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  • 1
    Keywords: Germany ; IN-VIVO ; VIVO ; IMAGES ; imaging ; SIGNAL ; PARAMETERS ; UNCERTAINTY ; DIFFUSION TENSOR ; ARTIFACTS ; DIFFUSION ; radiology ; FRAMEWORK ; human brain ; USA ; Diffusion Tensor Imaging ; PHANTOMS ; phantom ; DTI ; Overestimation ; NOISE ; Artefacts ; ANISOTROPY ; SAMPLING SCHEMES ; Background noise ; DIFFUSION-TENSOR MRI ; Eigenvalues ; Eigenvector shift ; High b value ; LOW SNR ; RICIAN NOISE
    Abstract: The signal-to-noise ratio of in vivo diffusion tensor imaging (DTI) is usually very limited, especially if high resolution data is acquired. In a variety of settings, the signal of diffusion weighted images can drop below the background noise level yielding an underestimated diffusion constant. In this work, we report two new artefacts in DTI that are important in this regime. Both artifacts are described analytically and numerically and are demonstrated in DTI phantoms and in subjects in vivo. First, eigenvectors are systematically shifted towards distinct 'attractive' orientations of the gradient scheme. Second, certain eigenvalues can be overestimated due to the underestimation of the measured diffusion, which can result in the misordering of eigenvalues We show that these effects are relevant for current clinical settings of DTI
    Type of Publication: Journal article published
    PubMed ID: 19067007
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  • 2
    Keywords: brain ; MRI ; ASSOCIATION ; ONSET SCHIZOPHRENIA ; SCHIZOPHRENIA ; WORKING-MEMORY ; ABNORMALITIES ; ADULTS ; CORTEX ; Diffusion Tensor Imaging ; DTI ; ANISOTROPY ; FRACTIONAL ANISOTROPY ; CONNECTIVITY ; HASC ; Heteromodal association cortex ; Hypofrontality ; PREFRONTAL CORTEX DYSFUNCTION
    Abstract: Several diffusion tensor imaging (DTI) studies involving adults and adolescents with schizophrenia have examined fractional anisotropy (FA) in the corpus callosum (CC) with conflicting findings. This may be due to confounding factors such as the chronicity of the disorder, long-term medication with psychotropics or methodological differences. To provide a clearer picture of early alterations, we examined 13 adolescents with first-admission schizophrenia and 13 healthy controls using a region-of-interest approach based on probabilistic voxel classification. We quantified FA in four subdivisions of the CC and hypothesized that adolescents with schizophrenia display a reduced FA in the genu associated with 'hypofrontality' and a reduced FA in the body of the CC linked to the heteromodal association cortex. Fiber integrity measurements revealed significant FA decreases in the genu and body of the CC in adolescents with schizophrenia compared to healthy controls. These findings emphasize the central role of the CC in even the early stages of schizophrenia and lend weight to hypotheses about frontal alterations and the central role of the heteromodal association cortex in the aetiopathogenesis of the disorder.
    Type of Publication: Journal article published
    PubMed ID: 22373786
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