Biomedical subjects

Vincent J Schmithorst

Publications and source records attributed to Vincent J Schmithorst.

27 records · Page 2Linked to original sources

PubMed2004

Event-related fMRI technique for auditory processing with hemodynamics unrelated to acoustic gradient noise.

Acoustic noise from the imaging gradients presents a major difficulty in functional MRI (fMRI) studies of auditory cortical function. For studies involving hearing-impaired pediatric subjects, the auditory stimuli should be presented during completely silent gradient intervals. In addition, the scan time is limited by constraints involving subject motion and subject compliance. A novel event-related method for conducting fMRI studies of auditory function is proposed. Auditory stimuli are presented during completely silent gradient intervals, but using a variable TR. A general nonlinear model (GNLM) is proposed as a postprocessing methodology for the data. The technique increases the flexibility of the experimental design, with minimal loss of sensitivity compared to standard fMRI acquisition techniques, and may therefore be useful for fMRI studies of auditory function in hearing-impaired pediatric subjects.

Adult↗

PubMed2004

Empirical validation of the triple-code model of numerical processing for complex math operations using functional MRI and group Independent Component Analysis of the mental addition and subtraction of fractions.

The suitability of a previously hypothesized triple-code model of numerical processing, involving analog magnitude, auditory verbal, and visual Arabic codes of representation, was investigated for the complex mathematical task of the mental addition and subtraction of fractions. Functional magnetic resonance imaging (fMRI) data from 15 normal adult subjects were processed using exploratory group Independent Component Analysis (ICA). Separate task-related components were found with activation in bilateral inferior parietal, left perisylvian, and ventral occipitotemporal areas. These results support the hypothesized triple-code model corresponding to the activated regions found in the individual components and indicate that the triple-code model may be a suitable framework for analyzing the neuropsychological bases of the performance of complex mathematical tasks.

Adult↗

PubMed2004

High-resolution functional MRI at 3T in healthy and epilepsy subjects: hippocampal activation with picture encoding task.

Functional MRI (fMRI) studies of memory with coarse resolution of 4 x 4 x 5 mm often fail to demonstrate blood oxygenation level-dependent (BOLD) activation in the hippocampal formation. This failure occurs when nonactivating white matter is averaged with the signal from hippocampal gray matter, attenuating the total BOLD signal from a single voxel due to the "partial volume effect." In this study, we evaluated the suitability of high-resolution fMRI at 3T (voxel size 2 x 2 x 3 mm) for improved visualization of hippocampal activation during memory encoding in 21 healthy and 6 epilepsy subjects. We used a picture encoding task (block design) that involved memorization of indoor and outdoor scenes along with an appropriate resting task. Region-of-interest (ROI) analysis was performed; laterality indices (LIs) were calculated based on hippocampal ROIs (hROIs) or on global medial temporal ROIs (mtROIs). In 19 healthy subjects, robust bilateral BOLD signal changes within both ROIs were noted. The mean LI+/-SD for the hROIs is -0.12+/-0.06 and that for the medial temporal ROIs -0.12+/-0.05, with correlation between the LIs (r = 0.59, P = 0.009). Good concordance was noted between the surgical outcome and memory lateralization with the fMRI task employed in this study. The preliminary results are encouraging, and with continuing improvements in MRI scanner technology, we expect fMRI of the hippocampal formation at higher resolution to be possible and preferable. Furthermore, these results suggest that a larger study to test the utility of high-resolution fMRI in epilepsy presurgical evaluation is needed.

Adult↗

PubMed2003

The effect of musical training on music processing: a functional magnetic resonance imaging study in humans.

Previous studies have demonstrated changes in neuronal activity in trained musicians relative to controls while performing various music processing tasks. In this study the neural correlates of the effect of music training on two aspects of music processing, melody and harmony, are investigated using functional magnetic resonance imaging (fMRI). Fifteen subjects, seven with continuous musical training from early childhood to adulthood and eight without, underwent a passive fMRI listening paradigm designed to test the effects of melodic and harmonic processing. Melodic processing activated the most anterior part of the superior temporal gyrus for both musicians and non-musicians, while harmonic processing activated different visual association areas for musicians relative to non-musicians. The inferior parietal lobules were recruited only by musicians for both tasks. We conclude that musical training results in the recruitment of different neural networks for these aspects of music processing.

Acoustic Stimulation↗

PubMed2002

Differences in white matter architecture between musicians and non-musicians: a diffusion tensor imaging study.

Previous studies found structural brain differences between musicians and non-musicians. In order to determine possible differences in white matter architecture, diffusion tensor imaging was performed on five adult subjects with musical training since early childhood, and seven adult controls. The musicians displayed significantly greater fractional anisotropy (FA) in the genu of the corpus callosum, while significantly less FA was found in the corona radiata and the internal capsule bilaterally. Further areas also showed significant differences. We hypothesize that these changes are due to the cognitive and motor effects, respectively, of musical training.

Adult↗

PubMed2002

Assessment of spatial normalization of whole-brain magnetic resonance images in children.

