1
|
Yang C, Liao X, Zhang L, Zhang M, Liu Q. Virtual coil augmentation for MR coil extrapoltion via deep learning. Magn Reson Imaging 2023; 95:1-11. [PMID: 36241031 DOI: 10.1016/j.mri.2022.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 09/29/2022] [Accepted: 10/01/2022] [Indexed: 11/07/2022]
Abstract
Magnetic resonance imaging (MRI) is a widely used medical imaging modality. However, due to the limitations in hardware, scan time, and throughput, it is often clinically challenging to obtain high-quality MR images. In this article, we propose a method of using artificial intelligence to expand the coils to achieve the goal of generating the virtual coils. The main characteristic of our work is utilizing dummy variable technology to expand/extrapolate the receive coils in both image and k-space domains. The high-dimensional information formed by coil expansion is used as the prior information to improve the reconstruction performance of parallel imaging. Two main components are incorporated into the network design, namely variable augmentation technology and sum of squares (SOS) objective function. Variable augmentation provides the network with more high-dimensional prior information, which is helpful for the network to extract the deep feature information of the data. The SOS objective function is employed to solve the deficiency of k-space data training while speeding up convergence. Experimental results demonstrated its great potentials in accelerating parallel imaging reconstruction.
Collapse
Affiliation(s)
- Cailian Yang
- Department of Electronic Information Engineering, Nanchang University, Nanchang 330031, China
| | - Xianghao Liao
- Department of Electronic Information Engineering, Nanchang University, Nanchang 330031, China
| | - Liu Zhang
- Department of Electronic Information Engineering, Nanchang University, Nanchang 330031, China
| | - Minghui Zhang
- Department of Electronic Information Engineering, Nanchang University, Nanchang 330031, China
| | - Qiegen Liu
- Department of Electronic Information Engineering, Nanchang University, Nanchang 330031, China.
| |
Collapse
|
2
|
Stocker D, Manoliu A, Becker AS, Barth BK, Nanz D, Klarhöfer M, Donati OF. Impact of different phased-array coils on the quality of prostate magnetic resonance images. Eur J Radiol Open 2021; 8:100327. [PMID: 33644263 PMCID: PMC7889823 DOI: 10.1016/j.ejro.2021.100327] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 01/21/2021] [Accepted: 01/21/2021] [Indexed: 11/19/2022] Open
Abstract
Image quality is similar for different body phased-array receive coil setups. An 18-channel body phased-array receive coil setup achieved good image quality. 60-channel body phased-array receive coil setup slightly improves SNR in T2W images.
Purpose To evaluate the influence of body phased-array (BPA) receive coil setups on signal-to-noise ratio (SNR) and image quality (IQ) in prostate MRI. Methods This prospective study evaluated axial T2-weighted images (T2W-TSE) and DWI of the prostate in ten healthy volunteers with 18-channel (18CH), 30-channel and 60-channel (60CH) BPA receive coil setups. SNR and ADC values were assessed in the peripheral and transition zones (TZ). Two radiologists rated IQ features. Differences in qualitative and quantitative image features between BPA receive coil setups were compared. After correction for multiple comparisons, p-values <0.004 for quantitative and p-values <0.017 for qualitative image analysis were considered statistically significant. Results Significantly higher SNR was found in T2W-TSE images in the TZ using 60CH BPA compared to 18CH BPA coil setups (15.20 ± 4.22 vs. 7.68 ± 2.37; p = 0.001). There were no significant differences between all other quantitative (T2W-TSE, p = 0.007−0.308; DWI, p = 0.024−0.574) and qualitative image features (T2W-TSE, p = 0.083–1.0; DWI, p = 0.046–1.0). Conclusion 60CH BPA receive coil setup showed marginal SNR improvement in T2W-TSE images. Good IQ could be achieved with 18CH BPA coil setups.
Collapse
Key Words
- 18CH, BPA 18-channel body array coil
- 30CH, BPA 30-channel body array coil
- 60CH, BPA 60-channel body array coil
- ANOVA, Analysis of variances
- BPA, Body phased-array
- ERC, Endorectal coil
- ICC, Intra-class correlation coefficient
- IQR, Interquartile range
- Magnetic resonance imaging
- PSTT, Post-hoc paired-sample t-tests
- Prostate imaging
- ROIs, Region of interests
- SD, Standard deviation
- SNR, Signal to noise ratio
- Signal-to-noise ratio
- T2W-TSE, T2-weighted turbo spin echo
- mpMRI, Multi-parametric magnetic resonance imaging
- ss-DWI-EPI, Single-shot diffusion-weighting spin-echo echo-planar imaging
Collapse
Affiliation(s)
- Daniel Stocker
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
| | - Andrei Manoliu
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
- Max-Planck UCL Centre for Computational Psychiatry and Ageing Research, London, UK
- Wellcome Trust Centre for Human Neuroimaging, UCL, London, UK
- Psychiatric University Hospital, University of Zurich, Switzerland
| | - Anton S. Becker
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
| | - Borna K. Barth
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
| | - Daniel Nanz
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
- Swiss Center for Musculoskeletal Imaging, SCMI, Balgrist Campus AG, Switzerland and Medical Faculty, University of Zurich, Zurich, Switzerland
| | | | - Olivio F. Donati
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich and University of Zurich, Switzerland
- Corresponding author at: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, CH-8091, Zurich, Switzerland.
| |
Collapse
|
3
|
Hennig J, Kiviniemi V, Riemenschneider B, Barghoorn A, Akin B, Wang F, LeVan P. 15 Years MR-encephalography. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2020; 34:85-108. [PMID: 33079327 PMCID: PMC7910380 DOI: 10.1007/s10334-020-00891-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 09/02/2020] [Accepted: 09/29/2020] [Indexed: 02/07/2023]
Abstract
Objective This review article gives an account of the development of the MR-encephalography (MREG) method, which started as a mere ‘Gedankenexperiment’ in 2005 and gradually developed into a method for ultrafast measurement of physiological activities in the brain. After going through different approaches covering k-space with radial, rosette, and concentric shell trajectories we have settled on a stack-of-spiral trajectory, which allows full brain coverage with (nominal) 3 mm isotropic resolution in 100 ms. The very high acceleration factor is facilitated by the near-isotropic k-space coverage, which allows high acceleration in all three spatial dimensions. Methods The methodological section covers the basic sequence design as well as recent advances in image reconstruction including the targeted reconstruction, which allows real-time feedback applications, and—most recently—the time-domain principal component reconstruction (tPCR), which applies a principal component analysis of the acquired time domain data as a sparsifying transformation to improve reconstruction speed as well as quality. Applications Although the BOLD-response is rather slow, the high speed acquisition of MREG allows separation of BOLD-effects from cardiac and breathing related pulsatility. The increased sensitivity enables direct detection of the dynamic variability of resting state networks as well as localization of single interictal events in epilepsy patients. A separate and highly intriguing application is aimed at the investigation of the glymphatic system by assessment of the spatiotemporal patterns of cardiac and breathing related pulsatility. Discussion MREG has been developed to push the speed limits of fMRI. Compared to multiband-EPI this allows considerably faster acquisition at the cost of reduced image quality and spatial resolution.
Collapse
Affiliation(s)
- Juergen Hennig
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany. .,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany.
| | - Vesa Kiviniemi
- Oulu Functional NeuroImaging Group, Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland
| | - Bruno Riemenschneider
- Department of Radiology, Center for Biomedical Imaging, New York University Grossman School of Medicine, New York, NY, USA
| | - Antonia Barghoorn
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Burak Akin
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Fei Wang
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Pierre LeVan
- Departments of Radiology and Paediatrics, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| |
Collapse
|
4
|
Gao Y, Han J, Zhu Y, Wang J, Wei X, Xin X. Channel-combination method for phase-based |B 1+| mapping techniques. Magn Reson Imaging 2019; 65:1-7. [PMID: 31670236 DOI: 10.1016/j.mri.2019.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 09/06/2019] [Accepted: 09/15/2019] [Indexed: 10/25/2022]
Abstract
PURPOSE The aim of this study was to propose a channel combination method for |B1+| mapping methods using phase difference to reconstruct |B1+| map. THEORY AND METHODS Phase-based |B1+| mapping methods commonly consider the phase difference of two scans to measure |B1+|. Multiple receiver coils acquire a number of images and the phase difference at each channel is theoretically the same in the absence of noise. Affected by noise, phase difference is approximately governed by Gaussian distribution. Considering data from all channels as samples, estimation can be achieved by maximum likelihood method. With this method, all phase differences at each channel are combined into one. In this study, the proposed method is applied with Bloch-Siegert shift |B1+| mapping method. Simulations are performed to illustrate the phase difference distribution and demonstrate the feasibility and facility of the proposed method. Phantom and vivo experiments are carried out at 1.5 T scanner equipped with 8-channel receiver coil. In all experiments, the proposed method is compared with weighted averaging (WA) method. RESULTS Simulations revealed appropriateness of approximating the distribution of phase difference to Gaussian distribution. Compared with WA method, the proposed method reduces errors of |B1+| calculation. Phantom and vivo experiments provide further validation. CONCLUSION Considering phase noise distribution, the proposed method achieves channel combination by finding the estimation from data acquired by multiple receivers coil. The proposed method reduces |B1+| reconstruction errors caused by noise.
