Arvin Arani¹, Christopher G. Schwarz¹, Matthew C. Murphy¹, Joshua D. Trzasko¹, Jeffrey L. Gunter¹, Matthew L. Senjem¹, Heather J. Wiste¹, Kiaran P. McGee¹, Matthew A. Bernstein¹, John Huston III¹, and Clifford R. Jack Jr.^1
1Mayo Clinic, Rochester, MN, United States

In magnetic resonance imaging (MRI) many factors can contribute to non-tissue specific image intensity inhomogeneity. However, the potential clinical impact or systematic biases of these effects have not been extensively investigated across multiple MRI vendors and models for neuroimaging applications. Specifically, left-right intensity comparisons are commonly used by radiologists to verify/identify pathology. If significant systematic left-right intensity asymmetries (LRIA) exist, it may lead to diagnostic uncertainty and result in unnecessary imaging follow-up and patient burden. This study shows that LRIA are common, system specific, systematic, can mimic disease, create diagnostic uncertainty, and can impact multiple sequences (T1-weighted and FLAIR).

Franz Patzig¹, Bertram Wilm¹, and Klaas Paul Pruessmann^1
1Institut for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

A caveat in using trajectories with long readout durations are artefacts due to B₀ inhomogeneity. Correcting these based on B₀-maps or reverse-phase-encoded EPI requires additional scan time and is unattractive for some applications. In this work, the capability of coil-arrays to extrapolate information in k-space is shown to also allow the extraction of temporal information such as the time-varying phase introduced by B₀-offsets. An optimization problem is formulated to retrieve an estimate of B₀ from measured data without making assumptions on the employed trajectory. B₀ estimation and self-correction of single-shot spiral and EPI in-vivo data (up to R=4) is demonstrated.

Constantin von Deuster^1,2, Stefan Sommer^1,2, Christoph Germann^3,4, Natalie Hinterholzer², Robin M. Heidemann⁵, Reto Sutter^3,4, and Daniel Nanz^2,4
1Siemens Healthcare, Zurich, Switzerland, ²Swiss Center for Musculoskeletal Imaging (SCMI), Balgrist Campus, Zurich, Switzerland, ³Radiology, Balgrist University Hospital, Zurich, Switzerland, ⁴University of Zurich, Zurich, Switzerland, ⁵Siemens Healthcare, Erlangen, Germany

The large water-fat frequency difference at 7 T renders imaging of the musculoskeletal (MSK) anatomy very challenging. In particular, through-slice chemical-shift artifacts may manifest in state-of-the-art 2D turbo-spin-echo (TSE) images as partial or locally complete fat-signal loss that radiologists are usually not trained to account for from lower field strengths. In this work, we demonstrate the range of possible through-slice artifacts in MSK images and show that matched RF-pulse bandwidths as high as 1500 Hz for the excitation and refocusing RF-pulses are necessary to consistently perform successful, non-fat suppressed MSK imaging at 7 T.

Julian Rauch^1,2, Frederik B. Laun³, Theresa Palm³, Jan Martin^3,4, Maxim Zaitsev^5,6, Mark E. Ladd^1,2,7, Peter Bachert^1,2, and Tristan A. Kuder^1
1Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Faculty of Physics and Astronomy, Heidelberg University, Heidelberg, Germany, ³Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany, ⁴Division of Physical Chemistry, Lund University, Lund, Sweden, ⁵Medical Physics, Department of Radiology, Faculty of Medicine, Medical Center University of Freiburg, Freiburg, Germany, ⁶High Field Magnetic Resonance Center, Center for Medical Physics and Biomedical Engineering Medical University of Vienna, Vienna, Austria, ⁷Faculty of Medicine, Heidelberg University, Heidelberg, Germany

Concomitant or Maxwell fields cause intravoxel dephasing which can lead to strong image artifacts. In this study, we present a new method for concomitant field correction in double diffusion encoding sequences with single pairs of bipolar gradients on each axis. Additionally implemented oscillating gradients remove the dephasing without changing the desired image. Phase and magnitude images are analyzed with respect to concomitant field induced artifacts and the proposed correction method. We show that the compensation eliminates these artifacts without further consequences for image quality. The method also may be included in other imaging sequences to achieve concomitant field compensation.

Daehyun Yoon¹, Philip Lee², Krishna Nayak³, and Brian Hargreaves^1
1Radiology, Stanford University, Stanford, CA, United States, ²Electrical Engineering, Stanford University, Stanford, United Kingdom, ³Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, United States

Multi-spectral imaging (MSI) including view-angle-tilting (VAT) is the dominant technique to correct for severe off-resonance artifacts near metallic implants. While VAT mitigates the signal pile-up and translation artifact in the area of severe off-resonance, it also causes global blurring and SNR loss in the on-resonance area away from metal. In this work, we introduce a novel spectrally encoded MSI approach, denoted SEMSI, that resolves pile-up and translation artifacts without VAT or z-phase encoding. Phantom imaging results show the promise of SEMSI to provide high-quality, artifact-free images in the presence of metallic implants without global blurring.

