Ex vivo Evaluation of ADC Values within Spinal Cord White Matter Tracts

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Fig 1.
MR image and corresponding histologic sections from normal rat spinal cord. A, Schematic diagram of major ascending and descending tracts in the rat spinal cord overlaid on a b = 0 (T2-weighted) image of a rat spinal cord. Regions of interest were drawn in the following tracts: rubrospinal tract (RST), reticulospinal tract (ReST), vestibulospinal (VST), fasciculus gracilis (FG), fascisulus cuneatus (FC), and dorsal corticospinal tract (dCST). While the dorsal white matter tracts are homogeneous, the ventral and lateral tracts are mixed with other fibers from the STT-spinothalamic tract and dSCT-dorsal spinocerebellar tract. A significant difference between the human and rat spinal cord is the location of the corticospinal tract. In the human, the corticospinal tract is located in the lateral white matter, while in the rat it is located in the dorsal white matter.
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Fig 1.
B–G, 1-μm-thick histologic sections at 40×, stained with toluidine blue of the RST (B), ReST (C), VST (D), FG (E), FC (F), and dCST (G), respectively (black bar = 50 μ). Note that the largest axons appear to be within the VST.

TABLE 1:

Overall transverse ADC, longitudinal ADC and anisotropy indices for PF and GL-PF specimens

Note.—lADC of white matter in GL-PF fixed spinal cords is significantly elevated, and the AI is significantly decreased, as compared with specimens fixed with PF only. Significant results (P < .05) are italicized.

TABLE 2:

Comparison of longitudinal and transverse ADCs and anisotropy indices among spinal cord tracts in PF and GL-PF specimens

Spinal Cord Tract	PF lADC (10⁻⁴ mm²/s) Mean ± SE	GL-PF lADC (10⁻⁴ mm²/s) Mean ± SE	P Value Comparison of lADC Values	PF tADC (10⁻⁴ mm²/s) Mean ± SE	GL-PF tADC (10⁻⁴ mm²/s) Mean ± SE	P Value Comparison of tADC Values	PF (AI = tADC/lADC) Mean ± SE	GL and PF (AI = tADC/lADC) Mean ± SE	P Value Comparison of AI Values
dCST	7.459 ± 0.473	8.531 ± 0.432	P = .129	0.834 ± 0.067	0.843 ± 0.061As ANOVA was Not significant, No post hoc test Comparisons were performed for rows 5-7	0.113 ± 0.009	0.100 ± 0.008	P = .355
FG	8.788 ± 0.363	9.857 ± 0.332	P = .058	1.055 ± 0.076	1.082 ± 0.069		0.121 ± 0.011	0.112 ± 0.010	P = .568
FC	8.665 ± 0.385	9.460 ± 0.351	P = .161	1.063 ± 0.066	1.145 ± 0.061		0.124 ± 0.010	0.123 ± 0.010	P = .937
VST	8.893 ± 0.322	10.358 ± 0.294	P = .0083	1.411 ± 0.093	1.390 ± 0.084		0.159 ± 0.011	0.135 ± 0.010	P = .119
RST	8.248 ± 0.304	9.947 ± 0.277	P = .0026	1.099 ± 0.057	1.015 ± 0.052		0.134 ± 0.007	0.103 ± 0.007	P = .012
ReST	7.180 ± 0.306	8.594 ± 0.280	P = .0078	1.029 ± 0.073	1.064 ± 0.067		0.143 ± 0.010	0.125 ± 0.009	P = .189

Note.—Significant elevations (P < .0083, significant results italicized) of the lADC were seen in the VST, RST, and ReST of the GL-PL specimens as compared with PF specimens. Post hoc comparisons of tADC values between fixatives were not performed, as the ANOVA was not significant. No significant differences (P < .0083) were seen in the AI of individual tracts between the GL-PF specimens and the PF specimens (SE = standard error).