Collapse
Affiliation(s)
- Yunyu Gao
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Jijun Han
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Yurong Zhu
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Jiajia Wang
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Xinhua Wei
- Department of Radiology, Guangzhou First People's Hospital, South China University of Technology, No. 1 Panfu Road, Yuexiu District, Guangzhou City, Guangzhou Province 510180, China
| | - Xuegang Xin
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China; School of Medicine, South China University of Technology, Guangzhou Higher Education Mega Centre, Panyu District, Guangzhou City, Guangzhou Province 510006, China.
| |
Collapse
|
5
|
An Ultra-Area-Efficient 1024-Point In-Memory FFT Processor. MICROMACHINES 2019; 10:mi10080509. [PMID: 31370261 PMCID: PMC6722736 DOI: 10.3390/mi10080509] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2019] [Revised: 07/19/2019] [Accepted: 07/30/2019] [Indexed: 11/16/2022]
Abstract
Current computation architectures rely on more processor-centric design principles. On the other hand, the inevitable increase in the amount of data that applications need forces researchers to design novel processor architectures that are more data-centric. By following this principle, this study proposes an area-efficient Fast Fourier Transform (FFT) processor through in-memory computing. The proposed architecture occupies the smallest footprint of around 0.1 mm 2 inside its class together with acceptable power efficiency. According to the results, the processor exhibits the highest area efficiency ( FFT / s / area ) among the existing FFT processors in the current literature.
Collapse
|
6
|
Clément J, Gruetter R, Ipek Ö. A combined 32-channel receive-loops/8-channel transmit-dipoles coil array for whole-brain MR imaging at 7T. Magn Reson Med 2019; 82:1229-1241. [PMID: 31081176 PMCID: PMC6618274 DOI: 10.1002/mrm.27808] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 04/17/2019] [Accepted: 04/18/2019] [Indexed: 12/24/2022]
Abstract
Purpose Multichannel receive arrays provide high SNR and parallel‐imaging capabilities, while transmit‐only dipole arrays have been shown to achieve a large coverage of the whole‐brain including the cerebellum. The aim of this study was to develop and characterize the performances of a 32‐channel receive‐only loop array combined with an 8‐channel dipole coil array at 7T for the first time. Methods The 8Tx‐dipoles/32Rx‐loops coil array was characterized by the SNR, g‐factors, noise correlation matrix, accelerated image quality, and B1+ maps, and compared with a commercial 1Tx‐birdcage/32Rx‐loops array. Simulated and measured B1+ maps were shown for the 8Tx‐dipoles/32Rx‐loops coil array and compared with the 8Tx/Rx dipole array. Results The in‐house built 32‐channel receive coil demonstrated a large longitudinal coverage of the brain, particularly the upper neck area. G‐factors and accelerated MR acquisitions demonstrated robust performances up to R = 4 in 2D, and R = 8 (4 × 2) in 3D. A 83% increase in SNR was measured over the cerebellum with the in‐house built 8Tx/32Rx coil array compared to the commercial 1Tx/32Rx, while similar performances were obtained in the cerebral cortex. Conclusions The combined 32‐channel receive/8‐channel transmit coil array demonstrated high transmit‐receive performances compared to the commercial receive array at 7T, notably in the cerebellum. We conclude that in combination with parallel transmit capabilities, this coil is particularly suitable for whole‐brain MR studies at 7T.
Collapse
Affiliation(s)
- Jérémie Clément
- LIFMET, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Rolf Gruetter
- LIFMET, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.,Department of Radiology, University of Geneva, Geneva, Switzerland.,Department of Radiology, University of Lausanne, Lausanne, Switzerland
| | - Özlem Ipek
- CIBM-AIT, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.,School of Biomedical Engineering & Imaging, King's College London, London, United Kingdom
| |
Collapse
|
7
|
ASIC modelling of SENSE for parallel MRI. Comput Biol Med 2019; 109:53-61. [PMID: 31035071 DOI: 10.1016/j.compbiomed.2019.04.028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 04/17/2019] [Accepted: 04/21/2019] [Indexed: 11/21/2022]
Abstract
Magnetic Resonance Imaging (MRI) is widely used in medical diagnostics and image reconstruction is a vital part of MRI systems. In Parallel MRI (pMRI), imaging process is accelerated by acquiring less data (undersampled) using multiple receiver coils and offline reconstruction algorithms are applied to reconstruct the fully sampled image. In this research, an Application Specific Integrated Circuits (ASIC) model of SENSE (a pMRI algorithm) is presented which reconstructs the image from the undersampled data right on the data acquisition module of the scanner. The proposed ASIC HDL architecture is compared with SENSE reconstruction model implemented on FPGAs, Multi-core CPU and Graphics Processing Units. The proposed architecture is validated using simulated brain data with 8-channel receiver coils and a human cardiac dataset with 20-channel receiver coils. The quality of the reconstructed images is analyzed using Artifact Power (0.0098), Peak Signal-to-Noise Ratio (53.4) and Structured Similarity Index (0.871) which validate the quality of the reconstructed images using the proposed design. The results show that the proposed ASIC HDL SENSE reconstruction model is ∼8000 times faster as compared to the multi-core CPU reconstruction, ∼700 times faster than the GPU implementation and ∼16 times faster as compared to the FPGA reconstruction model. The proposed architecture is suitable for image reconstruction right on the data acquisition system of the scanner and will open new ways for faster image reconstruction on portable MRI scanners.
Collapse
|
8
|
Fast Abdominal Contrast-Enhanced Imaging With High Parallel-Imaging Factors Using a 60-Channel Receiver Coil Setup. Invest Radiol 2018; 53:602-608. [DOI: 10.1097/rli.0000000000000481] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
9
|
Hendriks AD, Luijten PR, Klomp DWJ, Petridou N. Potential acceleration performance of a 256-channel whole-brain receive array at 7 T. Magn Reson Med 2018; 81:1659-1670. [PMID: 30257049 PMCID: PMC6585755 DOI: 10.1002/mrm.27519] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 08/09/2018] [Accepted: 08/11/2018] [Indexed: 11/21/2022]
Abstract
Purpose Assess the potential gain in acceleration performance of a 256‐channel versus 32‐channel receive coil array at 7 T in combination with a 2D CAIPIRINHA sequence for 3D data sets. Methods A 256‐channel receive setup was simulated by placing 2 small 16‐channel high‐density receive arrays at 2 × 8 different locations on the head of healthy participants. Multiple consecutive measurements were performed and coil sensitivity maps were combined to form a complete 256‐channel data set. This setup was compared with a standard 32‐channel head coil, in terms of SNR, noise correlation, and acceleration performance (g‐factor). Results In the periphery of the brain, the receive SNR was on average a factor 1.5 higher (ranging up to a factor 2.7 higher) than the 32‐channel coil; in the center of the brain the SNR was comparable or lower, depending on the size of the region of interest, with a factor 1.0 on average (ranging from 0.7 up to a factor of 1.6). The average noise correlation between coil elements was 3% for the 256‐channel coil, and 5% for the 32‐channel coil. At acceptable g‐factors (< 2), the achievable acceleration factor using SENSE and 2D CAIPIRINHA was 24 and 28, respectively, versus 9 and 12 for the 32‐channel coil. Conclusion The receive performance of the simulated 256 channel array was better than the 32‐channel reference. Combined with 2D CAIPIRINHA, a peak acceleration factor of 28 was assessed, showing great potential for high‐density receive arrays.
