In the news again

GE Global Research is soon to change its name (yet unknown) and structure following the separation of the company into three independent businesses. The official announcement was made in mid September, and was covered in the media, (times union article), as well as in the public blog posted here. The new structure can be summarized by the key words: three co-located research centers, and will preserve much of the existing functions, people, and funding sources (mostly government). It remains to be seen how this change will affect the contents and scope of the Center's research in the coming years in the field of MRI.

Awesome August

August 2022 was highly productive and filled with good news in the world of CIEL friends. The news stories are summarized below to wrap up this remarkable month.

(1) Prof. JY Park's DIANA paper was finally accepted by the journal Science. The acceptance letter was issued just days after submission of the 2nd revision, without additional peer review that was widely anticipated. This pleasant surprise indicates that the editor was probably personally supportive and in favor of the paper, and trusted the authors based on progress made in the first round of revision. The long and tireless efforts by Prof. Park and his Vietnamese PhD student Phan Tan Toi, the first author, that made this a reality cannot be over-praised. They have overcome an enormous technical as well as political hurdles in producing data for this work, the latter coming from a jealous senior academic who had actively hindered progress and bad-mouthed the team. Now it is only matter of time that the exciting new discovery, that time-shuffled MRI can track neuronal activities in vivo, will make a big splash in the broad MRI and biology communities.

(2) Dr. Seulki Yoo, the first CIEL graduate student at SKKU, was granted a Korean government's new PhD research funding for the next 2 years. This was done even before she officially graduated, which technically happened on 8/25. This exciting early accomplishment will certainly go a long way to jump start her academic career, and makes her friends and mentors feel proud of her.

(3) Three CIEL students graduated from the graduate school of SKKU. Apart from Dr. Yoo mentioned above, Mr. Hyeong-Seop Kim and Mr. Byung-Pan Song got their Master's degree this month. Both of them have published multiple first-authored and co-authored papers during their time as graduate students in SKKU. They have positively impacted people around them through their friendly manners, positive attitudes, and their skills in hands-on electrical work in the lab.

Latest citation to Yoo et al., the head-tilting paper

A couple of authors from the French Neurospin team -- known for their 20-year efforts on 11.7T brain MRI -- recently published in MAGMA: official journal of ESMRMB, a full-length article on physical limits of brain B0 shimming. The title is "Physical limits to human brain B0 shimming with spherical harmonics, engineering implications thereof" and the full text is freely available here. An interesting, eye-catching sentence is "We establish a ~13Hz inhomogeneity hard shim limit at 7T for whole brain SH (spherical harmonic) shimming, ... only be attained at shimming degree higher than 90."

Since the B0 inhomogeneity is generated largely by the surface current in the brain itself, it is well-known that external shim current cannot completely cancel such fields. These authors tested this theoretical limit based on experimental B0 map data from 100 subjects. 

In terms of citation, the paper prominently cited the SKKU CIEL group's 2020 paper on head-tilted imaging by Yoo et al., dedicating a full sentence which mentioned the latter as an example of non-conventional way of pre-frontal cortex shimming.

MAGMA had another article on brain B0 shimming in the same batch of (total 19) articles called topical collection: Basic Science - Engineering. In this other paper, the authors (half of whom were apparently from the Boston team promoting combined shim + RF array) basically said that a combined local shim + RF phased array is too complicated, and a simpler 8 channel shim array can already do very well in 7T brain shimming. B0 shimming lives on! 

Latest publication

 I will occasionally use this page to explain and reflect on public presentation of my own academic works. Here is one about gradient coil efficiency, published last month in MRM (here).

One would think that there is nothing much left to publish on how to make static magnetic field coils, such as those for gradient or higher-order harmonic fields that are much used in MRI. This publication addresses something closely related -- how to characterize and compare different gradient coils -- and does show that there is still something to be learned about magnetostatics of MRI field coils.

One interesting finding is that the efficiency of a gradient coil, when normalized to account for different number of turns (that is, discounting efficiency gains obtained just by increasing number of turns for a given design), very well follows the power law: [efficiency] ∝ [diameter]^-2.5.

The following figure demonstrates this. This is from an earlier version of the work, which was eventually turned into a figure in the paper. Each of the 24 markers corresponds to a distinct gradient coil in the public record, with all sorts of sizes and designs, and they line up surprisingly well along the predicted 2.5-th power-law dependence.