Zhiyang Fu^1,2, Maria I Altbach^1,3, and Ali Bilgin^1,2,3
1Department of Medical Imaging, University of Arizona, Tucson, AZ, United States, ²Department of Electrical and Computer Engineering, University of Arizona, Tucson, AZ, United States, ³Department of Biomedical Engineering, University of Arizona, Tucson, AZ, United States

In radial imaging, streaks due to gradient inhomogeneities can appear even when Nyquist criterion is fulfilled. Earlier techniques targeting this type of streaks remove coils contributing prominent streaks at the cost of signal loss.  A phased array beamforming based technique (B-STAR), that can achieve a good trade-off between streak reduction and signal preservation, was proposed as a post-processing method. We propose CACTUS, an alternative technique for streak cancellation, which can be used either as a preprocessing method or with iterative reconstructions. In vivo abdominal experiments show enhanced image reconstructions and improved quantitative parameter maps.

Simon Daniel Robinson^1,2,3, Beata Bachrata^3,4, Korbinian Eckstein³, Saskia Bollmann¹, Steffen Bollmann⁵, Siegfried Trattnig³, Christian Enzinger², and Markus Barth^5
1Centre for Advanced Imaging, University of Queensland, Brisbane, Australia, ²Department of Neurology, Medical University of Graz, Graz, Austria, ³Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria, ⁴Christian Doppler Laboratory for Clinical Molecular MR Imaging, Medical University of Vienna, Vienna, Austria, ⁵School of Electrical Engineering and Information Technology, University of Queensland, Brisbane, Australia

We propose an improved dynamic distortion correction method for fMRI. A fast (4s) multi-echo GE reference scan is used to calculate coil sensitivities and other non-ΔB₀-related contributions to coil phase, and one EPI volume in which the readout direction is reversed allows a phase gradient in the readout direction which is specific to EPI to be determined. Knowledge of these quantities allow fieldmaps to be calculated from the phase of each single-echo EPI volume. Reverse-Encoded First Image and Low resoLution reference scan (REFILL) fieldmaps accurately measure ΔB₀ as it changes due to motion and respiration.

Ziyi Pan¹, Meng Han², Yawei Kuang², Hao Sun², Kai Zhang³, Yuan Lian¹, Yishi Wang⁴, Wenbo Liu², Guangzhi Wang⁵, and Hua Guo^1
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, ²Sinovation Medical, Beijing, China, ³Beijing Tiantan Hospital, Capital Medical University, Beijing, China, ⁴Philips Healthcare, Beijing, China, ⁵Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China

MR-guided laser-interstitial thermal therapy (MRgLITT) is a minimally invasive therapeutic method that has created new options for surgically challenging lesions. Most MRgLITT procedures depend on proton-resonance-frequency (PRF) shift-based MR thermometry. However, it can be hampered by magnetic susceptibility changes generated during laser ablation. In this work, we demonstrate for the first time that laser-heating induced susceptibility changes can lead to significant temperature errors, with ex-vivo (pig muscle and brain tissues), in-vivo (Doberman) and clinical (epilepsy patient) experiments. A new algorithm based on multi-echo GRE instead of the conventional single-echo GRE is also introduce to correct the susceptibility-induced temperature errors.

Zahra Shams¹, Dennis W.J. Klomp¹, Vincent O. Boer², Jannie P. Wijnen¹, and Evita C. Wiegers^1
1Department of radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark

In this work, we proposed a new strategy to identify the source of potential artifacts in single voxel 1H MRS by taking into account the intrinsic B₀ field gradients in the human brain. We mapped the intrinsic gradient fields inside the human head to assess the level of signal crushing of each pathway in the entire field of view of the receiver coil. This will enable subject and location specific design of optimal crusher gradient scheme in SV MRS.

Toru Sasaki¹, Ryuichi Nanaumi¹, Mitsuo Nishimura¹, Kazuhiko Fukutani¹, Shuichi Kobayashi¹, Kazuya Okamoto², Hiroshi Kusahara², and Kazuto Nakabayashi^2
1Medical Products Technology Development Center, R&D Headquarters, Canon Inc., Tokyo, Japan, ²Advanced MRI Development PJ Team, Canon Medical Systems Corp., Kanagawa, Japan

We have developed a markerless tracking system enabling to estimate head pose through limited apertures of a head coil. The system, composed of a mirror and four MR compatible cameras, tracks the patient's facial features. The patient’s face image through the head coil’s apertures is monitored during scanning. To demonstrate its feasibility for tracking, a volunteer was moving his head arbitrarily inside a scanner. Despite the limited apertures of the head coil, the facial features were successfully tracked.