Dataset Information

Frequency difference mapping applied to the corpus callosum at 7T.

ABSTRACT:

Purpose

Frequency difference mapping (FDM) is a phase processing technique which characterizes the nonlinear temporal evolution of the phase of gradient echo (GE) signals. Here, a novel FDM-processing algorithm is introduced, which is shown to reveal information about white matter microstructure. Unlike some other phase-processing techniques, the FDM algorithm presented here does not require the use of phase unwrapping or sophisticated image processing. It uses a series of scaled complex divisions to unwrap phase and remove background fields.

Methods

Ten healthy subjects underwent a series of single-slice, sagittal multi-echo GE scans at 7T with the slice positioned at the midline. Phase data were processed with the novel FDM algorithm, and the temporal evolution of the magnitude signal and frequency difference was examined in 5 regions of the corpus callosum (CC; genu, anterior body, middle body, posterior body, and splenium).

Results

Consistent frequency difference contrast relative to surrounding tissue was observed in all subjects in the CC and in other white matter regions where the nerve fibers run perpendicular to B0 , such as the superior cerebellar peduncle. Examination of the frequency difference curves shows distinct variations over the CC, with the genu and splenium displaying larger frequency differences than the other regions (in addition to a faster decay of signal magnitude).

Conclusion

The novel FDM algorithm presented here yields images sensitive to tissue microstructure and microstructural differences over the CC in a simple manner, without the requirement for phase unwrapping or sophisticated image processing.

SUBMITTER: Tendler BC

PROVIDER: S-EPMC6492142 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Publications

Frequency difference mapping applied to the corpus callosum at 7T.

Tendler Benjamin C BC Bowtell Richard R

Magnetic resonance in medicine 20181223 5

<h4>Purpose</h4>Frequency difference mapping (FDM) is a phase processing technique which characterizes the nonlinear temporal evolution of the phase of gradient echo (GE) signals. Here, a novel FDM-processing algorithm is introduced, which is shown to reveal information about white matter microstructure. Unlike some other phase-processing techniques, the FDM algorithm presented here does not require the use of phase unwrapping or sophisticated image processing. It uses a series of scaled complex ...[more]

PMID: 30582226

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Project description:The Corpus Callosum (CC) is an important structure that includes the majority of fibers connecting the two brain hemispheres. Several neurodegenerative diseases may alter CC size and morphology leading to its atrophy and malfunction which may play a role in the pathological manifestations found in these diseases. The purpose of the current study is to determine any possible changes in CC size in patients suffering from Alzheimer's disease. The Study also investigated the effect of acetylcholinesterase inhibitors (AChEIs) on the size of CC and its association with improvement in the Alzheimer disease severity scores. Midsagittal size of CC were recorded prospectively from 439 routine T1-weighted MRI brain images in normal individuals. The internal skull surface was measured to calculate CC/ internal skull surface ratio. Two groups of patients were studied: 300 (150 male / 150 female) were healthy subjects and 130 (55 males / 75 females) had Alzheimer disease. Out of the 130 Alzheimer disease pateints, 70 patients were treated with Donepezil or Rivastigmine or both. The size of the CC was measured based on T1-weighted MRI images after the treatment to investigate any possible improvement in CC size. The mean surface area of CC in controls was 6.53±1.105 cm2. There was no significant difference between males and females (P < 0.627), and CC/ internal skull surface ratio was 4.41±0.77%. Patients with mild or severe Alzheimer disease showed a significant reduction in CC size compared to healthy controls. Treating mild Alzheimer patients with either Donepezil or Rivastigmine exerts a comparable therapeutic effect in improving the CC size. There was more improvement in the size of CC in patients with severe Alzheimer disease by using combined therapy of Donepezil and Rivastigmine than using single a medication. we measured the mean size of the various portions of the corpus callosum in normal individuals and Alzheimer patients before and after taking Donepezil and Rivastigmine. Alzheimer patients have pronounced reduction in CC which is corrected after taking Donepezil and Rivastigmine leading to remarkable improvement in Alzheimer disease severity scores.

Project description:ObjectiveLow-frequency fiber-tract stimulation has been shown to be effective in treating mesial temporal lobe epilepsies through activation of the hippocampal commissure in rodents and human patients. The corpus callosum is a major pathway connecting the two hemispheres of the brain; however, few experiments have documented corpus callosum stimulation. The objective is to determine the efficacy of corpus callosum stimulation at low frequencies to suppress cortical seizures.Methods4-Aminopyridine was injected in the primary motor cortex of 24 rats under anesthesia. Recording electrodes were placed in the contralateral motor cortex and hippocampus. Three pairs of stimulating electrodes were inserted into the corpus callosum along its longitudinal axis. Local field potentials were recorded 1 hour before, during, and after stimulation to determine the effect of stimulation on seizure duration. Stimulation was delivered from each pair of electrodes independently in separate experiments. Furthermore, electrical stimulation was applied to the region of the corpus callosum with the highest degree of innervation of the seizure focus to compare the efficacy of different stimulation frequencies (1-30 Hz) on seizure suppression.ResultsCorpus callosum stimulation was effective at suppressing seizures at 10 Hz by 76% (P < 0.05, n = 5) and at 20 Hz by 95% (P < 0.0001, n = 14). Stimulation at frequencies of 1 and 30 Hz did not have a significant effect on reducing the total time spent seizing (P > 0.9999, n = 5). Furthermore, stimulation was only effective at suppressing seizures when the pair of electrodes was placed within the section of corpus callosum containing fibers innervating the seizure focus. Secondarily generalized seizures in the hippocampus were eliminated when seizures in the cortical focus were suppressed.SignificanceLow-frequency fiber-tract stimulation of the corpus callosum suppresses both cortical and cortically induced hippocampal seizures in an acute model of focal cortical seizures. The stimulation paradigm is selective, as it is only effective when targeted to specific regions of the corpus callosum that project maximally to cortical regions generating the seizure activity. Selective placement of stimulation electrodes along the corpus callosum could be used as a patient-specific treatment for cortical epilepsies.

Dataset Information

Frequency difference mapping applied to the corpus callosum at 7T.

Purpose

Methods

Results

Conclusion

Publications

Frequency difference mapping applied to the corpus callosum at 7T.

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