title: Transient relationships among BOLD, CBV, and CBF changes in rat brain as detected by functional MRI.
abstract: The transient relationship between arterial cerebral blood flow (CBF(A)) and total cerebral blood volume (CBV(T)) was determined in the rat brain. Five rats anesthetized with urethane (1.2 g/kg) were examined under graded hypercapnia conditions (7.5% and 10% CO(2) ventilation). The blood oxygenation level-dependent (BOLD) contrast was determined by a gradient-echo echo-planar imaging (GE-EPI) pulse sequence, and CBV(T) changes were determined after injection of a monocrystalline iron oxide nanocolloid (MION) contrast agent using an iron dose of 12 mg/kg. The relationship between CBV(T) and CBF(A) under transient conditions is similar to the power law under steady-state conditions. In addition, the transient relationship between CBV(T) and CBF(A) is region-specific. Voxels with > or =15% BOLD signal changes from hypercapnia (7.5% CO(2) ventilation) have a larger power index (alpha = 3.26), a larger maximum possible BOLD response (M = 0.85), and shorter T(*)(2) (32 ms) caused by deoxyhemoglobin, compared to voxels with <15% BOLD signal changes (alpha = 1.82, M = 0.16, and T(*)(2) = 169 ms). It is suggested that the biophysical model of the BOLD signal can be extended under the transient state, with a caution that alpha and M values are region-specific. To avoid overestimation of the cerebral metabolic rate of oxygen changes seen using fMRI, caution should be taken to not include voxels with large veins and a large BOLD signal.
authors.affiliation: Biophysics Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin 53226-0509, USA.
authors.forename: Gaohong
authors.initials: G
authors.lastname: Wu
authors.forename: Feng
authors.initials: F
authors.lastname: Luo
authors.forename: Zhu
authors.initials: Z
authors.lastname: Li
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhao
authors.forename: Shi-Jiang
authors.initials: SJ
authors.lastname: Li
mesh_terms: D000818:Animals; D001810:Blood Volume; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003287:Contrast Media; D017352:Echo-Planar Imaging / Q000379:methods*; D007089:Image Enhancement; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D023421:Models, Animal; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D010100:Oxygen