Effects of hypercapnia on DTI quantitation

Posters - Diffusion Perfusion: Animal Models: No. 4046The accuracy of DTI derived parameters can directly affect the interpretation of underlying biological microstructures. However, the diffusivity measurements are likely to be confounded by the presence of vasculature. Nevertheless, little is known about to what degree blood signal from vasculature affects the diffusion quantitation. In this study, we examined the effects of hypercapnia on DTI quantification indices in anesthetized rat brains. It was found statistically significant changes occurred in all parametric DTI maps indicating that hemodynamic alterations can potentially affect the DTI indices and detection of tissue microstructures. Therefore, cautions must be taken when interpreting DTI parameters in vivo.postprin

The effects of hypercapnia on DTI quantification in anesthetized rat brain

Conference Theme: Engineering the Future of BiomedicineDiffusion Tensor Imaging (DTI) offers a valuable in vivo tool to characterize water diffusion behavior in biological tissues, particularly brain tissues. The accuracy of DTI derived parameters can directly affect the interpretation of underlying microstructures, physiology or pathologies. It is anticipated that measurement of apparent diffusion coefficient (ADC) using DTI could be influenced and complicated by the presence of water molecules in brain vasculature. However, little is known about to what degree does blood signal from vasculature affect the diffusion quantitation. In this study, we examined the effects of hypercapnia on DTI quantification in rat brains using inhalation of 5% carbon dioxide (CO2). It was found that statistically significant changes occurred in parametric DTI maps in response to cerebrovascular challenges, indicating that vascular factors could interfere with in vivo DTI characterization of neural tissues. Consequently, hemodynamic alterations can potentially affect the DTI quantitation and detection of tissue microstructures and pathological alterations. Therefore, cautions must be taken when interpreting DTI parameters in vivo. ©2009 IEEE.published_or_final_versionThe 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2009), Minneapolis, MN., 3-6 September 2009. In Proceedings of the 31st EMBC, 2009, p. 2711-271

Magnetic resonance spectroscopy reveals N-acetylaspartate reduction in hippocampus and cingulate cortex after fear conditioning

The fear conditioning in rodents provides a valuable translational tool to investigate the neural basis of learning and memory and potentially the neurobiology of post-traumatic stress disorder (PTSD). Neurobiological changes induced by fear conditioning have largely been examined ex vivo while progressive 'real-time' changes in vivo remain under-explored. Single voxel proton magnetic resonance spectroscopy (1H MRS) of the hippocampus, cingulate cortex and thalamus of adult male C57BL/6N mice (N=12) was performed at 1 day before, 1 day and 1 week after, fear conditioning training using a 7T scanner. N-acetylaspartate (NAA), a marker for neuronal integrity and viability, significantly decreased in the hippocampus at 1 day and 1 week post-conditioning. Significant NAA reduction was also observed in the cingulate cortex at 1 day post-conditioning. These findings of hippocampal NAA decrease indicate reduced neuronal dysfunction and/or neuronal integrity, contributing to the trauma-related PTSD-like symptoms. The neurochemical changes characterized by 1H MRS can shed light on the biochemical mechanisms of learning and memory. Moreover, such information can potentially facilitate prompt intervention for patients with psychiatric disorders. © 2012 Elsevier Ireland Ltd.postprin

In vivo diffusion tensor imaging in rat model of chronic spinal cord compression

Session 64: Advanced Spinal Cord Imaging - Oral presentationWe have employed DTI to investigate the pathophysiology of chronic spinal cord compression in this study. Average diffusion characteristic curves and fiber tracking have been done to evaluate the lesion and intact regions. DTI is sensitive to the damage and it is potential to monitor the progressive structural and functional changes in such chronic spinal cord diseases.published_or_final_versionThe 17th Scientific Meeting & Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM), Honolulu, HI., 18-24 April 2009. In Proceedings of ISMRM 17th Scientific Meeting & Exhibition, 2009, p. 63

MEMRI study neonatal hypoxic-ischemic injury in the late stage

Session 16: Manganese Enhanced MRI: Methods & Applications - Oral presentationIn this study, in vivo MEMRI was employed to investigate the hypoxic-ischemic injury in the late phase. Mn2+ induced signal changes were examined using SPM coregistration and ROI analysis. T1WIs SI increase was detected in the perilesional region 24 hours after Mn2+ administration and it colocalized with the increase in glial cell density in GFAP staining, demonstrating the existence of reactive gliosis in the late phase after H-I injury.published_or_final_versionThe 17th Scientific Meeting & Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM), Honolulu, HI., 18-24 April 2009. In Proceedings of ISMRM 17th Scientific Meeting & Exhibition, 2009, p. 15

