Test-Retest Reproducibility of In Vivo Magnetization Transfer Ratio and Saturation Index in Mice at 9.4 Tesla.

BACKGROUND: Magnetization transfer saturation (MTsat) imaging was developed to reduce T1 dependence and improve specificity to myelin, compared to the widely used MT ratio (MTR) approach, while maintaining a feasible scan time. As MTsat imaging is an emerging technique, the reproducibility of MTsat compared to MTR must be evaluated. PURPOSE: To assess the test-retest reproducibility of MTR and MTsat in the mouse brain at 9.4 T and calculate sample sizes potentially required to detect effect sizes ranging from 6% to 14%. STUDY TYPE: Prospective. SUBJECTS: Twelve healthy C57Bl/6 mice. FIELD STRENGTH/SEQUENCE: 9.4 T; magnetization transfer imaging using FLASH-3D Gradient Echo; T2-weighted TurboRARE spin echo. ASSESSMENT: All mice were scanned at two timepoints (5 days apart). MTR and MTsat maps were analyzed using mean region-of-interest (ROIs: corpus callosum [CC], internal capsule [IC], hippocampus [HC], cortex [CX], and thalamus [TH]), and whole brain voxel-wise analysis. STATISTICAL TESTS: Bland-Altman plots were used to assess biases between test-retest measurements. Test-retest reproducibility was evaluated via between and within-subject coefficients of variation (bsCV and wsCV, respectively). Sample sizes required were calculated (significance level: 95%; power: 80%), given effect sizes ranging from 6% to 14%, using both between and within-subject approaches. Results were considered statistically significant at P ≤ 0.05. RESULTS: Bland-Altman plots showed negligible biases between test-retest sessions (MTR: 0.0009; MTsat: 0). ROI-based and voxel-wise CVs revealed high reproducibility for both MTR (ROI-bsCV/wsCV: CC-4.5/2.8%; IC-6.1/5.2%; HC-5.7/4.6%; CX-5.1/2.3%; TH-7.4/4.9%) and MTsat (ROI-bsCV/wsCV: CC-6.3/4.8%; IC-7.3/5.1%; HC-9.5/6.4%; CX-6.7/6.5%; TH-7.2/5.3%). With a sample size of 6, changes on the order of 15% could be detected in MTR and MTsat, both between and within subjects, while smaller changes (6%-8%) required sample sizes of 10-15 for MTR, and 15-20 for MTsat. DATA CONCLUSION: MTsat exhibited comparable reproducibility to MTR, while providing sensitivity to myelin with less T1 dependence than MTR. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 1.

A systematic analysis of ultrastructural lesions in the Plasmodium coatneyi splenectomized rhesus macaque model of severe malaria.

Plasmodium falciparum remains one of the world's deadliest diseases and with ongoing concerns of evolving drug resistance, there is a need for continued refinement of the Plasmodium coatneyi infection model in macaques to study severe malaria. As such, the systemic ultrastructural lesions associated with P. coatneyi infection in splenectomized rhesus macaques was evaluated in 6 animals. Autopsy samples from multiple areas of the central nervous system (CNS), kidneys, heart, liver, and lungs of all 6 animals were processed for electron microscopy. A systematic analysis of the ultrastructural changes associated with the plasmodium was undertaken by multiple pathologists to ensure consensus. All tissues exhibited marked sequestration of infected red blood cells comprised either of cytoadherence to endothelium or rosette formation, associated with variable degrees of host cell damage in a range of tissues that in severe cases resulted in necrosis. This is the first complete systemic evaluation of ultrastructural tissue lesions in P. coatneyi-infected rhesus macaques, and the findings have important implications evaluating of the use of this model for the study of severe malaria caused by P. falciparum in humans.

The Effect of Three-Dimensional Whole, Major, and Small Vasculature on Mouse Brain Strain Under Both Diffuse and Focal Brain Injury Loading.

