A simple head‐sized phantom for realistic static and radiofrequency characterization at high fields

Brink, Wyger M.; Wu, Zhiyi; Webb, Andrew

doi:10.1002/mrm.27153

Cited by 19 publications

(25 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Field penetration was improved by connecting the same amplifier, without any modification or tuning, to a larger rectangular loop. Results suggest that a well-decoupled array built with these loops will provide higher B + 1 efficiency at the center (>0.5 μT/√W), as reported elsewhere for other 7 T head coils 40,41 and as experimentally obtained with a commercial head coil (Nova Medical Head Coil 1 Tx/32 Rx). The B + 1 generation at adequate power levels appears possible with this on-coil technology, at a cost of less than $5 per watt delivered to the coil.…”

Section: Discussionsupporting

confidence: 82%

Eight‐channel parallel transmit‐receive system for 7 T MRI with optically controlled and monitored on‐coil current‐mode RF amplifiers

Gudino

Zwart

Duyn

2020

Magnetic Resonance in Med

View full text Add to dashboard Cite

Purpose To demonstrate a practical implementation of an eight‐channel parallel‐transmit system for brain imaging at 7 T based on on‐coil amplifier technology. Methods An eight‐channel parallel transmit‐receive system was built with optimized on‐coil switch‐mode current RF power amplifiers. The amplifiers were optically controlled from an eight‐channel interface that was connected to a 7 T MRI scanner. The interface also optically received a down‐converted version of the coil current sensed in each amplifier for monitoring and feedback adjustments. Results Each on‐coil amplifier delivered more than 100 W peak power and provided enough amplifier decoupling (<−15 dB) for the implemented eight‐channel array configuration. Phantom and human images were acquired to demonstrate practical operation of this new technology in a 7 T MRI scanner. Conclusion Further development and improvement of previously demonstrated on‐coil technology led to successful implementation of an eight‐channel parallel‐transmit system able to deliver strong B1 fields for typical brain imaging applications. This is an important step forward toward implementation of on‐coil RF amplification for high‐field MRI.

show abstract

Section: Discussionsupporting

confidence: 82%

Eight‐channel parallel transmit‐receive system for 7 T MRI with optically controlled and monitored on‐coil current‐mode RF amplifiers

Gudino

Zwart

Duyn

2020

Magnetic Resonance in Med

View full text Add to dashboard Cite

show abstract

“…These measurements were carried out using the proton reference frequency method . A 3D gradient‐echo sequence was used for heating and also for carrying out the thermal measurements: TR/TE = 14/10 ms, flip angle (FA) = 10°, scan duration = 15 min. To induce measurable temperature changes the SAR limits of the scanner were disabled and the power absorbed by the sample was increased by applying a series of 100 kHz off‐resonance pre‐pulses during the imaging sequence (these far off‐resonance pulses do not interfere with the imaging itself).…”

Section: Methodsmentioning

confidence: 99%

Shielded‐coaxial‐cable coils as receive and transceive array elements for 7T human MRI

Ruytenberg

Webb

Živković

2019

Magnetic Resonance in Med

View full text Add to dashboard Cite

Purpose: To investigate the use of shielded-coaxial-cable (SCC) coils as elements for multi-channel receive-only and transceive arrays for 7T human MRI and to compare their performance with equivalently sized conventional loop coils. Methods: The SCC coil element consists of a coaxial loop with interrupted central conductor at the feed-point side and an interrupted shield at the opposite point. Interelement decoupling, transmit efficiency, and sample heating were compared with results from conventional capacitively segmented loop coils. Three multichannel arrays (a 4-channel receive-only array and 8-and 5-channel transceive arrays) were constructed. Their inter-element decoupling was characterized via measured noise correlation matrices and additionally under different flexing conditions of the coils.Thermal measurements were performed and in vivo images were acquired. Results: The measured and simulated B + 1 maps of both SCC and conventional loops were very similar. For all the arrays constructed, the inter-element decoupling was much greater for the SCC elements than the conventional ones. Even under high degrees of flexion, the coupling coefficients were lower than −10 dB, with a much smaller frequency shift than for the conventional coils. Conclusion: Arrays constructed from SCC elements are mechanically flexible and much less sensitive to changes of the coil shape from circular to elongated than arrays constructed from conventional loop coils, which makes them suitable for construction of size adjustable arrays. K E Y W O R D S7T arrays, coaxial coils, transceive coils

show abstract

“…Input reflection and coupling coefficients are shown in Table 1. For realistic loading conditions reflecting that of a human head and neck, these values were measured while the arrays were loaded with a human head shaped spherical phantom with short neck structure [34]. This human head shaped phantom (diameter: 150 mm and height: 180 mm) was filled with a PVP-agar gel mixture with known electrical properties (conductivity (σ) of 0.69 S/m and relative permittivity (εr) of 49).…”

Section: A Coil Design and Bench Measurementsmentioning

confidence: 99%

Evaluation of a 16-Channel Transceiver Loop + Dipole Antenna Array for Human Head Imaging at 10.5 Tesla

et al. 2020

View full text Add to dashboard Cite

We evaluated a 16-channel loop + dipole (LD) transceiver antenna array with improved specific absorption rate (SAR) efficiency for 10.5 Tesla (T) human head imaging applications. Three different array designs with equal inner dimensions were considered: an 8-channel dipole antenna, an 8channel loop, and a 16-channel LD antenna arrays. Signal-to-noise ratio (SNR) and B1 + efficiency (in units of µT per √W) were simulated and measured in 10.5 T magnetic resonance imaging (MRI) experiments. For the safety validation, 10 g SAR and SAR efficiency (defined as the B1 + over √ (peak 10 g SAR)) were calculated through simulation. Finally, high resolution porcine brain images were acquired with the 16channel LD antenna array, including a fast turbo-spin echo (TSE) sequence incorporating B1 shimming techniques. Both the simulation and experiments demonstrated that the combined 16-channel LD antenna array showed similar B1 + efficiency compared to the 8-channel dipole antenna and the 8-channel loop arrays in a circular polarized (CP) mode. In a central 2 mm × 2 mm region of the phantom, however, the 16-channel LD antenna array showed an improvement in peak 10 g SAR of 27.5 % and 32.5 % over the 8channel dipole antenna and the 8-channel loop arrays, respectively. We conclude that the proposed 16channel head LD antenna array design is capable of achieving ~7% higher SAR efficiency at 10.5 T compared to either the 8-channel loop-only or the 8-channel dipole-only antenna arrays of the same dimensions. INDEX TERMS dipole antenna array, human head array, loop array, magnetic resonance imaging, RF coil, ultra-high field

show abstract

A simple head‐sized phantom for realistic static and radiofrequency characterization at high fields

Cited by 19 publications

References 41 publications

Eight‐channel parallel transmit‐receive system for 7 T MRI with optically controlled and monitored on‐coil current‐mode RF amplifiers

Eight‐channel parallel transmit‐receive system for 7 T MRI with optically controlled and monitored on‐coil current‐mode RF amplifiers

Shielded‐coaxial‐cable coils as receive and transceive array elements for 7T human MRI

Evaluation of a 16-Channel Transceiver Loop + Dipole Antenna Array for Human Head Imaging at 10.5 Tesla

Contact Info

Product

Resources

About