Collapse
Affiliation(s)
- Arjan D Hendriks
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Peter R Luijten
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Dennis W J Klomp
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Natalia Petridou
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| |
Collapse
|
10
|
Bosshard JC, Yallapragada N, McDougall MP, Wright SM. Exploration of highly accelerated magnetic resonance elastography using high-density array coils. Quant Imaging Med Surg 2017; 7:195-204. [PMID: 28516045 PMCID: PMC5418148 DOI: 10.21037/qims.2017.04.02] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2017] [Accepted: 04/07/2017] [Indexed: 11/06/2022]
Abstract
BACKGROUND Magnetic resonance elastography (MRE) measures tissue mechanical properties by applying a shear wave and capturing its propagation using magnetic resonance imaging (MRI). By using high density array coils, MRE images are acquired using single echo acquisition (SEA) and at high resolutions with significantly reduced scan times. METHODS Sixty-four channel uniplanar and 32×32 channel biplanar receive arrays are used to acquire MRE wave image sets from agar samples containing regions of varying stiffness. A mechanical actuator triggered by a stepped delay time introduces vibrations into the sample while a motion sensitizing gradient encodes micrometer displacements into the phase. SEA imaging is used to acquire each temporal offset in a single echo, while multiple echoes from the same array are employed for highly accelerated imaging at high resolutions. Additionally, stiffness variations as a function of temperature are studied by using a localized heat source above the sample. A custom insertable gradient coil is employed for phase compensation of SEA imaging with the biplanar array to allow imaging of multiple slices. RESULTS SEA MRE images show a mechanical shear wave propagating into and across agar samples. A set of 720 images was obtained in 720 echoes, plus a single reference scan for both harmonic and transient MRE. A set of 2,950 wave image frames was acquired from pairs of SEA images captured during heating, showing the change in mechanical wavelength with the change in agar properties. A set of 240 frames was acquired from two slices simultaneously using the biplanar array, with phase images processed into displacement maps. Combining the narrow sensitivity patterns and SNR advantage of the SEA array coil geometry allowed acquisition of a data set with a resolution of 156 µm × 125 µm × 1,000 µm in only 64 echoes, demonstrating high resolution and high acceleration factors. CONCLUSIONS MRE using high-density arrays offers the unique ability to acquire a single frame of a propagating mechanical vibration with each echo, which may be helpful in non-repeatable or destructive testing. Highly accelerated, high resolution MRE may be enabled by the use of large arrays of coils such as used for SEA, but at lower acceleration rates supporting the higher resolution than provided by SEA imaging.
Collapse
Affiliation(s)
- John C. Bosshard
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
| | - Naresh Yallapragada
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
| | - Mary P. McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
| | - Steven M. Wright
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
- Department of Radiology, Texas A&M Health Science Center, Bryan, TX, USA
| |
Collapse
|
11
|
Sparse Parallel MRI Based on Accelerated Operator Splitting Schemes. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2016; 2016:1724630. [PMID: 27746824 PMCID: PMC5056009 DOI: 10.1155/2016/1724630] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 08/29/2016] [Indexed: 11/17/2022]
Abstract
Recently, the sparsity which is implicit in MR images has been successfully exploited for fast MR imaging with incomplete acquisitions. In this paper, two novel algorithms are proposed to solve the sparse parallel MR imaging problem, which consists of l1 regularization and fidelity terms. The two algorithms combine forward-backward operator splitting and Barzilai-Borwein schemes. Theoretically, the presented algorithms overcome the nondifferentiable property in l1 regularization term. Meanwhile, they are able to treat a general matrix operator that may not be diagonalized by fast Fourier transform and to ensure that a well-conditioned optimization system of equations is simply solved. In addition, we build connections between the proposed algorithms and the state-of-the-art existing methods and prove their convergence with a constant stepsize in Appendix. Numerical results and comparisons with the advanced methods demonstrate the efficiency of proposed algorithms.
Collapse
|
12
|
A 32-Channel Head Coil Array with Circularly Symmetric Geometry for Accelerated Human Brain Imaging. PLoS One 2016; 11:e0149446. [PMID: 26909652 PMCID: PMC4766089 DOI: 10.1371/journal.pone.0149446] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 01/31/2016] [Indexed: 11/29/2022] Open
Abstract
The goal of this study is to optimize a 32-channel head coil array for accelerated 3T human brain proton MRI using either a Cartesian or a radial k-space trajectory. Coils had curved trapezoidal shapes and were arranged in a circular symmetry (CS) geometry. Coils were optimally overlapped to reduce mutual inductance. Low-noise pre-amplifiers were used to further decouple between coils. The SNR and noise amplification in accelerated imaging were compared to results from a head coil array with a soccer-ball (SB) geometry. The maximal SNR in the CS array was about 120% (1070 vs. 892) and 62% (303 vs. 488) of the SB array at the periphery and the center of the FOV on a transverse plane, respectively. In one-dimensional 4-fold acceleration, the CS array has higher averaged SNR than the SB array across the whole FOV. Compared to the SB array, the CS array has a smaller g-factor at head periphery in all accelerated acquisitions. Reconstructed images using a radial k-space trajectory show that the CS array has a smaller error than the SB array in 2- to 5-fold accelerations.
Collapse
|
13
|
Ogier SE, Wright SM. A frequency translation approach for multichannel (13)C spectroscopy. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:1564-7. [PMID: 26736571 DOI: 10.1109/embc.2015.7318671] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Multi-channel receivers are commonplace in MRI, but very few of these receivers are capable of operating over a broad enough bandwidth to accommodate nuclei other than (1)H. While this is fine for imaging, the recent surge in interest in in vivo NMR has created a need for receive arrays to improve the often-poor sensitivity of other nuclei. However, the development of these arrays has been slowed by the scarcity of multi-channel, multinuclear receivers. Frequency translation is a method to solve this by using radiofrequency mixers to convert signals received from multinuclear arrays to the proton frequency, adapting narrow-band receivers to multinuclear use. This method works with a wide variety of nuclei and easily accommodates proton decoupling, a necessity for working with (13)C.
Collapse
|
14
|
Li L, Wyrwicz AM. Design of an MR image processing module on an FPGA chip. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 255:51-58. [PMID: 25909646 PMCID: PMC4441561 DOI: 10.1016/j.jmr.2015.03.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2015] [Revised: 03/10/2015] [Accepted: 03/11/2015] [Indexed: 06/04/2023]
Abstract
We describe the design and implementation of an image processing module on a single-chip Field-Programmable Gate Array (FPGA) for real-time image processing. We also demonstrate that through graphical coding the design work can be greatly simplified. The processing module is based on a 2D FFT core. Our design is distinguished from previously reported designs in two respects. No off-chip hardware resources are required, which increases portability of the core. Direct matrix transposition usually required for execution of 2D FFT is completely avoided using our newly-designed address generation unit, which saves considerable on-chip block RAMs and clock cycles. The image processing module was tested by reconstructing multi-slice MR images from both phantom and animal data. The tests on static data show that the processing module is capable of reconstructing 128×128 images at speed of 400 frames/second. The tests on simulated real-time streaming data demonstrate that the module works properly under the timing conditions necessary for MRI experiments.
Collapse
Affiliation(s)
- Limin Li
- Center for Basic MR Research, NorthShore University HealthSystem Research Institute, Evanston, IL, USA.
| | - Alice M Wyrwicz
- Center for Basic MR Research, NorthShore University HealthSystem Research Institute, Evanston, IL, USA; Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA
| |
Collapse
|
15
|
Hutchinson M, Raff U. Is the Fastest MRI a Hologram? J Neuroimaging 2014; 24:537-542. [DOI: 10.1111/jon.12141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 05/11/2014] [Indexed: 11/28/2022] Open
Affiliation(s)
| | - Ulrich Raff
- Department of Physics and Medicine; University of Santiago de Chile, Santiago; Región Metropolitana Chile
| |
Collapse
|
16
|
Trakic A, Jin J, Weber E, Crozier S. Model for b1 imaging in MRI using the rotating RF field. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2014; 2014:461647. [PMID: 24963336 PMCID: PMC4055257 DOI: 10.1155/2014/461647] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Accepted: 03/13/2014] [Indexed: 11/18/2022]
Abstract
Conventionally, magnetic resonance imaging (MRI) is performed by pulsing gradient coils, which invariably leads to strong acoustic noise, patient safety concerns due to induced currents, and costly power/space requirements. This modeling study investigates a new silent, gradient coil-free MR imaging method, in which a radiofrequency (RF) coil and its nonuniform field (B 1 (+)) are mechanically rotated about the patient. The advantage of the rotating B 1 (+) field is that, for the first time, it provides a large number of degrees of freedom to aid a successful B 1 (+) image encoding process. The mathematical modeling was performed using flip angle modulation as part of a finite-difference-based Bloch equation solver. Preliminary results suggest that representative MR images with intensity deviations of <5% from the original image can be obtained using rotating RF field approach. This method may open up new avenues towards anatomical and functional imaging in medicine.
Collapse
Affiliation(s)
- Adnan Trakic
- The School of Information Technology and Electrical Engineering, The University of Queensland (UQ), Brisbane, QLD 4072, Australia
| | - Jin Jin
- The School of Information Technology and Electrical Engineering, The University of Queensland (UQ), Brisbane, QLD 4072, Australia
| | - Ewald Weber
- The School of Information Technology and Electrical Engineering, The University of Queensland (UQ), Brisbane, QLD 4072, Australia
| | - Stuart Crozier
- The School of Information Technology and Electrical Engineering, The University of Queensland (UQ), Brisbane, QLD 4072, Australia
| |
Collapse
|
17
|
Feng K, Wright SM. Rapid slice excitation without B0 gradients using large array coils. Quant Imaging Med Surg 2014; 4:145-51. [PMID: 24834427 DOI: 10.3978/j.issn.2223-4292.2014.04.15] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2014] [Accepted: 04/29/2014] [Indexed: 11/14/2022]
Abstract
In a large transmit planar pair phased array with the same power level in each channel, it is shown that controlling the phase shift between neighboring channels can yield different transmit slice thickness. Similarly, variation of the power level can move the slice less or further into the subject for imaging. The technique may be of particular interest as it allows curved slice excitation. These excitation patterns are achieved without complicated RF pulse sequences, i.e., without the use of multi-dimensional RF pulses. Simple simulations based on Biot-Savart law are used to predict the effect of the phase offset and power level variation. Planar and cylindrical formed planar pair coil arrays are both simulated and later built and tested using an MR scanner. The array is flexible and formed around the surface of objects under study, and the excitation is near the surface. Simulation results are compared with actual MRI images with good agreement. This technique is potentially useful for slice excitation in very rapid or ultra-short echo sequences.
