Brain-mapping techniques for evaluating poststroke recovery and rehabilitation: a review

Abstract

Brain-mapping techniques have proven to be vital in understanding the molecular, cellular, and functional mechanisms of recovery after stroke. This article briefly summarizes the current molecular and functional concepts of stroke recovery and addresses how various neuroimaging techniques can be used to observe these changes. The authors provide an overview of various techniques including diffusion-tensor imaging (DTI), magnetic resonance spectroscopy (MRS), ligand-based positron emission tomography (PET), single-photon emission computed tomography (SPECT), regional cerebral blood flow (rCBF) and regional metabolic rate of glucose (rCMRglc) PET and SPECT, functional magnetic resonance imaging (fMRI), near infrared spectroscopy (NIRS), electroencephalography (EEG), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS). Discussion in the context of poststroke recovery research informs about the applications and limitations of the techniques in the area of rehabilitation research. The authors also provide suggestions on using these techniques in tandem to more thoroughly address the outstanding questions in the field.

Figure 1

Depiction of water molecule movement. (A) Water molecule (black dots) diffuse more freely along white matter tracts (gray cylinders) than across them, where passage is less restricted, as represented by the black arrows and path of the water molecule. (B) Diffusion of water molecules can be quantified using the three-dimensional properties of an ellipsoid.

Figure 2

Phosphorous spectra from two brain locations. Representative [³¹P]-MRS spectra from a patient with a left internal capsule stroke. The single voxel (voxel size 13.8 cc) [³¹P]-MRS spectra are selected from the voxels indicated by the white boxes. Major [³¹P]-MRS metabolites such as inorganic phosphate (Pi), phosphocreatine (PCr), and adensosine triphosphates (γ-, α-, and β-ATP) are labeled. Reductions in gamma- and beta-ATP levels are evident in the spectrum from the left hemisphere.

Figure 3

Effects of stroke on FDG PET. Anatomical MRI and [¹⁸F]-FDG PET in a patient with left internal capsule infarction. Panels A and D show the stroke location (arrows) in axial and coronal slices, respectively. Although the premotor region (shown in B and E) appears structurally normal, the [¹⁸F]-FDG images (C and F) show a region of hypermetabolism in the premotor cortex of the contralesional hemisphere. [¹⁸F]-FDG images were acquired 10 months after infarct. All images are in radiological convention, as labeled in panel A, with the left side of the brain on the right side of each image.

Figure 4

Representative fMRI activation map. Changes in fMRI brain activation during wrist flexion/extension following 8 weeks of electrical stimulation with a neuroprosthetic device. Subject is a 52 year-old woman, 4 years after left hemisphere infarct. (A) Pretherapy scan with right (affected) wrist flexion/extension. (B) Posttherapy scan with right wrist flexion/extension showing increases in brain activation in bilateral motor regions. Posttherapy scan was conducted 13 weeks after the pretherapy scan. p < .01; n = 25 voxels. All images are in neurological convention with the left side of the brain on the right side of each image.