Presented at the Neonatal Society 2008 Autumn Meeting.
Kerr J1, Dudink J1, Paterson K1, Merchant N1,2, Allsop JM1, Rutherford MA1, Counsell SJ1, Edwards AD1,2
1 Division of Clinical Sciences and MRC Clinical Sciences Centre Hammersmith
2 Division of Neonatology, Imperial College Comprehensive Biomedical Research Centre, DuCane Road, London, W12 0HS, United Kingdom
Aims: Survivors of preterm birth have a high incidence of cognitive impairment and behavioural problems (1,2) which are poorly explained by abnormalities on conventional magnetic resonance (MR) imaging. It is possible that disrupted neural connectivity is responsible, at least in part, for these cognitive impairments. Diffusion tensor imaging (DTI) tractography provides a tool to assess connectivity in vivo. This study uses this approach to investigate the development of white matter tracts and the growth in connected regions of thalamus and the cortex in the developing preterm brain.
Methods: This study was approved by the Hammersmith Hospital Research Ethics Committee with written consent from parents obtained prior to scanning. Using the 3T Philips MRI scanner (Best, Netherlands) located within the Neonatal Intensive Care Unit. DTI images of the brain were obtained in infants born between 24.6 and 30.4 (median 28.8) weeks gestational age at two time points: preterm (29 – 33.4 weeks) and term-equivalent (39 – 44 weeks) age. Thalamo-cortical connectivity was assessed as described previously (3) by defining cortical and thalamic regions and using a probabilistic algorithm to define tracts connecting these structures, as implemented in FSL (www.fmrib.ox.ac.uk/fsl) (4). The thalamo-cortical connections between six cortical regions (motor, sensory, frontal, temporal, parietal, occipital) and thalamus were studied, and the region of thalamus connected to each cortical area defined.
Results: Increasing post-menstrual age was related to an increase in cortical volume, the volume of connected regions of thalamus, white matter tract volume and an increase in Fractional Anisotropy (FA). The cortex was found to grow at a faster rate than its related thalamic projection and the growth of cortex relative to thalamus was greatest in the frontal and temporal regions of the brain. Additionally, aberrant connectivity was visualised in one infant who had focal white matter lesions.
Conclusion: Probabilistic tractography is an effective tool to investigate thalamo-cortical growth and connectivity in the preterm brain. As thalamo-cortical units are fundamental to brain function and mature significantly from 23 weeks on, and as all sensory input to cortex passes through thalamic relays, this approach offers the potential to investigate a potential cause of aberrant brain development in preterm infants.
References
1. Larroque B et al; Lancet 2008; 371; 82
2. Marlow NWD et al; N Engl J Med 2005; 6; 9-19
3. Counsell SJ et al. Neuroimage 2007; 896-90
4. Smith SM, et al. Neuroimage 2004; 23; S208-S219