Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2012
This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different r... more This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different routes of Mn2+ administrations for visuotopic brain mapping of retinal, callosal, cortico-subcortical, transsynaptic and horizontal connections in normal adult rats. Upon fractionated intravitreal Mn2+ injection, Mn enhancements were observed in the contralateral superior colliculus (SC) and lateral geniculate nucleus (LGN) by 45-60% at 1-3 days after initial Mn2+ injection and in the contralateral primary visual cortex (V1) by about 10% at 2-3 days after initial Mn2+ injection. Direct, single-dose Mn2+ injection to the LGN resulted in Mn enhancement by 13-21% in V1 and 8-11% in SC of the ipsilateral hemisphere at 8 to 24 hours after Mn2+ administration. Intracortical, single-dose Mn2+ injection to the visual cortex resulted in Mn enhancement by 53-65% in ipsilateral LGN, 15-26% in ipsilateral SC, 32-34% in the splenium of corpus callosum and 17-25% in contralateral V1/V2 transition zone at 8 to 24 hours after Mn2+ administration. Notably, some patchy patterns were apparent near the V1/V2 border of the contralateral hemisphere. Laminar-specific horizontal cortical connections were also observed in the ipsilateral hemisphere. The current results demonstrated the sensitivity of MEMRI for assessing the neuroarchitecture of the visual brains in vivo without depth-limitation, and may possess great potentials for studying the basic neural components and connections in the visual system longitudinally during development, plasticity, pharmacological interventions and genetic modifications.
The rodents are an increasingly important model for understanding the mechanisms of development, ... more The rodents are an increasingly important model for understanding the mechanisms of development, plasticity, functional specialization and disease in the visual system. However, limited tools have been available for assessing the structural and functional connectivity of the visual brain network globally, in vivo and longitudinally. There are also ongoing debates on whether functional brain connectivity directly reflects structural brain connectivity. In this study, we explored the feasibility of manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administration for visuotopic brain mapping and understanding of physiological transport in normal and visually deprived adult rats. In addition, resting-state functional connectivity MRI (RSfcMRI) was performed to evaluate the intrinsic functional network and structural-functional relationships in the corresponding anatomical visual brain connections traced by MEMRI. Upon intravitreal, subcortical, and intracortical Mn(2+) injection, different topographic and layer-specific Mn enhancement patterns could be revealed in the visual cortex and subcortical visual nuclei along retinal, callosal, cortico-subcortical, transsynaptic and intracortical horizontal connections. Loss of visual input upon monocular enucleation to adult rats appeared to reduce interhemispheric polysynaptic Mn(2+) transfer but not intra- or inter-hemispheric monosynaptic Mn(2+) transport after Mn(2+) injection into visual cortex. In normal adults, both structural and functional connectivity by MEMRI and RSfcMRI was stronger interhemispherically between bilateral primary/secondary visual cortex (V1/V2) transition zones (TZ) than between V1/V2 TZ and other cortical nuclei. Intrahemispherically, structural and functional connectivity was stronger between visual cortex and subcortical visual nuclei than between visual cortex and other subcortical nuclei. The current results demonstrated the sensitivity of MEMRI and RSfcMRI for assessing the neuroarchitecture, neurophysiology and structural-functional relationships of the visual brains in vivo. These may possess great potentials for effective monitoring and understanding of the basic anatomical and functional connections in the visual system during development, plasticity, disease, pharmacological interventions and genetic modifications in future studies.
Purpose To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of ti... more Purpose To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients. Materials and Methods A single-breathhold electrocardiogram-triggered black-blood multi-echo spin-echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients.
Background The superior colliculus (SC) and lateral geniculate nucleus (LGN) are important subcor... more Background The superior colliculus (SC) and lateral geniculate nucleus (LGN) are important subcortical structures for vision. Much of our understanding of vision was obtained using invasive and small field of view (FOV) techniques. In this study, we use non-invasive, large FOV blood oxygenation level-dependent (BOLD) fMRI to measure the SC and LGN's response temporal dynamics following short duration (1 s) visual stimulation.
In rats, the superior colliculus (SC) is a main destination for retinal ganglion cells and is an ... more In rats, the superior colliculus (SC) is a main destination for retinal ganglion cells and is an important subcortical structure for vision. Electrophysiology studies have observed that many SC neurons are highly sensitive to moving objects, but complementary non-invasive functional imaging studies with larger fields of view have been rarely conducted.