Blood vessels are much stiffer than brain parenchyma and their effects in finite element (FE) brain models need to be investigated. Despite the publication of some comprehensive three-dimensional (3D) brain vasculature models, no mechanical model exists for the mouse brain vasculature. Moreover, how the vasculature affects the mechanical behavior of brain tissue remains controversial. Therefore, we developed FE mouse brain models with detailed 3D vasculature to investigate the effect of the vasculature on brain strains under both diffuse (closed-head impact) and focal injury (controlled cortical impact (CCI)) loading, two commonly laboratory models of traumatic brain injury. The effect of the vasculature was examined by comparing maximum principal strain in mouse brain FE models with and without the vasculature. On average, modeling comprehensive vasculature under diffuse injury loading reduced average brain strain predictions by 32% with nonlinear elastic properties. Nearly three-fourths of the 32% strain reduction was attributable to the effects of the major branches of the vasculature. Meanwhile, during focal open-skull CCI injury loading, the contribution of the vasculature was limited, producing a less than 5% reduction in all cases. Overall, the vasculature, especially the major branches, increased the load-bearing capacity of the brain FE model and thus reduced brain strain predictions.

Reduced brain glutamine in female varsity rugby athletes after concussion and in non-concussed athletes after a season of play.

The purpose of this study was to use non-invasive proton magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) to monitor changes in prefrontal white matter metabolite levels and tissue microstructure in female rugby players with and without concussion (ages 18-23, n = 64). Evaluations including clinical tests and 3 T MRI were performed at the beginning of a season (in-season) and followed up at the end of the season (off-season). Concussed athletes were additionally evaluated 24-72 hr (n = 14), three months (n = 11), and six months (n = 8) post-concussion. Reduced glutamine at 24-72 hr and three months post-concussion, and reduced glutamine/creatine at three months post-concussion were observed. In non-concussed athletes (n = 46) both glutamine and glutamine/creatine were lower in the off-season compared to in-season. Within the MRS voxel, an increase in fractional anisotropy (FA) and decrease in radial diffusivity (RD) were also observed in the non-concussed athletes, and correlated with changes in glutamine and glutamine/creatine. Decreases in glutamine and glutamine/creatine suggest reduced oxidative metabolism. Changes in FA and RD may indicate neuroinflammation or re-myelination. The observed changes did not correlate with clinical test scores suggesting these imaging metrics may be more sensitive to brain injury and could aid in assessing recovery of brain injury from concussion.

Management of Latent Tuberculosis Infection Among Healthcare Workers: 10-Year Experience at a Single Center.

BACKGROUND: The risk of infection with Mycobacterium tuberculosis among healthcare workers (HCWs) is estimated to be higher than the general population. However, HCW acceptance and compliance with available latent tuberculosis infection (LTBI) treatment regimens has been problematic. Recently, regimens have become available that might improve HCW acceptance and compliance with LTBI treatment. METHODS: A retrospective single-center review of Employee Health and Wellness Services records of all HCWs diagnosed with LTBI was conducted. HCWs diagnosed with LTBI were offered 9-month isoniazid (INH), 4-month rifampin (RIF), weekly rifapentine/isoniazid (RPT/INH) for 12 weeks, or no treatment. Acceptance, completion rates, and side effects were reported for each regimen. Comparisons of regimens were assessed using Fisher exact test. RESULTS: Between 2005 and 2014, 363 of 927 (39%) HCWs diagnosed with LTBI accepted treatment. Of 363, 202 chose INH, 106 RIF, and 55 RPT/INH. Completion rates for each regimen were 58%, 80%, and 87%, respectively. HCWs were significantly more likely to have completed treatment with RIF (P < .0001) or RPT/INH (P < .0001) than INH. Rates of discontinuation owing to side effects were 35% for INH, 21% for RIF, and 10% for RPT/INH. Discontinuation of therapy due to side effects was significantly more frequent in the INH than the RPT/INH group (P = .0042). CONCLUSIONS: Completion of RIF and RPT/INH for LTBI in an HCW population is more likely than INH. Rates of discontinuation due to side effects were lower among those taking RPT/INH. Shorter LTBI treatment regimens should be more widely considered for HCWs in the United States.

Metalloproteinase inhibition prevents inhibitory synapse reorganization and seizure genesis.

