Applications of RF Pulse Designs: Inner Volume Imaging, SMS, B1 Shimming & pTx

Outcomes/Objectives: Following the educational talk on radio frequency (RF) pulse design theory, this talk will provide insight on a few interesting RF pulse applications: -Inner volume imaging: for higher resolution and/or accelerated imaging -Simultaneous multislice (SMS) imaging: for accelerated imaging -B1 Shimming: for transmit field homogenization -Parallel transmit: for homogenization of , added degrees of freedom to pulse design, safer imaging at high fields, and much more

Minimum Out-of-Slice Error SMS RF Pulse Design with Direct Peak, Power, and In-Slice Error Constraints

No abstract available

Design of spectralâ spatial phase prewinding pulses and their use in smallâ tip fast recovery steadyâ state imaging

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141089/1/mrm26794_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141089/2/mrm26794.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141089/3/mrm26794-sup-0001-suppinfo.pd

A Simple Method for Constrained Optimal Control RF Pulse Design

Optimal control (OC) methods for RF pulse design are useful in cases where the small-tip angle (STA) approximation is violated. Furthermore, designs with physically meaningful constraints (e.g., RF peak amplitude and integrated power) eliminate the need for parameter tuning to create realizable pulses. In this abstract we introduce a constrained fast OC method that easily generalizes to a variety of RF pulse designs. We demonstrate with examples of SMS and spectral prewinding pulses in simulation and in vivo. The constrained fast OC method guarantees that RF pulses will meet physical constraints while outperforming their non-OC counterparts

Ultra-high field MRI: parallel-transmit arrays and RF pulse design

This paper reviews the field of multiple or parallel radiofrequency (RF) transmission for magnetic resonance imaging (MRI). Currently the use of ultra-high field (UHF) MRI at 7 tesla and above is gaining popularity, yet faces challenges with non-uniformity of the RF field and higher RF power deposition. Since its introduction in the early 2000s, parallel transmission (pTx) has been recognized as a powerful tool for accelerating spatially selective RF pulses and combating the challenges associated with RF inhomogeneity at UHF. We provide a survey of the types of dedicated RF coils used commonly for pTx and the important modeling of the coil behavior by electromagnetic (EM) field simulations. We also discuss the additional safety considerations involved with pTx such as the specific absorption rate (SAR) and how to manage them. We then describe the application of pTx with RF pulse design, including a practical guide to popular methods. Finally, we conclude with a description of the current and future prospects for pTx, particularly its potential for routine clinical use

Cardiac Vagal Tone Impairment is Associated with Reduced Cerebral Blood Flow in Collegiate Athletes Following Concussion

Reduced cerebral blood flow (CBF) is linked to functional disturbances following concussion. Since cardiac vagal tone (an index of cardiac health) is associated with disturbances in the autonomic nervous system, deficits in CBF are likely associated with cardiac vagal tone impairment post-concussion. PURPOSE: The current study examined cardiac vagal tone and CBF on days 3, 21 and 90 following concussion in comparison to non-injured control athletes. The association between these two variables was also evaluated. METHODS: Concussed male and female collegiate athletes were evaluated day-3 (N=29), day-21 (N=25) and day-90 (N=17) post concussion and matched controls were enrolled (N=29). A 3-lead electrocardiogram was used to assess cardiac vagal tone in the high frequency domain (HF; 0.15-0.4 Hz). Beat-to-beat mean arterial pressure (MAP) was obtained via finger photoplethysmography and transcranial Doppler ultrasonography (TCD) was used to assess middle cerebral blood flow velocity (MCAV). To measure vascular tone, cerebrovascular conductance index (CVCi) was estimated by dividing MCAV with MAP. Symptom severity and cognition were assessed using the Sports Concussion Assessment Tool-3rd Edition (SCAT-3) and executive function was assessed with the Trails test A & B. RESULTS: On day-3, concussed athletes had lower cognition (SAC 28±1vs.26±2,P=0.0005; Trails B 48±8vs.58±15sec,P=0.006) and HF power (52±12vs.36±14,P=0.006) compared to controls. On days 21 and 90, values were comparable to the controls. However, concussed participants were also categorized based on day-3 MCAV (divided at the median), into low and high MCAV groups. On day-3, the group with lower MCAV exhibited lower HF power (29±13vs.42±11.P=0.006) and lower CVCi (0.60±0.13vs.0.88±0.13,PCONCLUSION:Cardiac vagal tone was impaired 3 days following concussion compared to controls. Lower CBF was also associated with higher cerebrovascular tone. Additionally, lower CBF was linked to blunted cardiac vagal tone and functional outcome on day-21. On day-90, CBF recovered with normalization of functional outcome. Future studies with large sample are recommended to validate these findings

First In Vivo Images from an InHouse Parallel Transmit (pTx) Coil for MRI at 7 Tesla

No abstract available

The Student Movement Volume 105 Issue 2: Clubs Fare Well: Clubs Preserve Community During COVID

