Brain Ischemia/diagnosis; Brain/blood supply; Brain/pathology; Diffusion Magnetic Resonance Imaging/methods; Stroke/diagnosis; Adolescent; Adult; Aged; Aged, 80 and over; Anisotropy; Brain Ischemia/physiopathology; Diffusion Magnetic Resonance Imaging/standards; Female; Functional Laterality/physiology; Hand/innervation; Hand/physiopathology; Humans; Image Interpretation, Computer-Assisted/methods; Infarction, Middle Cerebral Artery/diagnosis; Infarction, Middle Cerebral Artery/physiopathology; Male; Middle Aged; Muscle Weakness/diagnosis; Muscle Weakness/etiology; Muscle Weakness/physiopathology; Muscle, Skeletal/innervation; Muscle, Skeletal/physiopathology; Nerve Fibers, Myelinated/pathology; Neural Pathways/blood supply; Neural Pathways/pathology; Neural Pathways/physiopathology; Paresis/diagnosis; Paresis/etiology; Paresis/physiopathology; Predictive Value of Tests; Pyramidal Tracts/blood supply; Pyramidal Tracts/pathology; Pyramidal Tracts/physiopathology; Severity of Illness Index; Stroke/physiopathology