Neonatal monocular enucleation (ME) is often employed to study the developmental mechanisms under... more Neonatal monocular enucleation (ME) is often employed to study the developmental mechanisms underlying visual perception and the cross-modal changes in the central nervous system caused by early loss of the visual input. However, underlying biochemical or metabolic mechanisms that accompany the morphological, physiological and behavioral changes after ME are not fully understood. Male Sprague-Dawley rats (N= 14) were prepared and divided into 2 groups.
Abstract The aim of this study is to employ tract-based spatial statistics (TBSS) to analyze the ... more Abstract 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.
Exposure to early life stress results in behavioural changes, and these dysfunctions may persist ... more Exposure to early life stress results in behavioural changes, and these dysfunctions may persist throughout adulthood. In this study, we investigated whether hippocampus volume and neurochemical changes were involved in the appearance of these effects in the maternal separation (MS) animal model using the noninvasive techniques of structural magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS).
Fear conditioning is widely used to study the neural basis of learning and memory [1]. It allows ... more Fear conditioning is widely used to study the neural basis of learning and memory [1]. It allows an organism to quickly assess and react to stimuli and predict danger. However, it was mostly restricted to behavioral or histological studies [2, 3]. Recent studies have been using BOLD-fMRI to detect the neural activity in living animals [4]. However it is technically difficult due to subject motion and is limited by poor spatial resolution.
Biological systems are often made up of multiple compartments, or heterogeneous in nature [1]. As... more Biological systems are often made up of multiple compartments, or heterogeneous in nature [1]. As a result, the usually assumed water diffusion probability, Gaussian distribution, might not be appropriate to describe the true diffusion process in vivo. By means of characterizing non-Gaussian water diffusion using diffusion kurtosis imaging (DKI)[2], more information regarding the biological systems, particularly central nervous system, might become available.
Quantitative diffusion tensor imaging (DTI) offers a valuable tool to probe the microstructural c... more Quantitative diffusion tensor imaging (DTI) offers a valuable tool to probe the microstructural changes in neural tissues in vivo, where absolute quantitation accuracy and reproducibility are essential. It has been long recognized that measurement of apparent diffusion coefficient (ADC) using DTI could be influenced by the presence of water molecules in cerebrovasculature. However, little is known about to what extent such blood signal affects DTI quantitation.
MATERIALS AND METHODS: Animal Preparation: Adult C57BL/6N mice (18-22g, N= 8) were divided into 2... more MATERIALS AND METHODS: Animal Preparation: Adult C57BL/6N mice (18-22g, N= 8) were divided into 2 groups (n= 4 each) and were subjected to 30min-transient MCAO with procedures previously described [7]. The mice were evaluated for neurological deficits 24 hours after MCAO [7], showing no significant differences in the neurological scores between two groups (p> 0.05).
Methods-Animal preparation: Sprague-Dawley rats (N= 7) between two and three months of age were u... more Methods-Animal preparation: Sprague-Dawley rats (N= 7) between two and three months of age were used in this study. Each animal was anesthetized with 3% isofluorane for induction and 1–1.5% for maintenance. Once sedated, animals were placed in a 7T MRI scanner (Bruker PharmaScan) with a brain surface receiver coil (Bruker BioSpin). Respiration rate was monitored with a pressure sensor (SA Instruments) and heart rate and blood oxygen level were monitored with a pulse oximeter (SA Instruments).
To speed up the process of central nervous system (CNS) recovery after injury, the need for real-... more To speed up the process of central nervous system (CNS) recovery after injury, the need for real-time measurement of axon regeneration in vivo is essential to assess the extent of injury, as well as the optimal timing and delivery of therapeutics and rehabilitation. It was necessary to develop a chronic animal model with an in vivo measurement technique to provide a real-time monitoring and feedback system.
Brain hypothermia has demonstrated pronounced neuroprotective effect in patients with cardiac arr... more Brain hypothermia has demonstrated pronounced neuroprotective effect in patients with cardiac arrest, ischemia and acute liver failure. However, its underlying neuroprotective mechanisms remain to be elucidated in order to improve therapeutic outcomes. Single voxel proton magnetic resonance spectroscopy (1H-MRS) was performed using a 7 Tesla MRI scanner on normal Sprague–Dawley rats (N= 8) in the same voxel under normothermia (36.5° C) and 30min mild hypothermia (33.5° C).
Abstract Diffusion kurtosis imaging (DKI), an extension of diffusion tensor imaging (DTI), provid... more Abstract 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.
