Shuyang Chai¹, Yue Zhu^2,3, Ming Lu^2,3, John C Gore^1,2,3, and Xinqiang Yan^2,3
1Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ²Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, United States, ³Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States

Wearable RF coils are receiving increasing attention since they can improve patient comfort and maximize SNR. For wearable coil arrays, however, the geometrical relationships between coils may change when they are bent and/or stretched. This in turn may decrease the performance of conventional decoupling methods such as overlapping and L/C network, especially for transmit/receive coil where the preamp decoupling is not feasible. In this work, we proposed a novel coaxial self-decoupled coil that has robustness decoupling performance versus coil distance and coil shapes. High isolations of <-15 dB can be achieved when the coils are gapped, overlapped, and/or stretched.

Yunsuo Duan^1,2, Feng Liu^1,2, Rachel Marsh^1,2, Matthew Riddle^1,2, Gaurav H. Patel^1,2, John Gray^1,2, Alayar Kangarlu^1,2, Lawrence S. Kegeles^1,2, and John T. Vaughan Jr.^3
1MRI Research Center, Department of Psychiatry, Columbia University, New York, NY, United States, ²New York State Psychiatric Institute, New York, NY, United States, ³Zuckerman Institute, Columbia University, New York, NY, United States

To improve the SNR in deep brain of human head images acquired using RF coil arrays with high coil element count, we proposed a 32-ch coil array with enlarged and over-overlapped coil loop elements laid out on a semi-flexible 3D-printed coil former. The experiment results showed that both the overall homogeneity of images and the SNR in deep brain are significantly improved.

Siyuan Liu¹, Jiahao Lin^1,2, Marvin Bergsneider³, Rock Hadley⁴, Giyarpuram N Prashant³, Sophie Peeters³, Kyunghyun Sung², and Robert N Candler^1,5
1Electrical and Computer Engineering, University of California Los Angeles, Los Angeles, CA, United States, ²Department of Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States, ³Department of Neurosurgery, University of California Los Angeles, Los Angeles, CA, United States, ⁴Department of Radiology, University of Utah, Salt Lake City, UT, United States, ⁵California NanoSystems Institute, Los Angeles, CA, United States

We simulate and experimentally verify SNR improvement from a miniature flexible coil with the ultimate goal to identify microadenomas in the pituitary gland that are currently undetectable. Through scans of a phantom at multiple angles, we show a maximum of 12 to 20 times, and a minimum of 2 to 4 times of SNR improvements compared to the commercial head coil. We also perform high-resolution PD-TSE scans to confirm the visual improvement of our flexible coil.

Xinqiang Yan^1,2, Yue Zhu^1,2, and Ming Lu^1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States

Transmit arrays improves the transmit field homogeneity while reducing the local hot spot. Current array designs for the head are not optimized for arterial spin labeling and simultaneous brain and cervical spinal cord applications caused by the short longitudinal coverage. To approach this problem, we designed and constructed a three-row Tx array covering the whole brain and cervical spinal cords (length: 28 cm). The overall performance of the coil is good with return losses < -20 dB while having adjacent coils’ coupling averaging -25.3 dB and diagonal coil’s coupling averaging -14.6 dB. The coil’s detune circuit also worked as intended.

Xinqiang Yan^1,2, Yue Zhu^1,2, and Ming Lu^1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States

Transmit (Tx) array with multiple independent coil elements is a well-recognized approach to addressing the B1 inhomogeneity and high local SAR issues at ultrahigh fields. However, Tx arrays typically have a lighter loading and more severe coil coupling. We designed a self-shielded and self-decoupled 2x8 Tx array with high inter-element isolation for 7T head imaging. Each Tx element is based on the corner-fed self-decoupled coil. Four coil elements were constructed to prove the concept is viable. The coil elements are highly decoupled (inter element response < -15 dB) while maintaining good tuning/matching characteristics (power reflection < -20 dB).

