Quick Iron Imaging of the Striatum using R2’ – Study Protocol Comparison on a 64-Channel Head Coil
Presented During: Poster Session 3
Friday, June 27, 2025: 01:45 PM - 03:45 PM
Friday, June 27, 2025: 01:45 PM - 03:45 PM
Presented During: Poster Session 4
Saturday, June 28, 2025: 01:45 PM - 03:45 PM
Saturday, June 28, 2025: 01:45 PM - 03:45 PM
Poster No:
1749
Submission Type:
Abstract Submission
Authors:
Valur Olafsson1, Rebecca Hennessy1, Nicholas Kathios1, Kelsie Lopez1, Rishitha Kudaravalli1, Psyche Loui1, Laurel Gabard-Durnam1, Juliet Davidow1
Institutions:
1Northeastern University, Boston, MA
First Author:
Co-Author(s):
Introduction:
Several quantitative MRI measures have been used to spatially map iron concentration in the brain, such as the irreversible (R2=1/T2), effective (R2*=1/T2*) , and reversible (R2'=R2*-R2) relaxation rates (Haacke et al., 2005; Haacke et al., 2010). Although all are strongly linear proportional to age-related iron content in deep gray matter (GM), R2' is potentially a more specific measure of deep GM iron content (Sedlacik et al., 2014).
A recent study (Larsen et al., 2020), using a Siemens mMR dual modality PET/MR scanner with a 12-channel head coil, found evidence that supported the sensitivity of R2' as an indirect measure of vesicular dopamine (DA) concentration, as measured by PET, in the striatal reward system in youth, such as the nucleus accumbens (NAcc). This would offer an MR imaging method for participants that are unable to undergo PET imaging of the DA system.
R2' mapping is inherently sensitive to sources of macroscopic susceptibility, such as the sinuses. The sinus can cause artificially inflated R2' values in parts of the striatum and consequently lead to the exclusion of subject data (Larsen et al., 2020). One way of combatting these effects is to collect the images at higher resolution to reduce the effects of through-plane gradients, particularly in the slice direction.
Here we investigated the benefits of increasing the image resolution compared to the (Larsen et al., 2020) study, by increasing the parallel imaging acceleration factor on a 64-channel head coil while maintaining near-equivalent brain coverage and scan time to the original study.
A recent study (Larsen et al., 2020), using a Siemens mMR dual modality PET/MR scanner with a 12-channel head coil, found evidence that supported the sensitivity of R2' as an indirect measure of vesicular dopamine (DA) concentration, as measured by PET, in the striatal reward system in youth, such as the nucleus accumbens (NAcc). This would offer an MR imaging method for participants that are unable to undergo PET imaging of the DA system.
R2' mapping is inherently sensitive to sources of macroscopic susceptibility, such as the sinuses. The sinus can cause artificially inflated R2' values in parts of the striatum and consequently lead to the exclusion of subject data (Larsen et al., 2020). One way of combatting these effects is to collect the images at higher resolution to reduce the effects of through-plane gradients, particularly in the slice direction.
Here we investigated the benefits of increasing the image resolution compared to the (Larsen et al., 2020) study, by increasing the parallel imaging acceleration factor on a 64-channel head coil while maintaining near-equivalent brain coverage and scan time to the original study.
Methods:
Two subjects were scanned on a 3T Siemens Prisma with a 64-channel head/neck coil. The R2' map was generated by subtracting R2 from R2*, with both maps estimated using a quadratic penalized least-squares based reconstruction (Larsen et al., 2020). The R2 and R2* reconstructions required multi-echo turbo spin echo (mTSE) and multi-echo gradient echo (mGRE) data respectively. Both were collected with the original lower resolution protocol (LRP) (1.72x1.72x3mm; 40 slices; GRAPPA-factor=2; mTSE-TE=[12, 98,184]ms, mTSE-TA=2min10s; mGRE-TE=[3.63, 8.64, 12.58, 16.52, 23.00]ms, mGRE-TA=1min34s), and new higher resolution protocol (HRP) (1.15x1.15x2mm; 60 slices; GRAPPA-factor=3; mTSE-TE=[9.3, 56,103]ms; mTSE-TA=2min32s; mGRE-TE=[4.62, 8.54, 12.46, 16.38, 20.30, 24.22]ms; mGRE-TA=2min40s). A T1w 1x1x1mm MPRAGE was also collected. R2' was calculated in MNI space after warping both R2 and R2* maps.
Results:
Fig. 1 shows four panels, each with crosshair-located axial/coronal/sagittal views of the estimated R2' map for both subjects and resolutions. The NAcc is overlayed in red, and the crosshair is on the left-NAcc (l-NAcc). The yellow arrow highlights an area with a sinus-related susceptibility artifact. Comparing the LRP and HRP for both subjects shows a visible reduction of the artifact in the HRP. This allows for more precise R2' estimates in the l-NAcc, especially for Subject 02. The right-NAcc showed similar results.
Fig. 2 shows a scatter plot of R2' voxel values in the NAcc (N=1408), comparing the estimated R2' when using LRP versus HRP. The R2' values for Subject 01 shows that both protocols result in comparable R2' values (linear least-squares fit: R-squared = 0.54, slope=0.7), although the HRP produces slightly higher R2' values due to reduced partial-volume effect (intercept=3.2 1/s). As indicated by the green circle, due to the spatial extent of the susceptibility artifact for Subject 02 some of the LRP-based NAcc R2' estimates are artificially inflated compared to the HRP R2' estimates.
Fig. 2 shows a scatter plot of R2' voxel values in the NAcc (N=1408), comparing the estimated R2' when using LRP versus HRP. The R2' values for Subject 01 shows that both protocols result in comparable R2' values (linear least-squares fit: R-squared = 0.54, slope=0.7), although the HRP produces slightly higher R2' values due to reduced partial-volume effect (intercept=3.2 1/s). As indicated by the green circle, due to the spatial extent of the susceptibility artifact for Subject 02 some of the LRP-based NAcc R2' estimates are artificially inflated compared to the HRP R2' estimates.
·Fig. 1: Estimated R2’ maps for both subjects (left/right column) and resolutions (top/bottom rows). The NAcc is overlayed in red, with the crosshair located in the l-NAcc.
·Fig. 2: Scatter plot of R2’ voxel values (N=1408 per subject) in the NAcc, comparing each R2’ voxel value when collected using the LRP versus HRP.
Conclusions:
A new HRP, facilitated by a high channel count head coil, was compared to the original LRP in (Larsen et al., 2020), and showed clear visual and quantitative improvement for R2' estimation in the striatum. The HRP total acquisition time is slightly longer than LRP. Future work would focus on lowering it without impacting the benefits currently provided by HRP.
Modeling and Analysis Methods:
Methods Development
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Normal Development
Subcortical Structures 1
Neuroanatomy Other 2
Keywords:
Acquisition
Basal Ganglia
Development
Dopamine
STRUCTURAL MRI
1|2Indicates the priority used for review
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Provide references using APA citation style.
Haacke, E. M. (2010). Correlation of putative iron content as represented by changes in R2* and phase with age in deep gray matter of healthy adults. J Magn Reson Imaging, 32(3), 561-576. doi:10.1002/jmri.22293
Larsen, B. (2020). Maturation of the human striatal dopamine system revealed by PET and quantitative MRI. Nat Commun, 11(1), 846. doi:10.1038/s41467-020-14693-3
Sedlacik, J. (2014). Reversible, irreversible and effective transverse relaxation rates in normal aging brain at 3T. Neuroimage, 84, 1032-1041. doi:10.1016/j.neuroimage.2013.08.051