken with longer readouts show stronger undersampling artifacts, which can cause small or subtle image features to disappear. These features are preserved in a comparable O-Space image. CONCLUSIONS High resolution O-Space imaging yields highly undersampled images of high resolution and minimal artifacts. The additional nonlinear gradient field improves image quality beyond conventional radial imaging.
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Affiliation(s)
- Haifeng Wang
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA
| | - Leo Tam
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA
| | - Emre Kopanoglu
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA
| | - Dana C Peters
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA
| | - R Todd Constable
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA; Department of Neurosurgery, Yale University, New Haven, CT 06520, USA
| | - Gigi Galiana
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT 06520, USA.
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Wang H, Tam L, Kopanoglu E, Peters DC, Constable RT, Galiana G. Experimental O-space turbo spin echo imaging. Magn Reson Med 2016; 75:1654-61. [PMID: 25981343 PMCID: PMC4644719 DOI: 10.1002/mrm.25741] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 03/23/2015] [Accepted: 03/26/2015] [Indexed: 11/08/2022]
Abstract
PURPOSE Turbo spin echo (TSE) imaging reduces imaging time by acquiring multiple echoes per repetition (TR), requiring fewer TRs. O-space can also require fewer TRs by using a combination of nonlinear magnetic gradient fields and surface coil arrays. Although to date, O-space has only been demonstrated for gradient echo imaging, it is valuable to combine these two techniques. However, collecting multiple O-space echoes per TR is difficult because of the different local k-space trajectories and variable T2-weighting. THEORY AND METHODS A practical scheme is demonstrated to combine the benefits of TSE and O-space for highly accelerated T2-weighted images. The scheme uses a modified acquisition order and filtered projection reconstruction to reduce artifacts caused by T2 decay, while retaining T2 contrast that corresponds to a specific echo time. RESULTS The experiments revealed that the proposed method can produce highly accelerated T2-weighted images. Moreover, the method can generate multiple images with different T2 contrasts from a single dataset. CONCLUSIONS The proposed O-space TSE imaging method requires fewer echoes than conventional TSE and fewer repetitions than conventional O-space imaging. It retains resilience to undersampling, clearly outperforming Cartesian SENSE at high levels of undersampling, and can generate undistorted images with a range of T2 contrast from a single acquired dataset.
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Affiliation(s)
- Haifeng Wang
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
| | - Leo Tam
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
| | - Emre Kopanoglu
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
| | - Dana C. Peters
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
| | - R. Todd Constable
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
- Department of Biomedical Engineering, Yale University, New Haven, CT,
USA
| | - Gigi Galiana
- Department of Diagnostic Radiology, Yale University, New Haven, CT,
USA
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Wang H, Tam LK, Constable RT, Galiana G. Fast rotary nonlinear spatial acquisition (FRONSAC) imaging. Magn Reson Med 2016; 75:1154-65. [PMID: 25950279 PMCID: PMC4637004 DOI: 10.1002/mrm.25703] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 02/20/2015] [Accepted: 02/26/2015] [Indexed: 11/10/2022]
Abstract
PURPOSE Nonlinear spatial encoding magnetic fields (SEMs) have been studied to reconstruct images from a minimum number of echoes. Previous work has also explored single shot trajectories in nonlinear SEMs. However, the search continues for optimal schemes that apply nonlinear SEMs to improve spatial encoding efficiency and image quality. THEORY AND METHODS We enhance the encoding efficiency of standard linear gradient trajectories by adding a rapidly rotating nonlinear SEM of moderate amplitude, the so called FRONSAC (Fast ROtary Nonlinear Spatial ACquisition) imaging. This additional gradient greatly improves the image quality of highly undersampled single-shot trajectories, including EPI, Spiral, and Rosette trajectories. RESULTS Our simulations, including noise and dephasing effects, test the effect of adding FRONSAC gradients, demonstrating the applicability of this approach. Performance is explained by demonstrating the additional k-space sampling the nonlinear gradient provides. Studies of the optimal amplitude and frequency of the additional FRONSAC field are presented, and the role of enhanced sampling during the readout demonstrated. Dynamic field mapping in a second-order gradient system shows the proposed gradient waveforms are feasible. CONCLUSION Images resulting from highly undersampled existing k-space trajectories, such as EPI, Spiral, and Rosette, are greatly enhanced simply by adding a rotating nonlinear SEM field.
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Affiliation(s)
- Haifeng Wang
- Department of Diagnostic Radiology, Yale University, New Haven, CT, USA
| | - Leo K. Tam
- Department of Diagnostic Radiology, Yale University, New Haven, CT, USA
| | - R. Todd Constable
- Department of Diagnostic Radiology, Yale University, New Haven, CT, USA
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
- Department of Neurosurgery, Yale University, New Haven, CT, USA
| | - Gigi Galiana
- Department of Diagnostic Radiology, Yale University, New Haven, CT, USA
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Stockmann JP, Witzel T, Keil B, Polimeni JR, Mareyam A, LaPierre C, Setsompop K, Wald LL. A 32-channel combined RF and B0 shim array for 3T brain imaging. Magn Reson Med 2015; 75:441-51. [PMID: 25689977 DOI: 10.1002/mrm.25587] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Accepted: 11/26/2014] [Indexed: 01/06/2023]
Abstract
PURPOSE We add user-controllable direct currents (DC) to the individual elements of a 32-channel radio-frequency (RF) receive array to provide B0 shimming ability while preserving the array's reception sensitivity and parallel imaging performance. METHODS Shim performance using constrained DC current (± 2.5A) is simulated for brain arrays ranging from 8 to 128 elements. A 32-channel 3-tesla brain array is realized using inductive chokes to bridge the tuning capacitors on each RF loop. The RF and B0 shimming performance is assessed in bench and imaging measurements. RESULTS The addition of DC currents to the 32-channel RF array is achieved with minimal disruption of the RF performance and/or negative side effects such as conductor heating or mechanical torques. The shimming results agree well with simulations and show performance superior to third-order spherical harmonic (SH) shimming. Imaging tests show the ability to reduce the standard frontal lobe susceptibility-induced fields and improve echo planar imaging geometric distortion. The simulation of 64- and 128-channel brain arrays suggest that even further shimming improvement is possible (equivalent to up to 6th-order SH shim coils). CONCLUSION Including user-controlled shim currents on the loops of a conventional highly parallel brain array coil is feasible with modest current levels and produces improved B0 shimming performance over standard second-order SH shimming.
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Affiliation(s)
- Jason P Stockmann
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - Thomas Witzel
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.,Harvard Medical School, Boston, Massachusetts, USA
| | - Boris Keil
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.,Harvard Medical School, Boston, Massachusetts, USA
| | - Jonathan R Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.,Harvard Medical School, Boston, Massachusetts, USA
| | - Azma Mareyam
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - Cristen LaPierre
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.,Harvard Medical School, Boston, Massachusetts, USA
| | - Lawrence L Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.,Harvard Medical School, Boston, Massachusetts, USA.,Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA
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