Reversible, reproducible reduction of brain water apparent diffusion coefficient by cortical electroshocks (original) (raw)
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AJNR. American journal of neuroradiology
Diffusion-weighted MR imaging has emerged as a noninvasive tool for the detection of regional neuronal damage. We hypothesize that changes in diffusion-weighted images will correlate with pathophysiologic alterations caused by pilocarpine-induced status epilepticus. MR images of brain tissues were examined in vivo by use of T2- and diffusion-weighted imaging at 3, 6, 12, and 24 hours after pilocarpine-induced seizures. Histologic verification of neuronal damage was also performed after imaging to assess the extent and the time course of neuronal cell death. The piriform cortex, amygdala, and retrosplenial (and somatosensory) cortex displayed significant apparent diffusion coefficient (ADC) decreases 12 hours after seizure initiation. In contrast, an ADC rise of 19% was observed in the hippocampus 24 hours after seizure induction. Histologic data from the piriform cortex and amygdala confirmed severe neuronal loss, whereas hippocampal damage was much less pronounced at 12 hours. Inte...
Transient decrease in water diffusion observed in human occipital cortex during visual stimulation
Proceedings of the National Academy of Sciences, 2001
Using MRI, we report the observation of a transient decrease of the apparent diffusion coefficient (ADC) of water in the human brain visual cortex during activation by a black and white 8-Hz-flickering checkerboard. The ADC decrease was small (<1%), but significant and reproducible, and closely followed the time course of the activation paradigm. Based on the known sensitivity of diffusion MRI to cell size in tissues and on optical imaging studies that have revealed changes in the shape of neurons and glial cells during activation, the observed ADC findings have been tentatively ascribed to a transient swelling of cortical cells. These preliminary results suggest a new approach to produce images of brain activation with MRI from signals directly associated with neuronal activation, and not through changes in local blood flow.
Temporal trajectory of brain tissue property changes induced by electroconvulsive therapy
NeuroImage, 2021
Background: After more than eight decades of electroconvulsive therapy (ECT) for pharmaco-resistant depression, the mechanisms governing its anti-depressant effects remain poorly understood. Computational anatomy studies using longitudinal T1-weighted magnetic resonance imaging (MRI) data have demonstrated ECT effects on hippocampus volume and cortical thickness, but they lack the interpretational specificity about underlying neurobiological processes. Methods: We sought to fill in the gap of knowledge by acquiring quantitative MRI indicative for brain's myelin, iron and tissue water content at multiple time-points before, during and after ECT treatment. We adapted established tools for longitudinal spatial registration of MRI data to the relaxometry-based multi-parameter maps aiming to preserve the initial total signal amount and introduced a dedicated multivariate analytical framework. Results: The whole-brain voxel-based analysis based on a multivariate general linear model showed that there is no brain tissue oedema contributing to the predicted ECT-induced hippocampus volume increase neither in the short, nor in the long-term observations. Improvements in depression symptom severity over time were associated with changes in both volume estimates and brain tissue properties expanding beyond mesial temporal lobe structures to anterior cingulate cortex, precuneus and striatum. Conclusion: The obtained results stemming from multi-contrast MRI quantitative data provided a fingerprint of ECT-induced brain tissue changes over time that are contrasted against the background of established morphometry findings. The introduced data processing and statistical testing algorithms provided a reliable analytical framework for longitudinal multi-parameter brain maps. The results, particularly the evidence of lack of ECT impact on brain tissue water, should be considered preliminary considering the small sample size of the study.
Water diffusion in brain cortex closely tracks underlying neuronal activity
Proceedings of the National Academy of Sciences, 2013
Neuronal activity results in a local increase in blood flow. This concept serves as the basis for functional MRI. Still, this approach remains indirect and may fail in situations interfering with the neurovascular coupling mechanisms (drugs, anesthesia). Here we establish that water molecular diffusion is directly modulated by underlying neuronal activity using a rat forepaw stimulation model under different conditions of neuronal stimulation and neurovascular coupling. Under nitroprusside infusion, a neurovascular-coupling inhibitor, the diffusion response and local field potentials were maintained, whereas the hemodynamic response was abolished. As diffusion MRI reflects interactions of water molecules with obstacles (e.g., cell membranes), the observed changes point to a dynamic modulation of the neural tissue structure upon activation, which remains to be investigated. These findings represent a significant shift in concept from the current electrochemical and neurovascular coupling principles used for brain imaging, and open unique avenues to investigate mechanisms underlying brain function.
