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Maurya SK, Schmidt R. Shaping the RF Transmit Field in 7T MRI Using a Nonuniform Metasurface Constructed of Short Conducting Strips. ACS APPLIED MATERIALS & INTERFACES 2024; 16:47284-47293. [PMID: 39215392 PMCID: PMC11403565 DOI: 10.1021/acsami.4c10402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
The ability of metamaterial structures to offer unique properties and new solutions has opened new avenues in a wide range of applications, including super-resolution in optics and efficient antennas in radiofrequency (RF) engineering. In magnetic resonance imaging (MRI), metamaterials hold the promise of increasing the RF magnetic field intensity while minimizing power deposition. Here, we propose a metasurface based on a two-dimensional (2D) array of short conducting strips combined with a high dielectric substrate, which was tuned to operate at ultrahigh field 7T human MRI. While studied in optics and electromagnetics in the GHz-to-THz range, this study is the first to design such a metasurface for proton imaging at 7T MRI. We performed electromagnetic (EM) simulation of the brain MRI setup with the new metasurface placed in the proximity to the temporal lobe, which showed 2.2-fold local increase in the RF transmit efficiency, with superior performance than an array of electric dipoles. In this study, we also investigate the effect of the spatial distribution of the subunits to control the target RF field's distribution. While the common design is based on a uniform distribution of the subunits, nonuniform distribution, such as a denser center (convex) or more condensed edges (concave), provides an extra dimension to tailor both the magnetic and electric fields. The concave distribution achieved 1.5-1.8-fold reduction in the power deposition compared to the uniform distribution in the brain MRI setups examined.
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Affiliation(s)
- Santosh Kumar Maurya
- Department of Brain Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel
- The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Rita Schmidt
- Department of Brain Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel
- The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot 7610001, Israel
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Jacobs PS, Wilson N, Brink W, Swain A, Armbruster R, Hanumapur A, Tisdall MD, Detre J, Nanga RPR, Elliott MA, Reddy R. In vivo B 1 + enhancement of calf MRI at 7 T via optimized flexible metasurfaces. Magn Reson Med 2024; 92:1277-1289. [PMID: 38469893 PMCID: PMC11209820 DOI: 10.1002/mrm.30060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 01/18/2024] [Accepted: 02/05/2024] [Indexed: 03/13/2024]
Abstract
PURPOSE Ultrahigh field (≥7 T) MRI is at the cutting edge of medical imaging, enabling enhanced spatial and spectral resolution as well as enhanced susceptibility contrast. However, transmit (B 1 + $$ {\mathrm{B}}_1^{+} $$ ) field inhomogeneity due to standing wave effects caused by the shortened RF wavelengths at 7 T is still a challenge to overcome. Novel hardware methods such as dielectric pads have been shown to improve theB 1 + $$ {\mathrm{B}}_1^{+} $$ field inhomogeneity but are currently limited in their corrective effect by the range of high-permittivity materials available and have a fixed shelf life. In this work, an optimized metasurface design is presented that demonstrates in vivo enhancement of theB 1 + $$ {\mathrm{B}}_1^{+} $$ field. METHODS A prototype metasurface was optimized by an empirical capacitor sweep and by varying the period size. Phantom temperature experiments were performed to evaluate potential metasurface heating effects during scanning. Lastly, in vivo gradient echo images andB 1 + $$ {\mathrm{B}}_1^{+} $$ maps were acquired on five healthy subjects on a 7 T system. Dielectric pads were also used as a comparison throughout the work as a standard comparison. RESULTS The metasurfaces presented here enhanced the average relative SNR of the gradient echo images by a factor of 2.26 compared to the dielectric pads factor of 1.61. AverageB 1 + $$ {\mathrm{B}}_1^{+} $$ values reflected a similar enhancement of 27.6% with the metasurfaces present versus 8.9% with the dielectric pads. CONCLUSION The results demonstrate that metasurfaces provide superior performance to dielectric padding as shown byB 1 + $$ {\mathrm{B}}_1^{+} $$ maps reflecting their direct effects and resulting enhancements in image SNR at 7 T.
