CP #3: Parallel MRI for High Field Neuroimaging

Parallel MRI for High Field Neuroimaging

Significance:

fMRI has revolutionized our approach for studying cognitive processes in humans. However, the fMRI signal associated with many cognitive processes is contaminated by cardiac and respiratory physiological noise and susceptibility signal loss (Figure 1). The role of parallel transmission (pTx) for the correction of susceptibility effects has been clearly demonstrated in the literature [1-3]. Correction of physiological contamination, on the other hand, is often limited by the accuracy with which the respiratory and/or cardiac signal variations can be estimated from the images. Accurate estimation requires sampling at or above the underlying Nyquist frequency, which is sometimes hampered by the need to use a long TR in order to provide adequate whole brain coverage. Recently there has been a great deal of excitement over a new rapid imaging technique called “multiplexing” or Simultaneous Multi-Slice (SMS) imaging [4]. This method uses “multi-band” RF (MB-RF) pulses, complex modulated single-slice pulses,for the simultaneous excitation of N slices. The aliased slices are separated during reconstruction using coil sensitivity information from multiple receiver coils. Further improvement in SMS performance is obtained using Echo Planar Imaging (EPI) with z-gradient blips (“blipped-CAIPI”) [5]. SMS imaging holds great promise for numerous applications including fMRI because it allows for significant increases in acquisition speed. Greater speed in fMRI allows for high sampling of the BOLD response, which will facilitate the correction of physiological contamination from cardiac and respiratory processes. Although SMS imaging is gaining recognition, there has been little to no work on extending SMS excitations to multi-dimensional TRF pulses and pTx. pTx is naturally suited for SMS excitations because of the localized nature of the transmitters.

Aims:

The overall aim of the project is to develop synergistic extensions of SMS for pTx that capitalize on the inherently more efficient spatial localization that can be achieved using parallel transmission. These extensions will include: 1) Optimized SMS using one-dimensional pTx pulses with B0 and B1+ compensation and optimized SAR; 2) Development of multi-dimensional TRF methods for SMS with reduced B1+ and B0 inhomogeneity artifacts and; 3) Non-Cartesian spiral-based methods for accelerated SMS acquisitions.

Approach:

In Specific Aim 1 we will demonstrate that pTx can offer improved ability to optimize B1+ homogeneity, RF power, and SAR. We will also develop a novel 3D pTx coil designed for improved SMS pTx imaging. To the best of our knowledge, there have been no publications on utilizing multi-dimensional TRF for SMS pulses. In Specific Aim 2 we will implement novel designs for SMS TRF including “MB-Spokes” and “kT-PINS” pulses. We will also extend preliminary working designs for these pulses. Spiral encoding is highly efficient and typically allows for shorter acquisition times and further increases in speed or resolution. In Specific Aim 3 we will, therefore, implement an innovative 3D k-space theory and algorithm for SMS imaging that allows for flexibility in trajectory choice and image reconstruction. We will also develop a blipped-CAIPI spiral that is capable of whole brain acquisition in 2/3 the time of the comparable EPI sequence. We will also validate the SMS methods in using relevant measures such as BOLD activation and degree of susceptibility and/or physiological artifact removal. All the studies will be carried out on a clinical 3T scanner (Magnetom TIM Trio, Siemens AG, Erlangen) using a custom-built pTx array with four channels. As part of our collaboration with CAI2R, we will also develop specific implementations that are tailored for the FDA-approved, pTx-enabled Magnetom Skyra, a 3T system on which the use of pTx will have practical clinical applications.

Push-Pull Relationship with TR&D Project #2:

Parallel transmission is often hampered by excessively conservative constraints on the power allowed through each individual excitation channel. The SAR monitoring technology from TR&D #2 will used to evaluate the specific benefits of the proposed SMS designs and to determine the true SAR limits applicable to this technique.  This will benefit the CP (pull), and will motivate extensions of the BTRC methods to SMS applications (push).  The CP will also benefit (pull) from rapid B1+  calibrations derived from the “plug and play pTx” method [6] in TR&D #2, and will also serve as a key test bed (push) for the dramatically simplified pTx workflow associated with the method. 

Principal Investigator: 

Sponsors

Latest Updates

10/31/2017 - 11:54
10/31/2017 - 11:37

Philanthropic Support

We gratefully acknowledge generous support for radiology research at NYU Langone Medical Center from:
 
• The Big George Foundation
• Raymond and Beverly Sackler
• Bernard and Irene Schwartz

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