METHODS: Experimental Procedures: Sprague4Dawley female rats (2504280g, N= 11) were divided into ... more METHODS: Experimental Procedures: Sprague4Dawley female rats (2504280g, N= 11) were divided into 2 groups and were prepared to induce ocular hypertension unilaterally in the right eye by photocoagulation of episcleral and limbal veins using an argon laser [3]. A second laser treatment in the same setting was applied 7 days later to maintain a consistent IOP elevation by about 1.5 times above the normal level. Group A (n= 6) and Group B (n= 5) were scanned 2 weeks and 1 month, respectively, after first laser treatment.
MATERIALS AND METHODS: Sprague-Dawley rats (250-300 g, N= 6) were prepared and injected intraperi... more MATERIALS AND METHODS: Sprague-Dawley rats (250-300 g, N= 6) were prepared and injected intraperitoneally with MnCl2 solution at 45mg/kg and 100mM. MEMRI was performed before, and at 1, 5 and 12 days after injection. All MRI measurements were acquired utilizing a 7 T Bruker scanner under inhaled isoflurane anaesthesia.
Neonatal hypoxic-ischemic (HI) cerebral injury is a major cause of permanent damage to neuronal c... more Neonatal hypoxic-ischemic (HI) cerebral injury is a major cause of permanent damage to neuronal cells which associated with high morbidity and mortality in the perinatal period, leading to cerebral palsy or impaired cognition1, 2. After undergoing massive cell death and atrophy at the first week after injury, the neonatal brain undergoes regenerative processes toward the functional restitution which continues late after the HI injury when the infarct lesion stabilizes and lasts for at least 6 months3, 4.
Abstract This study employed blood oxygenation level-dependent functional MRI (BOLD-fMRI) to eval... more Abstract This study employed blood oxygenation level-dependent functional MRI (BOLD-fMRI) to evaluate the visual responses in the superior colliculus of the developing rat brain from the time of eyelid opening to adulthood. Upon flash illumination to the contralateral eye, the regional BOLD response underwent a systematic increase in amplitude with age especially after the third postnatal week. However, no significant difference in BOLD signal increase was found between postnatal days 14 and 21.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2012
This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different r... more This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different routes of Mn2+ administrations for visuotopic brain mapping of retinal, callosal, cortico-subcortical, transsynaptic and horizontal connections in normal adult rats. Upon fractionated intravitreal Mn2+ injection, Mn enhancements were observed in the contralateral superior colliculus (SC) and lateral geniculate nucleus (LGN) by 45-60% at 1-3 days after initial Mn2+ injection and in the contralateral primary visual cortex (V1) by about 10% at 2-3 days after initial Mn2+ injection. Direct, single-dose Mn2+ injection to the LGN resulted in Mn enhancement by 13-21% in V1 and 8-11% in SC of the ipsilateral hemisphere at 8 to 24 hours after Mn2+ administration. Intracortical, single-dose Mn2+ injection to the visual cortex resulted in Mn enhancement by 53-65% in ipsilateral LGN, 15-26% in ipsilateral SC, 32-34% in the splenium of corpus callosum and 17-25% in contralateral V1/V2 transition zone at 8 to 24 hours after Mn2+ administration. Notably, some patchy patterns were apparent near the V1/V2 border of the contralateral hemisphere. Laminar-specific horizontal cortical connections were also observed in the ipsilateral hemisphere. The current results demonstrated the sensitivity of MEMRI for assessing the neuroarchitecture of the visual brains in vivo without depth-limitation, and may possess great potentials for studying the basic neural components and connections in the visual system longitudinally during development, plasticity, pharmacological interventions and genetic modifications.
