An eight channel transmit system for Transmit SENSE at 3T

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

doi:10.1109/isbi.2011.5872520

Cited by 5 publications

(6 citation statements)

References 7 publications

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“…We have suggested methods for improving 3D tailored pulse design , but it is still challenging to tailor to the whole brain including regions with high field inhomogeneity (e.g., near frontal sinus). A potential solution is to use parallel transmission to reduce the pulse duration, and we plan to explore the feasibility of 3D STFR functional protocol using an 8‐channel parallel transmit head array .…”

Section: Discussionmentioning

confidence: 99%

Steady‐state functional MRI using spoiled small‐tip fast recovery imaging

Sun

Fessler

Noll

et al. 2014

Magnetic Resonance in Med

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Purpose To determine whether a recently-proposed steady-state magnetic resonance imaging (MRI) sequence, “small-tip fast recovery” (STFR), can be used for functional brain imaging. Compared to existing functional MRI (fMRI) based on T2*-contrast and long echo time (TE), STFR has the potential for high-resolution imaging with reduced B0 artifacts such as geometric distortions, blurring, or local signal dropout. Methods We used Monte Carlo Bloch simulations to calculate the voxel-averaged steady-state signal during rest and activation, for BOLD and STFR. STFR relies on a tailored “tip-up” radiofrequency (RF) pulse to align the spins with the longitudinal axis after each data readout segment, and here we performed proof-of-concept in vivo STFR fMRI experiments using a tip-up pulse tailored to a 2D region-of-interest (ROI) in motor cortex. Experiments were performed on multiple subjects to test reliability of the functional activation maps. Results Bloch simulations predict a detectable functional signal that depends mainly on intra-voxel dephasing, and only weakly on spin diffusion. STFR produces similar activation maps and signal change as BOLD in finger-tapping experiments, and shows reliability comparable to BOLD. Conclusion STFR can produce functional contrast (even with short TE), and is a potential alternative to long-TE (T2*) fMRI. The functional contrast arises primarily from the interaction between T2*-like dephasing and the tailored tip-up pulse, and not from spin diffusion.

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Section: Discussionmentioning

confidence: 99%

Steady‐state functional MRI using spoiled small‐tip fast recovery imaging

Sun

Fessler

Noll

et al. 2014

Magnetic Resonance in Med

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“…Alternatively, parallel RF transmission should allow for improved RF pulse accuracy for a given pulse duration. Parallel excitation has been an active research area in recent years, including by our group , and commercial support for such systems is emerging.…”

Section: Discussionmentioning

confidence: 99%

Strategies for improved 3D small‐tip fast recovery imaging

Sun

Fessler

Noll

et al. 2013

Magnetic Resonance in Med

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Purpose Small-tip fast recovery (STFR) imaging is a recently proposed steady-state sequence that has similar image contrast as balanced steady-state free precession (bSSFP) but has the potential to simultaneously remove banding artifacts and transient fluctuation. STFR relies on a “tip-up” radiofrequency (RF) pulse tailored to the accumulated phase during the free precession (data acquisition) interval, designed to bring spins back to the longitudinal axis, thereby preserving transverse magnetization as longitudinal magnetization for the next TR. We recently proposed an RF-spoiled STFR sequence suitable for thin slab imaging, however in many applications, e.g., functional MRI or isotropic-resolution structural imaging, 3D steady-state imaging is desirable. Unfortunately, 3D STFR imaging is challenging due to the need for 3D tailored RF pulses. Here we propose new strategies for improved 3D STFR imaging, based on (i) unspoiled imaging, and (ii) joint design of non-slice-selective tip-down/tip-up RF pulses. Theory and Methods We derive an analytic signal model for the proposed unspoiled STFR sequence, and propose two strategies for designing the 3D tailored tip-down/tip-up RF pulses. We validate the analytic results using phantom and in-vivo imaging experiments. Results Our analytic model and imaging experiments demonstrate that the proposed unspoiled STFR sequence is less sensitive to tip-up excitation error compared to the corresponding spoiled sequence, and may therefore be an attractive candidate for 3D imaging. The proposed “joint” RF pulse design method, in which we formulate the tip-down/tip-up RF pulse design task as a magnitude least squares problem, produces modest improvement over a simpler “separate” design approach. Using the proposed unspoiled sequence and joint RF pulse design, we demonstrate proof-of-principle 3D STFR brain images with bSSFP-like signal properties but with reduced banding. Conclusion Using the proposed unspoiled sequence and joint RF pulse design, STFR brain images in a 3D region of interest (ROI) with bSSFP-like signal properties but with reduced banding can be obtained.

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“…The modulated waveforms pass through a first gain stage prior to the ultra-low output impedance amplifiers [10]. The array coil consists of eight fully shielded rung elements behind transmit/receive switches.…”

Section: Parallel Transmit System Overviewmentioning

confidence: 99%

Eight-channel transmit/receive head array for use with ultra-low output impedance amplifiers

Moody

Hollingsworth

Nielsen

et al. 2013

2013 IEEE 10th International Symposium on Biomedical Imaging

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Parallel transmit technology for magnetic resonance imaging can mitigate the challenges with the transmit field (B 1 ) inhomogeneity and capture the increased signal-to-noise ratio benefit at high field strengths. Most of the available parallel transmit systems use conventional amplifier architectures with array coils that employ complex decoupling methods to isolate the individual elements. Current sources and ultra-low output impedance amplifiers offer the advantage of providing some additional decoupling to the array elements, allowing more flexibility in the array design. We present our work designing and building an eight-channel transmit/receive head array to work with ultralow output impedance amplifiers on a 3 Tesla GE clinical scanner.

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An eight channel transmit system for Transmit SENSE at 3T

Cited by 5 publications

References 7 publications

Steady‐state functional MRI using spoiled small‐tip fast recovery imaging

Steady‐state functional MRI using spoiled small‐tip fast recovery imaging

Strategies for improved 3D small‐tip fast recovery imaging

Eight-channel transmit/receive head array for use with ultra-low output impedance amplifiers

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