Sayim Gokyar¹, Henning U. Voss², Victor Taracila³, Fraser Robb³, Douglas J. Ballon¹, and Simone Winkler^1
1Radiology, Weill Cornell Medicine, New York, NY, United States, ²College of Human Ecology, Cornell University, Ithaca, NY, United States, ³General Electric Healthcare, Aurora, OH, United States

We propose a two-dimensional cylindrical high-pass ladder (2D c-HPL) coil concept and investigate the contribution of the longitudinal dimension to utilize a bore-mounted general-purpose clinical volume coil for ultra-high field MRI. Theory and in-silico results show that this architecture exhibits improved B1 field uniformity for specific anatomies and regions such as brain (a coefficient of variation of 12.3%), cerebellum (4.9%), heart (16.7%), prostate (2.8%), and whole chest (36.8%). This could prove particularly useful for whole-body clinical imaging and could open new pathways for clinical diagnostics in UHF MRI.

Komlan Payne¹ and Xiaoliang Zhang^1
1Jacobs School of Medicine & Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, NY, United States

The quest for ultimate intrinsic signal-to-noise ratio (uiSNR) and higher spatial resolution at ultra-high field for parallel magnetic resonance imaging is contingent to the integrity of the magnetic flux density map from individual channel. RF coils design using hair-pin matching technique is introduced to provide intrinsic decoupling performance within array of elements. This technique does not require any additional circuit between coil elements or large value of lumped inductance to provide simultaneous decoupling between adjacent and non-adjacent coils. The simulated results including decoupling performance, field distribution, and SNR are provided to validate the feasibility of the proposed design.

Komlan Payne¹, Salik Inayat Khan¹, and Xiaoliang Zhang^1
1Jacobs School of Medicine & Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, NY, United States

Parallel imaging using quadrature coil arrays can help to reach their ultimate intrinsic signal-to-noise ratio (uiSNR) and higher spatial resolution at ultra-high fields, because quadrature RF coils provide higher sensitivity and reduced excitation power over the commonly used linear polarized RF transceivers. However, due to the complicated structure and difficulties in achieving sufficient electromagnetic decoupling, it is technically challenging in designing multichannel quadrature RF coil arrays, particularly at ultrahigh fields. In this work, we design and investigate the magnetic wall decoupled common-mode differential mode quadrature RF arrays for ultrahigh field 7T MR imaging applications.

Tianyu Gao¹ and Xiaoliang Zhang^2
1Biomedical engineering, University at buffalo, buffalo, NY, United States, ²Biomedical Engineering, University at buffalo, buffalo, NY, United States

Microstrip resonator has been used as the radio frequency (RF) transceiver for magnetic resonance signal excitation and reception. Its application in parallel imaging could achieve faster imaging speed and better image quality. Mutual coupling is one of the major challenges in designing a multichannel RF transceiver array required in parallel imaging technology. The mutual coupling among the array elements causes resonant frequency shift, input impedance changes, and radiation pattern change, and thus degrade the imaging quality. 

Xin Li¹, Hannes M. Wiesner¹, Xiao-Hong Zhu¹, and Wei Chen^1
1Center for Magnetic Resonance Research (UMN), Minneapolis, MN, United States

We integrated a permittivity-tunable ultrahigh dielectric constant (uHDC) disk with copper film shielding (for tuning) and a pick-up coil (for matching) for performing ¹⁷O MRS imaging (MRSI) at 10.5T. We conducted a phantom ¹⁷O imaging study to compare the coil performance and signal-to-noise ratio between the newly designed uHDC resonator with a surface loop coil of the same diameter as the disk. The results indicate a better performance of the uHDC resonator at the room temperature(21 C^o), and a much better performance when the ceramic disk temperature was cooling to 16 C^o, owing to a large denoising effect.