In vivo diffusion tensor imaging of chronic spinal cord compression in rat model

Conference Theme: Engineering the Future of BiomedicineChronic spinal cord compression induced cervical myelopathy is a comon cause of spinal cord dysfunction. The exact mechanisms of underlying progressive cell death remain to be elucidated. In this study, in vivo diffusion tensor imaging (DTI) has been applied to investigate the microstructural changes of white matter (WM) in this neurodegenerative disease. Compared with conventional MRI techniques, DTI is believed to be more specific to pathological changes. Radial diffusivity (λ⊥) is higher in the ipilesional region, suggesting demyelination or axonal degradation may occur after prolonged compression. Near the epicenter of lesion, axial diffusivity (λ∥) is lower. Also, caudal-rostral asymmetry has been observed in λ∥. Feasibility of using DTI to detect microstructural changes in chronic disease has been demonstrated. ©2009 IEEE.published_or_final_versionThe 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2009), Minneapolis, MN., 3-6 September 2009. In Proceedings of the 31st EMBC, 2009, p. 2715-271

Tract-based spatial statistics (TBSS): application to detecting white matter tract variation in mild hypoxic-ischemic neonates

The aim of this study is to employ tract-based spatial statistics (TBSS) to analyze the voxel-wise differences in DTI parameters between normal and mild hypoxic-ischemic (HI) neonatal brains. Forty-one full term neonates (24 normal controls and 17 with mild HI injury) and 31 preterm neonates (20 normal controls and 11 with mild HI injury) underwent T1 weighted imaging, T2 weighted imaging and diffusion tensor imaging (DTI) within 28 days after birth. The voxel differences of fractional anisotropy (FA), lambda1, lambda2, and lambda3 values between mild HI group and control group were analyzed in preterm and full term neonates respectively. The significantly decreased FA with increased lambda2, lambda3 in corticospinal tract, genu of corpus callosum (GCC), external capsule (EC) and splenium of the corpus callosum (SCC) in mild HI neonates suggested deficits or delays in both myelination and premyelination. Such impaired corticospinal tract, in both preterm and term neonates, may directly lead to the subsequent poor motor performance. Impaired EC and SCC, the additional injured sites observed in full term neonates with mild HI injury, may be causally responsible for the dysfunction in coordination and integration. In conclusion, TBSS provides an objective, independent and sensitive method for DTI data analysis of neonatal white matter alterations after mild HI injury.published_or_final_versio

Shared behavioral mechanisms underlie <i>C. elegans</i> aggregation and swarming

In complex biological systems, simple individual-level behavioral rules can give rise to emergent group-level behavior. While collective behavior has been well studied in cells and larger organisms, the mesoscopic scale is less understood, as it is unclear which sensory inputs and physical processes matter a priori. Here, we investigate collective feeding in the roundworm C. elegans at this intermediate scale, using quantitative phenotyping and agent-based modeling to identify behavioral rules underlying both aggregation and swarming—a dynamic phenotype only observed at longer timescales. Using fluorescence multi-worm tracking, we quantify aggregation in terms of individual dynamics and population-level statistics. Then we use agent-based simulations and approximate Bayesian inference to identify three key behavioral rules for aggregation: cluster-edge reversals, a density-dependent switch between crawling speeds, and taxis towards neighboring worms. Our simulations suggest that swarming is simply driven by local food depletion but otherwise employs the same behavioral mechanisms as the initial aggregation

Diffusion kurtosis imaging with tract-based spatial statistics reveals white matter alterations in preschool children

Diffusion kurtosis imaging (DKI), an extension of diffusion tensor imaging (DTI), provides a practical method to describe non-Gaussian water diffusion in neural tissues. The sensitivity of DKI to detect the subtle changes in several chosen brain structures has been studied. However, intuitive and holistic methods to validate the merits of DKI remain to be explored. In this paper, tract-based spatial statistics (TBSS) was used to demonstrate white matter alterations in both DKI and DTI parameters in preschool children (1-6 years; n=10). Correlation analysis was also performed in multiple regions of interest (ROIs). Fractional anisotropy, mean kurtosis, axial kurtosis and radial kurtosis increased with age, while mean diffusivity and radial diffusivity decreased significantly with age. Fractional anisotropy of kurtosis and axial diffusivity were found to be less sensitive to the changes with age. These preliminary findings indicated that TBSS could be used to detect subtle changes of DKI parameters on the white matter tract. Kurtosis parameters, except fractional anisotropy of kurtosis, demonstrated higher sensitivity than DTI parameters. TBSS may be a convenient method to yield higher sensitivity of DKI.published_or_final_versio

Monitoring iron chelation effect in hearts of thalassaemia patients with improved sensitivity using reduced transverse relaxation rate (RR2)

Posters - Myocardial Viability: Human Models: No. 3660Accurate MRI characterization of myocardial iron is needed to improve the diagnosis and management of thalassaemia patients with transfusional iron overload. This study aimed to demonstrate that a new transverse relaxation index, the reduced R2 (RR2) that is estimated from non-monoexponential multi-echo CPMG signal decay and sensitive to ferritin iron, could detect the myocardial iron changes immediately following 1-week iron chelation suspension in thalassaemia patients at 3T.postprin