Sultan Haider

Diffusion Tensor Imaging Detects Rarefaction of Optic Radiation in Glaucoma Patients

RATIONALE AND OBJECTIVES Diffusion tensor imaging (DTI) can depict rarefaction of the optical fibres. Hence, we applied DTI to assess pathological changes of the optic radiation in glaucoma patients. MATERIALS AND METHODS Fifty glaucoma patients and 50 healthy age-matched controls were examined by a 3T high-field magnetic resonance scanner. Fiber tracts were volume rendered using a semiquantitative approach to assess rarefaction and results were correlated with the extent of optic nerve atrophy and reduced spatial-temporal contrast sensitivity of the retina using established ophthalmological examinations. RESULTS Twenty-two glaucoma patients (44%) showed significant rarefaction of the optic radiation: the volume was reduced to 67 ± 16% compared with controls. Hereby, the glaucomatous optic nerve atrophy stage correlated with the presence of DTI-derived rarefied optic radiation (Kendall tau-b 0.272, P = .016). Aside, cerebral microangiopathy affecting the optic radiation was significantly higher among glaucoma patients compared to controls (10 patients compared with 2 patients, P < .05). CONCLUSION In patients with glaucomatous optic nerve atrophy, there is anterograde and-most likely because of microangiopathic lesions within the optic radiation-retrograde transneuronal rarefaction of the optic radiation that can be assessed in vivo using DTI with good correlation to established ophthalmological examinations.

A New Semi-quantitative Approach for Analysing 3T Diffusion Tensor Imaging of Optic Fibres and Its Clinical Evaluation in Glaucoma

RATIONALE AND OBJECTIVES Diffusion tensor imaging can depict rarefaction of the optical fibers. Manual segmentation is time consuming. The purposes of the study were (1) to present a new semiquantitative segmentation approach for analyzing 3-T diffusion tensor imaging of optical fibers and (2) to clinically test the new approach by comparing optic fiber rarefaction in patients with glaucoma to that in age-matched, healthy controls. MATERIALS AND METHODS To perform semiautomated and quantitative segmentation of the optical radiation, a Mathcad-based software program was developed. The results were compared to the manual evaluation of the images performed by two experienced neuroradiologists. The eyes of 42 subjects (22 patients with glaucoma and 20 controls) aged 37 to 86 years were assessed in full ophthalmologic examinations. Magnetic resonance imaging was performed using a 3-T high-field scanner. RESULTS The evaluation using the new approach matched 94% with manually acquired rarefaction of the optical radiation; Cronbachs α was >0.81 for calculation of the manually and semiautomatically derived volumes. CONCLUSION The new approach seems to be robust and is clearly faster compared to the more tedious manual segmentation. Using diffusion tensor imaging at 3 T, it could be shown that there was increasing atrophy of the optical radiation (fourth neuron) with increasing age in patients with glaucoma. Compared to age-matched, healthy patients, more pronounced atrophy of the fourth neuron was found in patients with glaucoma.

Voxel Based Analysis of Diffusion Indices in Patients with Primary Open-Angle Glaucoma Using Tract-Based Spatial Statistics

Background and purpose: Diffusion tensor imaging can provide information about microstructural changes of the visual pathway in glaucoma patients. Tract-based spatial statistics (TBSS) has been established for analysis of fractional anisotropy (FA) and has successfully been used for analysis of DTI data of glaucoma patients. However there are certain DTI indices such as mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) and mode of anisotropy (MO), which can also be analyzed using TBSS. Hence, we tested whether TBSS is useful for analysis of non-FA data in glaucoma patients and for identification of microstructural changes in patients with primary openangle glaucoma characterized by these non-FA DTI indices. Material and methods: Our study comprised 46 patients with primary open-angle glaucoma (POAG) and a healthy, age-matched control group of 23 subjects. TBSS was used for analysis of FA as well as MO, MD, RD and AD. Results: For an automated analysis of non-FA diffusion indices we could establish a workflow using TBSS in addition to its primary purpose, the analysis of FA. Our results reveal clusters of voxels with overlapping decreased FA and increased RD and MD in the optic radiation as well as in visual association tracts. Conclusion: TBSS is a useful tool not only for analysis of FA but also of non-FA diffusion indices in glaucoma patients. Overlapping decreased FA and increased MD and RD can be found in POAG patients not only in the optic radiation but also in visual association tracts, suggestive for significant neurodegeneration in POAG.