The rodents are an increasingly important model for understanding the mechanisms of development, ... more The rodents are an increasingly important model for understanding the mechanisms of development, plasticity, functional specialization and disease in the visual system. However, limited tools have been available for assessing the structural and functional connectivity of the visual brain network globally, in vivo and longitudinally. There are also ongoing debates on whether functional brain connectivity directly reflects structural brain connectivity. In this study, we explored the feasibility of manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administration for visuotopic brain mapping and understanding of physiological transport in normal and visually deprived adult rats. In addition, resting-state functional connectivity MRI (RSfcMRI) was performed to evaluate the intrinsic functional network and structural-functional relationships in the corresponding anatomical visual brain connections traced by MEMRI. Upon intravitreal, subcortical, and intracortical Mn(2+) injection, different topographic and layer-specific Mn enhancement patterns could be revealed in the visual cortex and subcortical visual nuclei along retinal, callosal, cortico-subcortical, transsynaptic and intracortical horizontal connections. Loss of visual input upon monocular enucleation to adult rats appeared to reduce interhemispheric polysynaptic Mn(2+) transfer but not intra- or inter-hemispheric monosynaptic Mn(2+) transport after Mn(2+) injection into visual cortex. In normal adults, both structural and functional connectivity by MEMRI and RSfcMRI was stronger interhemispherically between bilateral primary/secondary visual cortex (V1/V2) transition zones (TZ) than between V1/V2 TZ and other cortical nuclei. Intrahemispherically, structural and functional connectivity was stronger between visual cortex and subcortical visual nuclei than between visual cortex and other subcortical nuclei. The current results demonstrated the sensitivity of MEMRI and RSfcMRI for assessing the neuroarchitecture, neurophysiology and structural-functional relationships of the visual brains in vivo. These may possess great potentials for effective monitoring and understanding of the basic anatomical and functional connections in the visual system during development, plasticity, disease, pharmacological interventions and genetic modifications in future studies.
Purpose To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of ti... more Purpose To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients. Materials and Methods A single-breathhold electrocardiogram-triggered black-blood multi-echo spin-echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients.
Background The superior colliculus (SC) and lateral geniculate nucleus (LGN) are important subcor... more Background The superior colliculus (SC) and lateral geniculate nucleus (LGN) are important subcortical structures for vision. Much of our understanding of vision was obtained using invasive and small field of view (FOV) techniques. In this study, we use non-invasive, large FOV blood oxygenation level-dependent (BOLD) fMRI to measure the SC and LGN's response temporal dynamics following short duration (1 s) visual stimulation.
In rats, the superior colliculus (SC) is a main destination for retinal ganglion cells and is an ... more In rats, the superior colliculus (SC) is a main destination for retinal ganglion cells and is an important subcortical structure for vision. Electrophysiology studies have observed that many SC neurons are highly sensitive to moving objects, but complementary non-invasive functional imaging studies with larger fields of view have been rarely conducted.
Neonatal monocular enucleation (ME) is often employed to study the developmental mechanisms under... more Neonatal monocular enucleation (ME) is often employed to study the developmental mechanisms underlying visual perception and the cross-modal changes in the central nervous system caused by early loss of the visual input. However, underlying biochemical or metabolic mechanisms that accompany the morphological, physiological and behavioral changes after ME are not fully understood. Male Sprague-Dawley rats (N= 14) were prepared and divided into 2 groups.
Abstract The aim of this study is to employ tract-based spatial statistics (TBSS) to analyze the ... more Abstract 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.
Exposure to early life stress results in behavioural changes, and these dysfunctions may persist ... more Exposure to early life stress results in behavioural changes, and these dysfunctions may persist throughout adulthood. In this study, we investigated whether hippocampus volume and neurochemical changes were involved in the appearance of these effects in the maternal separation (MS) animal model using the noninvasive techniques of structural magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS).
Fear conditioning is widely used to study the neural basis of learning and memory [1]. It allows ... more Fear conditioning is widely used to study the neural basis of learning and memory [1]. It allows an organism to quickly assess and react to stimuli and predict danger. However, it was mostly restricted to behavioral or histological studies [2, 3]. Recent studies have been using BOLD-fMRI to detect the neural activity in living animals [4]. However it is technically difficult due to subject motion and is limited by poor spatial resolution.
Biological systems are often made up of multiple compartments, or heterogeneous in nature [1]. As... more Biological systems are often made up of multiple compartments, or heterogeneous in nature [1]. As a result, the usually assumed water diffusion probability, Gaussian distribution, might not be appropriate to describe the true diffusion process in vivo. By means of characterizing non-Gaussian water diffusion using diffusion kurtosis imaging (DKI)[2], more information regarding the biological systems, particularly central nervous system, might become available.
Quantitative diffusion tensor imaging (DTI) offers a valuable tool to probe the microstructural c... more Quantitative diffusion tensor imaging (DTI) offers a valuable tool to probe the microstructural changes in neural tissues in vivo, where absolute quantitation accuracy and reproducibility are essential. It has been long recognized that measurement of apparent diffusion coefficient (ADC) using DTI could be influenced by the presence of water molecules in cerebrovasculature. However, little is known about to what extent such blood signal affects DTI quantitation.
