Lead authors: Seulki Yoo (GBME, 4th year graduate student in Master-PhD program), Hayoung Song (GBME, Master 2019, now at Univ. of Chicago)
Title of paper: Feasibility of head-tilted brain scan to reduce susceptibility-induced signal loss in the prefrontal cortex in gradient echo-based imaging
Author interviewed: Seulki Yoo
1. Please
describe what you did.
We proposed a novel solution to a well-known problem in
high-field brain MRI. The problem is that the static magnetic field (B0) is
very inhomogeneous just above the nose/sinus cavity. That is where the bottom
of the frontal brain lobe is. Traditionally, the B0 field is so non-uniform in
this region that typical functional MRI has very poor quality, often with a
“black hole” in part of the region. We found that if we image subjects with
their head tilted backward (in a “star-gazer” or “hair-salon” position), the B0
field becomes much more uniform and much of the lost signal is recovered.
2. Please explain to the GBME students why this work is important.
The benefit of ultra-high-field brain MRI is partly negated
by the presence of strong B0 non-uniformity. Prefrontal region is particularly
notorious. Many researchers (tens, if not hundreds) have published methods to
tackle this, by shim coils, sequence modification, and post-processing. Our
method does not require any of these, but shows that simple backward head
tilting can greatly improve the B0 uniformity in the prefrontal brain. We found
many volunteers could easily be scanned with the new head positioning. In the
future this work may enable more robust imaging in fMRI, diffusion MRI, and R2*
and QSM studies in the pre-frontal region.
3. Please describe any “aha” moment, “wow” moment, and “oh, crap” moment.
- Aha! (inspiration): When we first imaged a volunteer (my
advisor) in head-tilted position and saw a day-and-night difference in the EPI
signal in the prefrontal region.
- Wow! (excitement): When we saw that fMRI activation was
enhanced even in areas outside the prefrontal cortex, although we still don’t
know exactly why. Also, when we saw that the B0 map is more homogeneous than
with (simulated) 3rd-order shimming.
- Crap! (frustration): For some volunteers the head tilting
angle was limited by their chin running into the coil housing.
4. What kind of future papers should cite this?
- Any paper that discusses MRI image quality in the
prefrontal cortex.
- Papers that mention various ways to improve B0 uniformity.
- Papers on multi-orientation imaging, of humans or animals.
5. To the extent you can disclose, how can this work be followed up in the future?
This work was done at 3T. I want to see if 7T MRI can also benefit from this method, even if the head coil there (Nova coil) has more limited internal space for head rotation. Also, this work may be combined with other methods to improve pre-frontal imaging, such as the one with a new spatio-temporal encoding (ERASE) from Prof. Jang-Yeon Park’s lab.
For more information, see the link to the publication:
https://doi.org/10.1016/j.neuroimage.2020.117265
