Design of a high power <scp>PIN</scp>‐diode controlled switchable <scp>RF</scp> transmit array for <scp>TRASE RF</scp> imaging

Der, Eric T.; Volotovskyy, Vyacheslav; Sun, Hui; Tomanek, Bogusław; Sharp, Jonathan C.

doi:10.1002/cmr.b.21365

Cited by 9 publications

(9 citation statements)

References 11 publications

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“…These relatively longer delays are due to the time necessary to move the switch mechanically and to the switching delays of its driver circuit [33]. The increased delays by adding such driver circuit is also demonstrated in a recent work [44] using a PIN diode driver for high-power pulses where the rise-time is close to 1 µs and the fall-time increases to 7.4 µs, which are comparable to the results obtained with controlled MEMSs. Delays are nevertheless of the same order as optical-based decoupling circuits with 13.6 µs and 1.7 µs for tuning and detuning, respectively [23], which proved to be effective.…”

Section: Discussionsupporting

confidence: 66%

Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

Raki¹,

Koon²,

Saniour³

et al. 2020

IEEE Sensors J.

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MEMS (Micro Electro Mechanical System) switches were assessed and compared to PIN diode in fulfilling the task of active decoupling of Receiver Endoluminal Coils (RECs). Three prototype RECs with the PIN diode in parallel (pPIN), MEMS in parallel (pMEMS) and MEMS in series (sMEMS) with the REC loop were built. Quality factors (Q-values), decoupling efficiency and switching delays were characterized on bench and Signal-to-Noise Ratios (SNRs) established on images at 1.5 T. Q-values were equal to 62.5, 41.2 and 65.1 for pPIN, sMEMS and pMEMS, respectively. In the decoupled state, reflection coefficients S11 and S21 at resonance frequency both indicated proper decoupling. Switching delays were less than 0.7 µs and 10 µs for pPIN and MEMS RECs, respectively. Decoupling/coupling delays of MEMS remained compatible with most Magnetic Resonance (MR) clinical applications. For all prototypes, MR images displayed no signal saturation and similar elliptical image sensitivity patterns. No artifacts due to active decoupling failure were observed. Mean SNR values obtained with pMEMS REC were higher than those obtained with sMEMS REC but lower than with pPIN REC because of the use of additional instrumentation to render the scanner compatible with the MEMS utilization. MEMS in parallel are an interesting alternative to PIN diode for decoupling and could lead to better SNR with a compatible MR system (dedicated control signal). The MEMS in series can be used for both decoupling and reconfiguration of the REC loop geometry for colon wall examination.

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Section: Discussionsupporting

confidence: 66%

Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

Raki¹,

Koon²,

Saniour³

et al. 2020

IEEE Sensors J.

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“…The strong coupling between concentric solenoids can place a significant demand on the design of active decoupling circuitry, due to high induced RF voltages. 5 Use of geometric decoupling would allow the elimination of PIN diode control and power subsystem, which would be advantageous for low-cost MRI applications. One technical challenge of active switching at low RF frequencies is avoidance of interactions, such as noise and switching transients, between the RF and switching circuits, which operate in close frequency ranges.…”

Section: Overview Of Trase Array Decoupling Techniquesmentioning

confidence: 99%

“…Unlike conventional MRI encoding methods which rely on the use of main field (

B_{0}

) gradients, the substitution of

B_{0}

gradients by

B_{1}

phase gradients using simple RF technologies allows compact MRI systems to be made, particularly suitable for low‐field, low‐cost scenarios . Recent work suggest that clinical‐level millimeter spatial resolution is practically achievable, under both in vivo and phantom situations …”

Section: Introductionmentioning

confidence: 99%

“…Other reported phase gradient coil designs have included Helmholtz‐Maxwell, Birdcage‐Maxwell pairs, and spiral birdcage geometries. The target‐field method has also been used for the design of TRASE phase gradient coils, aiming at minimizing concomitant fields and maximizing the usable field‐of‐view (FOV)…”

Section: Introductionmentioning

confidence: 99%

“…Depending on the coil geometry and driving configurations, different approaches have been proposed. Active PIN diode controls have been commonly used in the TRASE literature, including spiral birdcage pair, Helmholtz‐Maxwell pair, and the combination of these two types . Stockmann applied a toroidal transformer to cancel the mutual inductance between Birdcage‐Maxwell coil pair, while Sun utilized the inherent orthogonal

