Ultra-high field MRI for primate imaging using the travelling-wave concept

Mallow, Johannes; Herrmann, Tim; Kim, Kyoung-Nam; Stadler, Jörg; Mylius, Judith; Brosch, Michael; Bernarding, Johannes

doi:10.1007/s10334-012-0358-z

Cited by 8 publications

(14 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…12 This excitation, however, if not aided by additional electrodynamic elements (dielectrics or metamaterials), is highly localized, which results in rapid power dissipation in the body and quick attenuation with distance away from the antenna. In addition, the traveling-wave concept has been mostly invoked and tested in 60-cm MRI bores at 7 T. [13][14][15] On the other hand, there exist several traveling-wave-inspired designs at 3 T employing a parallel-plate waveguide, 16 dielectric inserts, 17 and a cylindrical metallic waveguide as an RF shield, 18 respectively, to facilitate RF field coupling to the subject. In fact, the main area of engineering research in advancing next-generation MRI scanners at high (B 0 = 3 T) and ultrahigh (B 0 > 3 T) polarizing fields is in improving RF coils and B 1 fields in a MRI bore loaded with a human body or a phantom.…”

Section: Introductionmentioning

confidence: 99%

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

Athalye

Sekeljic

Ilić

et al. 2016

Concepts Magn Reson

View full text Add to dashboard Cite

A novel method for excitation of RF B1 field in high‐field (3‐T) magnetic resonance imaging (MRI) systems using a subject‐loaded quadrifilar helical antenna as an RF coil is proposed, evaluated, and demonstrated. Design, analysis, characterization, and evaluation of the novel coil when situated in a 3‐T MRI bore and loaded with different phantoms are performed and cross‐validated by extensive numerical simulations using multiple computational electromagnetics techniques. The results for the quadrifilar helical‐antenna RF body coil show (a) strong field penetration in the entire phantoms; (b) excellent right‐hand circular polarization (RCP); (c) high spatial uniformity of RCP RF magnetic field, B1+, throughout the phantoms; (d) large field of view (FOV); (e) good transmit efficiency; and (f) low local specific absorption rate (SAR). The examples show that the new RF coil provides substantially better B1+‐field uniformity and much larger FOV than any of the previously reported numerical and experimental results for the existing RF coil designs at 3 T in literature that enable comparison. In addition, helical RF body coils of different lengths can, for instance, easily provide an excellent RCP and highly uniform B1+‐field within the MRI maximum FOV length of 50 cm, and even 100 cm. The proposed MRI RF coil yields a remarkable improvement in the field uniformity in the longitudinal direction, for various phantoms, with comparable efficiency and SAR levels.

show abstract

Section: Introductionmentioning

confidence: 99%

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

Athalye

Sekeljic

Ilić

et al. 2016

Concepts Magn Reson

View full text Add to dashboard Cite

show abstract

“…The patch antenna serves as a transmitter for a homogenous B 1 + field in a central region of interest (ROI) with a diameter of about 10 cm. The B 1 + field homogeneity in this central ROI is nearly equivalent to the "gold-standard" birdcage architecture, as shown in Mallow et al 2013 [9]. …”

Section: Discussionmentioning

confidence: 65%

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Herrmann¹,

Mallow²,

Plaumann³

et al. 2015

PLoS ONE

Self Cite

View full text Add to dashboard Cite

IntroductionNeuroimaging of macaques at ultra-high field (UHF) is usually conducted by combining a volume coil for transmit (Tx) and a phased array coil for receive (Rx) tightly enclosing the monkey’s head. Good results have been achieved using vertical or horizontal magnets with implanted or near-surface coils. An alternative and less costly approach, the travelling-wave (TW) excitation concept, may offer more flexible experimental setups on human whole-body UHF magnetic resonance imaging (MRI) systems, which are now more widely available. Goal of the study was developing and validating the TW concept for in vivo primate MRI.MethodsThe TW Primate System (TWPS) uses the radio frequency shield of the gradient system of a human whole-body 7 T MRI system as a waveguide to propagate a circularly polarized B1 field represented by the TE11 mode. This mode is excited by a specifically designed 2-port patch antenna. For receive, a customized neuroimaging monkey head receive-only coil was designed. Field simulation was used for development and evaluation. Signal-to-noise ratio (SNR) was compared with data acquired with a conventional monkey volume head coil consisting of a homogeneous transmit coil and a 12-element receive coil.ResultsThe TWPS offered good image homogeneity in the volume-of-interest Turbo spin echo images exhibited a high contrast, allowing a clear depiction of the cerebral anatomy. As a prerequisite for functional MRI, whole brain ultrafast echo planar images were successfully acquired.ConclusionThe TWPS presents a promising new approach to fMRI of macaques for research groups with access to a horizontal UHF MRI system.

