Double‐row dipole/loop combined array for human whole brain imaging at 7 T

Avdievich, NI; Nikulin, A. V.; Ruhm, Loreen; Magill, Arthur W.; Henning, A; Scheffler, Klaus

doi:10.1002/nbm.4773

Cited by 10 publications

(23 citation statements)

References 47 publications

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“…According to recent findings of the ultimate intrinsic SNR theory, maximum SNR deeper in the human body or near the brain center at 7 T and above can be obtained only by combining complementary conductive structures carrying different current patterns, for example, loops and dipole antennas 28,29 . Following these theoretical findings, we recently developed two novel 32‐element dipole/loop combined array designs, 20,30 and wherein our new findings can be potentially applied to improve parallel imaging. For both dipole/loop designs, the 3D parallel imaging can be further improved by using reconfigurable dipoles that can effectively increase the number of virtual rows of dipoles to 2 (first design) or 4 (second design).…”

Section: Discussionmentioning

confidence: 91%

Section: F I G U R Ementioning

confidence: 94%

“…Active detuning was implemented similarly as previously described 20 using the matching capacitor, PIN‐diode (MA4P7461–1072, MACOM), and inductance of the short piece (˜50 mm) of the coaxial cable (K_02252_D‐60, Huber+Suhner AG) as shown in Figure 3A. When the PIN diode was shorted, the short (the cable length less than quarter of the wave length) coaxial cable formed an inductor, which was adjusted by changing the length of the cable.…”

Section: Methodsmentioning

confidence: 99%

“…FIGURE S2.

{\mathrm{B}}_1^{+}

map of the 8‐element transmit loop array in the homogeneous phantom, acquired using a centric‐reordered 3D saturated single‐shot turboFlash (3DsatTFL) sequence 20 …”

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confidence: 99%

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Reconfigurable dipole receive array for dynamic parallel imaging at ultra‐high magnetic field

Nikulin

Glang

Avdievich

et al. 2023

Magnetic Resonance in Med

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Purpose To extend the concept of 3D dynamic parallel imaging, we developed a prototype of an electronically reconfigurable dipole array that provides sensitivity alteration along the dipole length. Methods We developed a radiofrequency array coil consisting of eight reconfigurable elevated‐end dipole antennas. The receive sensitivity profile of each dipole can be electronically shifted toward one or the other end by electrical shortening or lengthening the dipole arms using positive‐intrinsic‐negative‐diode lump‐element switching units. Based on the results of electromagnetic simulations, we built the prototype and tested it at 9.4 T on phantom and healthy volunteer. A modified 3D SENSE reconstruction was used, and geometry factor (g‐factor) calculations were performed to assess the new array coil. Results Electromagnetic simulations showed that the new array coil was capable of alteration of its receive sensitivity profile along the dipole length. Electromagnetic and g‐factor simulations showed closely agreeing predictions when compared to the measurements. The new dynamically reconfigurable dipole array provided significant improvement in geometry factor compared to static dipoles. We obtained up to 220% improvement for 3 × 2 (Ry × Rz) acceleration compared to the static configuration case in terms of maximum g‐factor and up to 54% in terms of mean g‐factor for the same acceleration. Conclusion We presented an 8‐element prototype of a novel electronically reconfigurable dipole receive array that permits rapid sensitivity modulations along the dipole axes. Applying dynamic sensitivity modulation during image acquisition emulates two virtual rows of receive elements along the z‐direction, and therefore improves parallel imaging performance for 3D acquisitions.

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Section: Discussionmentioning

confidence: 91%

Section: F I G U R Ementioning

confidence: 94%

Section: Methodsmentioning

confidence: 99%

“…FIGURE S2.

