Cerebral vascular reserve

Technetium ( Tcj Bicisate Injection. A sterile colorless solution of bicisate is complexed with Tc-99m pertech-neuite after reduction with a stannous salt. The precise structure of the technetium complex is fN,N -ethylene-di-L-cy.steinato(3-) oxo "Tc]technetium(V) diethyl ester. This radiopharmaceutical is a neutral and lipophilic complex that crosses the blotxl-brain barrier and is selectively retained in the brain. Therefore, this radiotracer is used as a brain-perfusion imaging agent. After intravenous injection of 20 mCi (740 MBq) of Tc-99m bicisate, about 5% of the injected dose is localized within the brain cells 5 minutes after injection and demonstrates rapid renal excretion (74% in 24 hours). This radiotracer is used clinically to evaluate dementia, stroke, lack of brain perfusion ("brain death"), cerebral vascular reserve, or risk of stroke (acetazolamide challenge. study) and to localize a seizure focus for surgical removal. 

In patients with known chronic cerebral ischemia related to underlying carotid artery stenotic lesions, CBF is usually preserved, at least initially, because of the cerebrovascular reserve. The cerebrovascular reserve represents the vasodilatation ability of cerebral arteries to compensate for a CBF tending to decrease and maintain this CBF at a normal level. In patients with chronic cerebral vascular disorders, it is necessary to quantify the residual cerebrovascular reserve and to distinguish tissue that has used only a limited fraction of its vasodilatation ability and still has cerebrovascular reserve available as a bulfer from tissue that has exhausted its vasodilatation ability and cerebrovascular reserve. The latter is at risk of ischemia, which can be triggered by any hemodynamic stress, and requires intervention to increased CBF, usually through carotid stenosis surgery or endovascular treatment, or extracranial-intracranial artery bypass (Nariai et al. 1995). 

Nariai T, Suzuki R, Hirakawa K, Maehara T, Ishii K, Senda M (1995) Vascular reserve in chronic cerebral ischemia measured by the acetazolamide challenge test comparison with positron emission tomography. AJNR Am J Neuroradiol 16 563-570... 

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