Microstructural characterization of corticospinal tract in subacute and chronic stroke patients with distal lesions by means of advanced diffusion MRI

Abstract

Purpose: The aim of the paper is to evaluate if advanced dMRI techniques, including diffusion kurtosis imaging (DKI) and neurite orientation dispersion and density imaging (NODDI), could provide novel insights into the subtle microarchitectural modifications occurring in the corticospinal tract (CST) of stroke patients in subacute and chronic phases.

Methods: Seventeen subjects (age 68 ± 11 years) in the subacute phase (14 ± 3 days post-stroke), 10 of whom rescanned in the chronic phase (231 ± 36 days post-stroke), were enrolled. Images were acquired using a 3-T MRI scanner with a two-shell EPI protocol (20 gradient directions, b = 700 s/mm², 3 b = 0; 64 gradient directions, b = 2000 s/mm², 9 b = 0). DTI-, DKI-, and NODDI-derived parameters were calculated in the posterior limb of the internal capsule (PLIC) and in the cerebral peduncle (CP).

Results: In the subacute phase, a reduction of FA, AD, and KA values was correlated with an increase of ODI, RD, and AK parameters, in both the ipsilesional PLIC and CP, suggesting that increased fiber dispersion can be the main structural factor. In the chronic phase, a reduction of FA and an increase of ODI persisted in the ipsilesional areas. This was associated with reduced F_ic and increased MD, with a concomitant reduction of MK and increase of RD, suggesting that fiber reduction, possibly due to nerve degeneration, could play an important role.

Conclusions: This study shows that advanced dMRI approaches can help elucidate the underpinning architectural modifications occurring in the CST after stroke. Further follow-up studies on bigger cohorts are needed to evaluate if DKI- and NODDI-derived parameters might be proposed as complementary biomarkers of brain microstructural alterations.

Keywords: Corticospinal tract; DKI; DTI; NODDI; Subacute and chronic stroke.

Fig. 1

Examples of ROIs outlined at the level of the PLIC (upper panels) and the CP (lower panels) are shown in the axial and coronal planes. The red ROI delineates the ipsilesional hemisphere whereas the green ROI delimits the contralesional hemisphere

Fig. 2

Parametric maps of DTI (FA and MD), NODDI (ODI, F_ic, F_iso), and DKI (KA, MK, AK, RK) parameters are shown in the subacute (a) and in the chronic (b) phase. The area including the PLIC is indicated by a white arrow

Fig. 3

Box plots reporting DTI, DKI, and NODDI parameters calculated for the PLIC in the subacute phase in both the ipsilateral and contralateral hemisphere. Parameters values corresponding to each subject are displayed as red circles. Asterisks refer to the statistical significance of the difference between groups

Fig. 4

Parametric maps of DTI (FA and MD), NODDI (ODI, F_ic, F_iso) and DKI (KA, MK, AK, RK) parameters are shown in the subacute (a) and in the chronic (b) phase. The area including the CP is indicated by a white arrow

Fig. 5

Box plots reporting DTI, DKI, and NODDI parameters calculated for the CP in the subacute phase in both the ipsilateral and contralateral hemisphere. Parameter values corresponding to each subject are displayed as red circles. Asterisks refer to the statistical significance of the difference between groups

Fig. 6

Box plots reporting DTI, DKI, and NODDI parameters calculated for the PLIC in the chronic phase in both the ipsilateral and contralateral hemisphere. Parameters values corresponding to each subject are displayed as red circles. Asterisks refer to the statistical significance of the difference between groups

Fig. 7

Box plots reporting DTI, DKI, and NODDI parameters calculated for the CP in the chronic phase in both the ipsilateral and contralateral hemisphere. Parameters values corresponding to each subject are displayed as red circles. Asterisks refer to the statistical significance of the difference between groups

Fig. 8

Correlations between FA and ODI parameters evaluated in subacute and chronic phases in both PLIC and CP