Yongxian Qian^{1}, Tiejun Zhao^{2}, Kathik Lakshmanan^{1}, Timothy Shepherd^{1}, Yulin Ge^{1}, Yvonne W. Lui^{1}, and Fernando E. Boada^{1}

The literature reports a wide variance in CSF T2* values (46-64ms). This variance may suggest T2* heterogeneity of CSF. Here we explore the possibility of CSF T2* heterogeneity among healthy and neurologically-disordered brains.

Sodium ions in CSF are in fast and free motion
and thus have a mono-exponential T2* relaxation (Eq. 1)^{10}. If sodium
signal, y(t), is measured at two echo times of TE1 and TE2,
T2* value is estimated via a curve fitting in Eq. 2. The distractive variation
of T2* value with B0 field inhomogeneity was minimized through a correction in
Eq. 3. The B0 field map was attained using the phase difference between the two
TE images^{5}. CSF was selected in lateral ventricles (left and right)
for the T2* measurement. Multiple neighboring slices were used to define the extension
of ventricles. T2* value was calculated voxel-by-voxel and then averaged over a
CSF volume of voxels 70±50 in a range of 16-169.

Eq. [1]. $$$ y(TE)=Aexp(-TE/T_2^*) $$$

Eq. [2]. $$$ T_2^*=(TE_2-TE_1)/ln(y_1/y_2) $$$

Eq. [3]. $$$ 1/T_{2c}^*=1/T_2^*-\gamma|\delta B_0| $$$

- Reddy R, Shinar M, Wang Z, Leigh JS. Multiple-quantum filters of spin-3/2 with pulse of arbitrary flip angle. J Magn Reson 1994; B104:148-152.
- Hancu I, Boada FE, Shen GX. Three-dimensional triple-quantum-filtered (23)Na imaging of in vivo human brain . Magn Reson Med. 1999 Dec;42(6):1146-54.
- Kline RP, Wu EX, Petrylak DP, Szabolcs M, Alderson PO, Weisfidt ML, Cannon P, Katz J. Rapid in vivo monitoring of chemotherapeutic response using weighted sodium magnetic resonance imaging. Clin Cancer Res 2000; 6:2146-2156.
- Stobbe R, Beaulieu C. In vivo sodium magnetic resonance imaging of the human brain using soft inversion recovery fluid attenuation. Magn Reson Med 2005; 54:1305-1310.
- Qian Y, Panigrahy A, Laymon CM, Lee VK, Drappatz J, Lieberman FS, Boada FE, Mountz JM. Short-T2 imaging for quantifying concentration of sodium (23 Na) of bi-exponential T2 relaxation. Magn Reson Med 2015; 74:162-174.
- Qian Y, Zhao T, Lakshmanan K, Ge Y, Lui Y, Shepherd T, Boada FE. Proof of concept for the separation of free and bound sodium in human brain through two-TE acquisitions at 3T. In the Proceedings of the 25th Annual Meeting of ISMRM, Honolulu, Hawai, USA, 2017, p.2956.
- Bartha R, Menon RS. Long component time constant of 23Na T*2 relaxation in healthy human brain. Magn Reson Med. 2004 Aug;52(2):407-10.
- Fleysher L, Oesingmann N, Stoeckel B, Grossman RI, Inglese M. Sodium long-component T2* mapping in human brain at 7 Tesla. Magn Reson Med. 2009 Nov;62(5):1338-41.
- Blunck Y, Josan S, Taqdees SW, Moffat BA, Ordidge RJ, Cleary JO, Johnston LA. 3D-multi-echo radial imaging of 23 Na (3D-MERINA) for time-efficient multi-parameter tissue compartment mapping. Magn Reson Med 2018; 79:1950-1961.
- Jaccard G, Wimperis S, Bodenhausen G. Multiple-quantum NMR spectroscopy of S=3/2 spins in isotropic phase: A new probe for multiexponential relaxation. J Chem Phys 1986; 85: 6282-6293.
- Lakshmanan K, Brown R, Madelin G, Qian Y, Boada F, Wiggins GC. An eight-channel sodium/proton coil for brain MRI at 3 T. NMR Biomed 2018; 31 e3867.
- Boada FE, Gillen JS, Shen GX, Chang SY, Thulborn KR. Fast three dimensional sodium imaging. Magn Reson Med 1997; 37:706–715.

Fig. 1. A case of mTBI
patient: (a, b) sodium images at two TEs of 0.3ms and 5ms, (c, d) T2* maps
before and after the correction (T2*c), and
(e) B0 field map derived from (a) and (b) and used in (d). The ventricular CSF has large T2* values (deep red) but small
inhomogeneity of B0 field (light yellow).

Fig. 2. T2*
values of the subject groups,
with and
without the B0 correction. The “mixed” patient group
includes epilepsy, bipolar, and MS. The
“*” represents a statistically
significant difference between the healthy and TBI groups (p=0.02) and
between the TBI and “mixed” groups (p=0.04). The
difference of corrected T2* (or T2*c) between the healthy and mixed groups is not
significant (p=0.37).

Fig. 3.
The
corrected T2* (or T2*c) values between male and female inside
individual
groups. No significant difference was found, with a p-value of 0.43 for the
healthy group and 0.71 for the mTBI.

Fig. 4. The
corrected T2* (or T2*c) versus age for all the subjects studied. No correlation between the two
variables is found.