The integrity and stability of interneurons in a cortical network are essential for proper network function. Loss of interneuron synaptic stability and precise organization can lead to disruptions in the excitation/inhibition balance, a characteristic of epilepsy. This study aimed to identify alterations to the GABAergic interneuron network in the piriform cortex (PC: a cortical area believed to be involved in the development of seizures) after kindling-induced seizures. Immunohistochemistry was used to mark perineuronal nets (PNNs: structures in the extracellular matrix that provide synaptic stability and restrict reorganization of inhibitory interneurons) and interneuron nerve terminals in control and kindled tissues. We found that PNNs were significantly decreased around parvalbumin-positive interneurons after the induction of experimental epilepsy. Additionally, we found layer-specific increases in GABA release sites originating from calbindin, calretinin, and parvalbumin interneurons, implying that there is a re-wiring of the interneuronal network. This increase in release sites was matched by an increase in GABAergic post-synaptic densities. We hypothesized that the breakdown of the PNN could be due to the activity of matrix metalloproteinases (MMP) and that the prevention of PNN breakdown may reduce the rewiring of interneuronal circuits and suppress seizures. To test this hypothesis we employed doxycycline, a broad spectrum MMP inhibitor, to stabilize PNNs in kindled rats. We found that doxycycline prevented PNN breakdown, re-organization of the inhibitory innervation, and seizure genesis. Our observations indicate that PNN degradation may be necessary for the development of seizures by facilitating interneuron plasticity and increased GABAergic activity.

Evaluation of the calmodulin-SOX9 interaction by "magnetic fishing" coupled to mass spectrometry.

Disruption of calmodulin (CaM)-based protein interactions has been touted as a potential means for modulating several disease pathways. Among these is SOX9, which is a DNA binding protein that is involved in chrondrocyte differentiation and regulation of the hormones that control sexual development. In this work, we employed a "magnetic fishing"/mass spectrometry assay in conjunction with intrinsic fluorescence to examine the interaction of CaM with the CaM-binding domain of SOX9 (SOX-CAL), and to assess the modulation of this interaction by known anti-CaM compounds. Our data show that there is a high affinity interaction between CaM and SOX-CAL (27±9 nM), and that SOX-CAL bound to the same location as the well-known CaM antagonist melittin; unexpectedly, we also found that addition of CaM-binding small molecules initially produced increased SOX-CAL binding, indicative of binding to both the well-known high-affinity CaM binding site and a second, lower-affinity binding site.

Polysialylated NCAM and ephrinA/EphA regulate synaptic development of GABAergic interneurons in prefrontal cortex.

A novel function for the neural cell adhesion molecule (NCAM) was identified in ephrinA/EphA-mediated repulsion as an important regulatory mechanism for development of GABAergic inhibitory synaptic connections in mouse prefrontal cortex. Deletion of NCAM, EphA3, or ephrinA2/3/5 in null mutant mice increased the numbers and size of perisomatic synapses between GABAergic basket interneurons and pyramidal cells in the developing cingulate cortex (layers II/III). A functional consequence of NCAM loss was increased amplitudes and faster kinetics of miniature inhibitory postsynaptic currents in NCAM null cingulate cortex. NCAM and EphA3 formed a molecular complex and colocalized with the inhibitory presynaptic marker vesicular GABA transporter (VGAT) in perisomatic puncta and neuropil in the cingulate cortex. EphrinA5 treatment promoted axon remodeling of enhanced green fluorescent protein-labeled basket interneurons in cortical slice cultures and induced growth cone collapse in wild-type but not NCAM null mutant neurons. NCAM modified with polysialic acid (PSA) was required to promote ephrinA5-induced axon remodeling of basket interneurons in cortical slices, likely by providing a permissive environment for ephrinA5/EphA3 signaling. These results reveal a new mechanism in which NCAM and ephrinAs/EphA3 coordinate to constrain GABAergic interneuronal arborization and perisomatic innervation, potentially contributing to excitatory/inhibitory balance in prefrontal cortical circuitry.

Conditional Sox9 ablation reduces chondroitin sulfate proteoglycan levels and improves motor function following spinal cord injury.

Chondroitin sulfate proteoglycans (CSPGs) found in perineuronal nets and in the glial scar after spinal cord injury have been shown to inhibit axonal growth and plasticity. Since we have previously identified SOX9 as a transcription factor that upregulates the expression of a battery of genes associated with glial scar formation in primary astrocyte cultures, we predicted that conditional Sox9 ablation would result in reduced CSPG expression after spinal cord injury and that this would lead to increased neuroplasticity and improved locomotor recovery. Control and Sox9 conditional knock-out mice were subject to a 70 kdyne contusion spinal cord injury at thoracic level 9. One week after injury, Sox9 conditional knock-out mice expressed reduced levels of CSPG biosynthetic enzymes (Xt-1 and C4st), CSPG core proteins (brevican, neurocan, and aggrecan), collagens 2a1 and 4a1, and Gfap, a marker of astrocyte activation, in the injured spinal cord compared with controls. These changes in gene expression were accompanied by improved hind limb function and locomotor recovery as evaluated by the Basso Mouse Scale (BMS) and rodent activity boxes. Histological assessments confirmed reduced CSPG deposition and collagenous scarring at the lesion of Sox9 conditional knock-out mice, and demonstrated increased neurofilament-positive fibers in the lesion penumbra and increased serotonin immunoreactivity caudal to the site of injury. These results suggest that SOX9 inhibition is a potential strategy for the treatment of SCI.