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Affiliation(s)
- Paul S Jacobs
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Neil Wilson
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Wyger Brink
- Magnetic Detection and Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
| | - Anshuman Swain
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Ryan Armbruster
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Aniketh Hanumapur
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - M. Dylan Tisdall
- Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - John Detre
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
- Department of Neurology, University of Pennsylvania, Philadelphia, PA, United States
| | - Ravi Prakash Reddy Nanga
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Mark A. Elliott
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
| | - Ravinder Reddy
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
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Koloskov V, Brink WM, Webb AG, Shchelokova A. Flexible metasurface for improving brain imaging at 7T. Magn Reson Med 2024; 92:869-880. [PMID: 38469911 DOI: 10.1002/mrm.30088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 02/14/2024] [Accepted: 03/01/2024] [Indexed: 03/13/2024]
Abstract
PURPOSE Ultra-high field MRI offers unprecedented detail for noninvasive visualization of the human brain. However, brain imaging is challenging at 7T due to the B 1 + $$ {}_1^{+} $$ field inhomogeneity, which results in signal intensity drops in temporal lobes and a bright region in the brain center. This study aims to evaluate using a metasurface to improve brain imaging at 7T and simplify the investigative workflow. METHODS Two flexible metasurfaces comprising a periodic structure of copper strips and parallel-plate capacitive elements printed on an ultra-thin substrate were optimized for brain imaging and implemented via PCB. We considered two setups: (1) two metasurfaces located near the temporal lobes and (2) one metasurface placed near the occipital lobe. The effect of metasurface placement on the transmit efficiency and specific absorption rate was evaluated via electromagnetic simulation studies with voxelized models. In addition, their impact on signal-to-noise ratio (SNR) and diagnostic image quality was assessed in vivo for two male and one female volunteers. RESULTS Placement of metasurfaces near the regions of interest led to an increase in homogeneity of the transmit field by 5% and 10.5% in the right temporal lobe and occipital lobe for a male subject, respectively. SAR efficiency values changed insignificantly, dropping by less than 8% for all investigated setups. In vivo studies also confirmed the numerically predicted improvement in field distribution and receive sensitivity in the desired ROI. CONCLUSION Optimized metasurfaces enable homogenizing transmit field distribution in the brain at 7T. The proposed lightweight and flexible structure can potentially provide MR examination with higher diagnostic value images.
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Affiliation(s)
- Vladislav Koloskov
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | - Wyger M Brink
- Magnetic Detection & Imaging Group, TechMed Centre, University of Twente, Enschede, The Netherlands
| | - Andrew G Webb
- C.J. Gorter MRI Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Alena Shchelokova
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
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Jacobs PS, Brink W, Reddy R. A review of recent developments and applications of high-permittivity dielectric shimming in magnetic resonance. NMR IN BIOMEDICINE 2024; 37:e5094. [PMID: 38214202 DOI: 10.1002/nbm.5094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 10/20/2023] [Accepted: 11/29/2023] [Indexed: 01/13/2024]
Abstract
We present a review outlining the basic mechanism, background, recent technical developments, and clinical applications of aqueous dielectric padding in the field of MRI. Originally meant to be a temporary solution, it has gained traction as an effective method for correcting B1 + inhomogeneities due to the unique properties of the calcium titanate and barium titanate perovskites used. Aqueous dielectric pads have used a variety of high-permittivity materials over the years to improve the quality of MRI acquisitions at 1.5 and 3 T and more recently for 7 T neuroimaging applications. The technical development and assessment of these pads have been advanced by an increased use of mathematical modeling and electromagnetic simulations. These tools have allowed for a more complete understanding of the physical interactions between dielectric pads and the RF coil, making testing and safety assessments more accurate. The ease of use and effectiveness that dielectric pads offer have allowed them to become more commonplace in tackling imaging challenges in more clinically focused environments. More recently, they have seen usage not only in anatomical imaging methods but also in specialized metabolic imaging sequences such as GluCEST and NOEMTR . New colossally high-permittivity materials have been proposed; however, practical utilization has been a continued challenge due to unfavorable frequency dependences as well as safety limitations. A new class of metasurfaces has been under development to address the shortcomings of conventional dielectric padding while also providing increased performance in enhancing MRI images.
