Assessment of the structure and networking of the human brain in traumatic brain injury using advanced magnetic resonance imaging techniques

This research investigates the chronic effect of moderate to severe traumatic brain injury on brain white matter integrity, as reflected by diffusion tensor imaging metrics, and assesses their correlation to neuropsychological response. Thirteen male participants with traumatic brain injury (8.4 years average post-injury time) were compared to a matched group of neurologically healthy controls. None of the traumatic brain injury subjects had received post-acute neurocognitive and/or neuropsychological rehabilitation. Between group comparison of global fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity was performed for the whole brain. A comparison between Shannon entropy and fractional anisotropy as regards their ability to separate TBI participants from controls led to the choice not to include in the study Shannon Entropy, in addition to the diffusion tensor water diffusion parameters. Neuropsychological response in visual and verbal (working and episodic) memory tasks was correlated to water diffusion parameters in a between-groups comparative process, as well as in a separate group assessment for selected regions of interest, that is, the corpus callosum, the fornix and the uncinate fasciculi. Significant changes in global fractional anisotropy, mean diffusivity, and radial diffusivity were associated with traumatic brain injury, indicating the chronic loss of white matter integrity in TBI participants. An extensive battery of visual and verbal memory tasks was employed for the comparative assessment of neurocognitive performance. Visual memory capacity was reduced in traumatic brain injury, and this deficit was correlated to white matter integrity loss at the corpus callosum and right uncinate fasciculus. Participants with traumatic brain injury underperformed controls in verbal memory as well. This deficit was correlated to white matter integrity loss at the corpus callosum, fornix and right uncinate fasciculus. White matter changes at the corpus callosum were correlated with visual and verbal working and episodic memory, at fornix with verbal episodic memory and at the right uncinate fasciculus with visual and verbal episodic memory. Changes in whole brain, corpus callosum, fornix and diffusion tensor metrics inflicted by moderate to severe traumatic brain injury are still evident several years post-injury and relate to neurocognitive impairment, while loss of white matter integrity seems to correlate with visual and verbal (working and episodic) memory impairment.Η εργασία διερευνά τις χρόνιες επιπτώσεις της μέτριας – σοβαρής τραυματικής εγκεφαλικής βλάβης (ΤΕΒ) στην ακεραιότητα της λευκής ουσίας, όπως αυτές περιγράφονται από τα βαθμωτά μεγέθη του τανυστή υδατικής διάχυσης, και αξιολογεί τη συσχέτιση τους με τη νευρογνωσιακή απόκριση. Δεκατρείς άρρενες με τραυματική εγκεφαλική βλάβη (μέσο χρονικό διάστημα μετά τον τραυματισμό 8.4 έτη) συγκρίθηκαν με μια ανάλογα προσαρμοσμένη νευρολογικά υγιή ομάδα. Κανένας από τους συμμετέχοντες με τραυματική εγκεφαλική βλάβη δεν είχε λάβει νευρογνωσιακή ή/και νευροψυχολογική αποκατάσταση. Οι δύο ομάδες συγκρίθηκαν ως προς τα μεγέθη της κλασματικής ανισοτροπίας, της μέσης διαχυτότητας, της αξονικής διαχυτότητας και της ακτινικής διαχυτότητας σε όλο τον εγκέφαλο. Μια σύγκριση που πραγματοποιήθηκε ανάμεσα στην κλασματική ανισοτροπία και στην εντροπία Shannon οδήγησε στην επιλογή μη συμπερίληψης της εντροπίας Shannon στις προαναφερόμενες παραμέτρους. H νευροψυχολογική απόκριση των ομάδων σε δοκιμασίες οπτικής και λεκτικής (εργαζόμενης/επεισοδικής) μνήμης συσχετίστηκε με τις παραμέτρους υδατικής διάχυσης σε μια συγκριτική διαδικασία, καθώς και σε μια διαδικασία αξιολόγησης για κάθε ομάδα ξεχωριστά, σε επιλεγμένες περιοχές ενδιαφέροντος, δηλαδή στο μεσολόβιο, την ψαλίδα και τις αγκιστρωτές δέσμες. Σημαντικές αλλοιώσεις σε όλο το εύρος του εγκεφάλου σε ότι αφορά την κλασματική ανισοτροπία, τη μέση διαχυτότητα και την ακτινική διαχυτότητα κατέδειξαν τη χρόνια απώλεια της ακεραιότητας της λευκής ουσίας στους συμμετέχοντες με τραυματική εγκεφαλική βλάβη. Ένα εκτεταμένο σύνολο δοκιμασιών οπτικής και λεκτικής μνήμης χρησιμοποιήθηκε για συγκριτική αξιολόγηση της νευρογνωσιακής απόδοσης των ομάδων. Στην τραυματική εγκεφαλική βλάβη παρατηρήθηκε έκπτωση στην απόδοση οπτικής μνήμης η οποία συσχετίστηκε με απώλεια της ακεραιότητας της λευκής ουσίας στο μεσολόβιο και στη δεξιά αγκιστρωτή δέσμη. Ανάλογη έκπτωση παρατηρήθηκε και στην περίπτωση της λεκτικής μνήμης, η οποία συσχετίστηκε με απώλεια της ακεραιότητας της λευκής ουσίας στο μεσολόβιο, στην ψαλίδα και στη δεξιά αγκιστρωτή δέσμη. Η αλλοίωση της λευκής ουσίας στο μεσολόβιο συσχετίστηκε με οπτική και λεκτική, εργαζόμενη και επεισοδική μνήμη, στην ψαλίδα συσχετίστηκε με λεκτική επεισοδική μνήμη, στη δεξιά αγκιστρωτή δέσμη συσχετίστηκε με οπτική και λεκτική επεισοδική μνήμη. Οι αλλοιώσεις στο μεσολόβιο, την ψαλίδα, τη δεξιά αγκιστρωτή δέσμη και στο σύνολο του εγκεφάλου που προκλήθηκαν από τραυματική εγκεφαλική βλάβη εξακολουθούν να εντοπίζονται αρκετά χρόνια μετά τον τραυματισμό και συσχετίζονται με νευρογνωσιακή έκπτωση, ενώ η απώλεια της ακεραιότητας της λευκής ουσίας στον εγκέφαλο φαίνεται να συσχετίζεται με έκπτωση στην οπτική και λεκτική (εργαζόμενη/επεισοδική) μνήμη

