Torgil Vangberg

Changes in white matter diffusion anisotropy in adolescents born prematurely

Being born with very low birth weight (VLBW, birth weight<or=1500 g) or small for gestational age (SGA) carries an increased risk of cerebral white matter damage. The reduced cognitive and motor skills these two groups exhibit suggest that the early injuries to white matter persist into adolescence. White matter integrity was assessed using voxel-wise statistical analysis of fractional anisotropy (FA) maps between three groups of adolescents at age 15; the VLBW group (n=34), the SGA group (n=42) and a control group with normal birth weight (n=47). The FA maps were normalized to a study specific template and group differences were assessed using an analysis of covariance with gender as a confounder (FDR-corrected P<0.05). The main finding is that the VLBW group has significantly reduced FA values in several white matter regions, including the corpus callosum, internal capsule and superior fasciculus compared to the control group. Some of the observed reduction in anisotropy, particularly that observed in the corpus callosum, may have been caused by inaccurate spatial normalization, but this can only explain 30% of the area with reduced anisotropy. Analysis of the eigenvalues of the diffusion tensor show that the reduced FA values in the VLBW group is primarily due to an increase in the two lowest eigenvalues of the diffusion tensor. We speculate that this may be caused by reduced myelination. For the SGA group, we find no statistically significant differences in anisotropy compared to the control group.

Segmental brain volumes and cognitive and perceptual correlates in 15-year-old adolescents with low birth weight.

OBJECTIVE To determine whether preterm very low birth weight (VLBW) or term born small for gestational age (SGA) adolescents have reduced regional brain volumes. We also asked which perinatal factors are related to reduced brain volume in VLBW adolescents, which regional brain volumes are associated with cognitive and perceptual functioning, and if these differ between the groups. STUDY DESIGN Fifty adolescent preterm VLBW (< or =1500 g) births and 49 term SGA births (birth weight <10th percentile) were compared with 57 normal-weight term births. An automated MRI segmentation technique was used. Cognitive and perceptual functions were evaluated by WISC-III and Visual Motor Integration (VMI) tests. RESULTS The VLBW group had reduced volumes for thalamus and cerebellar white matter (P < .002). The SGA group had smaller total brains, and proportionally smaller regional brain volumes. Cerebellar white matter in the VLBW, hippocampus in the SGA, and cerebral cortical in the control group were volumes that significantly predicted cognitive and perceptual functions. CONCLUSIONS We speculate that white matter injury may explain the impaired cognitive and perceptual functioning in the prematurely born, whereas hippocampal injury may be related to cognitive dysfunction in term SGA adolescents.

Motor Network Changes Associated With Successful Motor Skill Relearning After Acute Ischemic Stroke : A Longitudinal Functional Magnetic Resonance Imaging Study

Background. Motor learning mechanisms may be operative in stroke recovery and possibly reinforced by rehabilitative training. Objectives. To assess early motor network changes after acute ischemic stroke in patients treated with very early mobilization and task-oriented physical therapy in a comprehensive stroke unit, to investigate the association between neuronal activity and improvements in hand function, and to qualitatively explore the changes in neuronal activity in relation to motor learning. Methods. Patients were assessed by functional magnetic resonance imaging and by clinical tests within the first week after stroke and 3 months later. After discharge, all participants were offered functional training of the affected arm according to individual needs. Results. A total of 359 patients were screened, with 12 patients experiencing first-ever stroke, excluding primary sensorimotor cortex (MISI), with severe to moderately impaired hand function fulfilling the inclusion criteria. Laterality indexes (LIs) for MISI increase significantly during follow-up. There is increased cerebellar and striatal activation acutely, replaced by increased activation of ipsilesional MISI in the chronic phase. Bilateral somatosensory association areas and contralesional secondary somatosensory cortex (SII) area are also more active in the chronic phase. Activation of the latter region also correlates positively with improved hand function. Conclusions. Restoration of hand function is associated with highly lateralized MISI. Activity in bilateral somatosensory association area and contralesional SII may represent cortical plasticity involved in successful motor recovery. The changes in motor activity between acute and chronic phases seem to correspond to a motor learning process.

White matter abnormalities and executive function in children with very low birth weight

The aim of this study was to investigate any structural–functional relationship between changes in white matter microstructure seen on diffusion tensor imaging and results of an executive function test in adolescents with very low birth weight (VLBW). Thirty-four VLBW adolescents were examined at 15 years of age. Executive function was assessed by the Wisconsin Card Sorting Test. Diffusion tensor imaging scans were performed at 1.5 T for calculation of individual fractional anisotropy maps. Through a voxel-wise regression analysis, correlations were found between the results on Wisconsin Card Sorting Test and fractional anisotropy values in the left cingulum and both inferior fronto-occipital fascicles. We speculate that impairments in executive function in VLBW children may be influenced by disturbed connectivity between posterior brain regions and the prefrontal cortex.

