Attila Schwarcz

The existence of biexponential signal decay in magnetic resonance diffusion-weighted imaging appears to be independent of compartmentalization.

It is generally believed that the apparent diffusion coefficient (ADC) changes measured by diffusion‐weighted imaging (DWI) in brain pathologies are related to alterations in the water compartments. The aim of this study was to elucidate the role of compartmentalization in DWI via biexponential analysis of the signal decay due to diffusion. DWI experiments were performed on mouse brain over an extended range of b‐values (up to 10000 mm–2 s) under intact, global ischemic, and cold‐injury conditions. DWI was additionally applied to centrifuged human erythrocyte samples with a negligible extracellular space. Biexponential signal decay was found to occur in the cortex of the intact mouse brain. During global ischemia, in addition to a drop in the ADC in both components, a shift from the volume fraction of the rapidly diffusing component to the slowly diffusing one was observed. In cold injury, the biexponential signal decay was still present despite the electron‐microscopically validated disintegration of the membranes. The biexponential function was also applicable for fitting of the data obtained on erythrocyte samples. The results suggest that compartmentalization is not an essential feature of biexponential decay in diffusion experiments. Magn Reson Med 51:278–285, 2004.

Multi-Modal Magnetic Resonance Imaging in the Acute and Sub-Acute Phase of Mild Traumatic Brain Injury: Can We See the Difference?

Advanced magnetic resonance imaging (MRI) methods were shown to be able to detect the subtle structural consequences of mild traumatic brain injury (mTBI). The objective of this study was to investigate the acute structural alterations and recovery after mTBI, using diffusion tensor imaging (DTI) to reveal axonal pathology, volumetric analysis, and susceptibility weighted imaging (SWI) to detect microhemorrhage. Fourteen patients with mTBI who had computed tomography with negative results underwent MRI within 3 days and 1 month after injury. High resolution T1-weighted imaging, DTI, and SWI, were performed at both time points. A control group of 14 matched volunteers were also examined following the same imaging protocol and time interval. Tract-Based Spatial Statistics (TBSS) were performed on DTI data to reveal group differences. T1-weighted images were fed into Freesurfer volumetric analysis. TBSS showed fractional anisotropy (FA) to be significantly (corrected p<0.05) lower, and mean diffusivity (MD) to be higher in the mTBI group in several white matter tracts (FA=40,737; MD=39,078 voxels) compared with controls at 72 hours after injury and still 1month later for FA. Longitudinal analysis revealed significant change (i.e., normalization) of FA and MD over 1 month dominantly in the left hemisphere (FA=3408; MD=7450 voxels). A significant (p<0.05) decrease in cortical volumes (mean 1%) and increase in ventricular volumes (mean 3.4%) appeared at 1 month after injury in the mTBI group. SWI did not reveal microhemorrhage in our patients. Our findings present dynamic micro- and macrostructural changes occurring in the acute to sub-acute phase in mTBI, in very mildly injured patients lacking microhemorrhage detectable by SWI. These results underscore the importance of strictly defined image acquisition time points when performing MRI studies on patients with mTBI.

Effect of PACAP in Central and Peripheral Nerve Injuries

Pituitary adenylate cyclase activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. In addition to its more classic role as a neuromodulator, PACAP functions as a neurotrophic factor. Several neurotrophic factors have been shown to play an important role in the endogenous response following both cerebral ischemia and traumatic brain injury and to be effective when given exogenously. A number of studies have shown the neuroprotective effect of PACAP in different models of ischemia, neurodegenerative diseases and retinal degeneration. The aim of this review is to summarize the findings on the neuroprotective potential of PACAP in models of different traumatic nerve injuries. Expression of endogenous PACAP and its specific PAC1 receptor is elevated in different parts of the central and peripheral nervous system after traumatic injuries. Some experiments demonstrate the protective effect of exogenous PACAP treatment in different traumatic brain injury models, in facial nerve and optic nerve trauma. The upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central and peripheral nerve injuries show the important function of PACAP in neuronal regeneration indicating that PACAP may also be a promising therapeutic agent in injuries of the nervous system.

In vivo brain edema classification: New insight offered by large b-value diffusion-weighted MR imaging

To assess the role of large b‐value diffusion weighted imaging (DWI) in the characterization of the physicochemical properties of the water in brain edema under experimental and clinical conditions.