MATERIALS AND METHODS: Animal Preparation: Adult C57BL/6N mice (18-22g, N= 8) were divided into 2... more MATERIALS AND METHODS: Animal Preparation: Adult C57BL/6N mice (18-22g, N= 8) were divided into 2 groups (n= 4 each) and were subjected to 30min-transient MCAO with procedures previously described [7]. The mice were evaluated for neurological deficits 24 hours after MCAO [7], showing no significant differences in the neurological scores between two groups (p> 0.05).
Methods-Animal preparation: Sprague-Dawley rats (N= 7) between two and three months of age were u... more Methods-Animal preparation: Sprague-Dawley rats (N= 7) between two and three months of age were used in this study. Each animal was anesthetized with 3% isofluorane for induction and 1–1.5% for maintenance. Once sedated, animals were placed in a 7T MRI scanner (Bruker PharmaScan) with a brain surface receiver coil (Bruker BioSpin). Respiration rate was monitored with a pressure sensor (SA Instruments) and heart rate and blood oxygen level were monitored with a pulse oximeter (SA Instruments).
To speed up the process of central nervous system (CNS) recovery after injury, the need for real-... more To speed up the process of central nervous system (CNS) recovery after injury, the need for real-time measurement of axon regeneration in vivo is essential to assess the extent of injury, as well as the optimal timing and delivery of therapeutics and rehabilitation. It was necessary to develop a chronic animal model with an in vivo measurement technique to provide a real-time monitoring and feedback system.
Brain hypothermia has demonstrated pronounced neuroprotective effect in patients with cardiac arr... more Brain hypothermia has demonstrated pronounced neuroprotective effect in patients with cardiac arrest, ischemia and acute liver failure. However, its underlying neuroprotective mechanisms remain to be elucidated in order to improve therapeutic outcomes. Single voxel proton magnetic resonance spectroscopy (1H-MRS) was performed using a 7 Tesla MRI scanner on normal Sprague–Dawley rats (N= 8) in the same voxel under normothermia (36.5° C) and 30min mild hypothermia (33.5° C).
Abstract Diffusion kurtosis imaging (DKI), an extension of diffusion tensor imaging (DTI), provid... more Abstract 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.
METHODS: Experimental Procedures: Sprague4Dawley female rats (2504280g, N= 11) were divided into ... more METHODS: Experimental Procedures: Sprague4Dawley female rats (2504280g, N= 11) were divided into 2 groups and were prepared to induce ocular hypertension unilaterally in the right eye by photocoagulation of episcleral and limbal veins using an argon laser [3]. A second laser treatment in the same setting was applied 7 days later to maintain a consistent IOP elevation by about 1.5 times above the normal level. Group A (n= 6) and Group B (n= 5) were scanned 2 weeks and 1 month, respectively, after first laser treatment.
MATERIALS AND METHODS: Sprague-Dawley rats (250-300 g, N= 6) were prepared and injected intraperi... more MATERIALS AND METHODS: Sprague-Dawley rats (250-300 g, N= 6) were prepared and injected intraperitoneally with MnCl2 solution at 45mg/kg and 100mM. MEMRI was performed before, and at 1, 5 and 12 days after injection. All MRI measurements were acquired utilizing a 7 T Bruker scanner under inhaled isoflurane anaesthesia.
Neonatal hypoxic-ischemic (HI) cerebral injury is a major cause of permanent damage to neuronal c... more Neonatal hypoxic-ischemic (HI) cerebral injury is a major cause of permanent damage to neuronal cells which associated with high morbidity and mortality in the perinatal period, leading to cerebral palsy or impaired cognition1, 2. After undergoing massive cell death and atrophy at the first week after injury, the neonatal brain undergoes regenerative processes toward the functional restitution which continues late after the HI injury when the infarct lesion stabilizes and lasts for at least 6 months3, 4.
Abstract This study employed blood oxygenation level-dependent functional MRI (BOLD-fMRI) to eval... more Abstract This study employed blood oxygenation level-dependent functional MRI (BOLD-fMRI) to evaluate the visual responses in the superior colliculus of the developing rat brain from the time of eyelid opening to adulthood. Upon flash illumination to the contralateral eye, the regional BOLD response underwent a systematic increase in amplitude with age especially after the third postnatal week. However, no significant difference in BOLD signal increase was found between postnatal days 14 and 21.
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