Vanessa Landes, Krishna Nayak

We present a hardware-free way to mitigate RF envelope error that has the potential to be extremely fast (<1 min), and to benefit simultaneous multislice (SMS) balanced steady-state free precession (bSSFP) imaging. This approach improves RF waveform fidelity 9-fold in a variety of multiband pulses, and correspondingly reduces bSSFP spurious side-lobe excitation 3-fold. This provides 4-fold reduction in SMS bSSFP side-lobe signal.

Ruoyun Ma, Mehmet Akcakaya, Steen Moeller, Edward Auerbach, Kamil Ugurbil, Pierre-François Van de Moortele

DW-EPI suffers from geometric distortion induced by eddy current from strong diffusion gradients. Magnetic field monitoring using 19F probes followed by algebraic reconstruction incorporating higher order field perturbation has been proposed to address such issue and was applied for single-band acquisition at 3T. In this study, this approach was implemented for high resolution multiband in vivo brain DW-EPI acquisition at 7T, taking into account of scanner imposed global phase modulation for eddy-current correction. Preliminary results showed successful correction of the geometric distortion across all diffusion gradients. Further investigation needs to be made to increase the SNR of DW images.

Niklas Wehkamp, Elmar Fischer, Philipp Rovedo, Jürgen Hennig, Maxim Zaitsev

A new manufacturing method for the creation of magnetic field probes is presented. The method allows realizing field probes that can be frequency adjusted during MR acquisition. This opens up new possibilities for the use of field probes during MR experiments. In the presented proof-of-concept case, the field probe’s position in a standard gradient echo experiment was shifted within the field of view by changing its Larmor frequency using an additional micro-coil.

Sophia Kronthaler, Jürgen Rahmer, Peter Börnert, Dimitrios Karampinos

Reconstruction of high-quality ultrashort echo-time UTE images requires precise knowledge of the dynamic gradient magnetic fields used to perform the spatial encoding during the ramp up of the gradients. System delays and eddy currents can perturb the gradient fields and significantly degrade the image quality. The present study proposes the measurement of the gradient transfer response function with standard scanner hardware to correct the UTE readout gradients and to improve UTE image quality.

Ryan Topfer, Nibardo Lopez Rios, Alexandru Foias, Nicolas Arango, Lawrence L. Wald, Jason P. Stockmann, Julien Cohen-Adad

Spinal cord imaging remains challenging in large part due to the temporal variations in B₀ caused by respiration. This study introduces a simple circuit design for a capacitive respiratory sensor and demonstrates the utility of this device in the context of real-time shimming the neck using an 8-channel "AC/DC" (integrated RF receive + multi-coil shim) array. Using this approach, motion artifacts in a multi-echo T2*-weighted acquisition are shown to be considerably reduced.

Andreas Lesch, Christoph Aigner, Stefan Spann, Matthias Schloegl, Rudolf Stollberger

In this work we investigate the feasibility of a double shot acquisition for 3D Bloch-Siegert B₁⁺ mapping. Therefore, we combine the previously proposed variational reconstruction algorithm for highly subsampled Bloch-Siegert data with an EPI readout. The acquired dataset was retrospectively under-sampled and the reconstruction results are compared to the fully sampled reference, a zero padded low resolution estimate and to results acquired with a much more robust GRE readout. We can show that the results are in good accordance to the fully sampled reference and the GRE acquisition for acceleration factors of up to 100 making double shot acquisition possible.

Guangqi Li, Shuo Chen, Hua Guo

Gradient impulse response function (GIRF) can be used to characterize gradient systems. GIRF measurements typically require multiple triangular waveforms of different durations to be played in three gradient axes. Using the traditional method, the entire measurement takes more than 10 hours. In this study, we propose an interleaved off-isocenter method to measure GIRFs. It can save nearly 50% of measurement time. The measured results are consistent with those measured using the time-consuming traditional method.

Yulin Chang, Kun Zhou, W. Scott Hoge, Uvo Hoelscher, Wei Liu, Jonathan Polimeni

Echo-planar imaging is subject to Nyquist ghosting due to its use of fast gradient switching. To correct for this artifact, several methods have been proposed that involve a pair of calibration imaging frames acquired with opposite readout polarities. We show that a small, relative shift in the phase-encoding direction often exists between these calibration frames that may lead to compromised image quality. A simple method is proposed to account for the shift and it is shown to be effective at correcting residual Nyquist ghost in the dual-polarity GRAPPA approach. This is demonstrated in in vivo and phantom data from 3T and 7T.