Commonly used frameworks for spatial normalization of brain imaging data (e.g., Talairach-space) are based on one or more adult brains. As pediatric brains are different in size and shape from adult brains and continue to develop through childhood, we aimed to assess the influence of age on various spatial normalization parameters. One hundred forty-eight healthy children aged 5-18 years were included in this study. The linear scaling parameters and the deformations from the non-linear spatial normalization to both a standard adult and a custom pediatric template were analyzed within SPM99. The effect of using a brain mask on the linear and of using different levels of constraint on the non-linear spatial normalization was assessed. Of the linear scaling factors, only the X-dimension (left-right) showed a significant age-correlation when based on brain tissue, whereas the overall scaling was not correlated with age. When based on the whole head, a very strong age-effect can be found in all dimensions. Non-linear deformations also show localized correlations with age, most pronounced in parietal and frontal areas. The total amount of volume change is significantly lower when using a pediatric template. It is also substantially influenced by the degree of regularization that is exerted on the spatial normalization parameters. Our results suggest that in the cortical areas showing a strong correlation of deformation with age, caution should be used in assigning imaging results in children to a specific morphological structure. Also, to minimize the amount of deformation during non-linear spatial normalization, a pediatric template should be used. Further implications of our findings on developmental neuroimaging studies are discussed.

Adolescent↗

PubMed2002

Automatic gradient preemphasis adjustment: a 15-minute journey to improved diffusion-weighted echo-planar imaging.

Image distortion caused by gradient eddy currents is a major problem in the use of diffusion tensor imaging (DTI), as using the uncorrected images for calculation of apparent diffusion coefficient (ADC) and diffusion anisotropy will result in areas of artificially increased anisotropy and ADC at the edge of the images, as well as decreased spatial resolution and accuracy in ADC computations overall. This distortion may be substantially reduced by careful adjustment of the gradient preemphasis unit. A completely automatic method of adjusting the preemphasis unit is proposed which finds the optimal settings for all three gradient directions in approximately 15 min by estimating the magnitudes of the eddy currents at various delay times after a test gradient. The pixel shifts in a 64 x 128 echo-planar diffusion-weighted image with a diffusion gradient strength of 30 mT/m were reduced to less than 0.2.

Calibration↗

PubMed2002

Correlation of white matter diffusivity and anisotropy with age during childhood and adolescence: a cross-sectional diffusion-tensor MR imaging study.

PURPOSE: To evaluate differences in white matter diffusion properties as a function of age in healthy children and adolescents. MATERIALS AND METHODS: Echo-planar diffusion-tensor magnetic resonance (MR) imaging was performed in 33 healthy subjects aged 5-18 years who were recruited from a functional imaging study of normal language development. Results of neurologic, psychologic, and structural MR imaging examinations were within the normal range for all subjects. The trace of the apparent diffusion coefficient and fractional anisotropy in white matter were correlated as a function of age by using Spearman rank correlation. RESULTS: Statistically significant negative correlation of the trace of the apparent diffusion coefficient with age was found throughout the white matter. Significant positive correlation of fractional anisotropy with age was found in the internal capsule, corticospinal tract, left arcuate fasciculus, and right inferior longitudinal fasciculus. CONCLUSION: Diffusion-tensor MR imaging results indicate that white matter maturation assessed at different ages involves increases in both white matter density and organization during childhood and adolescence. The trace of the apparent diffusion coefficient and fractional anisotropy may reflect different physiologic processes in healthy children and adolescents.

Adolescent↗

PubMed2002

Mapping T2 relaxation time in the pediatric knee: feasibility with a clinical 1.5-T MR imaging system.

PURPOSE: To determine the feasibility of mapping the spatial variation of cartilage T2 relaxation time in vivo in the pediatric knee with a 1.5-T clinical magnetic resonance (MR) imaging system and the manufacturer's body gradient coil. MATERIALS AND METHODS: Twenty-five children and adolescents (age range, 5-17 years; mean age, 11.8 years) underwent a multisection-multiecho MR sequence for T2 relaxation time mapping. Quantitative transverse T2 maps of the patellar cartilage were calculated for 15 of the subjects. Sagittal T2 maps were calculated for the remaining 10 subjects. T2 profiles were generated for the patellar and distal femoral weight- and non-weight-bearing unossified epiphyseal and articular hyaline cartilage and for the distal femoral and proximal tibial physes. The Mann-Whitney U test was used to test for differences between paired profiles. RESULTS: Femoral non-weight-bearing unossified epiphyseal and articular cartilage showed spatial variation similar to that of weight-bearing unossified epiphyseal and articular cartilage, but with increased T2 values (P <.001). T2 spatial variations of the distal femoral and proximal tibial physes were similar to those of epiphyseal and articular cartilage but had a different pattern and increased magnitude (P <.001). The highest T2 values were measured in the distal femoral physis. CONCLUSION: T2 spatial variation of patellar hyaline cartilage in children is similar to that of patellar articular cartilage in adults. Mapping of spatial variation of T2 relaxation time of cartilage in the pediatric knee in vivo is feasible with a clinical 1.5-T MR imaging system and a body gradient coil.

Adolescent↗