Simone Waerntges

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.

Changes of radial diffusivity and fractional anisotropy in the optic nerve and optic radiation of glaucoma patients.

Purpose of this study was to evaluate with diffusion-tensor imaging (DTI) changes of radial diffusivity (RD) and fractional anisotropy (FA) in the optic nerve (ON) and optic radiation (OR) in glaucoma and to determine whether changes in RD and FA correlate with disease severity. Therefore, glaucoma patients and controls were examined using 3T. Regions of interest were positioned on RD and FA maps, and mean values were calculated for ON and OR and correlated with optic nerve atrophy and reduced spatial-temporal contrast sensitivity (STCS) of the retina. We found, that RD in glaucoma patients was significantly higher in the ON (0.74 ± 0.21 versus 0.58 ± 0.17·10−3 mm2 s−1; P < 0.05) and OR (0.79 ± 0.23 versus 0.62 ± 0.14·10−3 mm2 s−1; P < 0.05) compared to controls. Aside, FA was significantly decreased (0.48 ± 0.15 versus 0.66 ± 0.12 and 0.50 ± 0.20 versus 0.66 ± 0.11; P < 0.05). Hereby, correlation between changes in RD/FA and optic nerve atrophy/STCS was observed (r > 0.77). In conclusion, DTI at 3 Tesla allows robust RD and FA measurements in the ON and OR. Hereby, the extent of RD increase and FA decrease in glaucoma correlate with established ophthalmological examinations.

A New Approach to Assess Intracranial White Matter Abnormalities in Glaucoma Patients: Changes of Fractional Anisotropy Detected by 3T Diffusion Tensor Imaging

RATIONALE AND OBJECTIVES The aims of this study was to evaluate, using 3-T diffusion tensor imaging, changes of fractional anisotropy (FA) in the orbital and intracranial part of the optic nerve (ON), the optic chiasm, the lateral geniculate nucleus, and different parts of the optic radiation (OR) in patients with glaucoma compared to controls and to determine whether FA correlates with disease severity. MATERIALS AND METHODS Twenty patients with glaucoma and 22 age-matched controls were examined using 3-T diffusion tensor imaging. Regions of interest were positioned on the FA maps, and mean values were calculated for each ON, optic chiasm, lateral geniculate nucleus, and OR. Results were compared to those from controls and correlated with ON atrophy and reduced spatial-temporal contrast sensitivity of the retina. RESULTS Compared to controls, FA in patients with glaucoma was significantly lower in the intracranial part of the ON (0.48 ± 0.15 vs 0.66 ± 0.12, P < .05) and in the OR (0.40 ± 0.16 to 0.48 ± 0.17 vs 0.53 ± 0.20 to 0.64 ± 0.11, P < .05). A high correlation between reduced FA in the intracranial ON and OR and ON atrophy and spatial-temporal contrast sensitivity of the retina was observed (r > 0.81). Otherwise, there was no significant difference in FA between patients with glaucoma and controls measured in the orbital part of the ON, optic chiasm, and lateral geniculate nucleus. CONCLUSIONS Diffusion tensor imaging at 3 T allows robust FA measurements in the intracranial part of the ON and the OR. FA is significantly reduced in patients with glaucoma compared to controls, with a good correlation with established ophthalmologic examinations.

Cerebral Microinfarcts in Primary Open-Angle Glaucoma Correlated With DTI-Derived Integrity of Optic Radiation

PURPOSE To evaluate the correlation between the extent of cerebral white matter lesions (WMLs) and the integrity of the visual pathway represented by fractional anisotropy (FA) in patients with primary open-angle glaucoma (POAG). METHODS This case-control study included a total of 61 German patients (39 POAG patients, 22 controls) matched for age and sex. Fractional anisotropy of the optic radiation was determined by 3-Tesla diffusion tensor imaging. White matter lesions and brain volumes were manually measured by using a T2-weighted, 3-D fluid-attenuated inversion recovery sequence. RESULTS In POAG patients WML volumes were significantly (P = 0.04) increased in the subcortical area. This applied for both absolute and relative units to the specific patients brain volume, compared to controls. The WML volumes were significantly (P = 0.003) greater in middle-aged (40-59 years) POAG patients than control patients. In controls there was a significant age correlation of WML volumes in the total brain, subcortical, and optic radiation regions of interest. There was a significant correlation between FA and WML in POAG regarding the total brain, the periventricular region, and the optic radiation in both hemispheres. In POAG, FA left and right optic radiation correlated significantly with age (P = 0.002). CONCLUSIONS We were able to demonstrate that (1) POAG patients aged 40 to 60 years had higher volumes of cerebral microinfarcts and (2) POAG patients showed a significant correlation between cerebral microinfarcts and degeneration of the optic radiation. This indicates that cerebral microinfarcts might be an intracerebral risk factor for glaucomatous optic nerve atrophy.

Automatic Segmentation of the Optic Radiation Using DTI in Healthy Subjects and Patients with Glaucoma

The complexity of the diffusion tensor imaging (DTI) data and the interpersonal variability of the brain fiber structure make the identification of the fibers a difficult and time consuming task. In this work, an automated segmentation system of the optic radiation using DTI is proposed. The system is applicable to normal subjects and glaucoma patients. It is intended to aid future glaucoma studies. The automation of the system is based on utilizing physiological and anatomical information to produce robust initial estimates of the optic radiation. The estimated optic radiation initializes a statistical level set framework. The optic radiation is segmented by the surface evolution of the level set function. The system is tested using eighteen DTI-datasets of glaucoma patients and normal subjects. The segmentation results were compared to the manual segmentation performed by a physician experienced in neuroimaging and found to be in agreement with the known anatomy with 83% accuracy. The automation eliminates the necessity of medical experts’ intervention and facilitates studies with large number of subjects.

Diffusion Tensor Imaging for In Vivo Detection of Degenerated Optic Radiation

Glaucomatous optic nerve atrophy may continue to the linked optic radiation by transneuronal degeneration, as described in animal models of glaucoma. In vivo visualization of the visual pathway represents a new challenge in the field of ophthalmology. We present a new approach for illustration of the optic radiation by diffusion tensor imaging (DTI) based on magnetic resonance imaging (MRI). The DTI was established by use of a 3T high-field scanner. The case of a patient with primary open-angle glaucoma is opposed to this one of a healthy subject to demonstrate the visible rarefication of the optic radiation. The goal was to introduce the technique of the DTI also in ophthalmology and to demonstrate that it may be useful to judge glaucoma-related differences.