The Pathophysiology of Ischemic Stroke Studied by Radionuclide Imaging

Ischemic stroke is caused by interruption or significant impairment of blood supply to the brain, which leads to a cascade of metabolic and molecular alterations resulting in functional disturbance and morphological damage. The changes in regional cerebral blood flow and in regional metabolism can be assessed by radionuclide imaging, especially single photon emission tomography (SPECT) and positron emission tomography (PET). SPECT and PET have broadened our understanding of flow and metabolic thresholds critical for maintenance of brain function and morphology: PET was essential in the transfer of the concept of the penumbra to clinical stroke and thereby had a great impact on developing treatment strategies. Receptor-ligands can be applied as early markers of irreversible neuronal damage and can predict the size of the final infarcts, which is important for decisions of invasive therapy in large (“malignant”) infarction. With SPECT and PET the reserve capacity of blood supply can be tested in obstructive arteriosclerosis, which is essential for planning interventions. The effect of a stroke on surrounding and contralateral primarily not-affected tissue can be investigated helping to understand symptoms caused by disturbance in functional networks. Activation studies are useful to demonstrate alternative pathways to compensate for lesions and to test the effect of rehabilitative therapy. Radioisotope studies help to detect neuroinflammation and its effect on extension of tissue damage. Despite the limitations of broad clinical application of radionuclide imaging, this technology has a great impact on research in cerebrovascular diseases and still has various applications in the management of stroke. In this short review the contributions of PET- and SPECT-studies to the understanding of the pathophysiology of ischemic stroke are described.