History of simple febrile seizures is associated with hippocampal abnormalities in adults

Background: It is unclear whether the hippocampal abnormality in temporal lobe epilepsy (TLE) is a consequence or the cause of afebrile or febrile seizures (FSs). We investigated whether hippocampal abnormalities are present in healthy adults > 15 years after a simple FS.

Gustatory perception alterations in obesity: An fMRI study

The background of feeding associated and metabolic diseases is not sufficiently understood yet. Since gustatory alterations may be of particular significance in the above illnesses, in the present experiments, cerebral activation was detected by fMRI in twelve obese patients and twelve, age and gender matched healthy subjects. The gustatory stimulus solutions were delivered via intraorally positioned polyvinyl tubes. Each session consisted of three runs. Sucrose was used as a pleasant; quinine HCl as an aversive; and a high-calorie, vanilla flavored nourishment solution as a complex taste of high palatability. In each run, only one taste was used as a stimulus. During all runs, distilled water served as a neutral stimulus. Group analysis was made by using the FSL software package. The taste stimuli elicited characteristic and distinct activity changes of the two groups. In contrast to the controls, in the obese patients, stronger activation was detected in various cortical (anterior cingulate cortex, insular and opercular cortices, orbitofrontal cortex) and subcortical (amygdala, nucleus accumbens, putamen and pallidum) structures in case of all three stimuli. The present examinations elucidated differential activation of various brain structures to pleasant and unpleasant gustatory stimuli in obese patients compared to control subjects. These taste alterations are supposed to be of particular significance in obesity, and our findings may contribute to develop better strategies for prevention and effective therapies in the future.

Are there any gender differences in the hippocampus volume after head-size correction? A volumetric and voxel-based morphometric study

Previous findings on normal sexual dimorphism in hippocampal volume have not always been consistent. This study investigated gender differences in hippocampal volume using different head-size correction strategies. T1-weighted MR images were collected in 99 healthy, Caucasian, university students (66 female subjects; mean age: 23.1 ± 2.3, range: 19-31 years). Sexual dimorphism in hippocampus was investigated by automated MRI volumetry and voxel-based morphometry (VBM) using both general linear model (GLM) and proportion head-size correction strategies. Absolute hippocampal volumes were larger in men than women. After adjusting for head-size, the proportion method indicated larger hippocampi in women than men, while no gender differences were found using the GLM approach. Investigating absolute hippocampal volumes in 15 head-size matched pairs of males and females indicated no gender differences. We suggest that there is no sexual dimorphism in hippocampal size and the apparent gender differences found by the proportion method may have more to do with head-size than with sex. The GLM and proportion head-size correction strategies are not interchangeable and may yield different results. The importance of the present findings is mostly related to scientific reproducibility across MRI volumetry or VBM studies.

Changes of Migraine‐Related White Matter Hyperintensities After 3 Years: A Longitudinal MRI Study

The aim of this longitudinal study was to investigate changes of migraine‐related brain white matter hyperintensities 3 years after an initial study. Baseline quantitative magnetic resonance imaging (MRI) studies of migraine patients with hemispheric white matter hyperintensities performed in 2009 demonstrated signs of tissue damage within the hyperintensities. The hyperintensities appeared most frequently in the deep white matter of the frontal lobe with a similar average hyperintensity size in all hemispheric lobes. Since in this patient group the repeated migraine attacks were the only known risk factors for the development of white matter hyperintensities, the remeasurements of migraineurs after a 3‐year long follow‐up may show changes in the status of these structural abnormalities as the effects of the repeated headaches.

Does obstetric brachial plexus injury influence speech dominance

Right‐handedness and left‐sided language lateralization is an unresolved mystery with unknown cause/effect relations. Most studies suggest that the language lateralization is related to a fundamental brain asymmetry: right‐handedness may be secondary. We analyzed the possibility of an opposite cause/effect relation: whether asymmetric hand usage (as a cause) can influence language lateralization (as a consequence).

Quantitative MRI studies of chronic brain white matter hyperintensities in migraine patients.

The aim of this study was to examine chronic brain white matter hyperintensities in migraine and to gain data on the characteristics of the lesions.