In vivo determination of absolute cerebral blood volume using hemoglobin as a natural contrast agent: an MRI study using altered arterial carbon dioxide tension.

TitleIn vivo determination of absolute cerebral blood volume using hemoglobin as a natural contrast agent: an MRI study using altered arterial carbon dioxide tension.
Publication TypeJournal Article
Year of Publication1999
AuthorsUlatowski JA, Oja JM, Suarez JI, Kauppinen RA, Traystman RJ, van Zijl PC
JournalJournal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism
Volume19
Issue7
Pagination809-17
Date Published1999 Jul
Abstract

The ability of the magnetic resonance imaging transverse relaxation time, R2 = 1/T2, to quantify cerebral blood volume (CBV) without the need for an exogenous contrast agent was studied in cats (n = 7) under pentobarbital anesthesia. This approach is possible because R2 is directly affected by changes in CBF, CBV, CMRO2, and hematocrit (Hct), a phenomena better known as the blood-oxygenation-level-dependent (BOLD) effect. Changes in CBF and CBV were accomplished by altering the carbon dioxide pressure, PaCO2, over a range from 20 to 140 mm Hg. For each PaCO2 value, R2 in gray and white matter were determined using MRI, and the whole-brain oxygen extraction ratio was obtained from arteriovenous differences (sagittal sinus catheter). Assuming a constant CMRO2, the microvascular CBV was obtained from an exact fit to the BOLD theory for the spin-echo effect. The resulting CBV values at normal PaCO2 and normalized to a common total hemoglobin concentration of 6.88 mmol/L were 42+/-18 microL/g (n = 7) and 29+/-19 microL/g (n = 5) for gray and white matter, respectively, in good agreement with the range of literature values published using independent methodologies. The present study confirms the validity of the spin-echo BOLD theory and, in addition, shows that blood volume can be quantified from the magnetic resonance imaging spin relaxation rate R2 using a regulated carbon dioxide experiment.

Alternate JournalJ. Cereb. Blood Flow Metab.