Presented at the Neonatal Society 2003 Autumn Meeting.
Counsell SJ1, Kapellou O2, Boardman JP2, Shen Y1, Allsop JM1, Harrison M2, Cowan FM2, David Edwards2, Mary A Rutherford1
1 Robert Steiner MR Unit, Imaging Sciences Department, Hammersmith Hospital, Du Cane Road London W12 OHS, UK
2 Division of Paediatrics, Obstetrics & Gynaecology, Imperial College, Faculty of Medicine, Hammersmith Hospital, Du Cane Road, London W12 OHS, UK
Introduction: Diffusion tensor imaging (DTI) is a magnetic resonance imaging technique which can be used to assess brain tissue microstructure by allowing calculation of the apparent diffusion coefficient (ADC) (which quantifies the motion of water) and relative anisotropy (RA) (which defines the direction of water motion). These values relate to the structure of neural tissue and particularly to the direction of white matter tracts.
Aim: The aim of the present study was to test the hypothesis that both ADC and RA values were significantly different in preterm infants with diffuse excessive high signal intensity (DEHSI) (1). compared to those without when studied at term equivalent age, and to term born control infants.
Methods: Ethical approval for this study was granted by the Hammersmith Hospitals Trust Research Ethics Committee. MR imaging was obtained on 32 preterm infants (normal white matter, n=6; DEHSI, n=26) and 6 term born control infants using a 1.5 Tesla Eclipse scanner with a dedicated paediatric head coil. DTI was obtained in 6 non-colinear directions, with a b value of 710s/mm2 and a slice thickness of 5mm. The median (range) gestational age at birth of the preterm group was 31 (25-34) weeks, the median (range) birthweight was 1.46 (0.61-2.23) grams, and 16 infants were male.
Results: The median (range) gestational age at time of imaging of the preterm infants with DEHSI was 40 (39-44) weeks and those with normal white matter was 41 (40-42) weeks, and for term infants was 41 (38 -41) weeks. These values were not significantly different.
ADC values: There were no significant differences in ADC values in preterm infants with normal white matter and term born control infants (p = 0.41). ADC values were significantly higher in preterm infants with DEHSI than preterm infants with normal white matter (p = 0.03) and term born control infants (p = 0.01).
RA values: There were no significant differences in RA values in preterm infants with normal white matter and term born control infants (p = 0.78). RA values were significantly lower in preterm infants with DEHSI than preterm infants with normal white matter (p = 0.006) and term born control infants (p = 0.002).
Conclusion: This study demonstrates that preterm birth per se is not necessarily associated with abnormal white matter at term equivalent age. However infants with diffuse imaging abnormalities appear to have microstructural changes in the white matter.
References
1. Maalouf et al. Magnetic resonance imaging of the brain in a cohort of extremely preterm infants. J Pediatr 1999; 135: 351- 357.