Current and Emerging Techniques in Neuroimaging of Sport-Related Concussion

Abstract

Sport-related concussion (SRC) affects an estimated 1.6 to 3.8 million Americans each year. Sport-related concussion results from biomechanical forces to the head or neck that lead to a broad range of neurologic symptoms and impaired cognitive function. Although most individuals recover within weeks, some develop chronic symptoms. The heterogeneity of both the clinical presentation and the underlying brain injury profile make SRC a challenging condition. Adding to this challenge, there is also a lack of objective and reliable biomarkers to support diagnosis, to inform clinical decision making, and to monitor recovery after SRC. In this review, the authors provide an overview of advanced neuroimaging techniques that provide the sensitivity needed to capture subtle changes in brain structure, metabolism, function, and perfusion after SRC. This is followed by a discussion of emerging neuroimaging techniques, as well as current efforts of international research consortia committed to the study of SRC. Finally, the authors emphasize the need for advanced multimodal neuroimaging to develop objective biomarkers that will inform targeted treatment strategies after SRC.

Figure 1:

T1-weighted magnetic resonance imaging (MRI): A) Coronal view of T1-weighted MR image of the brain. B) Segmentation using FreeSurfer 7.2: Surface of pial (red) and white matter boundary (blue) superimposed on T1-weighted image. The distance between the two surfaces can then be used to calculate cortical thickness. C) Segmentation using FreeSurfer 7.2: Label maps of subcortical gray matter volumes superimposed on T1-weighted image.

Figure 2:

Diffusion tensor imaging (DTI): A) Tract-based spatial statistics (TBSS) may reveal voxels with statistically significant differences in diffusion metrics between groups (blue areas) superimposed on white matter skeleton (green). B) Two-tensor tractography of an individual’s white matter. DTI can be used to delineate white matter tracts and to evaluate diffusion metrics of specific white matter tracts (tractography).

Figure 3:

Susceptibility-weighted imaging (SWI): SWI is sensitive to microhemorrhages following brain injury. Microhemorrhages appear as punctate regions of signal drop out with blooming artifact (red arrow).

Figure 4:

Magnetic resonance spectroscopy (MRS): Representative spectrum obtained from the posterior cingulate gyrus (inset) of a collegiate athlete post-concussion. The spectrum (red) is shown whereby each of the metabolites are fitted to the raw data. The chemical shift indicated by frequency is used to identify each metabolite and quantified by the fitting to produce concentrations or ratios to creatine. tCho: total choline, tCr: total creatine, tNAA: total N-acetyl aspartate, mI: myoinositol, Glx: glutamate and glutamine, GABA: gamma amino butyric acid, GSH: glutathione, ppm: parts per million.

Figure 5:

Arterial spin labeling (ASL): A) and B) Labeling plane (hatched area) for labeling blood-water flowing to the brain in internal carotid arteries and vertebral arteries on both sides using radiofrequency inversion, and image acquisition volume (orange box). C) Cerebral blood flow (CBF) map of the brain. Image shown was obtained using pseudo-continuous ASL (pCASL).