Collapse
Affiliation(s)
- Ke Feng
- 1 Department of Electrical and Computer Engineering, 2 Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA ; 3 Department of Radiology, Texas A&M Health Science Center, Bryan, TX 77807, USA
| | - Steven M Wright
- 1 Department of Electrical and Computer Engineering, 2 Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA ; 3 Department of Radiology, Texas A&M Health Science Center, Bryan, TX 77807, USA
| |
Collapse
|
18
|
Li Y. Error decomposition for parallel imaging reconstruction using modulation-domain representation of undersampled data. Quant Imaging Med Surg 2014; 4:93-105. [PMID: 24834421 DOI: 10.3978/j.issn.2223-4292.2014.04.07] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 04/21/2014] [Indexed: 01/04/2023]
Abstract
This paper presents a quantitative approach to evaluating and optimizing parallel imaging reconstruction for a clinical requirement. By introducing a "modulation domain representation" for undersampled data, the presented approach decomposes parallel imaging reconstruction error into multiple error components that can be grouped into three categories: image fidelity error, residue aliasing artifacts, and amplified noise. It is experimentally found that these error components have different image-space patterns that compromise imaging quality in different fashions. An error function may be defined as the weighted summation of these error components. By choosing a set of weighting coefficients that can quantify desirable image quality, parallel imaging may be optimized for a clinical requirement. It is found that error decomposition model may improve clinical utility of parallel imaging, providing an application-oriented approach to clinical parallel imaging.
Collapse
Affiliation(s)
- Yu Li
- Imaging Research Center, Radiology Department, Cincinnati Children's Hospital Medical Center 3333 Burnet Avenue, Cincinnati, OH 45229, USA
| |
Collapse
|
19
|
Zhang T, Chowdhury S, Lustig M, Barth RA, Alley MT, Grafendorfer T, Calderon PD, Robb FJL, Pauly JM, Vasanawala SS. Clinical performance of contrast enhanced abdominal pediatric MRI with fast combined parallel imaging compressed sensing reconstruction. J Magn Reson Imaging 2013; 40:13-25. [PMID: 24127123 DOI: 10.1002/jmri.24333] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 07/14/2013] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To deploy clinically, a combined parallel imaging compressed sensing method with coil compression that achieves a rapid image reconstruction, and assess its clinical performance in contrast-enhanced abdominal pediatric MRI. MATERIALS AND METHODS With Institutional Review Board approval and informed patient consent/assent, 29 consecutive pediatric patients were recruited. Dynamic contrast-enhanced MRI was acquired on a 3 Tesla scanner using a dedicated 32-channel pediatric coil and a three-dimensional SPGR sequence, with pseudo-random undersampling at a high acceleration (R = 7.2). Undersampled data were reconstructed with three methods: a traditional parallel imaging method and a combined parallel imaging compressed sensing method with and without coil compression. The three sets of images were evaluated independently and blindly by two radiologists at one siting, for overall image quality and delineation of anatomical structures. Wilcoxon tests were performed to test the hypothesis that there was no significant difference in the evaluations, and interobserver agreement was analyzed. RESULTS Fast reconstruction with coil compression did not deteriorate image quality. The mean score of structural delineation of the fast reconstruction was 4.1 on a 5-point scale, significantly better (P < 0.05) than traditional parallel imaging (mean score 3.1). Fair to substantial interobserver agreement was reached in structural delineation assessment. CONCLUSION A fast combined parallel imaging compressed sensing method is feasible in a pediatric clinical setting. Preliminary results suggest it may improve structural delineation over parallel imaging.
Collapse
Affiliation(s)
- Tao Zhang
- Electrical Engineering, Stanford University, Stanford, California, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
20
|
Keil B, Wald LL. Massively parallel MRI detector arrays. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 229:75-89. [PMID: 23453758 PMCID: PMC3740730 DOI: 10.1016/j.jmr.2013.02.001] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 01/31/2013] [Accepted: 02/01/2013] [Indexed: 05/15/2023]
Abstract
Originally proposed as a method to increase sensitivity by extending the locally high-sensitivity of small surface coil elements to larger areas via reception, the term parallel imaging now includes the use of array coils to perform image encoding. This methodology has impacted clinical imaging to the point where many examinations are performed with an array comprising multiple smaller surface coil elements as the detector of the MR signal. This article reviews the theoretical and experimental basis for the trend towards higher channel counts relying on insights gained from modeling and experimental studies as well as the theoretical analysis of the so-called "ultimate" SNR and g-factor. We also review the methods for optimally combining array data and changes in RF methodology needed to construct massively parallel MRI detector arrays and show some examples of state-of-the-art for highly accelerated imaging with the resulting highly parallel arrays.
Collapse
Affiliation(s)
- Boris Keil
- A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA 02129, USA.
| | | |
Collapse
|
21
|
Webb AG. Radiofrequency microcoils for magnetic resonance imaging and spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 229:55-66. [PMID: 23142002 DOI: 10.1016/j.jmr.2012.10.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2012] [Revised: 10/07/2012] [Accepted: 10/09/2012] [Indexed: 06/01/2023]
Abstract
Small radiofrequency coils, often termed "microcoils", have found extensive use in many areas of magnetic resonance. Their advantageous properties include a very high intrinsic sensitivity, a high (several MHz) excitation and reception bandwidth, the fact that large arrays can fit within the homogeneous volume of the static magnetic field, and the very high resonance frequencies (several GHz) that can be achieved. This review concentrates on recent developments in the construction of single and multiple RF microcoil systems, and new types of experiments that can be performed using such assemblies.
Collapse
Affiliation(s)
- A G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
| |
Collapse
|
22
|
Ersoz A, Arpinar VE, Muftuler LT. Highly accelerated projection imaging with coil sensitivity encoding for rapid MRI. Med Phys 2013; 40:022305. [PMID: 23387767 DOI: 10.1118/1.4789488] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Rapid magnetic resonance imaging (MRI) acquisition is typically achieved by acquiring all or most lines of k-space after one radio frequency (RF) excitation. Parallel imaging techniques can further accelerate data acquisition by acquiring fewer phase-encoded lines and utilizing the spatial sensitivity information of the RF coil arrays. The goal of this study was to develop a new MRI data acquisition and reconstruction technique that is capable of reconstructing a two-dimensional (2D) image using highly undersampled k-space data without any special hardware. Such a technique would be very efficient, as it would significantly reduce the time wasted during multiple RF excitations or phase encoding and gradient switching periods. METHODS The essence of this new technique is to densely sample a small number of projections, which should be acquired at an angle other than 0° or multiples of 45°. This results in multiple rays passing through a voxel and provides new and independent measurements for each voxel. Then the images are reconstructed using the unique information coming from these projections combined with RF coil sensitivity profiles. The feasibility of this new technique was investigated with realistic simulations and experimental studies using a phantom and compared with conventional nonuniform fast Fourier transform technique. Eigenvalue analysis and error calculations were conducted to find optimal projection angles and minimum requirements for dense sampling. RESULTS Reconstruction of 64 × 64 images was done using a single projection from simulated data under different noise levels. Simulated reconstruction was also tested with two projections to assess the improvement. Experimental phantom images were reconstructed at higher resolution using 4, 8, and 16 projections. Cross-sectional profiles illustrate that the new technique resolved compartment boundaries clearly. CONCLUSIONS Simulations demonstrated that only a single k-space line might be sufficient to reconstruct a 2D image using this new technique. Experimental results showed that this is a promising new technique for fast imaging. Using the information from the simulations and fast imaging parameters published in the literature, it could be predicted that a two-dimensional image could be acquired in about 10 ms. One of the major advantages of this new technique is that it does not require any additional hardware and can be implemented on a conventional scanner with an eight-channel coil.