One more to mention: I have uploaded a highly mathematical paper on how to calculate surface coil patterns for gradient fields in different coordinate systems. This can be found in the IEEE's pre-print server TechRxiv, here (https://doi.org/10.36227/techrxiv.20057135.v1). It is now waiting for suitable reviewers for customary peer review.

ISMRM 2022 under way

 The 30th Annual Meeting of ISMRM is under way in a "hybrid" format. The physical meeting appears to be very well attended, while all posters are digital and available for remote watch. A game-like remote collaboration platform, Gather Town, was adopted in some of the scientific sessions. As far as I can tell, those who are participating in person in London are enjoying their stay. Being able to watch recorded videos for many presentations is clearly a pandemic benefit, which I hope will continue in the future meetings.

One general take of mine is that compared to several years ago, there are more sessions touching upon non-technical aspects of MRI. This year, "Small Data" issue was highlighted, and there were several historical sessions such as one in memory of Richard Ernst (who passed away last year), those looking back at historical milestones, and region-specific (India) discussions. This may well be a reflection of the fact that MRI is becoming mature as a technology.

Among corporate symposia, Canon highlighted light, flexible RF coil arrays (Shape Coil), GE showcased Deep-Learning reconstruction and high performance gradients, and Philips introduced a new whole-body scanner (MR7700) with a more powerful wide-bore gradient coil. It was said that Siemens presented heavily on 0.55T scanner and their new human Connectome gradient hardware.

Master's theses published

Korean research literature database, called RISS (Research Information Sharing Service, www.riss.or.kr), publishes Master's and PhD theses from Korean academic institutions on-line. The theses by Byung-Pan Song and So-Hee Lee appear to have been submitted in Dec 2021, and the unsigned versions are now available for free download under Creative Commons license terms from the links below:

http://www.riss.kr/link?id=T16068181 (Song, B-P)

송병판. "A Novel Coil Design for Improving SNR in MR microscopy and a Convenient Imaging Method Using Inductively Coupling." 국내석사학위논문 성균관대학교 일반대학원, 2022. 서울

http://www.riss.kr/link?id=T16068008 (Lee, S-H)

이소희. "Fabrication of imaging setup of ex vivo tissue sample with spherical container for multi-orientation MRI experiments." 국내석사학위논문 성균관대학교 일반대학원, 2022. 서울

Byung-Pan's thesis is based on his research on inductively coupled and multi-turn histology coils that enable MRI of very thin (40 micrometers) tissue samples in a clinical 3T scanner. The thesis contains significant materials on the experimental methods and data for the novel RF coils. The SNR improvement shown in rat brain slices, enabled by the multi-turn design, is quite impressive. The proposed coil design can be utilized in future research in MR microscopy, especially multiplexed and multi-orientation studies. Hope there will be significant follow-up by other researchers in the field!

ISMRM 2022 Abstract announcement

The annual meeting of ISMRM of 2022 will be held from May 7-12 in London, UK. The organizers have announced abstract acceptance results last week. Approximately 5000 abstracts were accepted in various presentation formats. From the work done in 2021 by the CIEL team, the abstract by Seulki Yoo ("Investigation of MR visibility control of water-based (CaTiO3) dielectric padding with iron oxide contrast agent in 7T human brain MRI") was accepted for poster presentation. This interesting work explores a method to reduce MR visibility of water-based dielectric padding, used to improve B1 homogeneity at 7T. We had found that conventional calcium titanium oxide-based padding is often highly visible in T1 weighted images which hindered brain segmentation. Adding commercially available iron nanoparticles to the padding made it completely invisible in T1 images, by virtue of T2* being shortened below ~2 ms. Importantly, the amount of iron needed to do this did not contribute significant susceptibility artifacts, making this method an effective and practical means to "discreetly" address RF homogeneity at 7T.

On the other hand, the more theory-oriented abstract on BOLD signal suppression in DIANA imaging was not accepted. Given the high interest in direct neuronal activity imaging, this decision is somewhat puzzling and disheartening, but it is also true that the whole field is highly competitive and often controversial, so purely theoretical work can be met with high level of skepticism. The work -- a rigorous analysis of how slow-varying pixel amplitude changes translate into (suppressed) dynamic image contrast in 2D k-space line-scan imaging -- will be further refined and packaged for another venue of publication.