show abstract

“…The choice to select a macaque, which is about 45 cm tall, as an in vivo subject for imaging is motivated by the goal to acquire data from complex biological structures under the above-mentioned spatial restrictions of the MRAS-equipped bore of the MRI system. A second rationale was to provide the neuroscience research group of our site working with macaques monkeys [ 21 , 24 , 32 ] with a new and potentially better data acquisition concept. For the experiments with the water-NaCl-isopropanol phantom and crab-eating macaque, the MRAS was configured as a two ring antenna systems both for transmit and receive which were placed at the end positions of the VoI ( Fig 5A ).…”

Section: Methodsmentioning

confidence: 99%

“…This approach yields a sufficiently uniform B 1 + field distribution for the imaging of a human extremity (leg) [ 20 ] or for neuroimaging of smaller non-human primates [ 21 ], thus enabling the imaging at VoIs of intermediate size. Unfortunately, the B 1 + transmit efficiency, i.e., the required RF energy to generate the B 1 + field is lower than that of both the body coils conventionally used in clinical 3 T MRI systems [ 22 ] and of the UHF body-part volume resonators of birdcage architecture [ 23 , 24 ]. Usually, birdcage volume coils confine the RF energy in the structure enclosed by the RF coil.…”

Section: Introductionmentioning

confidence: 99%

Metamaterial-based transmit and receive system for whole-body magnetic resonance imaging at ultra-high magnetic fields

et al. 2018

Self Cite

View full text Add to dashboard Cite

Magnetic resonance imaging (MRI) at ultra-high fields (UHF), such as 7 T, provides an enhanced signal-to-noise ratio and has led to unprecedented high-resolution anatomic images and brain activation maps. Although a variety of radio frequency (RF) coil architectures have been developed for imaging at UHF conditions, they usually are specialized for small volumes of interests (VoI). So far, whole-body coil resonators are not available for commercial UHF human whole-body MRI systems. The goal of the present study was the development and validation of a transmit and receive system for large VoIs that operates at a 7 T human whole-body MRI system. A Metamaterial Ring Antenna System (MRAS) consisting of several ring antennas was developed, since it allows for the imaging of extended VoIs. Furthermore, the MRAS not only requires lower intensities of the irradiated RF energy, but also provides a more confined and focused injection of excitation energy on selected body parts. The MRAS consisted of several antennas with 50 cm inner diameter, 10 cm width and 0.5 cm depth. The position of the rings was freely adjustable. Conformal resonant right-/left-handed metamaterial was used for each ring antenna with two quadrature feeding ports for RF power. The system was successfully implemented and demonstrated with both a silicone oil and a water-NaCl-isopropanol phantom as well as in vivo by acquiring whole-body images of a crab-eating macaque. The potential for future neuroimaging applications was demonstrated by the acquired high-resolution anatomic images of the macaque’s head. Phantom and in vivo measurements of crab-eating macaques provided high-resolution images with large VoIs up to 40 cm in xy-direction and 45 cm in z-direction. The results of this work demonstrate the feasibility of the MRAS system for UHF MRI as proof of principle. The MRAS shows a substantial potential for MR imaging of larger volumes at 7 T UHF. This new technique may provide new diagnostic potential in spatially extended pathologies such as searching for spread-out tumor metastases or monitoring systemic inflammatory processes.

show abstract

Ultra-high field MRI for primate imaging using the travelling-wave concept

Abstract: The TW concept opens up a new approach for MRI of medium-sized animals in horizontal UHF scanners.

Cited by 8 publications

References 15 publications

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Metamaterial-based transmit and receive system for whole-body magnetic resonance imaging at ultra-high magnetic fields

Contact Info

Product

Resources

About

Ultra-high field MRI for primate imaging using the travelling-wave concept

Abstract: The TW concept opens up a new approach for MRI of medium-sized animals in horizontal UHF scanners.

Cited by 8 publications

References 15 publications

Subject‐loaded quadrifilar helical‐antenna RF coil with high B1+ field uniformity and large FOV for 3‐T MRI

Subject‐loaded quadrifilar helical‐antenna RF coil with high B1+ field uniformity and large FOV for 3‐T MRI

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Metamaterial-based transmit and receive system for whole-body magnetic resonance imaging at ultra-high magnetic fields

Contact Info

Product

Resources

About

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI