PET imaging in ischemic cerebrovascular disease: current status and future directions

Abstract

Cerebrovascular diseases are caused by interruption or significant impairment of the blood supply to the brain, which leads to a cascade of metabolic and molecular alterations resulting in functional disturbance and morphological damage. These pathophysiological changes can be assessed by positron emission tomography (PET), which permits the regional measurement of physiological parameters and imaging of the distribution of molecular markers. PET has broadened our understanding of the fl ow and metabolic thresholds critical for the maintenance of brain function and morphology: in this application, PET has been essential in the transfer of the concept of the penumbra (tissue with perfusion below the functional threshold but above the threshold for the preservation of morphology) to clinical stroke and thereby has had great impact on developing treatment strategies. Radioligands for receptors can be used as early markers of irreversible neuronal damage and thereby can predict the size of the fi nal infarcts; this is also important for decisions concerning invasive therapy in large ("malignant") infarctions. With PET investigations, the reserve capacity of blood supply to the brain can be tested in obstructive arteriosclerosis of the supplying arteries, and this again is essential for planning interventions. The effect of a stroke on the surrounding and contralateral primarily unaffected tissue can be investigated, and these results help to understand the symptoms caused by disturbances in functional networks. Chronic cerebrovascular disease causes vascular cognitive disorders, including vascular dementia. PET permits the detection of the metabolic disturbances responsible for cognitive impairment and dementia, and can differentiate vascular dementia from degenerative diseases. It may also help to understand the importance of neuroinfl ammation after stroke and its interaction with amyloid deposition in the development of dementia. Although the clinical application of PET investigations is limited, this technology had and still has a great impact on research into cerebrovascular diseases.

Mapping of cerebral metabolic rate of oxygen using dynamic susceptibility contrast and blood oxygen level dependent MR imaging in acute ischemic stroke

“…Previous studies have found imaging of the oxygen extraction fraction (OEF) in acute stroke imaging to be useful for distinguishing and determining the extent of the tissue at risk of infarction and the ischemic core [19]. In both tissue areas, impaired perfusion causes not only reduced supply of oxygenated hemoglobin but also slowed removal of deoxyhemoglobin [7].…”

“…In both tissue areas, impaired perfusion causes not only reduced supply of oxygenated hemoglobin but also slowed removal of deoxyhemoglobin [7]. Therefore, since OEF is increased within tissue at risk of infarction as demonstrated with PET [19], the accumulation of deoxyhemoglobin is expected to increase accordingly, as detected in previous studies [7,12]. Bauer et al showed significant differences in T2′ values between perfusion-impaired, diffusion-restricted, and healthy tissue in a smaller sample size; yet, T2′-measurements demonstrated the highest values within the infarct core, which is not expected to contain tissue with the highest oxygen extraction fraction in acute stroke, as proven by PET previously [7].…”

18F-FNDP for PET Imaging of Soluble Epoxide Hydrolase

“…Clinically stroke is evaluated primarily through anatomic and functional magnetic resonance imaging, with molecular approaches limited due to a lack of viable radiotracers for this indication beyond those used to measure perfusion with single photon emission computed tomography (15). A PET agent for sEH may enable distinction between AD and VCI in vivo, rather than having to rely on postmortem observation of Aβ plaques and neurofibrillary tangles (16,17).…”

Advances in chronic cerebral circulation insufficiency

“…PET is regarded as the “gold standard” that affords an advantage of quantitatively assessing multiple parameters related to the cerebral physiological and metabolic conditions. Evaluation of CCCI can be accomplished with PET, which estimates cerebral perfusion via measuring the CBF and oxygen extraction fraction (OEF) . However, it is not considered as a first‐line option because of a relatively high cost and demand for technique as well as a low penetration rate.…”