Treatment with an anti-CD11d integrin antibody reduces neuroinflammation and improves outcome in a rat model of repeated concussion.

BACKGROUND: Concussions account for the majority of traumatic brain injuries (TBI) and can result in cumulative damage, neurodegeneration, and chronic neurological abnormalities. The underlying mechanisms of these detrimental effects remain poorly understood and there are presently no specific treatments for concussions. Neuroinflammation is a major contributor to secondary damage following more severe TBI, and recent findings from our laboratory suggest it may be involved in the cumulative properties of repeated concussion. We previously found that an anti-CD11d monoclonal antibody that blocks the CD11d/CD18 integrin and adhesion molecule interaction following severe experimental TBI reduces neuroinflammation, oxidative activity, and tissue damage, and improves functional recovery. As similar processes may be involved in repeated concussion, here we studied the effects of the anti-CD11d treatment in a rat model of repeated concussion. METHODS: Rats were treated 2 h and 24 h after each of three repeated mild lateral fluid percussion injuries with either the CD11d antibody or an isotype-matched control antibody, 1B7. Injuries were separated by a five-day inter-injury interval. After the final treatment and either an acute (24 to 72 h post-injury) or chronic (8 weeks post-injury) recovery period had elapsed, behavioral and pathological outcomes were examined. RESULTS: The anti-CD11d treatment reduced neutrophil and macrophage levels in the injured brain with concomitant reductions in lipid peroxidation, astrocyte activation, amyloid precursor protein accumulation, and neuronal loss. The anti-CD11d treatment also improved outcome on tasks of cognition, sensorimotor ability, and anxiety. CONCLUSIONS: These findings demonstrate that reducing inflammation after repeated mild brain injury in rats leads to improved behavioral outcomes and that the anti-CD11d treatment may be a viable therapy to improve post-concussion outcomes.

Multi-parameter in vitro toxicity testing of crizotinib, sunitinib, erlotinib, and nilotinib in human cardiomyocytes.

Tyrosine kinase inhibitors (TKi) have greatly improved the treatment and prognosis of multiple cancer types. However, unexpected cardiotoxicity has arisen in a subset of patients treated with these agents that was not wholly predicted by pre-clinical testing, which centers around animal toxicity studies and inhibition of the human Ether-à-go-go-Related Gene (hERG) channel. Therefore, we sought to determine whether a multi-parameter test panel assessing the effect of drug treatment on cellular, molecular, and electrophysiological endpoints could accurately predict cardiotoxicity. We examined how 4 FDA-approved TKi agents impacted cell viability, apoptosis, reactive oxygen species (ROS) generation, metabolic status, impedance, and ion channel function in human cardiomyocytes. The 3 drugs clinically associated with severe cardiac adverse events (crizotinib, sunitinib, nilotinib) all proved to be cardiotoxic in our in vitro tests while the relatively cardiac-safe drug erlotinib showed only minor changes in cardiac cell health. Crizotinib, an ALK/MET inhibitor, led to increased ROS production, caspase activation, cholesterol accumulation, disruption in cardiac cell beat rate, and blockage of ion channels. The multi-targeted TKi sunitinib showed decreased cardiomyocyte viability, AMPK inhibition, increased lipid accumulation, disrupted beat pattern, and hERG block. Nilotinib, a second generation Bcr-Abl inhibitor, led to increased ROS generation, caspase activation, hERG block, and an arrhythmic beat pattern. Thus, each drug showed a unique toxicity profile that may reflect the multiple mechanisms leading to cardiotoxicity. This study demonstrates that a multi-parameter approach can provide a robust characterization of drug-induced cardiomyocyte damage that can be leveraged to improve drug safety during early phase development.