Uten Yarach, Matt Bernstein, John Huston III, Myung-Ho In, Daehun Kang, Yunhong Shu, Erin Gray, Nolan Meyer, Joshua Trzasko

Echo planar imaging (EPI) is widely used clinically for its speed, but is known to be sensitive to non-idealities like B0 field inhomogeneity, eddy currents, and gradient nonlinearity. Such non-idealities are not typically managed during image reconstruction, resulting in geometrically distorted images. Post-processing corrections (e.g., image-based interpolation) usually tend to degrade resolution.  In this work, a comprehensive model-based reconstruction framework that prospectively and simultaneously accounts for non-idealities in accelerated single-shot EPI acquisitions is proposed. Sparsity regularization is also incorporated to mitigate noise amplification.  The proposed algorithm is demonstrated on brain MRI data acquired on a compact 3T MRI system. 

Philipp Eirich, Tobias Wech, Manuel Stich, Julian Richter, Thorsten Bley, Herbert Köstler

The Gradient System Transfer Function (GSTF) was used to implement a fully automatic gradient pre-emphasis, enabling double-oblique MR imaging for arbitrary k-space trajectories. The developed method was tested using a standard 2D FLASH spiral sequence with several orientations in a structural phantom and an exemplary in vivo cardiac study.

Sagar Mandava, Mahesh Keerthivasan, Diego Martin, Maria Altbach, Ali Bilgin

Streaking artifacts are a common source of image quality degradation in radial MRI even with sufficient sampling. While coil removal is popularly used to mitigate streaking artifacts, this method is known to suffer from undesirable signal loss. Recently, a streak artifact reduction method has been proposed that offers a better balance between artifact reduction and signal retention. This approach endows the channel combination maps with the ability to suppress streaking artifacts and is implemented as a post-processing step. In this work, we present a computationally efficient refinement of this approach and extend it to multi-contrast imaging and parameter mapping applications.

Yuhang Shi, Hui Liu, Lingzhi Hu

For a whole-body scan, shimming are required to be carried out in multiple bed positions to provide homogeneous field for imaging different body parts. Thus, techniques to shorten the shimming time are required. This work presents a rapid B0 field prediction method for whole-body shimming based on a large field map database of different body parts. A range of applications could benefit from this technique.

Kun Zhou, Dehe Weng, Fang Dong, Wei Liu, Yulin V Chang

Fat suppression and motion artifacts are still challenging in clinical MRI for certain body regions. In this work a novel acquisition method combining Dixon’s method and BLADE (or PROPELLER, periodically rotated overlapping parallel lines with enhanced reconstruction) is proposed, to address fat suppression and motion artifacts simultaneously. We show that the proposed technique acquires data efficiently while avoiding the potential misalignment between echoes as well as the phase inconsistency introduced by different readout directions.

Mark Bydder, Vahid Ghodrati, Fadil Ali, Peng Hu

Motion is common in MR image acquisitions.  It causes artefacts in image quality that requires repeated scans, increasing the burden for patients and providers.  There have been advances on hardware and software fronts in the quest to avoid such issues.  The latter include data consistency methods which require no additional installation but can fail to detect high frequency outliers in k-space.  We propose a Deep CNN approach to detect motion-corrupted phase encode lines, coupled with a low-rank reconstruction.   This approach improves outlier detection in comparison to low-rank only methods and accelerates reconstruction time. 

Samy Abo Seada, Anthony Price, Joseph Hajnal, Shaihan Malik

Cardiac balanced SSFP using simultaneous multi-slice acquisition is limited by RF pulse duration and SAR. The interplay of these constraints means that the minimum pulse duration does not usually yield the minimum TR. We show that multiband RF pulses designed using VERSE to directly minimize TR can yield a reduced TR. The result is demonstrated in a multiband-2 sequence on a 3T clinical system where the TR is only 15% longer than for single-slice excitation and the time per slice is reduced by 44%.