Tuning ultra-low output impedance amplifiers for optimal power and decoupling in parallel transmit MRI

Hollingsworth, Neal A.; Moody, Katherine Lynn; Nielsen, Jon‐Fredrik; Noll, Douglas C.; McDougall, Mary P.; Wright, Steven M.

doi:10.1109/isbi.2013.6556632

Cited by 3 publications

(3 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ideally, a capacitor should be placed between any two coils for perfect decoupling of the arrays. This and more sophisticated types of decoupling strategies are being explored , but in this work we used the more common approach consisting of only placing decoupling capacitors between nearest neighbors. Thus, the designs 1r/4cpr, 1r/8cpr, 1r/16cpr, and 2r/4cpr were studied in both their capacitively and ideally decoupled configurations—and the designs 1r/24cpr, 2r/8cpr, 3r/8cpr, and 4r/8cpr only were studied as ideally decoupled configurations.…”

Section: Resultsmentioning

confidence: 99%

Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics

et al. 2014

View full text Add to dashboard Cite

Purpose We compare the performance of 8 parallel transmit (pTx) body arrays with up to 32 channels and a standard birdcage design. Excitation uniformity, local SAR, global SAR and power metrics are analyzed in the torso at 3 T for RF-shimming and 2-spoke excitations. Methods We used a fast co-simulation strategy for field calculation in the presence of coupling between transmit channels. We designed spoke pulses using magnitude least squares (MLS) optimization with explicit constraint of SAR and power and compared the performance of the different pTx coils using the L-curve method. Results PTx arrays outperformed the conventional birdcage coil in all metrics except peak and average power efficiency. The presence of coupling exacerbated this power efficiency problem. At constant excitation fidelity, the pTx array with 24 channels arranged in 3 z-rows could decrease local SAR more than 4-fold (2-fold) for RF-shimming (2-spoke) compared to the birdcage coil for pulses of equal duration. Multi-row pTx coils had a marked performance advantage compared to single row designs, especially for coronal imaging. Conclusion PTx coils can simultaneously improve the excitation uniformity and reduce SAR compared to a birdcage coil when SAR metrics are explicitly constrained in the pulse design.

show abstract

Section: Resultsmentioning

confidence: 99%

Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics

et al. 2014

View full text Add to dashboard Cite

show abstract

“…The proposed method was also applied to human knee imaging. All of the experiments were performed on two GE 3T scanners (GE Healthcare, Milwaukee, WI), using GE single channel transmit/receive head coils or an eight‐channel custom parallel transmit/receive system . Table 1 summarizes all the experiments discussed in this paper.…”

Section: Methodsmentioning

confidence: 99%

Four dimensional spectral‐spatial fat saturation pulse design

Zhang

Nielsen

Noll

2013

Magnetic Resonance in Med

View full text Add to dashboard Cite

Purpose The conventional spectrally selective fat saturation pulse may perform poorly with inhomogeneous B0 and/or B1 fields. We propose a 4D spectral-spatial fat saturation pulse that is more robust to B0/B1 inhomogeneity and also shorter than the conventional fat saturation pulse. Theory The proposed pulse is tailored for local B0 inhomogeneity, which avoids the need of a sharp transition band in the spectral domain, so it improves both performance and pulse length. Furthermore, it can also compensate for B1 inhomogeneity. The pulse is designed sequentially by small-tip-angle approximation design and an automatic rescaling procedure. Methods The proposed method is compared to the conventional fat saturation in phantom experiments and in-vivo knee imaging at 3T for both single-channel and parallel excitation versions. Results Compared to the conventional method, the proposed method produces superior fat suppression in the presence of B0 and B1 inhomogeneity, and reduces pulse length by up to half of the standard length. Conclusion The proposed 4D spectral-spatial fat saturation suppresses fat more robustly with shorter pulse length than the conventional fat saturation in the presence of B0 and B1 inhomogeneity.

show abstract

“…We performed phantom experiments to demonstrate the proposed regularized BS B 1 map estimation on a 3T GE scanner (GE Healthcare, Milwaukee, WI, USA) equipped with an 8-channel custom parallel transmit/receive system [20] [21]. We used a spherical phantom filled with distilled water.…”

Section: Regularized Bs B1 Estimationmentioning

confidence: 99%

Regularized Estimation of Magnitude and Phase of Multi-Coil $B_1$ Field Via Bloch–Siegert $B_1$ Mapping and Coil Combination Optimizations

Zhang

Fessler

Wright

et al. 2014

IEEE Trans. Med. Imaging

View full text Add to dashboard Cite

Parallel excitation requires fast and accurate B1 map estimation. Bloch-Siegert (BS) B1 mapping is very fast and accurate over a large dynamic range. When applied to multi-coil systems, however, this phase-based method may produce low SNR estimates in low magnitude regions due to localized excitation patterns of parallel excitation systems. Also, the imaging time increases with the number of coils. In this work, we first propose to modify the standard BS B1 mapping sequence so that it avoids the scans required by previous B1 phase estimation methods. A regularized method is then proposed to jointly estimate the magnitude and phase of multi-coil B1 maps from BS B1 mapping data, improving estimation quality by using the prior knowledge of the smoothness of B1 magnitude and phase. Lastly, we use Cramer-Rao Lower Bound analysis to optimize the coil combinations, to improve the quality of the raw data for B1 estimation. The proposed methods are demonstrated by simulations and phantom experiments.

show abstract

Tuning ultra-low output impedance amplifiers for optimal power and decoupling in parallel transmit MRI

Cited by 3 publications

References 9 publications

Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics

Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics

Four dimensional spectral‐spatial fat saturation pulse design

Regularized Estimation of Magnitude and Phase of Multi-Coil $B_1$ Field Via Bloch–Siegert $B_1$ Mapping and Coil Combination Optimizations

Contact Info

Product

Resources

About