Deformability of Fe(II)CO and Fe(III)CN groups in heme protein models: nonlocal density functional theory calculations

Abstract High-quality nonlocal density functional calculations have been carried out on the deformability of Fe(II)CO and Fe(III)CN units in model compounds of heme proteins. The results confirm our previous finding with a local functional that the Fe(II)CO unit is significantly deformable with respect to tilting and bending. This deformability stems in large part from a large, negative interaction constant between the FeC tilt and FeCO bend coordinates. The Fe(III)CN unit is also significantly deformable, but in this case the deformability results from a very small Fe(III)CN bend force constant and the ability of the cyano nitrogen to act as a hydrogen bond acceptor. The prediction that the energetic penalty associated with deforming the Fe(II)CO unit is relatively modest indicates that such deformations are unlikely to be the dominant contributor to myoglobins discrimation against CO in favor of O2.

How Does the Accuracy of Intracranial Volume Measurements Affect Normalized Brain Volumes? Sample Size Estimates Based on 966 Subjects from the HUNT MRI Cohort

BACKGROUND AND PURPOSE: The intracranial volume is commonly used for correcting regional brain volume measurements for variations in head size. Accurate intracranial volume measurements are important because errors will be propagated to the corrected regional brain volume measurements, possibly leading to biased data or decreased power. Our aims were to describe a fully automatic SPM-based method for estimating the intracranial volume and to explore the practical implications of different methods for obtaining the intracranial volume and normalization methods on statistical power. MATERIALS AND METHODS: We describe a method for calculating the intracranial volume that can use either T1-weighted or both T1- and T2-weighted MR images. The accuracy of the method was compared with manual measurements and automatic estimates by FreeSurfer and SPM-based methods. Sample size calculations on intracranial volume–corrected regional brain volumes with intracranial volume estimates from FreeSurfer, SPM, and our proposed method were used to explore the benefits of accurate intracranial volume estimates. RESULTS: The proposed method for estimating the intracranial volume compared favorably with the other methods evaluated here, with mean and absolute differences in manual measurements of −0.1% and 2.2%, respectively, and an intraclass correlation coefficient of 0.97 when using T1-weighted images. Using both T1- and T2-weighted images for estimating the intracranial volume slightly improved the accuracy. Sample size calculations showed that both the accuracy of intracranial volume estimates and the method for correcting the regional volume measurements affected the sample size. CONCLUSIONS: Accurate intracranial volume estimates are most important for ratio-corrected regional brain volumes, for which our proposed method can provide increased power in intracranial volume–corrected regional brain volume data.

An apparent unidirectional influx constant for manganese as a measure of myocardial calcium channel activity

To develop an in vivo MR method for evaluation of myocardial calcium channel activity through quantification of apparent unidirectional manganese influx constants following manganese dipyridoxyl‐diphosphate (MnDPDP) infusions.

Visual function and white matter microstructure in very-low-birth-weight (VLBW) adolescents - A DTI study

Premature birth is associated with visual impairments, due to both cerebral and ocular pathology. This study examined the relationship between cerebral white matter microstructure, evaluated by diffusion tensor imaging (DTI), and visual function, in 30 preterm born adolescents with very low birth weight (VLBW=birth weight⩽1500g) and an age-matched group of 45 term born controls. Visual acuity correlated positively with fractional anisotropy (FA) in corpus callosum and in frontal white matter areas in the VLBW participants, but not in the control participants. Callosal visual connections may play a more important role in the development of good visual acuity than previously acknowledged in preterm born children.

Relaxation enhancing properties of MnDPDP in human myocardium.

To assess magnitude and duration of changes in myocardial longitudinal relaxation rate (R1) in humans following infusion of the manganese (Mn) releasing contrast agent MnDPDP (Mn‐dipyridoxyl‐diphosphate).

Valence ionization potentials and cation radicals of prototype porphyrins. The remarkable performance of nonlocal density functional theory

Abstract. Nonlocal density functional theory (NLDFT) has been used to calculate the lower ionized states of the free-base forms of porphin, bacteriochlorin, and porphyrazine and also zinc porphin. For porphin, the calculated vertical ionization potentials (IPs) quantitatively reproduce the low-energy end of the experimental gas-phase ultraviolet photoelectron spectrum, which suggests that NLDFT could be an exceptionally useful tool for studying IPs and cation radical states of a variety of porphyrinic materials.