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Editors Selection IGR 12-4
New Approaches: DT-MRI in assessing ON damage
Comment by Carlo Nucci on:
27437 A new semi-quantitative approach for analysing 3T diffusion tensor imaging of optic fibres and its clinical evaluation in glaucoma, Engelhorn T; Haider S; Michelson G et al., Academic Radiology, 2010; 17: 1313-1316
Yücel's observation in primates that neurodegenerative changes induced by experimental glaucoma extended to the central visual pathways1 stimulated the search for neuroimaging techniques that could document this involvement in humans as well. Using 1.5T MRI, Gupta et al. demonstrated LGN volume reductions in glaucoma patients,2 and the diffusor tensor (DT)-MRI study of Garaci et al. documented degenerative involvement of the optic radiations.3 Engelhorn et al. (2059) compared manual analysis of DT-MRI images of the optic radiations with a new semiautomatic method. The new method saved time, did not have to be carried out by an expert radiologist, and displayed excellent (94%) concordance with manual analysis. They also found reduced optic radiation volumes in patients with glaucoma, strengthening the view that glaucomatous nerve damage also involves central visual pathways and highlighting the value of DT-MRI in assessing this damage.
The manuscript has certain shortcomings. First, there is no mention of: 1) the criteria used to enroll the two groups of participants; 2) the criteria used to stage the glaucoma, the number of patients with bilateral involvement, or even the type of glaucoma (high or normal tension); 3) statistical tests used to compare the two groups, and results obtained with the two methods or to evaluate intra- and interoperator variability (although the Discussion mentions the method's high reproducibility). As for the Results, means, standard deviation, and medians need to be provided for the reported data.
It is well known that DT-MRI provides reconstructions of axonal architecture based on the diffusion of water molecules along the fibers. In histologic studies, changes in the axonal architecture correlate with specific DT-MRI parameters4 ‐ namely mean diffusivity and fractional anisotropy ‐ which thus represent markers of the neurological damage. It is not clear why the authors investigated only DT-MRI measurement of optic radiation volume instead of including these validated markers.
References
- Yücel Y, Gupta N. Glaucoma of the Brain: a disease model for the study of transsynaptic neural degeneration. Prog. Brain Res. 2008:173;465-478.
- Gupta N, Greenberg G, de Tilly LN, Gray B, Polemidiotis M, Yücel YH. Atrophy of the lateral geniculate nucleus in human glaucoma detected by magnetic resonance imaging. Br J Ophthalmol. 2009;(1):56-60.
- Garaci FG, Bolacchi F, Cerulli A, Melis M, Spanò A, Cedrone C, Floris R, Simonetti G, Nucci C. Optic nerve and optic radiation neurodegeneration in patients with glaucoma: in vivo analysis with 3-T diffusion-tensor MR imaging. Radiology. 2009;252(2):496-501.
- Hui ES, Fu Ql, So KF, Wu EX. Diffusion tensor MR study of optic nerve degeneration in glaucoma. Conf Proc IEEE Eng Med Biol Soc 2007:4312-4315.
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