A longitudinal microstructural MRI dataset in healthy C57Bl/6 mice at 9.4 Tesla.

Multimodal microstructural MRI has shown increased sensitivity and specificity to changes in various brain disease and injury models in the preclinical setting. Here, we present an in vivo longitudinal dataset, including a subset of ex vivo data, acquired as control data and to investigate microstructural changes in the healthy mouse brain. The dataset consists of structural T2-weighted imaging, magnetization transfer ratio and saturation imaging, and advanced quantitative diffusion MRI (dMRI) methods. The dMRI methods include oscillating gradient spin echo (OGSE) dMRI and microscopic anisotropy (µA) dMRI, which provide additional insight by increasing sensitivity to smaller spatial scales and disentangling fiber orientation dispersion from true microstructural changes, respectively. The technical skills required to analyze microstructural MRI data are complex and include MRI sequence development, acquisition, and computational neuroimaging expertise. Here, we share unprocessed and preprocessed data, and scalar maps of quantitative MRI metrics. We envision utility of this dataset in the microstructural MRI field to develop and test biophysical models, methods that model temporal brain dynamics, and registration and preprocessing pipelines.

Cancer surgeons' distress and well-being, II: modifiable factors and the potential for organizational interventions.

PURPOSE: We showed in a companion paper that the prevalence of burnout among surgical oncologists at a comprehensive cancer center was 42% and psychiatric morbidity 27%, and high quality of life (QOL) was absent for 54% of surgeons. Here we examine modifiable workplace factors and other stressors associated with burnout, psychiatric morbidity, and low QOL, together with interest in interventions to reduce distress and improve wellness. METHODS: Study-specific questions important for morale, QOL, and stressors associated with burnout were included in an anonymous Internet-based survey distributed to the surgical faculty at Memorial Sloan-Kettering Cancer Center. RESULTS: Among the 72 surgeons who responded (response rate of 73%), surgeons identified high stress from medical lawsuits, pressure to succeed in research, financial worries, negative attitudes to gender, and ability to cope with patients' suffering and death. Workplace features requiring greatest change were the reimbursement system, administrative support, and schedule. Work-life balance and relationship issues with spouse or partner caused high stress. Strongest correlations with distress were a desire to change communication with patients and the tension between the time devoted to work versus time available to be with family. Surgeons' preferences for interventions favored a fitness program, nutrition consultation, and increased socialization with colleagues, with less interest in interventions conventionally used to address psychological distress. DISCUSSION: Several opportunities to intervene at the organizational level permit efforts to reduce burnout and improve QOL.

Cancer surgeons' distress and well-being, I: the tension between a culture of productivity and the need for self-care.

BACKGROUND: Burnout is a prevalent and important occupational hazard among surgical oncologists. The well-being or distress experienced can have a significant effect on clinicians and their families, the quality of care provided to patients, and the success of the health care organization. METHODS: We aimed to measure the prevalence of burnout, psychiatric morbidity, and quality of life using standardized measures; characterize associated features; and ascertain the surgical faculty's views on potential interventions and obstacles to change. Additional questions about service commitment to well-being, use of annual leave, and attitudes about weekend surgical practice were constructed to guide future targeted interventions. RESULTS: Among the 72 surgeons who responded (response rate of 73%), we found that 42% of surgeons reported burnout and 27% psychiatric levels of distress, while 30% used alcohol and 13% used sleep medications as a possible means to cope. Only one third of surgeons reported high quality of life across physical, emotional, spiritual, and intellectual domains. DISCUSSION: Compared to general surgical practices, cancer surgeons achieved more personal fulfillment and made less use of distancing methods to cope with their patients. Institutional culture contributes to the nonuse of available annual leave, attitudes about weekend operating schedules, and missed opportunities for the leadership to attend to surgeons' well-being.

Oral vanoxerine prevents reinduction of atrial tachyarrhythmias: preliminary results.

