MRM Q&A posts
BY BLAKE DEWEY
In the early days of 2017, we sat down (virtually, of course) to have a conversation with Moritz Zaiss, Johannes Windschuh and Alexander Radbruch. Our topic was their recent MRM paper, “Downfield-NOE-Suppressed Amide-CEST-MRI at 7 Tesla Provides a Unique Contrast in Human Glioblastoma”. Chemical Exchange Saturation Transfer (CEST) imaging is an indirect imaging technique for the protons of certain metabolites, where saturation is applied off-resonance (with respect to water). Saturated protons are then allowed to exchange with water protons and then imaged using conventional imaging methods. However, frequency selection is not always enough to specifically target a functional group, such as amide groups, which are common in CEST imaging methods, producing a “mixed” contrast. Moritz, Johannes and Alexander, together with others in their group, have been slowly removing confounding effects in an attempt to isolate the measurement of amide proton transfer. In this paper, they continue their efforts by removing the downfield Nuclear Overhauser Effect (NOE), resulting in clinically relevant findings and correlation with gadolinium uptake in patients with glioblastoma.
BY MARK CHIEW
Two days after American Thanksgiving, we had the opportunity to speak with Lia Hocke, Yunjie Tong and Blaise Frederick about their recent MRM paper “Comparison of peripheral near-infrared spectroscopy low-frequency oscillations to other denoising methods in resting state functional MRI with ultrahigh temporal resolution”. Working out of the McLean Hospital, part of Harvard Medical School, they shared their perspective on the mutual information contained in peripheral NIRS (near infrared spectroscopy) and fMRI signals. They also used the word “photoplethysmograph” correctly in a sentence, and left us with a delightful shout-out to statistical rigor.
BY XIN MIAO
Dongwook Lee is currently a PhD student at the Korea Advanced Institute of Science and Technology (KAIST). He works on advanced image reconstruction techniques for dynamic MRI. His paper, selected as the Editor’s Pick for December, is entitled “Acceleration of MR parameter mapping using annihilating filter-based low rank Hankel matrix (ALOHA)”. ALOHA is a novel image reconstruction algorithm with the goal of clear, artifact free images acquired from very fast imaging schemes. For this paper, ALOHA was applied to accelerated MR parameter mapping, but could also be used for dynamic and parallel MRI, and even non-MR applications. We recently invited Dongwook and his supervisor, Dr. Jong Chul Ye, to talk about this paper.
α-trideuteromethyl[15N]glutamine: A long-lived hyperpolarized perfusion marker, by Markus Durst, Enrico Chiavazza, Axel Haase, Silvio Aime, Markus Schwaiger and Rolf F. Schultz.
December Editor’s Picks
Comparison of peripheral near-infrared spectroscopy low-frequency oscillations to other denoising methods in resting state functional MRI with ultrahigh temporal resolution, by Lia M. Hocke, Yunjie Tong, Kimberly P. Lindsey and Blaise de B. Frederick. Link to audio slides.
Acceleration of MR parameter mapping using annihilating filter-based low rank hankel matrix (ALOHA), by Dongwook Lee, Kyong Hwan Jin, Eung Yeop Kim, Sung-Hong Park and Jong Chul Ye. Link to audio slides.
BY THIJS DHOLLANDER
Recently, we had a chat with Elias Kellner, Valerij Kiselev and Marco Reisert from the University Medical Center Freiburg about their MRM paper entitled “Gibbs-Ringing Artifact Removal Based on Local Subvoxel-Shifts”. A challenge in time zone management, the interview was an early morning event for the MRM highlights editor (Nikola, in Montreal) and a late evening for the interviewer (Thijs, in Melbourne); however, that didn’t stop us discussing not only the paper, but also the art of paper writing and valuable lessons for the developers of novel acquisition strategies.
BY JESSICA MCKAY
This month’s Editor’s Pick features a project that makes kurtosis imaging more accessible to clinicians and researchers, alike, from a group in Denmark that includes our interviewees: Brian Hansen and Sune Jespersen. Diffusion kurtosis imaging (DKI) increases sensitivity to microstructural changes by extending the diffusion signal expression to account for non-Gaussian effects, but it typically requires time-consuming acquisitions with high diffusion weighting. Brian and Sune’s group had previously described a fast protocol, referred to as the 1-3-9 scheme, that includes three diffusion directions at a low b-value to determine the mean diffusivity and 9 specific diffusion directions at a higher b-value to calculate mean kurtosis [Hansen et al. MRM 69, 2013]. In this work, they extend the protocol to make it more robust to experimental imperfections by acquiring all 9 directions at the lower b-value, which they call 1-9-9. They further characterize the optimum b-values and propose a method to correct for imperfect diffusion directions. Keep reading to find out how their acquisition scheme expands the clinical value and feasibility of kurtosis imaging and you may even be inspired to add this ~1-minute scan onto your own protocol.
BY YOGESH MARIAPPAN
As the field of MRI is slowly but surely moving from qualitative to quantitative, and from imaging structures to imaging other properties, the choice of this month’s Highlights article is apt: the research group led by Ingolf Sack has been at the forefront of both of these aspects with their work on MR Elastography (MRE). This is a quantitative imaging technique capable of measuring the mechanical properties of tissues of interest and is available from all the major vendors. The current clinical application is focused on liver where the stiffness (measured in kilopascals) is used for fibrosis assessment. In this article they have provided recent results from their “In vivo wideband multi-frequency work” on liver and brain.
BY ADAM ELKHALED
In this edition of Highlights Q&A, we were treated to a virtual interview with Dr. Melissa Terpstra and Dr. Gülin Öz, whose work at the University of Minnesota Center for Magnetic Resonance Research (CMRR) has provided unique insight into the reproducibility of spectroscopic data. Our conversation revolved around their investigative efforts to understand how field strength influences consistent neurochemical quantification. By comparing short-echo semi-LASER data from 3T and 7T acquisitions, they managed to arrive at some interesting conclusions that bear direct relevance to other studies, and also underscore the necessity of quality assurance for purposes of clinical translation.
BY MATHIEU BOUDREAU
The September 2016 Editor’s Pick is from Manuel Murbach and Niels Kuster, researchers at the Foundation for Research on Information Technologies in Society (IT’IS) in Zurich. Their paper presents a simulation-based approach to evaluate the safety of the radiofrequency field (RF) shimming in magnetic resonance imaging (MRI). Current safety standards typically call for the whole-body averaged specific absorption rate (wbSAR) – a measure of the total RF power absorbed by the human body – to be limited to 4 W/kg, and assume that the thermoregulation capacity of the scanned patient is normal. However, new generations of MRI systems support RF shimming operating modes that may induce local SAR values that might be hazardous for patients with impaired or dysfunctional thermoregulation, increasing the risk of tissue damage after long scanning sessions. Manuel and Niels’s simulation study used the Virtual Population (ViP) human models to assess different RF shimming modes in several anatomical regions, and they’ve established safety recommendations for scanning patients with impaired thermoregulation. We recently spoke with Manuel and Niels about their project.
BY AKSHAY CHAUDHARI
Today we virtually sat down with David Reiter and Richard Spencer from the National Institute on Aging at the National Institutes of Health to talk about their recent publication entitled, ‘Anomalous T2 Relaxation in Normal and Degraded Cartilage’. This paper showed that the stretched exponential decay model reflects the microstructural complexity of cartilage matrix better than the conventional monoexponential decay model. Our conversation with David and Richard took us down a winding path filled with mathematics, modeling, MRI, and clinical translation, all towards, as Richard puts it, making cartilage great again.