Collapse
Affiliation(s)
- Ali Ersoz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | | | | |
Collapse
|
23
|
Bosshard JC, McDougall MP, Wright SM. An insertable nonlinear gradient coil for phase compensation in SEA imaging. IEEE Trans Biomed Eng 2013; 61:217-23. [PMID: 23314767 DOI: 10.1109/tbme.2013.2238537] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In magnetic resonance imaging with array coils with many elements, as the radiofrequency (RF) coil dimensions approach the voxel dimensions, the phase gradient due to the magnetic field pattern of the coil causes signal cancellation within each voxel. In single echo acquisition (SEA) imaging with coil arrays, a gradient pulse can be applied to compensate for this effect. However, because RF coil phase varies with distance from the array and reverses on opposite sides of a dual-sided array, this method of phase compensation can be optimized for only a single slice at a time. In this study, a nonlinear gradient coil was implemented to provide spatially varying phase compensation to offset the coil phase with slice position for dual-sided arrays of narrow coils. This nonlinear gradient coil allows the use of one phase compensation pulse for imaging multiple slices through a slab, and, importantly, is shown to enable simultaneous SEA imaging from opposite sides of a sample using a dual-sided receive array.
Collapse
|
24
|
McDougall MP, Wright SM. A parallel imaging approach to wide-field MR microscopy. Magn Reson Med 2012; 68:850-6. [PMID: 22139858 PMCID: PMC3319189 DOI: 10.1002/mrm.23258] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Revised: 08/26/2011] [Accepted: 09/24/2011] [Indexed: 11/08/2022]
Abstract
Magnetic resonance microscopy, suggested in the earliest papers on MRI, has always been limited by the low signal-to-noise ratio resulting from the small voxel size. Magnetic resonance microscopy has largely been enabled by the use of microcoils that provide the signal-to-noise ratio improvement required to overcome this limitation. Concomitant with the small coils is a small field-of-view, which limits the use of magnetic resonance microscopy as a histological tool or for imaging large regions in general. This article describes initial results in wide field-of-view magnetic resonance microscopy using a large array of narrow, parallel coils, which provides a signal-to-noise ratio enhancement as well as the ability to use parallel imaging techniques. Comparison images made between a volume coil and the proposed technique demonstrate reductions in imaging time of more than 100 with no loss in signal-to-noise ratio or resolution.
Collapse
Affiliation(s)
- Mary Preston McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA.
| | | |
Collapse
|
25
|
Lin FH, Tsai KW, Chu YH, Witzel T, Nummenmaa A, Raij T, Ahveninen J, Kuo WJ, Belliveau JW. Ultrafast inverse imaging techniques for fMRI. Neuroimage 2012; 62:699-705. [PMID: 22285221 PMCID: PMC3377851 DOI: 10.1016/j.neuroimage.2012.01.072] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 01/07/2012] [Accepted: 01/10/2012] [Indexed: 10/14/2022] Open
Abstract
Inverse imaging (InI) supercharges the sampling rate of traditional functional MRI 10-100 fold at a cost of a moderate reduction in spatial resolution. The technique is inspired by similarities between multi-sensor magnetoencephalography (MEG) and highly parallel radio-frequency (RF) MRI detector arrays. Using presently available 32-channel head coils at 3T, InI can be sampled at 10 Hz and provides about 5-mm cortical spatial resolution with whole-brain coverage. Here we discuss the present applications of InI, as well as potential future challenges and opportunities in further improving its spatiotemporal resolution and sensitivity. InI may become a helpful tool for clinicians and neuroscientists for revealing the complex dynamics of brain functions during task-related and resting states.
Collapse
Affiliation(s)
- Fa-Hsuan Lin
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
- Department of Biomedical Engineering and Computational Science, Aalto University School of Science and Technology, Espoo, Finland
| | - Kevin W.K. Tsai
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
| | - Ying-Hua Chu
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
| | - Thomas Witzel
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| | - Aapo Nummenmaa
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
- Department of Biomedical Engineering and Computational Science, Aalto University School of Science and Technology, Espoo, Finland
| | - Tommi Raij
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| | - Jyrki Ahveninen
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| | - Wen-Jui Kuo
- Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan
| | - John W. Belliveau
- MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| |
Collapse
|
26
|
Hennig J. Functional spectroscopy to no-gradient fMRI. Neuroimage 2012; 62:693-8. [DOI: 10.1016/j.neuroimage.2011.09.060] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 09/05/2011] [Accepted: 09/23/2011] [Indexed: 10/17/2022] Open
|
27
|
Ke Feng, Hollingsworth NA, McDougall MP, Wright SM. A 64-channel transmitter for investigating parallel transmit MRI. IEEE Trans Biomed Eng 2012; 59:2152-60. [PMID: 22552545 DOI: 10.1109/tbme.2012.2196797] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Multiple channel radiofrequency (RF) transmitters are being used in magnetic resonance imaging to investigate a number of active research topics, including transmit SENSE and B(1) shimming. Presently, the cost and availability of multiple channel transmitters restricts their use to relatively few sites. This paper describes the development and testing of a relatively inexpensive transmit system that can be easily duplicated by users with a reasonable level of RF hardware design experience. The system described here consists of 64 channels, each with 100 W peak output level. The hardware is modular at the level of four channels, easily accommodating larger or smaller channel counts. Unique aspects of the system include the use of vector modulators to replace more complex IQ direct digital modulators, 100 W MOSFET RF amplifiers with partial microstrip matching networks, and the use of digital potentiometers to replace more complex and costly digital-to-analog converters to control the amplitude and phase of each channel. Although mainly designed for B(1) shimming, the system is capable of dynamic modulation necessary for transmit SENSE by replacing the digital potentiometers controlling the vector modulators with commercially available analog output boards. The system design is discussed in detail and bench and imaging data are shown, demonstrating the ability to perform phase and amplitude control for B(1) shimming as well as dynamic modulation for transmitting complex RF pulses.
Collapse
Affiliation(s)
- Ke Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA.
| | | | | | | |
Collapse
|
28
|
Zhang T, Pauly JM, Vasanawala SS, Lustig M. Coil compression for accelerated imaging with Cartesian sampling. Magn Reson Med 2012; 69:571-82. [PMID: 22488589 DOI: 10.1002/mrm.24267] [Citation(s) in RCA: 165] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 02/10/2012] [Accepted: 02/29/2012] [Indexed: 11/09/2022]
Abstract
MRI using receiver arrays with many coil elements can provide high signal-to-noise ratio and increase parallel imaging acceleration. At the same time, the growing number of elements results in larger datasets and more computation in the reconstruction. This is of particular concern in 3D acquisitions and in iterative reconstructions. Coil compression algorithms are effective in mitigating this problem by compressing data from many channels into fewer virtual coils. In Cartesian sampling there often are fully sampled k-space dimensions. In this work, a new coil compression technique for Cartesian sampling is presented that exploits the spatially varying coil sensitivities in these nonsubsampled dimensions for better compression and computation reduction. Instead of directly compressing in k-space, coil compression is performed separately for each spatial location along the fully sampled directions, followed by an additional alignment process that guarantees the smoothness of the virtual coil sensitivities. This important step provides compatibility with autocalibrating parallel imaging techniques. Its performance is not susceptible to artifacts caused by a tight imaging field-of-view. High quality compression of in vivo 3D data from a 32 channel pediatric coil into six virtual coils is demonstrated.
Collapse
Affiliation(s)
- Tao Zhang
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
| | | | | | | |
Collapse
|
29
|
Stang PP, Conolly SM, Santos JM, Pauly JM, Scott GC. Medusa: a scalable MR console using USB. IEEE TRANSACTIONS ON MEDICAL IMAGING 2012; 31:370-9. [PMID: 21954200 PMCID: PMC3282593 DOI: 10.1109/tmi.2011.2169681] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Magnetic resonance imaging (MRI) pulse sequence consoles typically employ closed proprietary hardware, software, and interfaces, making difficult any adaptation for innovative experimental technology. Yet MRI systems research is trending to higher channel count receivers, transmitters, gradient/shims, and unique interfaces for interventional applications. Customized console designs are now feasible for researchers with modern electronic components, but high data rates, synchronization, scalability, and cost present important challenges. Implementing large multichannel MR systems with efficiency and flexibility requires a scalable modular architecture. With Medusa, we propose an open system architecture using the universal serial bus (USB) for scalability, combined with distributed processing and buffering to address the high data rates and strict synchronization required by multichannel MRI. Medusa uses a modular design concept based on digital synthesizer, receiver, and gradient blocks, in conjunction with fast programmable logic for sampling and synchronization. Medusa is a form of synthetic instrument, being reconfigurable for a variety of medical/scientific instrumentation needs. The Medusa distributed architecture, scalability, and data bandwidth limits are presented, and its flexibility is demonstrated in a variety of novel MRI applications.