BACKGROUND: Vanoxerine is a promising, new, investigational antiarrhythmic drug. The purpose of this study was to test the hypothesis that oral dosing of vanoxerine would first terminate induced atrial flutter (AFL) and atrial fibrillation (AF), and then prevent their reinduction. METHODS: In 5 dogs with sterile pericarditis, on the fourth day after creating the pericarditis, we performed electrophysiologic (EP) studies at baseline, measuring atrial excitability, refractoriness (AERP), and conduction time (CT) when pacing from the right atrial appendage, Bachmann's bundle (BB), and the posteroinferior left atrium at cycle lengths (CLs) of 400, 300, and 200 ms. Then, after induction of AFL or AF, all dogs received hourly oral doses of vanoxerine: 90 mg, followed by 180 mg and 270 mg. Blood was obtained to determine plasma vanoxerine concentrations at baseline, every 30 minutes, when neither AFL nor AF were inducible, and, finally, 1 hour after the 270 mg dose. Then we repeated the baseline EP studies. RESULTS: Four dogs had inducible, sustained AFL, and 1 dog only had induced, nonsustained AF. In 4 AFL episodes, oral vanoxerine terminated the AFL and then rendered it noninducible after an average of 111 minutes (range 75-180 minutes) after the first dose was administered. The mean vanoxerine plasma level at the point of noninducibility was 84 ng/mL, with a narrow range of 76-99 ng/mL. In the dog with induced, nonsustained AF, it was no longer inducible at a drug level of 75 ng/mL. Vanoxerine did not significantly (1) prolong the AERP except at BB, and then only at the faster pacing CLs; (2) change atrial excitability thresholds; (3) prolong atrial conduction time, the PR interval, the QRS complex or the QT interval. CONCLUSIONS: Orally administered vanoxerine effectively terminated AFL and rendered it noninducible. It also suppressed inducibility of nonsustained AF. These effects occurred at consistent plasma drug levels. Vanoxerine's insignificant or minimal effects on measured electrophysiologic parameters are consistent with little proarrhythmic risk.

The Armed Forces Research Institute of Medical Sciences: five decades of collaborative medical research.

The Armed Forces Research Institute of Medical Sciences (AFRIMS) is a 50-year-old joint institute of the US and Royal Thai Army Medical Departments located in Bangkok, Thailand. Investigators from the Institute have carried out research in Thailand and the region, in collaboration with many partners, focused on a large number of tropical infectious diseases. In celebration of the 50th anniversary, this paper summarizes highlights of this research, focusing on malaria, Japanese encephalitis, dengue, diarrhea and HIV. In addition, research done in support of the medical problems of refugees and of the health of Thai peace-keeping forces are summarized. The research carried out by AFRIMS and added to the scientific literature has contributed significantly to advancement in multiple areas of tropical infectious disease.

ß2 Integrin CD11d/CD18: From Expression to an Emerging Role in Staged Leukocyte Migration.

CD11d/CD18 is the most recently discovered and least understood ß2 integrin. Known CD11d adhesive mechanisms contribute to both extravasation and mesenchymal migration - two key aspects for localizing peripheral leukocytes to sites of inflammation. Differential expression of CD11d induces differences in monocyte/macrophage mesenchymal migration including impacts on macrophage sub-set migration. The participation of CD11d/CD18 in leukocyte localization during atherosclerosis and following neurotrauma has sparked interest in the development of CD11d-targeted therapeutic agents. Whereas the adhesive properties of CD11d have undergone investigation, the signalling pathways induced by ligand binding remain largely undefined. Underlining each adhesive and signalling function, CD11d is under unique transcriptional control and expressed on a sub-set of predominately tissue-differentiated innate leukocytes. The following review is the first to capture the nearly three decades of CD11d research and discusses the emerging role of CD11d in leukocyte migration and retention during the progression of a staged immune response.

Test-retest reproducibility of in vivo oscillating gradient and microscopic anisotropy diffusion MRI in mice at 9.4 Tesla.

