Double-Pulsed-Field Gradient MRI in the Long Evans shaker rats' spinal cords
Debbie Anaby1, Darya Morozov1, Ian D. Duncan2, and Yoram Cohen1,3

1School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel, 2Medical Sciences, The University of Wisconsin-Madison, Madison, WI, United States, 3Sagol School of Neurosciences, Tel Aviv University, Tel Aviv, Israel


Double pulsed-field gradient (d-PFG) MRI has recently been suggested as an additional methodology for studying microstructure in the CNS. The Long Evans shaker (les) rats’ CNS has been previously studied by q-space diffusion (QSI) and more recently by angular d-PFG MRI. Here, we characterize the microstructure of the les spinal cords by fitting the angular d-PFG MRI data to the multiple correlation function (MCF) and extracting the unique parameter L/R ratio and its fractions. Clearly, the angular d-PFG methodology is capable of distinguishing between the les and their controls, in white matter and even in some gray matter ROIs.


Double pulsed-field gradient (d-PFG) MRI has recently been suggested as an additional methodology for studying microstructure in the CNS1-3. Previously we had studied the CNS of the Long Evans shaker (les) rats using q-space diffusion MRI (QSI)4,5. More recently we have been interested in using the angular d-PFG MRI to study microstructural changes that occur in the spinal cords of the les rats, which are considered a model of dysmyelination. Here, the d-PFG MRI data was fitted to a model from which the unique parameter L/R ratio and its fractions were extracted.


MRI experiments were conducted on a Bruker Avance-III 14.1T scanner, capable of producing pulsed field gradients of up to 300 G/cm in each direction. Fixed ex-vivo control and les rat spinal cords of 33 days of age were immersed in PBS overnight and then placed in 5 mm glass tubes filled with Fluorinert, to assure fiber orientation along the z-direction. The d-PFG MRI experiments were conducted with a finite mixing time (tm) of 12 ms, on five controls and les spinal cords. G1 was fixed in the x-direction and the orientation of G2 was varied in the x-z plane (d-PFGxz) using 13 different values of φ between 0o and 360o. The measurements were conducted using a d-PFG MRI sequence with EPI readout3 and with the following parameters: slice thickness of 800 µm, field of view (FOV) of 4.8x4.8 mm2, in-plane spatial resolution of 50x50 µm2, 2 segments, TR/TE=3200/52 ms, δ12=1 ms, Δ12=15 ms and 120 averages (total acquisition time of ~3 hours). As required for the MCF analysis, each of the experiments were performed with 5 q-values (824-1030 cm-1) in addition to a q=0 experiment. A multiple correlation function (MCF) analysis was performed using an in-house Matlab code for six chosen ROIs in both the white matter (WM) and gray matter (GM).

Results and discussion

Figure 1 presents the six ROIs on a clustered d-PFG MRI image of a control spinal cord (tm=12 ms). These include three white matter (WM) ROIs; WM1, WM2 and WM3 and three gray matter (GM) ROIs; GM1, GM2 and GM3. Figure 2 shows E(φ) profiles and their fitting for four of the six ROIs in representative 33 days old control and les rats. Clearly, the data as well as its fitting appear to be robust, showing modulations of increased depths beginning from GM1 up to WM3. In both the control and les spinal cords, the modulations are most pronounced in the WM ROIs, as expected, due to the organized cylindrical like anisotropic microstructure. The GM ROIs show less pronounced modulations which are suggestive of the presence of less anisotropic microstructure. Note that the les spinal cord shows a more shallow modulation in most ROIs observed. This is expected due to their dysmyelination and less organized microstructure. Each of the six ROIs in the controls and les spinal cords was analyzed by the MCF, which provided the L/R ratios and their fractions, as shown in Figure 3. Note that the L/R distribution is wide and covers most values in both the control and les although the L/R fractions are much smaller in the les. This implies that the les spinal cords do comprise of some highly anisotropic microstructures (mainly in the WM ROIs) similar to the controls, although with much smaller fractions.


The MCF analysis is capable of fitting the data from angular d-PFGxz MRI experiments performed on controls and les rat spinal cords. The unique parameter, L/R ratio, is extracted together with its fraction. The angular d-PFGxz MRI experiments, analyzed by the MCF paradigm are capable of distinguishing between the control and les rat spinal cords.


No acknowledgement found.


1. N. Shemesh et al, NMR Biomed. 23:757-780 (2010) 2. M. Koch and J. Finsterbusch, Magn. Reson. Med. 60: 90-101 (2008) 3. N. Shemesh et al, Magn. Reson. Med. 68: 794-806 (2012) 4. D. Anaby et al, NMR Biomed. 26: 1879-1886 (2013) 5. D. Anaby et al. Magn. Reson. Imaging. 31: 1097-1104 (2013)


Six chosen ROIs for quantitative analysis, presented over a cluster analyzed image performed for a tm=12 ms and G1xG2xz experiment.

d-PFGxz MR E(φ) profiles and their fittings in GM1, GM3, WM1 and WM3 of 33 days old representative control and les rat spinal cords, using a diffusion coefficient (D0) of 1*10-5 m2/sec and five q-values; 824, 875, 927, 978 and 1030 cm-1. Raw data is represented by the empty red circles and fittings are represented by the blue lines.

L/R ratios and their fractions from the six ROIs of both of the 33 days old rat controls and les groups (n=5 for each group).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)