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Affiliation(s)
- Paul S Jacobs
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Wyger Brink
- Magnetic Detection and Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
| | - Ravinder Reddy
- Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Dudysheva N, Mauconduit F, Abdeddaim R, Gapais PF, Hosseinnezhadian S, Dubois M, Amadon A, Boulant N, Hertz-Pannier L, Vignaud A. The restricted SAR protocol: A method to assess MRI coil prototypes in an unconditionally safe manner. Magn Reson Med 2024; 91:1723-1734. [PMID: 38084471 DOI: 10.1002/mrm.29962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 10/24/2023] [Accepted: 11/17/2023] [Indexed: 02/03/2024]
Abstract
PURPOSE Testing an RF coil prototype on subjects involves laborious verifications to ensure its safety. In particular, it requires preliminary electromagnetic simulations and their validations on phantoms to accurately predict the specific absorption rate (SAR). For coil design validation with a simpler safety procedure, the restricted SAR (rS) mode is proposed, enabling representative first experiments in vivo. The goal of the developed approach is to accelerate the transition of a custom coil system from prototype to clinical use. METHODS The restricted specific absorption rate (SAR) (rS) mode imposes a radical limitation on the transmitted RF power based on a worst-case scenario of local RF power absorption. The limitations used are independent of the SAR spatial distribution, making this approach unconditionally safe. The developed rS protocol contains the sequences required for coil evaluation and satisfies the imposed rS conditions. It provides a quantitative characterization of the coil transmission and reception profiles and a qualitative evaluation of the anatomical images. Protocol validation was performed on commercial and pre-industrial prototype coils on a small cohort of healthy volunteers. RESULTS The proposed rS protocol enables coil evaluation within an acquisition time compatible with common clinical protocol duration. The total time of all evaluation steps does not exceed 17 min. At the same time, the global SAR remains 100 times less than the International Electrotechnical Commission safety limit for played sequences. CONCLUSION The rS protocol allows characterizing and comparing coil prototypes on volunteers without extensive electromagnetic calculations and phantom validations in an unconditionally safe way.
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Affiliation(s)
- Natalia Dudysheva
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
- Multiwave Imaging, Marseille, France
| | - Franck Mauconduit
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Redha Abdeddaim
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Institut Marseille Imaging, Marseille, France
| | | | | | | | - Alexis Amadon
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Nicolas Boulant
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Lucie Hertz-Pannier
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Alexandre Vignaud
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
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Gao Y, Liu T, Hong T, Fang Y, Jiang W, Zhang X. Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging. Nat Commun 2024; 15:2298. [PMID: 38485742 PMCID: PMC10940709 DOI: 10.1038/s41467-024-46638-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 03/05/2024] [Indexed: 03/18/2024] Open
Abstract
Magnetic resonance imaging (MRI) has diverse applications in physics, biology, and medicine. Uniform excitation of nuclei spins through circular-polarized transverse magnetic component of electromagnetic field is vital for obtaining unbiased tissue contrasts. However, achieving this in the electrically large human body poses a significant challenge, especially at ultra-high fields (UHF) with increased working frequencies (≥297 MHz). Canonical volume resonators struggle to meet this challenge, while radiative excitation methods like travelling-wave (TW) show promise but often suffer from inadequate excitation efficiency. Here, we introduce a new technique using a subwavelength dielectric waveguide insert that enhances both efficiency and homogeneity at 7 T. Through TE11-to-TM11 mode conversion, power focusing, wave impedance matching, and phase velocity matching, we achieved a 114% improvement in TW efficiency and mitigated the center-brightening effect. This fundamental advancement in TW MRI through effective wave manipulation could promote the electromagnetic design of UHF MRI systems.
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Affiliation(s)
- Yang Gao
- Hangzhou Institute of Technology, Xidian University, Hangzhou, China.
- School of Electronic Engineering, National Key Laboratory of Antennas and Microwave Technology, Xidian University, Xi'an, China.
- College of Electrical Engineering, Zhejiang University, Hangzhou, China.
| | - Tong Liu
- Hangzhou Institute of Technology, Xidian University, Hangzhou, China
| | - Tao Hong
- Hangzhou Institute of Technology, Xidian University, Hangzhou, China
- School of Electronic Engineering, National Key Laboratory of Antennas and Microwave Technology, Xidian University, Xi'an, China
| | - Youtong Fang
- College of Electrical Engineering, Zhejiang University, Hangzhou, China
| | - Wen Jiang
- Hangzhou Institute of Technology, Xidian University, Hangzhou, China
- School of Electronic Engineering, National Key Laboratory of Antennas and Microwave Technology, Xidian University, Xi'an, China
| | - Xiaotong Zhang
- College of Electrical Engineering, Zhejiang University, Hangzhou, China.
- Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, China.
- MOE Frontier Science Center for Brain Science and Brain-machine Integration, Zhejiang University, Hangzhou, China.
- Interdisciplinary Institute of Neuroscience and Technology, School of Medicine, Zhejiang University, Hangzhou, China.
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Alipour A, Seifert AC, Delman BN, Hof PR, Fayad ZA, Balchandani P. Enhancing the brain MRI at ultra-high field systems using a meta-array structure. Med Phys 2023; 50:7606-7618. [PMID: 37874014 DOI: 10.1002/mp.16801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 04/28/2023] [Accepted: 10/06/2023] [Indexed: 10/25/2023] Open
Abstract
BACKGROUND The main advantage of ultra-high field (UHF) magnetic resonance neuroimaging is theincreased signal-to-noise ratio (SNR) compared with lower field strength imaging. However, the wavelength effect associated with UHF MRI results in radiofrequency (RF) inhomogeneity, compromising whole brain coverage for many commercial coils. Approaches to resolving this issue of transmit field inhomogeneity include the design of parallel transmit systems (PTx), RF pulse design, and applying passive RF shimming such as high dielectric materials. However, these methods have some drawbacks such as unstable material parameters of dielectric pads, high-cost, and complexity of PTx systems. Metasurfaces are artificial structures with a unique platform that can control the propagation of the electromagnetic (EM) waves, and they are very promising for engineering EM device. Implementation of meta-arrays enhancing MRI has been explored previously in several studies. PURPOSE The aim of this study was to assess the effect of new meta-array technology on enhancing the brain MRI at 7T. A meta-array based on a hybrid structure consisting of an array of broadside-coupled split-ring resonators and high-permittivity materials was designed to work at the Larmor frequency of a 7 Tesla (7T) MRI scanner. When placed behind the head and neck, this construct improves the SNR in the region of the cerebellum,brainstem and the inferior aspect of the temporal lobes. METHODS Numerical electromagnetic simulations were performed to optimize the meta-array design parameters and determine the RF circuit configuration. The resultant transmit-efficiency and signal sensitivity improvements were experimentally analyzed in phantoms followed by healthy volunteers using a 7T whole-body MRI scanner equipped with a standard one-channel transmit, 32-channel receive head coil. Efficacy was evaluated through acquisition with and without the meta-array using two basic sequences: gradient-recalled-echo (GRE) and turbo-spin-echo (TSE). RESULTS Experimental phantom analysis confirmed two-fold improvement in the transmit efficiency and 1.4-fold improvement in the signal sensitivity in the target region. In vivo GRE and TSE images with the meta-array in place showed enhanced visualization in inferior regions of the brain, especially of the cerebellum, brainstem, and cervical spinal cord. CONCLUSION Addition of the meta-array to commonly used MRI coils can enhance SNR to extend the anatomical coverage of the coil and improve overall MRI coil performance. This enhancement in SNR can be leveraged to obtain a higher resolution image over the same time slot or faster acquisition can be achieved with same resolution. Using this technique could improve the performance of existing commercial coils at 7T for whole brain and other applications.
