Thalamus and cognitive impairment in mild traumatic brain injury: a diffusional kurtosis imaging study

Abstract

Conventional imaging is unable to detect damage that accounts for permanent cognitive impairment in patients with mild traumatic brain injury (mTBI). While diffusion tensor imaging (DTI) can help to detect diffuse axonal injury (DAI), it is a limited indicator of tissue complexity. It has also been suggested that the thalamus may play an important role in the development of clinical sequelae in mTBI. The purpose of this study was to determine if diffusional kurtosis imaging (DKI), a novel quantitative magnetic resonance imaging (MRI) technique, can provide early detection of damage in the thalamus and white matter (WM) of mTBI patients, and can help ascertain if thalamic injury is associated with cognitive impairment. Twenty-two mTBI patients and 14 controls underwent MRI and neuropsychological testing. Mean kurtosis (MK), fractional anisotropy (FA), and mean diffusivity (MD) were measured in the thalamus and several WM regions classically identified with DAI. Compared to controls, patients examined within 1 year after injury exhibited variously altered DTI- and DKI-derived measures in the thalamus and the internal capsule, while in addition to these regions, patients examined more than 1 year after injury also showed similar differences in the splenium of the corpus callosum and the centrum semiovale. Cognitive impairment was correlated with MK in the thalamus and the internal capsule. These findings suggest that combined use of DTI and DKI provides a more sensitive tool for identifying brain injury. In addition, MK in the thalamus might be useful for early prediction of permanent brain damage and cognitive outcome.

Figures

FIG. 1.

Representative T2-weighted (T2W) images and corresponding mean kurtosis (MK), fractional anisotropy (FA), and mean diffusivity (MD) maps (A, B, and C), from one 49 year old male patient with mild traumatic brain injury. Locations for regions of interest that were investigated in this study are indicated bilaterally as follows: (A) the thalamus and the anterior limb, genu, and posterior limb of the internal capsule; (B) the splenium of the corpus callosum; and (C) the centrum semiovale.

FIG. 2.

Plots displaying age- and gender-adjusted means (hash marks), and 95% confidence intervals (lines), for mean kurtosis (MK) and fractional anisotropy (FA) in the thalamus and the internal capsule of controls, cognitively-unimpaired mild traumatic brain injury (mTBI) patients, and cognitively-impaired mTBI patients. When cognitively-impaired patients were evaluated with respect to cognitively-unimpaired patients they exhibited significantly lower MK in the thalamus (p<0.01), and FA in the internal capsule (p=0.02).

FIG. 3.

Scatterplots with best-fit lines showing significant correlations between the baseline average values for mean kurtosis (MK) in the thalamus of Group 2 mild traumatic brain injury (mTBI) patients and their z scores on neuropsychological tests evaluating attention and concentration (r=0.67, p=0.03), and processing speed (r=0.65, p=0.02).