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David Bonekamp

Publications and source records attributed to David Bonekamp.

6 recordsLinked to original sources
PubMed2006

Diffusion tensor imaging in children and adolescents: reproducibility, hemispheric, and age-related differences.

UNLABELLED: We evaluated intra-rater, inter-rater, and between-scan reproducibility, hemispheric differences, and the effect of age on apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in healthy children (age range 5.5-19.1 years) examined with a clinical diffusion tensor imaging (DTI) protocol at 1.5 T, using a region of interest (ROI) methodology. Measures of reliability and precision were assessed in six ROIs using two different ROI shapes (polygonal and ellipsoidal). RESULTS: Highly reproducible values of ADC and FA were obtained with the polygonal method on intra-rater (coefficients of variation<or=2.7%) and inter-rater (coefficients of variation<or=4.8%) reproducibility. For between-scan reproducibility, the coefficients of variation were <or=5.0%. Mean asymmetry indices were in the range from -4% to 9% for FA and from -6% to 3% for ADC. ADC showed significant negative correlation with age in 13 of 15 examined fiber tracts and FA increased significantly in three fiber tracts. Our results show that the evaluated DTI protocol is suitable for clinical application in pediatric population.

Adolescent↗
PubMed2006

Morphometric and psychometric comparisons between non-substance-abusing patients with posttraumatic stress disorder and normal controls.

BACKGROUND: Hippocampal decrease in size in response to posttraumatic stress disorder (PTSD) is still a subject of controversy. The aims of this study were to: (1) confirm previous hippocampus findings in PTSD patients compared to controls, using ethnically similar study groups where alcohol and drug abuse were non-existent; (2) test influence of disease duration as well as depression scores on possible morphological changes; (3) test whether the voxel-based morphometry (VBM) data confirm the group differences seen in the region of interest (ROI) analysis, and (4) test the associations between the cognitive test scores and the morphological changes. METHODS: VBM and ROI-based analysis were applied in 23 patients and 17 healthy controls. Culture-neutral cognitive tests were used. RESULTS: The ROI-based method showed significantly decreased gray matter volumes for global hippocampal volume, as in a separate analysis of left and right sides in the PTSD group. Total volume of the hippocampus was significantly decreased on the left side, as in the global assessment. A multiple regression VBM model showed significant voxel clusters for group affiliation in the right hippocampus, modelling lowering of gray matter associated with the PTSD group. Disease duration was shown to be negatively correlated to bilateral hippocampal volume and high depression score to bilateral gray matter parahippocampal volume. No significant correlations were found between hippocampal or parahippocampal volumes and cognitive functions. CONCLUSION: The present and previous studies showed that morphologic differences do not appear to be due to drug or alcohol abuse. The VBM data partially confirm the group differences seen in the ROI-based method in the medial temporal lobe. The fact that the significantly lower score on the short-term memory test in the PTSD group is not correlated to hippocampal volume may suggest a more general basis for such memory impairment.

Adult↗
PubMed2005

Fast method for brain image segmentation: application to proton magnetic resonance spectroscopic imaging.

The interpretation of brain metabolite concentrations measured by quantitative proton magnetic resonance spectroscopic imaging (MRSI) is assisted by knowledge of the percentage of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) within each MRSI voxel. Usually, this information is determined from T(1)-weighted magnetic resonance images (MRI) that have a much higher spatial resolution than the MRSI data. While this approach works well, it is time-consuming. In this article, a rapid data acquisition and analysis procedure for image segmentation is described, which is based on collection of several, thick slice, fast spin echo images (FSE) of different contrast. Tissue segmentation is performed with linear "Eigenimage" filtering and normalization. The method was compared to standard segmentation techniques using high-resolution 3D T(1)-weighted MRI in five subjects. Excellent correlation between the two techniques was obtained, with voxel-wise regression analysis giving GM: R2 = 0.893 +/- 0.098, WM: R2 = 0.892 +/- 0.089, ln(CSF): R2 = 0.831 +/- 0.082). Test-retest analysis in one individual yielded an excellent agreement of measurements with R2 higher than 0.926 in all three tissue classes. Application of FSE/EI segmentation to a sample proton MRSI dataset yielded results similar to prior publications. It is concluded that FSE imaging in conjunction with Eigenimage analysis is a rapid and reliable way of segmenting brain tissue for application to proton MRSI.

Adult↗
PubMed2004

Asymmetry and gender effect in functionally lateralized cortical regions: a proton MRS imaging study.

PURPOSE: to compare metabolite concentrations and ratios in gray matter regions known for their anatomical/functional asymmetry and evaluate gender effect. MATERIALS AND METHODS: Proton MRS imaging was performed at 1.5 T with TR/TE 2300/280 msec in 20 healthy right-handed subjects (mean age 29.6 +/- 5.3 years, 10 men). Concentrations of N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr), and the peak area ratios NAA/Cho, NAA/Cr, and Cho/Cr were evaluated in hippocampal and parahippocampal gyri, thalamus, insula, Broca's and Wernicke's areas (and corresponding contralateral areas), primary and secondary visual areas, temporal, inferior parietal, cingulate, supplemental motor, dorsolateral prefrontal, and sensorimotor areas. Linear mixed-effects regression models were used for statistical analyses. RESULTS: NAA concentration and NAA/Cho were higher in the left thalamus by 21.9% and 20%, respectively (both P < 0.001). NAA concentration was 13% higher in the region contralateral to Wernicke's area (P < 0.02). No gender differences were found. CONCLUSION: Metabolite concentrations and ratios were symmetric and gender independent in most brain regions, however small hemispheric side differences in the thalamus and in Wernicke's area were found.

Adult↗
PubMed2004

Quantitative proton MR spectroscopic imaging of the mesial temporal lobe.

PURPOSE: To evaluate variations in regional metabolite concentrations in the anterior mesial temporal lobe (ATL), and compare metabolite concentrations between the allocortex and neocortex using quantitative proton MR spectroscopic imaging (MRSI). MATERIALS AND METHODS: Metabolite concentrations and ratios were measured in 20 healthy young subjects with the use of a multislice spin-echo (SE) sequence (TR/TE=2300/280 msec). Quantitation of MRSI data was performed by means of the phantom replacement methodology. RESULTS: The highest choline (Cho) concentration (4.1 +/- 1.1 mM) was found in the ATL (P=0.0015 compared to the middle mesial temporal lobe (MTL), and P=0.0008 compared to the posterior mesial temporal lobe (PTL)). The ATL also had a higher Cho/creatine (Cr) ratio and a lower N-acetyl aspartate (NAA)/Cho ratio compared to other examined regions (P <0.0001 and P < or = 0.052, respectively). In the allocortical regions, the average Cho concentration (3.5 +/- 0.8 mM) was 68% higher, and the NAA concentration (9.5 +/- 1.8 mM) was 13% lower than in the neocortex (P <10(-6) and P <0.008, respectively). Cho/Cr was 64% higher, NAA/Cr 14% lower, and NAA/Cho 47% lower in the allocortex than in the neocortex (P <10(-6), P=0.013, and P <10(-6), respectively). CONCLUSION: The mesial temporal lobe shows high levels of Cho, which presumably reflect a difference in cellular composition between the allocortex and neocortex. Regional metabolite variations must be considered when pathological conditions involving the mesial temporal lobe are evaluated.

Adult↗