Collapse
Affiliation(s)
- Pascal P Stang
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
| | | | | | | | | |
Collapse
|
30
|
Feng S, Ji J. 3D selective pulse design with variable spoke trajectories for parallel excitation. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2011:2845-8. [PMID: 22254934 DOI: 10.1109/iembs.2011.6090786] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Three dimensional spatial selective RF pulse of practical length has been demonstrated using parallel transmission technique in Magnetic Resonance Imaging. Currently, spoke trajectory, which is a set of parallel k-space straight lines, is widely used for 3-D slab excitation to achieve sharp slice profile and a uniform or smoothly varying in-plane profile. The better control of in-plane profile mainly comes from an increased number of spokes. In this paper, we proposed three types of modified spoke trajectories for the 3-D tailored RF pulse design which traverse k-space more efficiently. Simulations are used to characterize the proposed trajectories.
Collapse
Affiliation(s)
- Shuo Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843-3128, USA
| | | |
Collapse
|
31
|
Trakic A, Weber E, Li BK, Wang H, Liu F, Engstrom C, Crozier S. Electromechanical design and construction of a rotating radio-frequency coil system for applications in magnetic resonance. IEEE Trans Biomed Eng 2012; 59:1068-75. [PMID: 22231668 DOI: 10.1109/tbme.2012.2182993] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
While recent studies have shown that rotating a single radio-frequency (RF) coil during the acquisition of magnetic resonance (MR) images provides a number of hardware advantages (i.e., requires only one RF channel, avoids coil-coil coupling and facilitates large-scale multinuclear imaging), they did not describe in detail how to build a rotating RF coil system. This paper presents detailed engineering information on the electromechanical design and construction of a MR-compatible RRFC system for human head imaging at 2 T. A custom-made (bladeless) pneumatic Tesla turbine was used to rotate the RF coil at a constant velocity, while an infrared optical encoder measured the selected frequency of rotation. Once the rotating structure was mechanically balanced and the compressed air supply suitably regulated, the maximum frequency of rotation measured ~14.5 Hz with a 2.4% frequency variation over time. MR images of a water phantom and human head were obtained using the rotating RF head coil system.
Collapse
Affiliation(s)
- Adnan Trakic
- School of Information Technology and Electrical Engineering, The University of Queensland, Queensland, Australia.
| | | | | | | | | | | | | |
Collapse
|
32
|
Feng S, Ji J. A novel fast algorithm for parallel excitation: pulse design in MRI. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2012:1102-1105. [PMID: 23366088 DOI: 10.1109/embc.2012.6346127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Spatially selective excitations with parallel transmitters have been regarded as a key in solving several high field MRI problems such as inhomogeneity correction and reducing specific absorption rate. However, three-dimensional pulse design in general is very time consuming which may prevent it from real-time applications. In this work, we explore the sparsity in the pulse design system equation. The size of system equation is reduced after a sparse transform and therefore design speed can be significantly increased. Computer simulations in several common scenarios show that the proposed design method can achieve up to an order of magnitude speedup than the conventional design methods while maintaining similar excitation accuracy.
Collapse
Affiliation(s)
- Shuo Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843-3128, USA
| | | |
Collapse
|
33
|
Secchi F, Di Leo G, Papini GD, Giacomazzi F, Di Donato M, Sardanelli F. Optimizing dose and administration regimen of a high-relaxivity contrast agent for myocardial MRI late gadolinium enhancement. Eur J Radiol 2011; 80:96-102. [DOI: 10.1016/j.ejrad.2010.06.040] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 06/17/2010] [Accepted: 06/18/2010] [Indexed: 10/19/2022]
|
34
|
Lin FH, Nummenmaa A, Witzel T, Polimeni JR, Zeffiro TA, Wang FN, Belliveau JW. Physiological noise reduction using volumetric functional magnetic resonance inverse imaging. Hum Brain Mapp 2011; 33:2815-30. [PMID: 21954026 DOI: 10.1002/hbm.21403] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 05/31/2011] [Accepted: 06/14/2011] [Indexed: 11/06/2022] Open
Abstract
Physiological noise arising from a variety of sources can significantly degrade the detection of task-related activity in BOLD-contrast fMRI experiments. If whole head spatial coverage is desired, effective suppression of oscillatory physiological noise from cardiac and respiratory fluctuations is quite difficult without external monitoring, since traditional EPI acquisition methods cannot sample the signal rapidly enough to satisfy the Nyquist sampling theorem, leading to temporal aliasing of noise. Using a combination of high speed magnetic resonance inverse imaging (InI) and digital filtering, we demonstrate that it is possible to suppress cardiac and respiratory noise without auxiliary monitoring, while achieving whole head spatial coverage and reasonable spatial resolution. Our systematic study of the effects of different moving average (MA) digital filters demonstrates that a MA filter with a 2 s window can effectively reduce the variance in the hemodynamic baseline signal, thereby achieving 57%-58% improvements in peak z-statistic values compared to unfiltered InI or spatially smoothed EPI data (FWHM = 8.6 mm). In conclusion, the high temporal sampling rates achievable with InI permit significant reductions in physiological noise using standard temporal filtering techniques that result in significant improvements in hemodynamic response estimation.
Collapse
Affiliation(s)
- Fa-Hsuan Lin
- Institute of Biomedical Engineering and Environmental Sciences, National Taiwan University, Taipei, Taiwan
| | | | | | | | | | | | | |
Collapse
|
35
|
Feng S, Ji J. Parallel magnetic resonance imaging using localized receive arrays with sinc interpolation (PILARS). Magn Reson Med 2011; 67:1114-9. [PMID: 21858866 DOI: 10.1002/mrm.23079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Revised: 05/07/2011] [Accepted: 06/13/2011] [Indexed: 11/08/2022]
Abstract
Large arrays with localized coil sensitivity make it possible to use parallel imaging to significantly accelerate MR imaging speed. However, the need for auto calibration signals limits the actual acceleration factors achievable with large arrays. This paper presents a novel method for parallel imaging with large arrays. The method uses Sinc kernels for k-space data interpolation that only requires one phase parameter to be estimated using a small size of calibration signals. Simulations based on synthetic array data and phantom experiments show that the new method can achieve higher actual acceleration factors with comparable reconstruction quality.
Collapse
Affiliation(s)
- Shuo Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
| | | |
Collapse
|
36
|
Chang CW, Moody KL, McDougall MP. An Improved Element Design for 64-Channel Planar Imaging. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2011; 39:159-165. [PMID: 22267961 PMCID: PMC3259609 DOI: 10.1002/cmr.b.20203] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Investigation of highly accelerated MRI has developed into a lively corner in the hardware and methodology arena in recent years. At the extreme of (one-dimensional) acceleration, our group introduced Single Echo Acquisition (SEA) imaging, in which the need to phase encode a 64×N(readout) image is eliminated and replaced with the well-localized spatial information obtained from an array of 64 very narrow, long, parallel coils. The narrow coil width (2mm) that facilitates this is accompanied by a concomitant constraint on the useful imaging depth. This note describes a 64-element planar array, constructed within the same 8×13cm total footprint as the original SEA array, still enabling full acceleration in one dimension, but with an element design modified to increase the imaging depth. This was accomplished by lowering the outer conducting legs of the planar pair with respect to the center conductor and adding a geometric decoupling configuration away from the imaging field of view. The element has been called a dual-plane pair in that the current carrying rungs in the imaging FOV function exactly as the planar pair, but are simply placed in two separate planes (sides of PCB in this case).
Collapse
Affiliation(s)
- Chieh-Wei Chang
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA
| | - Katherine Lynn Moody
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA
| | - Mary Preston McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| |
Collapse
|
37
|
Koo C, Godley RF, Park J, McDougall MP, Wright SM, Han A. A magnetic resonance (MR) microscopy system using a microfluidically cryo-cooled planar coil. LAB ON A CHIP 2011; 11:2197-203. [PMID: 21603723 PMCID: PMC3131499 DOI: 10.1039/c1lc20056a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
We present the development of a microfluidically cryo-cooled planar coil for magnetic resonance (MR) microscopy. Cryogenically cooling radiofrequency (RF) coils for magnetic resonance imaging (MRI) can improve the signal to noise ratio (SNR) of the experiment. Conventional cryostats typically use a vacuum gap to keep samples to be imaged, especially biological samples, at or near room temperature during cryo-cooling. This limits how close a cryo-cooled coil can be placed to the sample. At the same time, a small coil-to-sample distance significantly improves the MR imaging capability due to the limited imaging depth of planar MR microcoils. These two conflicting requirements pose challenges to the use of cryo-cooling in MR microcoils. The use of a microfluidic based cryostat for localized cryo-cooling of MR microcoils is a step towards eliminating these constraints. The system presented here consists of planar receive-only coils with integrated cryo-cooling microfluidic channels underneath, and an imaging surface on top of the planar coils separated by a thin nitrogen gas gap. Polymer microfluidic channel structures fabricated through soft lithography processes were used to flow liquid nitrogen under the coils in order to cryo-cool the planar coils to liquid nitrogen temperature (-196 °C). Two unique features of the cryo-cooling system minimize the distance between the coil and the sample: (1) the small dimension of the polymer microfluidic channel enables localized cooling of the planar coils, while minimizing thermal effects on the nearby imaging surface. (2) The imaging surface is separated from the cryo-cooled planar coil by a thin gap through which nitrogen gas flows to thermally insulate the imaging surface, keeping it above 0 °C and preventing potential damage to biological samples. The localized cooling effect was validated by simulations, bench testing, and MR imaging experiments. Using this cryo-cooled planar coil system inside a 4.7 Tesla MR system resulted in an average image SNR enhancement of 1.47 ± 0.11 times relative to similar room-temperature coils.
