Browsing by Author "Dunn, Jeff"
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- ItemOpen AccessArtifact reduction in long-term monitoring of cerebral hemodynamics using near-infrared spectroscopy(Society of Photo-optical Instrumentation Engineers, 2015-05-26) Vinette, Sarah; Dunn, Jeff; Slone, Edward; Federico, PaoloNear-infrared spectroscopy (NIRS) is a noninvasive neuroimaging technique used to assess cerebral hemodynamics. Its portability, ease of use, and relatively low operational cost lend itself well to the long-term monitoring of hemodynamic changes, such as those in epilepsy, where events are unpredictable. Long-term monitoring is associated with challenges including alterations in behaviors and motion that can result in artifacts. Five patients with epilepsy were assessed for interictal hemodynamic changes and alterations in behavior or motion. Based on this work, visual inspection was used to identify NIRS artifacts during a period of interest, specifically prior to seizures, in four patients. A motion artifact reduction algorithm (MARA, also known as the spline interpolation method) was tested on these data. Alterations in the NIRS measurements often occurred simultaneously with changes in motion and behavior. Occasionally, sharp shift artifacts were observed in the data. When artifacts appeared as sustained baseline shifts in the data, MARA reduced the standard deviation of the data and the appearance improved. We discussed motion and artifacts as challenges associated with longterm monitoring of cerebral hemodynamics in patients with epilepsy and our group’s approach to circumvent these challenges and improve the quality of the data collected.
- ItemOpen AccessCortical Excitability after Mild Traumatic Brain Injury in Children(2015-12-04) Seeger, Trevor; Barlow, Karen; Kirton, Adam; Dunn, Jeff; Gallagher, Clare; Esser, MichaelIntroduction: Mild traumatic brain injury is frequently complicated by post-concussive syndrome. It is unknown why these symptoms persist, but recent research suggests that cortical excitability may play a role. Objectives: To determine if cortical excitability is different in pediatric mTBI, and if it correlates with symptom persistence. Methods:This was a cross-sectional controlled cohort study. Cortical excitability was measured using a variety of TMS paradigms in children with (symptomatic) and without (asymptomatic) persistent symptoms at one month post injury. The primary outcome measure was the corticalsilent period (cSP) (thought to represent GABAergic inhibition). Results: 57 children with mTBI (44% male; age 14.23 (SD:2.49)) and 28 controls were compared. cSP was similar between groups (F(2, 70)=0.53, p=0.591). There were no other significant group differences in cortical excitability. Conclusions: TMS was well tolerated in children with mTBI. Cortical excitability is similar to normal children at one-month following the injury.
- ItemOpen AccessInvestigating the Relationship Between Interhemispheric Coherence, Task, and Concussion History in an Adolescent Population(2021-07-08) Pearce, Sabrina Anne; Dunn, Jeff; Yeates, Keith; Kirton, AdamPediatric mild traumatic brain injury (mTBI), including concussion, is a public health burden. There is a need for objective imaging metrics to understand the injury and to guide clinical treatment guidelines. Functional near-infrared spectroscopy (fNIRS) is a light-based neuroimaging technology that can be a biomarker of mTBI by measuring functional connectivity between affected brain regions. This thesis aimed to determine how task affects fNIRS measures of functional connectivity, also known as coherence, from a resting state to determine effective tasks and activated regions for mTBI studies. A secondary goal was to characterize the difference in coherence between an asymptomatic adolescent group with a previous concussion and an adolescent group that had not sustained a concussion. Results indicated that tasks decrease interhemispheric coherence relative to a resting state, especially when they require increased attention. Using these results and specific interregional combinations, we observed a decrease in coherence in a sample of adolescents with a previous concussion relative to those without, although this result should be explored in a larger sample size. Overall, this thesis adds to evidence that fNIRS may be a sensitive biomarker to mTBI, especially when combined with specific tasks.
- ItemOpen AccessLimited somatosensory functional connectivity differences in youth with ASD, at rest(2017) Cechmanek, Brian; Bray, Signe; Lebel, Catherine; Dunn, Jeff; McCrimmon, Adam; Barlow, Karen; Curtin, SuzanneChildren and adolescents with autism spectrum disorder typically experience sensory sensitivities, involving over- and/or under-reactions to sensory stimuli. Tactile hyper-reactivity, in particular, is implicated in negative outcomes such as aversion to oral hygiene, dietary issues, and self-harm. Presently, there is no established overarching neurological basis for these sensitivities in autism. Understanding the underlying causes of these sensitivities may help guide pharmacological and behavioural interventions. Motivated by suggested linkages between over-connectivity measures and negative outcomes in ASD, this thesis used resting-state functional-MRI to examine somatosensory functional connectivity differences in youth with autism. Connectivity differences, arising in the somatosensory region, may represent a good marker of sensory sensitivities in ASD. Our findings show limited functional connectivity differences in ASD, and scarce changes in age by diagnosis interaction or autism symptom severity. This suggests that functional connectivity of the somatosensory network in youth with autism is not disrupted, at rest, compared to neurotypical controls.
