Structural MRI and tract-based spatial statistical analysis of diffusion tensor imaging in children with hemimegalencephaly
Tae Yeon JeonAndrew V. PoliakovSeth D. FriedmanXiuhua BozarthEdward J. NovotnyJason S. HauptmanSung‐Hoon MoonDennis Shaw
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Hemimegalencephaly
Neuroradiology
Background Hemimegalencephaly is a rare hamartomatous entity characterised by enlargement of all or part of the cerebral hemisphere ipsilaterally with cortical dysgenesis, large lateral ventricle and white matter hypertrophy with or without advanced myelination. Although conventional magnetic resonance imaging (MRI) is useful for detecting these diagnostic features, hemimegalencephaly is not always easily distinguished from other entities, especially when hemimegalencephaly shows blurring between the grey and white matter. Diffusion tensor imaging (DTI) is a functional MRI technique commonly used to assess the integrity of white matter. The usefulness of DTI in assessing hemimegalencephaly has not been fully elucidated. In this study, we clarified the characteristics of hemimegalencephaly with regard to DTI and its parameters including fractional anisotropy and apparent diffusion coefficient. Methods Three patients with hemimegalencephaly underwent MRI including DTI. We first visually compared fractional anisotropy mapping and conventional MRI. Next, we quantitatively measured the fractional anisotropy and apparent diffusion coefficient values in the subcortical white matter of the hemisphere with hemimegalencephaly and corresponding normal-appearing contralateral regions and analysed the values using the Mann–Whitney U test. Results On fractional anisotropy mapping, we could clearly distinguish the junction of grey and white matter and observed thicker white matter in the hemisphere with hemimegalencephaly, which was unclear on conventional MRI. The white matter in the hemisphere with hemimegalencephaly showed significantly higher fractional anisotropy ( P < 0.0001) and lower apparent diffusion coefficient ( P = 0.0022) values than the normal contralateral side. Conclusion DTI parameters showed salient hemimegalencephaly features and could be useful in its assessment.
Hemimegalencephaly
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Stereotactic radiosurgery (SRS) has been an effective treatment method for brain tumors; however, few data are available regarding radiation-induced white matter (WM) damage by SRS. In this work, diffusion tensor imaging (DTI) was used to investigate WM changes following SRS. Fifteen patients with gliomas were enrolled, with prescription doses ranging 18-25 Gy. Patients were scanned with magnetic resonance imaging (MRI) including DTI before and after SRS. Diffusion tensors were calculated and fiber tracking was performed. Non-irradiated WM volumes and irradiated WM volumes receiving ≥ 12 Gy and ≥ Gy were contoured as volumes of interest (VOI). Apparent diffusion coefficient (〈D〉), fractional anisotropy (FA) and number of fibers (NF) were calculated and assessed using the Wilcoxon signed-rank test. Compared with those of non-irradiated VOIs, FA and NF decreased considerably after two months of SRS in the irradiated WM VOIs. The variation in (〈D〉 was however small and was not statistically significant. The preliminary results suggested that FA and NF might potentially be more sensitive indicators than (〈D〉 in measuring radiation-induced WM changes and DTI could be a valuable tool to assess radiation-induced WM changes in SRS. Although it is still preliminary, this pilot study may be useful to provide insights for future studies.
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This study aimed to assess if quantitative diffusion magnetic resonance imaging analysis would improve prognostication of individual patients with severe traumatic brain injury.We analyzed images of 30 healthy controls to extract normal fractional anisotropy ranges along 18 white-matter tracts. Then, we analyzed images of 33 patients, compared their fractional anisotropy values with normal ranges extracted from controls, and computed severity of injury to white-matter tracts. We also asked 2 neuroradiologists to rate severity of injury to different brain regions on fluid-attenuated inversion recovery and susceptibility-weighted imaging. Finally, we built 3 models: (1) fed with neuroradiologists' ratings, (2) fed with white-matter injury measures, and (3) fed with both input types.The 3 models respectively predicted survival at 1 year with accuracies of 70%, 73%, and 88%. The accuracy with both input types was significantly better (P < 0.05).Quantifying severity of injury to white-matter tracts complements qualitative imaging findings and improves outcome prediction in severe traumatic brain injury.
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Hemimegalencephaly
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Purpose To study the potential of diffusion tensor imaging (DTI) to serve as a biomarker for radiation‐induced brain injury during chemo‐radiotherapy (RT) treatment. Materials and Methods Serial DTI data were collected from 18 high‐grade glioma (HGG) patients undergoing RT and 7 healthy controls. Changes across time in mean, standard deviation (SD), skewness, and kurtosis of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ a ), and transversal diffusivity (λ t ) within the normal‐appearing white matter (NAWM) were modeled using a linear mixed‐effects model to assess dose dependent changes of five dose bins (0–60 Gy), and global changes compared with a control group. Results Mean MD, λ a and λ t were all significantly increasing in >41 Gy dose regions (0.14%, 0.10%, and 0.18% per week) compared with <12 Gy regions. SD λ t had significant dose dependent time evolution of 0.019*dose per week. Mean and SD MD, λ a and λ t in the global NAWM of the patient group significantly increased (mean; 0.06%, 0.03%, 0.09%, and SD; 0.57%, 0.34%, 0.51 per week) compared with the control group. The changes were significant at week 6 of, or immediately after RT. Conclusion DTI is not sensitive to acute global NAWM changes during the treatment of HGG, but sensitive to early posttreatment changes. J. Magn. Reson. Imaging 2015;41:414–423. © 2013 Wiley Periodicals, Inc .
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