B_{1}

field between saddle and twisted solenoid for 1D TRASE encoding.…”

Section: Introductionmentioning

confidence: 99%

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A geometrically decoupled, twisted solenoid single‐axis gradient coil set for TRASE

Sun

AlZubaidi

Purchase³

et al. 2019

Magnetic Resonance in Med

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A highly efficient twisted solenoid coil was proposed recently for TRASE imaging for transverse B 0 geometries. This novel coil can be rotated to generate a phase gradient in any transverse direction, therefore, combining two such coils would double k-space coverage for single-axis encoding, resulting in higher spatial resolution. However, the strong inductive coupling between a pair of coaxial twisted solenoids must be overcome. Methods: Here, we demonstrate that two concentric twisted solenoids, designed using previously described Biot-Savart calculations, can be geometrically decoupled by attaching to each a regular solenoid in series. The regular solenoid geometry resulting in minimization of mutual inductance was determined from simulations using the FastHenry2 tool. The effects on TRASE encoding performance due to the regular solenoids were assessed from simulations and experiments. Results: The maximum resulting B 1 magnitude and phase distortions were 3.7% and 4.6 • , while a good isolation S 12 = −17.5 dB between the coil pair was obtained. TRASE experiments confirmed the double k-space coverage, and achieved a rapid spin echo train with 128 k-space points collected within 80 ms, allowing short T 2 samples to be accurately imaged. Conclusions: This study demonstrates that a pair of twisted solenoid phase gradient RF coils can be geometrically decoupled. Advantages over active PIN diode decoupling include faster switching, lower hardware complexity, and scalability. K E Y W O R D S geometric decoupling, RF coil, TRASE MRI, twisted solenoid 1 | INTRODUCTION 1.1 | TRASE overview and encoding principle Transmit Array Spatial Encoding (TRASE) is an MRI encoding approach that enables k-space data to be acquired using phase gradients in the radio frequency (RF) transmit fields (B 1). 1 Unlike conventional MRI encoding methods which rely on the use of main field (B 0) gradients, the substitution of B 0 gradients by B 1 phase gradients using simple RF technologies allows compact MRI systems to be made, particularly suitable for low-field, low-cost scenarios. 2 Recent work suggest that clinical-level millimeter spatial resolution is practically achievable, under both in vivo 3 and phantom situations. 1,2,4-6 | 1485 SUN et al. The fundamental concept of TRASE is that the pulse sequence consists of an echo train of 180 • refocusing pulses that are transmitted in an alternating pattern by switching the phase gradient B 1 field for each RF pulse. For onedimensional TRASE encoding, two different B 1 fields A and B with different phase gradients k A and k B are needed. These two phase gradients are transmitted alternatively down the spin echo train to impart a progressively increasing spatial phase modulation, with each k-space point collected by averaging the center points of each acquired echo. For higher dimensional TRASE encoding, more such B 1 phase gradient fields are needed, so for instance, three B 1 fields are sufficient for 2D TRASE encoding. Other reported phase gradient coil designs have included Helmholtz-M...

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Tackling SNR at low-field: a review of hardware approaches for point-of-care systems

Webb

O’Reilly

2023

Magn Reson Mater Phy

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Objective To review the major hardware components of low-field point-of-care MRI systems which affect the overall sensitivity. Methods Designs for the following components are reviewed and analyzed: magnet, RF coils, transmit/receive switches, preamplifiers, data acquisition system, and methods for grounding and mitigating electromagnetic interference. Results High homogeneity magnets can be produced in a variety of different designs including C- and H-shaped as well as Halbach arrays. Using Litz wire for RF coil designs enables unloaded Q values of ~ 400 to be reached, with body loss representing about 35% of the total system resistance. There are a number of different schemes to tackle issues arising from the low coil bandwidth with respect to the imaging bandwidth. Finally, the effects of good RF shielding, proper electrical grounding, and effective electromagnetic interference reduction can lead to substantial increases in image signal-to-noise ratio. Discussion There are many different magnet and RF coil designs in the literature, and to enable meaningful comparisons and optimizations to be performed it would be very helpful to determine a standardized set of sensitivity measures, irrespective of design.

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Design of a high power PIN‐diode controlled switchable RF transmit array for TRASE RF imaging

Cited by 9 publications

References 11 publications

Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

A geometrically decoupled, twisted solenoid single‐axis gradient coil set for TRASE

Tackling SNR at low-field: a review of hardware approaches for point-of-care systems

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