BACKGROUND AND PURPOSE: Microstructure imaging with advanced diffusion MRI (dMRI) techniques have shown increased sensitivity and specificity to microstructural changes in various disease and injury models. Oscillating gradient spin echo (OGSE) dMRI, implemented by varying the oscillating gradient frequency, and microscopic anisotropy (µA) dMRI, implemented via tensor valued diffusion encoding, may provide additional insight by increasing sensitivity to smaller spatial scales and disentangling fiber orientation dispersion from true microstructural changes, respectively. The aims of this study were to characterize the test-retest reproducibility of in vivo OGSE and µA dMRI metrics in the mouse brain at 9.4 Tesla and provide estimates of required sample sizes for future investigations. METHODS: Twelve adult C57Bl/6 mice were scanned twice (5 days apart). Each imaging session consisted of multifrequency OGSE and µA dMRI protocols. Metrics investigated included µA, linear diffusion kurtosis, isotropic diffusion kurtosis, and the diffusion dispersion rate (Λ), which explores the power-law frequency dependence of mean diffusivity. The dMRI metric maps were analyzed with mean region-of-interest (ROI) and whole brain voxel-wise analysis. Bland-Altman plots and coefficients of variation (CV) were used to assess the reproducibility of OGSE and µA metrics. Furthermore, we estimated sample sizes required to detect a variety of effect sizes. RESULTS: Bland-Altman plots showed negligible biases between test and retest sessions. ROI-based CVs revealed high reproducibility for most metrics (CVs < 15%). Voxel-wise CV maps revealed high reproducibility for µA (CVs ~ 10%), but low reproducibility for OGSE metrics (CVs ~ 50%). CONCLUSION: Most of the µA dMRI metrics are reproducible in both ROI-based and voxel-wise analysis, while the OGSE dMRI metrics are only reproducible in ROI-based analysis. Given feasible sample sizes (10-15), µA metrics and OGSE metrics may provide sensitivity to subtle microstructural changes (4-8%) and moderate changes (> 6%), respectively.

Neurite orientation dispersion and density imaging in a rodent model of acute mild traumatic brain injury.

BACKGROUND AND PURPOSE: Identification of changesin brain microstructure following mild traumatic brain injury (mTBI) could be instrumental in understanding the underlying pathophysiology. The purpose of this study was to apply neurite orientation dispersion and density imaging (NODDI) to a rodent model of mTBI to determine whether microstructural changes could be detected immediately following injury. METHODS: Fifteen adult male Wistar rats were scanned on a Bruker 9.4 Tesla small animal MRI using a multi-shell acquisition (30 b = 1000 s/mm2 and 60 b = 2000 s/mm2 ). Nine animals experienced a single closed head controlled cortical impact followed by NODDI from 1 to 4 h post injury. Region of interest analysis focused on the corpus callosum and hippocampus. A mixed analysis of variance (ANOVA) was used to determine statistically significant interactions in neurite density index (NDI), orientation dispersion index (ODI), fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity. Follow up repeated-measures ANOVAs were used to determine individual changes over time. RESULTS: NDI showed a significant increase in the hippocampus and corpus callosum following injury, while ODI showed increases in the corpus callosum. No significant changes were observed in the sham control animals. No changes were found in FA, MD, AD, or RD. Histological analysis revealed increased glial fibrillary acidic protein staining relative to controls in both the hippocampus and corpus callosum, with evidence of activated astrocytes in these regions. CONCLUSIONS: Changes in NODDI metrics were detected as early as 1 h following mTBI. No changes were detected with conventional diffusion tensor imaging (DTI) metrics, suggesting that NODDI provides greater sensitivity to microstructural changes than conventional DTI.

Repetitive mild traumatic brain injury in mice triggers a slowly developing cascade of long-term and persistent behavioral deficits and pathological changes.

We have previously reported long-term changes in the brains of non-concussed varsity rugby players using magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI) and functional magnetic imaging (fMRI). Others have reported cognitive deficits in contact sport athletes that have not met the diagnostic criteria for concussion. These results suggest that repetitive mild traumatic brain injuries (rmTBIs) that are not severe enough to meet the diagnostic threshold for concussion, produce long-term consequences. We sought to characterize the neuroimaging, cognitive, pathological and metabolomic changes in a mouse model of rmTBI. Using a closed-skull model of mTBI that when scaled to human leads to rotational and linear accelerations far below what has been reported for sports concussion athletes, we found that 5 daily mTBIs triggered two temporally distinct types of pathological changes. First, during the first days and weeks after injury, the rmTBI produced diffuse axonal injury, a transient inflammatory response and changes in diffusion tensor imaging (DTI) that resolved with time. Second, the rmTBI led to pathological changes that were evident months after the injury including: changes in magnetic resonance spectroscopy (MRS), altered levels of synaptic proteins, behavioural deficits in attention and spatial memory, accumulations of pathologically phosphorylated tau, altered blood metabolomic profiles and white matter ultrastructural abnormalities. These results indicate that exceedingly mild rmTBI, in mice, triggers processes with pathological consequences observable months after the initial injury.