Dynamic effects of point source electroporation on the rat brain tissue
Bioelectrochemistry, 2014
Keywords: Blood brain barrier Electroporation Brain Tumor MRI In spite of aggressive therapy, existing treatments offer poor prognosis for glioblastoma multiforme due to tumor infiltration into the surrounding brain as well as poor blood-brain barrier penetration of most therapeutic agents. In this paper we present a novel approach for a minimally invasive treatment and a non-invasive response assessment methodology consisting of applying intracranial point-source electroporation and assessing treatment effect volumes using magnetic resonance imaging. Using a unique setup of a single intracranial electrode and an external surface electrode we treated rats' brains with various electroporation protocols and applied magnetic resonance imaging to study the dependence of the physiological effects on electroporation treatment parameters. The extent of blood-brain barrier disruption and later volumes of permanent brain tissue damage were found to correlate significantly with the treatment voltages (r 2 = 0.99, p b 0.001) and the number of treatment pulses (r 2 = 0.94, p b 0.002). Blood-brain barrier disruption depicted 3.2 ± 0.3 times larger volumes than the final permanent damage volumes (p b 0.0001). These results indicate that it may be beneficial to use more than one modality of electroporation when planning a treatment for brain tumors.
Detection of apparent restricted diffusion in healthy rat brain at short diffusion times
Magnetic Resonance in Medicine, 1994
The application of bipolar diffusion sensitizing gradient pulses to significantly reduce the diffusion time is described. This approach is combined with the rapid U-FLARE imaging sequence. Three diffusion-sensitized types of experiments are compared and their suitability for detecting restricted diffusion is discussed. Experiments using a modification of the diffusion weighting by varying the diffusion time between 1.6 and 6.0 ms obtained nonmonoexponential signal attenuation curves from both healthy brains and postmortem. This behavior is indicative of restricted diffusion, but as it is detectable only at short diffusion times, in contrast to a restriction due to impermeable barriers, we have termed this "apparent restriction." Key words: magnetic resonance imaging; water diffusion; apparent restriction; rat brain.
Epilepsia, 2013
Purpose: Microstructural alterations seen in the epileptic cortex have been implicated as a cause and also result of multiple seizure activity. In the present study, we evaluated water diffusion changes at different cortical thickness fractions and in the underlying white matter of the epileptic cortex and compared them with electrographically normal cortex and also with corresponding cortical regions of healthy controls. Methods: We selected 18 children with normal magnetic resonance imaging (MRI) who underwent two-stage epilepsy surgery to control seizures of neocortical origin, and compared their MR images with those of 18 age-matched healthy controls. First, delineation of the gray-white and gray-pial intersection surfaces was performed on high-resolution volumetric T1 MR images. Using the delineated surfaces as reference, diffusion values were measured at different cortical thickness fractions and in the underlying white matter at various depths, using diffusion tensor imaging (DTI). Cortical regions representing seizure onset and electrographically normal cortex were differentiated by electrocorticography in the epilepsy patients. Key Findings: We observed different patterns of diffusion abnormalities in both the seizure onset and electrographically normal cortical regions when compared to healthy controls. In the seizure-onset regions, a marked increase in diffusivity was noted in the cortical gray matter, and this increase was most pronounced in the outer fraction of the gray matter. Similarly, increased diffusivity was noted in the white matter underlying the epileptic cortex. The electrographically normal cortex, in contrast, showed decreased diffusivity in inner and middle cortical fractions compared to the controls. The white matter underlying the electrographically normal cortex did not show any difference in diffusivity between the children with epilepsy and controls. Finally, both the cortical gray matter and the underlying white matter regions showed decreased anisotropy in epileptic as well as electrographically normal regions when compared to controls. Significance: Our results suggest specific patterns of diffusion changes in the cortical fractions and the underlying white matter of the epileptic region compared to electrographically normal and normal control regions. The abnormal increase in diffusivity of the superficial cortex might be associated with microstructural abnormalities commonly seen in layers II through IV of epileptic cortex. Such combined use of a high-resolution structural image to extract the laminar diffusion values, which are highly sensitive to microstructural alterations, could be of clinical value in localizing epileptogenic cortex.