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Affiliation(s)
- Akbar Alipour
- BioMedical Engineering and Imaging Institute and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
| | - Alan C Seifert
- BioMedical Engineering and Imaging Institute and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
| | - Bradley N Delman
- Department of Diagnostic, Molecular and Interventional Radiology, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
| | - Patrick R Hof
- The Nash Family Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
| | - Zahi A Fayad
- BioMedical Engineering and Imaging Institute and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
| | - Priti Balchandani
- BioMedical Engineering and Imaging Institute and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
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Puchnin V, Jandaliyeva A, Hurshkainen A, Solomakha G, Nikulin A, Petrova P, Lavrenteva A, Andreychenko A, Shchelokova A. Quadrature transceive wireless coil: Design concept and application for bilateral breast MRI at 1.5 T. Magn Reson Med 2023; 89:1251-1264. [PMID: 36336799 DOI: 10.1002/mrm.29507] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 09/20/2022] [Accepted: 10/09/2022] [Indexed: 11/09/2022]
Abstract
PURPOSE Development of a novel quadrature inductively driven transceive wireless coil for breast MRI at 1.5 T. METHODS A quadrature wireless coil (HHMM-coil) design has been developed as a combination of two linearly polarized coils: a pair of 'metasolenoid' coils (MM-coil) and a pair of Helmholtz-type coils (HH-coil). The MM-coil consisted of an array of split-loop resonators. The HH-coil design included two electrically connected flat spirals. All the wireless coils were coupled to a whole-body birdcage coil. The HHMM-coil was studied and compared to the linear coils in terms of transmit and SAR efficiencies via numerical simulations. A prototype of HHMM-coil was built and tested on a 1.5 T scanner in a phantom and healthy volunteer. We also proposed an extended design of the HHMM-coil and compared its performance to a dedicated breast array. RESULTS Numerical simulations of the HHMM-coil with a female voxel model have shown more than a 2.5-fold increase in transmit efficiency and a 1.7-fold enhancement of SAR efficiency compared to the linearly polarized coils. Phantom and in vivo imaging showed good agreement with the numerical simulations. Moreover, the HHMM-coil provided good image quality, visualizing all areas of interest similar to a multichannel breast array with a 32% reduction in signal-to-noise ratio. CONCLUSION The proposed quadrature HHMM-coil allows the B 1 + $$ {\mathrm{B}}_1^{+} $$ -field to be significantly better focused in the region-of-interest compared to the linearly polarized coils. Thus, the HHMM-coil provides high-quality breast imaging on a 1.5 T scanner using a whole-body birdcage coil for transmit and receive.
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Affiliation(s)
- Viktor Puchnin
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | | | - Anna Hurshkainen
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | - Georgiy Solomakha
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | - Anton Nikulin
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | - Polina Petrova
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
| | - Anna Lavrenteva
- Medical Institute named after Berezin Sergey (MIBS), St. Petersburg, Russia
| | - Anna Andreychenko
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia.,Research and Practical Clinical Center for Diagnostics and Telemedicine Technologies, Moscow Health Care Department, Moscow, Russia
| | - Alena Shchelokova
- School of Physics and Engineering, ITMO University, St. Petersburg, Russia
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Koloskov V, Zubkov M, Solomakha G, Puchnin V, Levchuk A, Efimtcev A, Melchakova I, Shchelokova A. Improving detection of fMRI activation at 1.5 T using high permittivity ceramics. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 348:107390. [PMID: 36774714 DOI: 10.1016/j.jmr.2023.107390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 01/27/2023] [Accepted: 01/29/2023] [Indexed: 06/18/2023]
Abstract
In this work, we propose an application of high permittivity materials (HPMs) to improve functional magnetic resonance imaging (fMRI) at 1.5 T, increasing the receive (Rx) sensitivity of a commercial multi-channel head coil. To evaluate the transmit efficiency, specific absorption rate (SAR), and the signal-to-noise ratio (SNR) changes introduced by the HPMs with relative permittivity of 4500, we considered the following configurations in simulation: a whole-body birdcage coil and an Rx-only multi-channel head coil with and without the HPM blocks in the presence of a homogeneous head phantom or a human body model. Experimental studies were also performed with a phantom and with volunteers. Seven healthy volunteers enrolled in a prospective study of fMRI activation in the motor cortex with and without HPMs. fMRI data were analyzed using group-level paired T-tests between acquisitions with and without HPM blocks. Both electromagnetic simulations and experimental measurements showed ∼25% improvement in the Rx sensitivity of a commercial head coil in the areas of interest when HPM blocks were placed in close proximity. It increased the detected motor cortex fMRI activation volume by an average of 56%, thus resulting in more sensitive functional imaging at 1.5 T.
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Affiliation(s)
- Vladislav Koloskov
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation
| | - Mikhail Zubkov
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation
| | - Georgiy Solomakha
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation
| | - Viktor Puchnin
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation
| | - Anatoliy Levchuk
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation; Department of Radiology, Federal Almazov North-West Medical Research Center, St. Petersburg, Russian Federation
| | - Alexander Efimtcev
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation; Department of Radiology, Federal Almazov North-West Medical Research Center, St. Petersburg, Russian Federation
| | - Irina Melchakova
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation
| | - Alena Shchelokova
- School of Physics and Engineering, ITMO University, St. Petersburg, Russian Federation.
