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Whitney E. Parker, Elizabeth K. Weidman, J. Levi Chazen, Sumit N. Niogi, Rafael Uribe-Cardenas, Michael G. Kaplitt and Caitlin E. Hoffman

OBJECTIVE

The authors tested the feasibility of magnetic resonance–guided focused ultrasound (MRgFUS) ablation of mesial temporal lobe epilepsy (MTLE) seizure circuits. Up to one-third of patients with mesial temporal sclerosis (MTS) suffer from medically refractory epilepsy requiring surgery. Because current options such as open resection, laser ablation, and Gamma Knife radiosurgery pose potential risks, such as infection, hemorrhage, and ionizing radiation, and because they often produce visual or neuropsychological deficits, the authors developed a noninvasive MRgFUS ablation strategy for mesial temporal disconnection to mitigate these risks.

METHODS

The authors retrospectively reviewed 3-T MRI scans obtained with diffusion tensor imaging (DTI). The study group included 10 patients with essential tremor (ET) who underwent pretreatment CT and MRI prior to MRgFUS, and 2 patients with MTS who underwent MRI. Fiber tracking of the fornix-fimbria pathway and inferior optic radiations was performed, ablation sites mimicking targets of open posterior hippocampal disconnection were modeled, and theoretical MRgFUS surgical plans were devised. Distances between the targets and optic radiations were measured, helmet angulations were prescribed, and the numbers of available MRgFUS array elements were calculated.

RESULTS

Tractograms of fornix-fimbria and optic radiations were generated in all ET and MTS patients successfully. Of the 10 patients with both the CT and MRI data necessary for the analysis, 8 patients had adequate elements available to target the ablation site. A margin (mean 8.5 mm, range 6.5–9.8 mm) of separation was maintained between the target lesion and optic radiations.

CONCLUSIONS

MRgFUS offers a noninvasive option for seizure tract disruption. DTI identifies fornix-fimbria and optic radiations to localize optimal ablation targets and critical surrounding structures, minimizing risk of postoperative visual field deficits. This theoretical modeling study provides the necessary groundwork for future clinical trials to apply this novel neurosurgical technique to patients with refractory MTLE and surgical contraindications, multiple prior surgeries, or other factors favoring noninvasive treatment.

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Sumit N. Niogi, Neal Luther, Kenneth Kutner, Teena Shetty, Heather J. McCrea, Ronnie Barnes, Leigh Weiss, Russell F. Warren, Scott A. Rodeo, Robert D. Zimmerman, Apostolos John Tsiouris and Roger Härtl

OBJECTIVE

Statistical challenges exist when using diffusion tensor imaging (DTI) to assess traumatic axonal injury (TAI) in individual concussed athletes. The authors examined active professional American football players over a 6-year time period to study potential TAI after concussion and assess optimal methods to analyze DTI at the individual level.

METHODS

Active American professional football players recruited prospectively were assessed with DTI, conventional MRI, and standard clinical workup. Subjects underwent an optional preseason baseline scan and were asked to undergo a scan within 5 days of concussion during gameplay. DTI from 25 age- and sex-matched controls were obtained. Both semiautomated region-of-interest analysis and fully automated tract-based spatial statistics (TBSS) were used to examine DTI at individual and group levels. Statistical differences were assessed comparing individual DTI data to baseline imaging versus a normative database. Group-level comparisons were also performed to determine if longer exposure to professional-level play or prior concussion cause white matter microstructural integrity changes.

RESULTS

Forty-nine active professional football players were recruited into the study. Of the 49 players, 7 were assessed at baseline during the preseason and after acute concussion. An additional 18 players were assessed after acute concussion only. An additional 24 players had only preseason baseline assessments. The results suggest DTI is more sensitive to suspected TAI than conventional MRI, given that 4 players demonstrated decreased fractional anisotropy (FA) in multiple tracts despite normal conventional MRI. Furthermore, the data suggest individual assessment of DTI data using baseline premorbid imaging is more sensitive than typical methods of comparing data to a normative control group. Among all subjects with baseline data, 1 reduced FA tract (± 2.5 standard deviations) was found using the typical normative database reference versus 10 statistically significant (p < 0.05) reduced FA tracts when referencing internal control baseline data. All group-level comparisons were statistically insignificant (p > 0.05).

CONCLUSIONS

Baseline premorbid DTI data for individual DTI analysis provides increased statistical sensitivity. Specificity using baseline imaging also increases because numerous potential etiologies for reduced FA may exist prior to a concussion. These data suggest that there is a high potential for false-positive and false-negative assessment of DTI data using typical methods of comparing an individual to normative groups given the variability of FA values in the normal population.