Whole brain and corpus callosum diffusion tensor metrics: How do they correlate with visual and verbal memory performance in chronic traumatic brain injury

This research investigates the chronic effect of moderate to severe traumatic brain injury on brain white matter integrity, as reflected by diffusion tensor imaging metrics, and the assessment of their correlation to neuropsychological response. Thirteen male participants with traumatic brain injury (8.4 years average post-injury time) were compared to a matched group of neurologically healthy controls. None of the traumatic brain injury subjects had received post-acute neurocognitive and/or neuropsychological rehabilitation. Between-group comparison of fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity was performed for the whole brain and corpus callosum. An extensive battery of visual and verbal memory tasks was employed for the comparative assessment of neurocognitive performance. Between-group and within-group performance differences were correlated with fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity of corpus callosum. Significant changes in global fractional anisotropy, mean diffusivity, and radial diffusivity were associated with traumatic brain injury. Visual memory capacity was reduced in traumatic brain injury, and this deficit was correlated to white matter integrity loss at the corpus callosum. Participants with traumatic brain injury underperformed controls in verbal memory as well, but no correlation with corpus callosum diffusion tensor imaging properties was established. Between-group performance difference was correlated with corpus callosum diffusion metrics in several tasks. Significant correlations were found between corpus callosum diffusion tensor imaging metrics and neuropsychological response within the traumatic brain injury group. Changes in whole brain and corpus callosum diffusion tensor metrics inflicted by moderate to severe traumatic brain injury are still evident several years post-injury and relate to neurocognitive impairment, while loss of white matter integrity seems to correlate with episodic and working memory impairment

Characterization of attenuation and respiratory motion artifacts and their influence on SPECT MP image evaluation using a dynamic phantom assembly with variable cardiac defects

BACKGROUND: A phantom assembly that simulates the respiratory motion of the heart was used to investigate artifacts and their impact on defect detection.METHODS: SPECT/CT images were acquired for phantoms with and without small and large cardiac defects during normal and deep breathing, and also at four static respiratory phases. Acquisitions were reconstructed with and without AC, and with misalignment of transmission and emission scans. A quantitative analysis was performed to assess artifacts. Two physicians reported on defect presence or absence and their results were evaluated.RESULTS: All large defects were correctly reported. Attenuation reduced uptake in the basal LV walls, increasing FN physicians' reports for small defects. Respiratory motion reduced uptake mainly in the anterior and inferior walls increasing FP and FN reports on images without and with small defects, respectively. Artifacts due to misalignment between CT and SPECT scans in normal breathing phantoms did not influence the physicians' reports.CONCLUSIONS: Attenuation and respiratory motion correction should be applied to reduce artifacts before reporting on small defects in deep breathing conditions. Artifacts due to misalignment between CT and SPECT scans do not affect defect detection in normal breathing when the LV is co-registered in SPECT and CT images prior to AC.</p