Characterization of white matter injury in a hypoxic-ischemic neonatal rat model by diffusion tensor MRI.
OBJECTIVE
We evaluate white matter (WM) injury after hypoxic-ischemic (HI) insult in a neonatal rat model using diffusion tensor imaging (DTI) to determine whether lambda(parallel) and lambda(perpendicular) are able to characterize type and severity of brain damage.


METHODS
Eighteen 7-day-old Sprague-Dawley rats underwent unilateral ligation of left common carotid artery followed by 50 minutes (n=9) or 90 minutes (n=9) of hypoxia at 37 degrees C. Rats were divided into 2 groups, according to absence (group A, n=11) or presence (group B, n=7) of cystic lesions on D7 post-HI T2-weighted imaging. DTI was performed for all rats at D1 and for group A rats at D7 post-HI. Signal intensity of ipsilateral and contralateral external capsule (EC) on D1 was compared by paired t test, with histological correlation.


RESULTS
Group A rats had significantly reduced FA, elevated trace, elevated lambda(perpendicular), and similar lambda(parallel) on D1 in the ipsilateral compared to contralateral EC, whereas group B rats had significant reduction in all parameters in the ipsilateral EC. Elevated trace normalized on D7 in group A rats. Histopathologic results demonstrated reduced myelination in group A noncystic HI and severe necrosis in group B cystic HI.


CONCLUSIONS
Increased lambda(perpendicular) with no significant change in lambda(parallel) appears to characterize noncystic WM injury with reduced myelination, whereas reduction in both lambda(parallel) and lambda(perpendicular) characterize severe damage with loss of structural integrity and necrosis. Combining with FA and trace, lambda(parallel) and lambda(perpendicular) provide additional information which reflects type and severity of HI injury.
Department of Diagnostic Radiology, The University of Hong Kong, 102 Pokfulam Rd, Hong Kong.
Silun
S
Wang
Ed X
EX
Wu
Chung Nga
CN
Tam
Ho-Fai
HF
Lau
Pik-To
PT
Cheung
Pek-Lan
PL
Khong
D000818:Animals; D000831:Animals, Newborn; D017536:Carotid Artery, Common; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D004195:Disease Models, Animal; D005260:Female; D020925:Hypoxia-Ischemia, Brain / Q000473:pathology*; D008026:Ligation; D008959:Models, Neurological; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D015588:Observer Variation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012720:Severity of Illness Index; D020521:Stroke / Q000473:pathology*