Collapse
Affiliation(s)
- Chiwan Koo
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, 77843 USA
| | - Richard F. Godley
- Department of Electrical & Computer Engineering, Texas A&M University, College Station, TX, 77843 USA
| | - Jaewon Park
- Department of Electrical & Computer Engineering, Texas A&M University, College Station, TX, 77843 USA
| | - Mary P. McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, 77843 USA
- Department of Electrical & Computer Engineering, Texas A&M University, College Station, TX, 77843 USA
| | - Steven M. Wright
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, 77843 USA
- Department of Electrical & Computer Engineering, Texas A&M University, College Station, TX, 77843 USA
| | - Arum Han
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, 77843 USA
- Department of Electrical & Computer Engineering, Texas A&M University, College Station, TX, 77843 USA
| |
Collapse
|
38
|
Nordmeyer-Massner JA, De Zanche N, Pruessmann KP. Noise figure characterization of preamplifiers at NMR frequencies. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 210:7-15. [PMID: 21439871 DOI: 10.1016/j.jmr.2011.01.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Revised: 01/22/2011] [Accepted: 01/27/2011] [Indexed: 05/30/2023]
Abstract
A method for characterizing the noise figure of preamplifiers at NMR frequencies is presented. The noise figure of preamplifiers as used for NMR and MRI detection varies with source impedance and with the operating frequency. Therefore, to characterize a preamplifier's noise behavior, it is necessary to perform noise measurements at the targeted frequency while varying the source impedance with high accuracy. At high radiofrequencies, such impedance variation is typically achieved with transmission-line tuners, which however are not available for the relatively low range of typical NMR frequencies. To solve this issue, this work describes an alternative approach that relies on lumped-element circuits for impedance manipulation. It is shown that, using a fixed-impedance noise source and suitable ENR correction, this approach permits noise figure characterization for NMR and MRI purposes. The method is demonstrated for two preamplifiers, a generic BF998 MOSFET module and an MRI-dedicated, integrated preamplifier, which were both studied at 128MHz, i.e., at the Larmor frequency of protons at 3 Tesla. Variations in noise figure of 0.01dB or less over repeated measurements reflect high precision even for small noise figures in the order of 0.4dB. For validation, large sets of measured noise figure values are shown to be consistent with the general noise-parameter model of linear two-ports. Finally, the measured noise characteristics of the superior preamplifier are illustrated by SNR measurements in MRI data.
Collapse
Affiliation(s)
- J A Nordmeyer-Massner
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | | | | |
Collapse
|
39
|
Feng S, Zhu Y, Ji J. Efficient large-array k-domain parallel MRI using channel-by-channel array reduction. Magn Reson Imaging 2011; 29:209-15. [DOI: 10.1016/j.mri.2010.08.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2010] [Revised: 08/02/2010] [Accepted: 08/27/2010] [Indexed: 11/26/2022]
|
40
|
Albrecht J, Burke M, Haegler K, Schöpf V, Kleemann AM, Paolini M, Wiesmann M, Linn J. Potential impact of a 32-channel receiving head coil technology on the results of a functional MRI paradigm. Clin Neuroradiol 2010; 20:223-9. [PMID: 20857080 DOI: 10.1007/s00062-010-0029-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Accepted: 08/10/2010] [Indexed: 11/28/2022]
Abstract
PURPOSE The authors investigated the potential of a 32-channel (32ch) receiving head coil for functional magnetic resonance imaging (fMRI) compared to a standard eight-channel (8ch) coil using a motor task. MATERIAL AND METHODS Brain activation was analyzed in 14 healthy right-handed subjects performing finger tapping with the right index finger (block design) during two experimental sessions, one with the 8ch and one with the 32ch coil (applied in a pseudorandomized order). Additionally, a phantom study was performed to compare signal-to-noise ratios (SNRs) of both coils. RESULTS During both fMRI sessions, analysis of motor conditions resulted in an activation of the left "hand knob" (precentral gyrus). Application of the 32ch coil obtained additional activation clusters in the right cerebellum, left superior frontal gyrus (SMA), left supramarginal gyrus, and left postcentral gyrus. The phantom study revealed a significantly higher SNR for the 32ch coil compared to the 8ch coil in superficial cortical areas located near the surface of the brain. CONCLUSION The 32ch technology has a potential impact on fMRI studies, especially in paradigms that result in activation of cortical areas located near the surface of the brain.
Collapse
Affiliation(s)
- J Albrecht
- Department of Neuroradiology, Ludwig Maximilians University, Munich, Germany.
| | | | | | | | | | | | | | | |
Collapse
|
41
|
Goense J, Logothetis NK, Merkle H. Flexible, phase-matched, linear receive arrays for high-field MRI in monkeys. Magn Reson Imaging 2010; 28:1183-91. [PMID: 20456890 DOI: 10.1016/j.mri.2010.03.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 02/23/2010] [Accepted: 03/05/2010] [Indexed: 10/19/2022]
Abstract
High signal-to-noise ratios (SNR) are essential for high-resolution anatomical and functional MRI. Phased arrays are advantageous for this but have the drawback that they often have inflexible and bulky configurations. Particularly in experiments where functional MRI is combined with simultaneous electrophysiology, space constraints can be prohibitive. To this end we developed a highly flexible multiple receive element phased array for use on anesthetized monkeys. The elements are interchangeable and different sizes and combinations of coil elements can be used, for instance, combinations of single and overlapped elements. The preamplifiers including control electronics are detachable and can serve a variety of prefabricated and phase matched arrays of different configurations, allowing the elements to always be placed in close proximity to the area of interest. Optimizing performance of the individual elements ensured high SNR at the cortical surface as well as in deeper laying structures. Performance of a variety of arrangements of gapped linear arrays was evaluated at 4.7 and 7T in high-resolution anatomical and functional MRI.
Collapse
Affiliation(s)
- Jozien Goense
- Department of Physiology of Cognitive Processes, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany.
| | | | | |
Collapse
|
42
|
Wright SM, McDougall MP, Feng K, Hollingsworth NA, Bosshard JC, Chang CW. Highly parallel transmit/receive systems for dynamic MRI. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2010; 2009:4053-6. [PMID: 19964097 DOI: 10.1109/iembs.2009.5333172] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Dynamic MRI continues to grow in interest and capability with the introduction of 64 and 128 channel receivers, and, more recently, 8 and 16 channel parallel transmitters. This talk will describe progress in developing a 64 channel transmitter and applications in high-speed MR imaging, reaching 1000 frames per second.
Collapse
Affiliation(s)
- Steven M Wright
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA.
| | | | | | | | | | | |
Collapse
|
43
|
Abstract
Conventionally, MR images are formed by applying gradients to the main static magnetic field (B0). However, the B0 gradient equipment is expensive, power-hungry, complex, and noisy and can induce eddy currents in nearby conducting structures, including the patient. Here, we describe a new silent, B0 gradient-free MRI principle, Transmit Array Spatial Encoding (TRASE), based on phase gradients of the radio-frequency (RF) field. RF phase gradients offer a new method of k-space traversal. Echo trains using at least two different RF phase gradients allow spin phase to accumulate, causing k-space traversal. Two such RF fields provide one-dimensional imaging and three are sufficient for two-dimensional imaging. Since TRASE is a k-space method, analogues of many conventional pulse sequences are possible. Experimental results demonstrate one-dimensional and two-dimensional RF MRI and slice selection using a single-channel, transmit/receive, 0.2 T, permanent magnet, human MR system. The experimentally demonstrated spatial resolution is much higher than that provided by RF receive coil array sensitivity encoding alone but lower than generally achievable with B0 gradients. Potential applications are those in which one or more of the features of simplified equipment, lower costs, silent MRI, or the different physics of the image formation process are particularly advantageous.
Collapse
Affiliation(s)
- Jonathan C Sharp
- Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, Alberta, Canada.
| | | |
Collapse
|
44
|
Feng S, Ji J. Coil reduction in parallel excitation with large array. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2010; 2010:3313-3316. [PMID: 21096820 DOI: 10.1109/iembs.2010.5627495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Parallel excitation using coil array has been introduced in MRI as an effective method to design multi-dimensional spatially selective RF pulses. Generally, all transmit coil elements are used simultaneously in parallel excitation. In case of large array, RF pulse design requires significant computation time and memory size. In this paper, a method using reduced number of coils for parallel excitation is proposed to take advantage of localized coil transmit sensitivity in large array. Specifically, a subset of coils in the large array can be selected based on coil sensitivity coverage and desired excitation pattern. Simulation results with both spiral and EPI k-space trajectories show that proposed method is effective in achieving high excitation resolution at different acceleration factors while the computation time and memory requirement are greatly reduced.