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Sokol SL, Colwell ZA, Kandala SK, Imani MF, Sohn SM. Flexible Metamaterial Wrap for Improved Head Imaging at 3 T MRI With Low-Cost and Easy Fabrication Method. IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 2022; 21:2075-2079. [PMID: 36388763 PMCID: PMC9648536 DOI: 10.1109/lawp.2022.3190696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Magnetic resonance imaging (MRI) requires spatial uniformity of the radiofrequency (RF) field inside the subject for maximum signal-to-noise ratio (SNR) and image contrast. Bulky high permittivity dielectric pads (HPDPs) focus magnetic fields into the region of interest (ROI) and increase RF field uniformity when placed between the patient and RF coils in the MR scanner. Metamaterials could replace HPDPs and reduce system bulkiness, but those in the literature often require a complicated fabrication process and cannot conform to patient body shape. Proposed is a flexible metamaterial for brain imaging made with a scalable fabrication process using conductive paint and a plastic laminate substrate. The effects of single and double-sided placement of the metamaterial around a human head phantom were investigated in a 3 T scanner. When two metamaterial sheets were wrapped around a head phantom (double-sided placement), the total average signal in the resulting image increased by 10.14% compared to placing a single metamaterial sheet underneath the phantom (single-sided placement). The difference between the maximum and minimum signal intensity values decreased by 57% in six different ROIs with double-sided placement compared to single-sided placement.
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Affiliation(s)
- Samantha L Sokol
- Dept. of Elect. Eng., Sch. of Elect. Comput. & Energy Eng. Arizona State Univ. Tempe, AZ, USA
| | - Zachary A Colwell
- School of Biological and Health Sciences Arizona State Univ. Tempe, AZ, USA
| | - Sri Kirthi Kandala
- School of Biological and Health Sciences Arizona State Univ. Tempe, AZ, USA
| | - Mohammadreza F Imani
- Dept. of Elect. Eng., Sch. of Elect. Comput. & Energy Eng. Arizona State Univ. Tempe, AZ, USA
| | - Sung-Min Sohn
- School of Biological and Health Sciences Arizona State Univ. Tempe, AZ, USA
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11
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Novel materials in magnetic resonance imaging: high permittivity ceramics, metamaterials, metasurfaces and artificial dielectrics. MAGNETIC RESONANCE MATERIALS IN PHYSICS, BIOLOGY AND MEDICINE 2022; 35:875-894. [PMID: 35471464 PMCID: PMC9596558 DOI: 10.1007/s10334-022-01007-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 02/18/2022] [Accepted: 03/07/2022] [Indexed: 11/01/2022]
Abstract
AbstractThis article reviews recent developments in designing and testing new types of materials which can be: (i) placed around the body for in vivo imaging, (ii) be integrated into a conventional RF coil, or (iii) form the resonator itself. These materials can improve the quality of MRI scans for both in vivo and magnetic resonance microscopy applications. The methodological section covers the basic operation and design of two different types of materials, namely high permittivity materials constructed from ceramics and artificial dielectrics/metasurfaces formed by coupled conductive subunits, either in air or surrounded by dielectric material. Applications of high permittivity materials and metasurfaces placed next to the body to neuroimaging and extremity imaging at 7 T, body and neuroimaging at 3 T, and extremity imaging at 1.5 T are shown. Results using ceramic resonators for both high field in vivo imaging and magnetic resonance microscopy are also shown. The development of new materials to improve MR image quality remains an active area of research, but has not yet found significant use in clinical applications. This is mainly due to practical issues such as specific absorption rate modelling, accurate and reproducible placement, and acceptable size/weight of such materials. The most successful area has been simple “dielectric pads” for neuroimaging at 7 T which were initially developed somewhat as a stop-gap while parallel transmit technology was being developed, but have continued to be used at many sites. Some of these issues can potentially be overcome using much lighter metasurfaces and artificial dielectrics, which are just beginning to be assessed.
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