{\mathrm{B}}_1^{+}

map of the 8‐element transmit loop array in the homogeneous phantom, acquired using a centric‐reordered 3D saturated single‐shot turboFlash (3DsatTFL) sequence 20 …”

mentioning

confidence: 99%

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Reconfigurable dipole receive array for dynamic parallel imaging at ultra‐high magnetic field

Nikulin

Glang

Avdievich

et al. 2023

Magnetic Resonance in Med

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“…For each array design variation, we evaluated Tx and SAR efficiencies for the quadrature circularly polarized (CP) mode, which is produced by an introduction of 45 phase shift between neighboring elements in each row. In addition, we evaluated five RF shimmed modes produced by an addition of a phase shift between the rows 1,22 varied from 20 to 100 in 20 steps. The phase shift of 0 corresponds to the CP mode.…”

Section: Em Simulations: Optimization Of the Array Geometrymentioning

confidence: 99%

Double‐row 16‐element folded‐end dipole transceiver array for 3D RF shimming of the whole human brain at 9.4 T

et al. 2023

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Homogeneity and longitudinal coverage of transmit (Tx) human head RF coils at ultrahigh field (UHF, ≥7 T) can be improved by 3D RF shimming, which requires using multi‐row Tx arrays. Examples of 3D RF shimming using double‐row UHF loop transceiver (TxRx) and Tx arrays have been described previously. Dipole antennas provide unique simplicity and robustness while offering comparable Tx efficiency and signal‐to‐noise ratio to conventional loop designs. Single‐row Tx and TxRx human head UHF dipole arrays have been previously described by multiple groups. Recently, we developed a novel type of dipole antenna, a folded‐end dipole, and presented single‐row eight‐element array prototypes for human head imaging at 7 and 9.4 T. These studies have shown that the novel antenna design can improve the longitudinal coverage and minimize peak local specific absorption rate (SAR) as compared with common unfolded dipoles. In this work, we developed, constructed, and evaluated a 16‐element double‐row TxRx folded‐end dipole array for human head imaging at 9.4 T. To minimize cross‐talk between neighboring dipoles located in different rows, we used transformer decoupling, which decreased coupling to a level below −20 dB. The developed array design was demonstrated to be capable of 3D static RF shimming and can be potentially used for dynamic shimming using parallel transmission. For optimal phase shifts between the rows, the array provides 11% higher SAR efficiency and 18% higher homogeneity than a folded‐end dipole single‐row array of the same length. The design also offers a substantially simpler and more robust alternative to the common double‐row loop array with about 10% higher SAR efficiency and better longitudinal coverage.

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Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

Solomakha,

Bosch,

Glang

et al. 2023

Magnetic Resonance in Med

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PurposeThe aim of this work is to evaluate a new eight‐channel transceiver (TxRx) coaxial dipole array for imaging of the human head at 9.4T developed to improve specific absorption rate (SAR) performance, and provide for a more compact and robust alternative to the state‐of‐the art dipole arrays.MethodsFirst, the geometry of a single coaxial element was optimized to minimize peak SAR and sensitivity to the load variation. Next, a multi‐tissue voxel model was used to numerically simulate a TxRx array coil that consisted of eight coaxial dipoles with the optimal configuration. Finally, we compared the developed array to other human head dipole arrays. Results of numerical simulations were verified on a bench and in the scanner including in vivo measurements on a healthy volunteer.ResultsThe developed eight‐element coaxial dipole TxRx array coil showed up to 1.1times higher SAR‐efficiency than a similar in geometry folded‐end and fractionated dipole array while maintaining whole brain coverage and low sensitivity of the resonance frequency to variation in the head size.ConclusionAs a proof of concept, we developed and constructed a prototype of a 9.4T (400 MHz) human head array consisting of eight TxRx coaxial dipoles. The developed array improved SAR‐efficiency and provided for a more compact and robust alternative to the folded‐end dipole design. To the best of our knowledge, this is the first example of using coaxial dipoles for human head MRI at ultra‐high field.

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Double‐row dipole/loop combined array for human whole brain imaging at 7 T

Cited by 10 publications

References 47 publications

Reconfigurable dipole receive array for dynamic parallel imaging at ultra‐high magnetic field

Reconfigurable dipole receive array for dynamic parallel imaging at ultra‐high magnetic field

Double‐row 16‐element folded‐end dipole transceiver array for 3D RF shimming of the whole human brain at 9.4 T

Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

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