Background: Estimation of brain damage following an ischemic stroke is most often performed
within the first few days after the insult, where large amounts of oedematous fluid have accu-
mulated. This can potentially hamper correct measurement of infarcted area, since oedema for-
mation poorly reflects infarct size. This study presents a non-invasive, easily applicable and
reliable method to accurately predict long-term evolution and late-stage infarction.
Objective: We performed a longitudinal analysis of brain infarct evolution after MCAO in mice, in
order to determine whether water-compensated N-Acetylaspartate (NAA) levels in the infarct
area, measured 24 h after the insult, is a suitable marker for late-stage infarction and thereby
prognosis.
Methods: Twenty mice were divided into 4 groups and scanned longitudinally at different time-
points after MCAO, followed by euthanisation for histology: Group 1) MRI/MRS at day 1 after
MCAO (n = 4), Group 2) MRI/MRS at days 1 and 7 after MCAO (n = 5), Group 3) MRI/MRS at
days 1, 7, and 14 after MCAO (n = 3), and Group 4) MRI/MRS at days 1, 7, 14, and 28 after
MCAO (n = 4). At days 1, 7, 14, and 28, NAA levels were correlated with histological determi-
nation of neuronal death based on Nissl and H&E stainings.
Results: Twenty-four hours after the insult, NAA levels in the infarcted area decreased by 35 %,
but steadily returned to normal after 28 days. In the acute phases, NAA levels strongly correlated
with loss of Nissl substance (r2 = 0.874, p = 0.002), whereas NAA levels in later stages reflect
glial metabolism and tissue reorganisation. Most importantly, NAA levels 24 h after MCAO was
highly correlated with late stage infarction at days 14 and 28 (r2 = 0.73, p = 0.01), in contrast to
T2 (r2 = 0.06, p = 0.59).
Conclusions: By using a fixed voxel, which is easily positioned in the affected area, it is possible to
obtain reliable measures of the extent of neuronal loss at early time points independent of oedema
and brain deformation. Importantly, NAA levels 24 h after MCAO accurately reflects late-stage
infarction, suggesting that NAA is a useful prognostic biomarker early after an ischemic stroke.