Collapse
Affiliation(s)
- Shuo Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843-3128, USA
| | | |
Collapse
|
45
|
Bosshard JC, Eigenbrodt EP, McDougall MP, Wright SM. A fourth gradient to overcome slice dependent phase effects of voxel-sized coils in planar arrays. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2010; 2010:6649-6652. [PMID: 21096734 DOI: 10.1109/iembs.2010.5627152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The signals from an array of densely spaced long and narrow receive coils for MRI are complicated when the voxel size is of comparable dimension to the coil size. The RF coil causes a phase gradient across each voxel, which is dependent on the distance from the coil, resulting in a slice dependent shift of k-space. A fourth gradient coil has been implemented and used with the system's gradient set to create a gradient field which varies with slice. The gradients are pulsed together to impart a slice dependent phase gradient to compensate for the slice dependent phase due to the RF coils. However the non-linearity in the fourth gradient which creates the desired slice dependency also results in a through-slice phase ramp, which disturbs normal slice refocusing and leads to additional signal cancelation and reduced field of view. This paper discusses the benefits and limitations of using a fourth gradient coil to compensate for the phase due to RF coils.
Collapse
Affiliation(s)
- John C Bosshard
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA.
| | | | | | | |
Collapse
|
46
|
Nunes RG, Hajnal JV, Larkman DJ. Combining RF encoding with parallel imaging: a simulation study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2009; 23:31-8. [PMID: 20024668 DOI: 10.1007/s10334-009-0191-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 10/13/2009] [Accepted: 11/16/2009] [Indexed: 11/30/2022]
Abstract
OBJECT The aim of this work was to investigate combining spatial encoding by radio frequency (RF) excitation with conventional parallel imaging (PI) methods to determine whether this could improve overall imaging performance. MATERIALS AND METHODS A simulation framework was developed to predict imaging performance for regular, central and random under-sampled parallel imaging methods augmented by RF spatial signal modulation. Optimisation methods were used to find the RF modulation patterns that produce optimal image reconstruction using the condition number of the PI encoding matrix as a quality metric. The diverse patterns of raw data sampling produced were compared using a measure of data uniformity across k-space. RESULTS Regular under-sampling of k-space provided the best reconstruction quality. When other under-sampling schemes were employed then RF modulation could be used to improve reconstruction, with the optimum achieved by redistributing the signal in k-space to return to regular sub-sampling. For all tested under-sampling patterns, no further improvements in image quality were attained. CONCLUSION Using the simulation framework and metrics described the interaction of different spatial encoding approaches could be investigated. Regular sub-sampling provided optimal reconstruction, independent of whether the spatial encoding was achieved by gradients only or a combination of gradient and RF.
Collapse
Affiliation(s)
- Rita G Nunes
- Robert Steiner MR Unit, Imaging Sciences Department, Hammersmith Campus, Imperial College, Du Cane Road, London, W12 0NN, UK.
| | | | | |
Collapse
|
47
|
Feng S, Ji J. Channel reduction in massive array parallel MRI. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2009; 2009:4045-8. [PMID: 19964340 DOI: 10.1109/iembs.2009.5333700] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
This paper presents a method to explore the flexibility of channel reduction in k-domain parallel imaging with massive arrays to improve the computation efficiency. MCMLI and GRAPPA are k-domain reconstruction methods that use a neighborhood of PE columns, FE line(s) and all channels in the interpolation kernels. For massive array which contains a large number of element coils computation cost can be a significant problem. In this paper, channel selection and reduction is performed according to the correlation between channel images for individual channel reconstructions. Simulation results show that the proposed channel reduction algorithm can achieve similar or improved reconstruction quality with significantly reduced computation for massive arrays with localized sensitivity.
Collapse
Affiliation(s)
- Shuo Feng
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843-3128, USA
| | | |
Collapse
|
48
|
Trakic A, Wang H, Weber E, Li BK, Poole M, Liu F, Crozier S. Image reconstructions with the rotating RF coil. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 201:186-198. [PMID: 19800824 DOI: 10.1016/j.jmr.2009.09.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Revised: 09/02/2009] [Accepted: 09/05/2009] [Indexed: 05/28/2023]
Abstract
Recent studies have shown that rotating a single RF transceive coil (RRFC) provides a uniform coverage of the object and brings a number of hardware advantages (i.e. requires only one RF channel, averts coil-coil coupling interactions and facilitates large-scale multi-nuclear imaging). Motion of the RF coil sensitivity profile however violates the standard Fourier Transform definition of a time-invariant signal, and the images reconstructed in this conventional manner can be degraded by ghosting artifacts. To overcome this problem, this paper presents Time Division Multiplexed-Sensitivity Encoding (TDM-SENSE), as a new image reconstruction scheme that exploits the rotation of the RF coil sensitivity profile to facilitate ghost-free image reconstructions and reductions in image acquisition time. A transceive RRFC system for head imaging at 2 Tesla was constructed and applied in a number of in vivo experiments. In this initial study, alias-free head images were obtained in half the usual scan time. It is hoped that new sequences and methods will be developed by taking advantage of coil motion.
Collapse
Affiliation(s)
- A Trakic
- The School of Information Technology and Electrical Engineering, The University of Queensland, Australia.
| | | | | | | | | | | | | |
Collapse
|
49
|
Wiggins GC, Polimeni JR, Potthast A, Schmitt M, Alagappan V, Wald LL. 96-Channel receive-only head coil for 3 Tesla: design optimization and evaluation. Magn Reson Med 2009; 62:754-62. [PMID: 19623621 DOI: 10.1002/mrm.22028] [Citation(s) in RCA: 190] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The benefits and challenges of highly parallel array coils for head imaging were investigated through the development of a 3T receive-only phased-array head coil with 96 receive elements constructed on a close-fitting helmet-shaped former. We evaluated several designs for the coil elements and matching circuitry, with particular attention to sources of signal-to-noise ratio (SNR) loss, including various sources of coil loading and coupling between the array elements. The SNR and noise amplification (g-factor) in accelerated imaging were quantitatively evaluated in phantom and human imaging and compared to a 32-channel array built on an identical helmet-shaped former and to a larger commercial 12-channel head coil. The 96-channel coil provided substantial SNR gains in the distal cortex compared to the 12- and 32-channel coils. The central SNR for the 96-channel coil was similar to the 32-channel coil for optimum SNR combination and 20% lower for root-sum-of-squares combination. There was a significant reduction in the maximum g-factor for 96 channels compared to 32; for example, the 96-channel maximum g-factor was 65% of the 32-channel value for acceleration rate 4. The performance of the array is demonstrated in highly accelerated brain images.
Collapse
Affiliation(s)
- Graham C Wiggins
- Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
| | | | | | | | | | | |
Collapse
|
50
|
Wright SM, McDougall MP. Single echo acquisition MRI using RF encoding. NMR IN BIOMEDICINE 2009; 22:982-993. [PMID: 19441080 DOI: 10.1002/nbm.1399] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Encoding of spatial information in magnetic resonance imaging is conventionally accomplished by using magnetic field gradients. During gradient encoding, the position in k-space is determined by a time-integral of the gradient field, resulting in a limitation in imaging speed due to either gradient power or secondary effects such as peripheral nerve stimulation. Partial encoding of spatial information through the sensitivity patterns of an array of coils, known as parallel imaging, is widely used to accelerate the imaging, and is complementary to gradient encoding. This paper describes the one-dimensional limit of parallel imaging in which all spatial localization in one dimension is performed through encoding by the radiofrequency (RF) coil. Using a one-dimensional array of long and narrow parallel elements to localize the image information in one direction, an entire image is obtained from a single line of k-space, avoiding rapid or repeated manipulation of gradients. The technique, called single echo acquisition (SEA) imaging, is described, along with the need for a phase compensation gradient pulse to counteract the phase variation contained in the RF coil pattern which would otherwise cause signal cancellation in each imaging voxel. Image reconstruction and resolution enhancement methods compatible with the speed of the technique are discussed. MR movies at frame rates of 125 frames per second are demonstrated, illustrating the ability to monitor the evolution of transverse magnetization to steady state during an MR experiment as well as demonstrating the ability to image rapid motion. Because this technique, like all RF encoding approaches, relies on the inherent spatially varying pattern of the coil and is not a time-integral, it should enable new applications for MRI that were previously inaccessible due to speed constraints, and should be of interest as an approach to extending the limits of detection in MR imaging.
Collapse
Affiliation(s)
- Steven M Wright
- Department of Electrical and Computer Engineering, Texas A&M University, TX, USA.
| | | |
Collapse
|