- ItemOpen AccessMagnetic Resonance Imaging for Tracking of Cells and Agents Targeted to Bone Fracture(2015-04-29) Taha, May; Dunn, Jeff; Matyas, JohnRegenerative medicine is likely to play a major role in the treatment of musculoskeletal diseases. Stem cell therapies could be used to restore damaged or diseased tissues by contributing to the healing process. Additionally, bone targeted nanoparticles could be of great use in this field, as they can be used to deliver therapies or to image an injury site. In order to evaluate and monitor new regenerative therapies in preclinical models over time, a non-invasive in vivo imaging tool is needed. Use of such an imaging method will enable testing new cell therapies in bone. Magnetic resonance imaging (MRI) holds considerable promise for this purpose. Considering that it is a non-invasive and non ionizing method makes it well-suited for repeated measurements studies. Initially, we optimized an MRI protocol for visualization of bone injuries, and then we compared the optimized MRI protocol with µCT as the gold standard for bone imaging. We found that MRI offers several advantages over µCT, including that it visualized soft tissue, edema, therapeutic biomaterials, and is especially useful when ionizing radiation is to be avoided. Subsequently, we used MRI to assess materials used in this study such as bone targeted nanoparticles, contrast agents and stem cell scaffolds. After establishing the MRI protocol, we labelled-differentiated ESCs, and then transplanted them in vivo for MR tracking. The results showed that MRI detected the labelled cells in vivo that under some conditions the MRI could detect migration of the differentiated ESC’s to remote site of injury. The findings were validated by histology and immunohistochemistry. To our knowledge, this is the first study to track cells in bone fracture using MRI. Based on the results of this research, future studies can use the developed cell tracking model for testing the effectiveness of novel cell therapies that promote bone repair.
- ItemOpen AccessMeasurement of brain oxygenation and metabolism in a mouse model of multiple sclerosis(2017) Johnson, Thomas Wade; Dunn, Jeff; Yong, V. Wee; Goodyear, BradMultiple sclerosis is a disease of the central nervous system, predominantly thought of as a white matter (WM) disease. However, evidence of the importance of grey matter (GM) involvement is beginning to accumulate. In this study, we set out to investigate whether altered oxygenation and metabolism was present in cortical and cerebellar brain GM using an auto-inflammatory mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Chronically implanted optical PO2 probes directly measured the tissue oxygen environment in GM in awake, unrestrained mice. Near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI) were used to detect hemoglobin oxygen saturation and blood flow in anaesthetized mice. This required the development of NIRS technologies to guide GM imaging. Numerical simulations were performed to determine NIRS sensitivity to brain tissue types in mice, rats and humans. NIRS on mice and rats is very sensitive to GM tissue in comparison to humans, and the region imaged can be determined through inter-fibre separation. Optical fibres were developed and their compatibility tested for use in a 9.4 T MRI system to enable simultaneous NIRS and MRI measurements on mice. The NIRS-MR system was validated by detecting changes in the cerebral metabolic rate for oxygen (CMRO2) when mice were subjected to hypothermia. Hypoxia, as measured by PO2 probes, was present in the cortex and cerebellum in approximately 50% of EAE mice, occurred much more frequently than hyperoxia, correlated with increased behavioural deficits and occurred before behavioural deficits appeared. NIRS-MR measurements found decreased cerebral blood flow, increased oxygen extraction fraction and constant CMRO2 at peak disease in EAE mice with high behavioural scores and inflammation-positive controls; no changes were found in naive controls. Some of these changes correlated with behavioural deficit. GM atrophy was observed in the cerebellar cortex, medulla and thalamus. Overall this study showed that NIRS-MR can detect changes in CMRO2 in mice, GM pathology exists in the EAE model and can be detected, and may be related to inflammation.
- ItemOpen AccessQuantitative Functional Magnetic Resonance Imaging of Multiple Sclerosis(2016) Bird, Jaimie; Pike, Bruce; Protzner, Andrea; Koch, Marcus; Dunn, JeffMagnetic resonance imaging (MRI) and functional MRI (fMRI) continue to advance the understanding of multiple sclerosis (MS) pathology, but these conventional imaging techniques have several limitations, which may render them insufficient to identify biomarkers of a disease as multifaceted as MS. This thesis employed quantitative fMRI to investigate uncharted measures of MS cerebral physiology, which can contribute to the development of new MS biomarkers; specifically, motor cortex flow-metabolism coupling and global grey matter cerebrovascular reactivity (CVR) were quantified. Data analysis of 12 MS patients and 11 healthy controls revealed between-group differences in cerebral blood flow (CBF) and oxygen metabolism. However, the ratio between CBF and oxygen metabolism, as well as CVR, had no significant between-group differences. These findings provide preliminary information about MS pathology and potential MS biomarkers. This research also demonstrates limitations of quantitative fMRI that impede the ability to make robust conclusions; therefore, further methodological research is needed.