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of chronic epilepsy. The next step is to identify the aetiological factors and how to intervene
to prevent this process.

Recent MRI developments

Diffusion-weighted imaging is very sensitive in the detection of early ischaemic changes, and
shows changes in status epilepticus34. Diffusion tensor imaging (DTI) reveals lesions found
with conventional MRI and also abnormalities that are not visualised on routine sequences35-
37. However, these occult abnormalities may be the result of and not the cause of chronic
epilepsy38. Tractography is a derivation of diffusion tensor imaging that allows identification
of nerve fibre tracts within the brain, and demonstrates the structural basis of connectivity
between brain regions39. Using tractography to interrogate the visual pathways it is possible
to predict the occurrence and extent of a visual field defect following anterior temporal lobe
resection (ATLR). A recent study found that the anterior extent of Meyer’s loop ranged from
2443 mm from the temporal pole. Significant post-operative visual field defects were only
seen in those individuals in whom the anterior aspect of Meyer’s loop was less than 35 mm
from the temporal pole40. Pre- and intra-operative tractography has also been used to
demonstrate the optic radiation in patients having temporal lobe resection and to predict the
extent of visual field defect41. Similar studies have been reported in patients with tumours
and may aid surgical planning of patients undergoing lesionectomy near eloquent cortex.
Tractography has the potential to demonstrate the structural reorganisation of networks
involved in memory and language that mirror changes in cerebral function. In a combined
fMRI–tractography study, controls and right TLE patients had a left-lateralised pattern of
both language-related activations and associated white matter organisation. Left TLE patients
had reduced left-hemisphere and increased right-hemisphere white matter pathways, in
comparison to controls and right TLE patients. Subjects with more lateralised functional
activation had more lateralised white matter pathways42. The arcuate fasciculus was shown
to be larger in the speech dominant hemisphere, and the left-right asymmetry was reduced if
there was dominant hemisphere pathology43.

Other promising new MRI sequences include magnetisation transfer ratio imaging44, double
inversion recovery imaging and fast FLAIR T2-mapping. Ultra-fast low-angle rapid
acquisition and relaxation enhancement is a sequence that may be useful for patients who are
restless and can only tolerate short studies45. A recently implemented MR sequence called
‘periodically rotated overlapping parallel lines with enhanced reconstruction’
(‘PROPELLER’) has an excellent in-plane resolution of 0.5 mm and is therefore able to
demonstrate internal hippocampal structures within a clinical acceptable time-frame46. This
may allow the detection of subtle hippocampal changes in patients with temporal lobe
epilepsy.

Continuous arterial spin labelling perfusion MR imaging can detect asymmetries in mesial
temporal lobe perfusion inter-ictally in patients with TLE47 and may identify focal cortical
dysplasia182.

Improved gradient performance is anticipated to improve speed and spatial resolution. Phased
array surface coils improve signal-to-noise ratio in superficial cortex and hippocampal
regions and this may lead to improved spatial resolution. Imaging at high field strengths may
also improve spatial resolution. 3T MRI scanners are now available as mature clinical
instruments and may increase the clinical yield by up to 20%48,183. The utility of higher field
strength scanners, up to 7T, is also being evaluated and may provide further insights into
subtle structural abnormalities184.