NEWS Clubs, Clubs, Clubs Galore, Taylor Uphus The Andreasen Center for Wellness Reopening, Amanda Cho Danielle Pilgrim Delivers Inspiring Message, Terika Williams PULSE Planning University Club Events Amidst a Pandemic, Masy Domecillo Research at the Science Complex During COVID-19, Jessica Rim Socializing During a Pandemic: Freshmen Perspectives, Interviewed by Wambui Karanja HUMANS BSCF Club Spotlight, Interviewed by TJ Hunter Distance Learning Student Interview, Sydney Saint-Jean Meet Lamson Hall\u27s Newest Dean, Interviewed by Pearl Parker Spiritual Leadership During COVID-19, Interviewed by Terika Williams ARTS & ENTERTAINMENT More Apples to Byte, Hannah Cruse Playing Out the Pandemic: Our Orchestras Dealing with COVID, Megan Napod Signal Boost: The Domino Effect, Pearl Parker Virtual Game Night: A Virtual Reality, Joshua Deonarine IDEAS How Climate Change is Fueling the West Coast Fires, Lyle Goulbourne Ideas That Heal Us: So You Think You\u27re Self-Aware, Evin N. Musgrove THE LAST WORD What am I Applying for & Who am I?, Daniel Selfhttps://digitalcommons.andrews.edu/sm-105/1002/thumbnail.jp

A nested eight-channel transmit array with open-face concept for human brain imaging at 7 tesla

Purpose: Parallel transmit technology for MRI at 7 tesla will significantly benefit from high performance transmit arrays that offer high transmit efficiency and low mutual coupling between the individual array elements. A novel dual-mode transmit array with nested array elements has been developed to support imaging the human brain in both the single-channel (sTx) and parallel-transmit (pTx) excitation modes of a 7 tesla MRI scanner. In this work, the design, implementation, validation, specific absorption rate (SAR) management, and performance of the head coil is presented. Methods: The transmit array consisted of a nested arrangement to improve decoupling between the second-neighboring elements. Two large cut-outs were introduced in the RF shield for an open-face design to reduce claustrophobia and to allow patient monitoring. A hardware interface allows the coil to be used in both the sTx and pTx modes. SAR monitoring is done with virtual observation points (VOP) derived from human body models. The transmit efficiency and coverage is compared with the commercial single-channel and parallel-transmit head coils. Results: Decoupling inductors between the second-neighboring coil elements reduced the coupling to less than −20 dB. Local SAR estimates from the electromagnetic (EM) simulations were always less than the EM-based VOPs, which in turn were always less than scanner predictions and measurements for static and dynamic pTx waveforms. In sTx mode, we demonstrate improved coverage of the brain compared to the commercial sTx coil. The transmit efficiency is within 10% of the commercial pTx coil despite the two large cut-outs in the RF shield. In pTx mode, improved signal homogeneity was shown when the Universal Pulse was used for acquisition in vivo. Conclusion: A novel head coil which includes a nested eight-channel transmit array has been presented. The large cut-outs improve patient monitoring and reduce claustrophobia. For pTx mode, the EM simulation and VOP-based SAR management provided greater flexibility to apply pTx methods without the limitations of SAR constraints. For scanning in vivo, the coil was shown to provide an improved coverage in sTx mode compared to a standard commercial head coil

The effects of RF coils and SAR supervision strategies for clinically applicable nonselective parallel-transmit pulses at 7 T

Purpose: To investigate the effects of using different parallel-transmit (pTx) head coils and specific absorption rate (SAR) supervision strategies on pTx pulse design for ultrahigh-field MRI using a 3D-MPRAGE sequence. Methods: The PTx universal pulses (UPs) and fast online-customized (FOCUS) pulses were designed with pre-acquired data sets (B0, B1+ maps, specific absorption rate [SAR] supervision data) from two different 8 transmit/32 receive head coils on two 7T whole-body MR systems. For one coil, the SAR supervision model consisted of per-channel RF power limits. In the other coil, SAR estimations were done with both per-channel RF power limits as well as virtual observation points (VOPs) derived from electromagnetic field (EMF) simulations using three virtual human body models at three different positions. All pulses were made for nonselective excitation and inversion and evaluated on 132 B0, B1+, and SAR supervision datasets obtained with one coil and 12 from the other. At both sites, 3 subjects were examined using MPRAGE sequences that used UP/FOCUS pulses generated for both coils. Results: For some subjects, the UPs underperformed when simulated on a different coil from which they were derived, whereas FOCUS pulses still showed acceptable performance in that case. FOCUS inversion pulses outperformed adiabatic pulses when scaled to the same local SAR level. For the self-built coil, the use of VOPs showed reliable overestimation compared with the ground-truth EMF simulations, predicting about 52% lower local SAR for inversion pulses compared with per-channel power limits. Conclusion: FOCUS inversion pulses offer a low-SAR alternative to adiabatic pulses and benefit from using EMF-based VOPs for SAR estimation