Mohan Lal Jayatilake^1,2, Christopher T Sica^2,3, Rommy Elyan², Rang Pang¹, Dhevin Karunanayaka², Anupa Ekanayaka⁴, and Prasanna Karunanayaka^2,5
1Department of Neurosurgery, Pennsylvania State University, Hershey, PA, United States, ²Center for Nuclear Magnetic Resonance Research, Pennsylvania State University, Hershey, PA, United States, ³Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, State College, PA, United States, ⁴Grodno State Medical University, Grodno, Belarus, ⁵Department of Radiology, Pennsylvania State University, Hershey, PA, United States

Optimal image quality for Magnetic Resonance Imaging (MRI) at high fields requires a homogeneous RF (B1) field; however, the dielectric properties of the human brain results in B1 field inhomogeneities, and signal loss at the periphery of the head. Selecting the appropriate permittivity and quantity of material for the shim is essential. Here, we introduce a theoretical framework for determining the requisite dielectric constant of the passive shim material directly.  

Xin Li¹, Hannes M. Wiesner¹, Xiao-Hong Zhu¹, and Wei Chen^1
1Center for Magnetic Resonance Research (UMN), Minneapolis, MN, United States

In this study, we conducted electromagnetic simulation of a surface loop coil to quantify the B₁⁺ transmit efficiency of five nuclei ( ¹H, ³¹P, ²³Na, ²H and ¹⁷O) from 1.5T to 21 T field strength. The simulation is validated by FID measurements. Furthermore, we investigated the loading effect on the RF coil B₁⁺ transmit efficiency and its dependence on B₀. Our study shows the X-nuclei flip angle can be reached using the same or even less coil driving voltage as for proton, thus, significantly reducing the required RF power and SAR concern.

Venkata Veerendranadh Chebrolu¹, Sina Tafti², Aaron Anderson³, and Brad Sutton^3,4
1Siemens Medical Solutions USA, Inc., Rochester, MN, United States, ²Siemens Medical Solutions USA, Inc., Urbana, IL, United States, ³Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, United States, ⁴Bioengineering Department, University of Illinois at Urbana-Champaign, Urbana, IL, United States

Transmit and Receive inhomogeneity accentuate with increase in MR main magnetic field strength. Recently uniform combined reconstruction (UNICORN) was proposed to improve receive uniformity and applied for improving intensity uniformity of two­-, three-, and N-dimensional 7T MRI data. In this work, we aim to improve both receive and transmit uniformity of 7T brain MRI by applying UNICORN in combination with transmit inhomogeneity correction methods. MP2RAGE images acquired with TrueForm, patient-specific and volume-selective B1 shimming methods were processed using the UNICORN algorithm. Significant improvement in uniformity was achieved using UNICORN compared to unnormalized images.

Xin Li¹, Matt Waks¹, Hannes M. Wiesner¹, Soo Han Soon¹, Xiao-Hong Zhu¹, and Wei Chen^1
1Center for Magnetic Resonance Research (UMN), Minneapolis, MN, United States

A 4-channel ²H loop and 4-channel ¹H microstrip head array coil with improved MRS/MRI sensitivity and imaging coverage for a human-head-like lightbulb phantom at 7T is reported. Each of the 4 ²H coils is a 22cmx14cm loop, providing excellent penetration of ²H MRS signal. The ²H loops are decoupled by multiple techniques including inductive decoupling circuits and geometric overlapping, providing S12~-20dB between any pair of ²H loop coils. The majority of measured signal-to-noise ratio of the water signal originating from the natural abundance HDO content are above 100 for the voxel size of 1.7 cc.

Chathura Kumaragamage¹, Peter B Brown¹, Scott McIntyre¹, Terence W Nixon¹, Henk M De Feyter¹, and Robin A de Graaf^1
1Radiology and Biomedical Imaging, Yale University, New Haven, CT, United States

The effect of asynchrony between RF and gradient modulated (GM) waveforms on the performance of 3 ms gradient modulated GOIA-WURST RF pulses (BW = 15 kHz) was evaluated in simulation and experimentally. Results demonstrate that a 20+ μs asynchrony between RF and GM functions substantially degrades inversion performance when using large RF offsets to achieve translation. A projection-based method is presented that was used to calibrate RF and GM asynchrony on a 4T human MR system, where a  ~40 µs asynchrony was present. The projection method allows a quick calibration of RF and GM asynchrony on pre-clinical/clinical MR systems.