Wl. Lin et al., EXPERIMENTAL HYPOXEMIC HYPOXIA - EFFECTS OF VARIATION IN HEMATOCRIT ON MAGNETIC-RESONANCE T2-ASTERISK-WEIGHTED BRAIN IMAGES, Journal of cerebral blood flow and metabolism, 18(9), 1998, pp. 1018-1021
T2-weighted gradient echo magnetic resonance images of rat brain were
obtained dynamically during acute hypoxemic hypoxia to investigate th
e relations between changes in cerebral blood oxygen saturation (Delta
Yb), blood hematocrit (Hct), and R2 (Delta R2*). Images from hypoxem
ic rats with normal Her (42.8% +/- 2.33%; n = 12) were compared with t
hose from hypoxemic rats with mild (33.4% +/- 1.88%; n = 8) or moderat
e (27.14% +/- 2.7%; n = 10) reduction of Hct. A linear relation betwee
n Delta Yb and Delta R2 was obtained for all three groups. However, t
he slopes of the linear regressions were statistically different from
one another (P < 0.001), with the slopes of the regression lines incre
asing inversely with Her; that is, the slope for normal Hct is less th
an the slope for mildly reduced Hct, which is less than the slope for
moderately reduced Hct. These data suggest that for any given reductio
n in the oxygen saturation of cerebral blood, the Delta R2 will be of
a lesser magnitude when the hemoglobin concentration is reduced; the
data are consistent with existing theoretical models of deoxyhemoglobi
n content-dependent effects in T2-weighted magnetic resonance imaging
.