Nuclear medicine in the rehabilitative treatment evaluation in stroke recovery. Role of diaschisis resolution and cerebral reorganization.

Abstract

There has recently been a tremendous increase in imaging technology and imaging methodology enabling noninvasive exploration of brain function to such an intricate degree as to enable measurements of very small spatial and short temporal cerebral operations responsible for neurological and functional recovery after stroke. This has allowed conceptualization of rehabilitation strategies designed to maximally enhance rehabilitation protocols tailored to the individual patient's deficits. Rehabilitation strategies may now be designed and optimized by employing methods to synchronize functional training of brain regions ascribed to those areas innately undergoing neuronal plasticity change responsible for stroke recovery. In order to effectively apply these noninvasive imaging methods, one must have a clear understanding of the physics and technique of the imaging methodologies and how these are best applied to understand brain physiology during the stroke recovery process to provide a solid rationale for development of rehabilitation protocols. Nuclear medicine imaging is first presented as a diagnostic method to assess the stroke process. The initial brain damage and resulting neurological disability can be primarily assessed in terms of changes in the vascular and hemodynamic status of the cerebral circulation in addition to alterations in the metabolic status around the infarction region. Techniques for assessing perfusion and metabolism include regional cerebral blood flow (rCBF), single photon emission computed tomography (SPECT), and F-18 2-Fluoro-2-deoxy-D-glucose (F-18 FDG) positron emission tomography (PET). In addition, hemodynamic vascular insufficiency can be assessed using O-15 O2 oxygen extraction PET and rest and Diamox rCBF SPECT. The status of the peri-infarction region can be characterized in terms of components of diaschisis and ischemia using proton magnetic resonance spectroscopy imaging ((1)H MRSI) and rest/stress rCBF assessment of cerebral vascular reserve. As the brain recovers from cerebral infarction, areas of reorganization and energy utilization by the brain can be measured using oxygen extraction methods with PET, F-18 FDG glucose utilization by PET, and functional magnetic resonance imaging (fMRI) measures using the blood oxygenation level dependent (BOLD) technique. In addition, high field MRI imaging of the brain is now able to provide detailed fractional anisotropy (FA) maps to characterize changes in white matter by fiber tracking mapping using diffusion tensor imaging. Imaging of the stroke recovery process focuses on the physiologic model of stroke characterized by rCBF, metabolism, 1H spectroscopic measures of N-acetyl aspartate (NAA), choline (Ch) and creatine (Cr) in the peri-infarction zone as well as in the extended stroke penumbra including areas of distant ''pure'' diaschisis unencumbered with the confound of cerebral ischemia. Data is presented describing the results of application of imaging methodologies as the patient undergoes rehabilitation that demonstrates the importance of blood flow and metabolic changes in the contralesional frontal lobe both during the resting state and during motor and speech activation paradigms. The results of advanced imaging technologies on cerebral damage and cerebral reorganization during rehabilitation are presented in the context of furthering designs of rehabilitation strategies. Success can be monitored to assess the optimization of rehabilitation strategy design to maximize neurological recovery from stroke by employing facilitatory methods to maximally synchronize rehabilitation techniques with recovery of functionally counterpart areas of viable brain.