Distinguishing microgliosis and tau deposition in the mouse brain using paramagnetic and diamagnetic susceptibility source separation

Tauopathies, including Alzheimer's disease (AD), are neurodegenerative disorders characterized by hyperphosphorylated tau protein aggregates in the brain. In addition to protein aggregates, microglia-mediated inflammation and iron dyshomeostasis are other pathological features observed in AD and other tauopathies. It is known that these alterations at the subcellular level occur much before the onset of macroscopic tissue atrophy or cognitive deficits. The ability to detect these microstructural changes with MRI therefore has substantive importance for improved characterization of disease pathogenesis. In this study, we demonstrate that quantitative susceptibility mapping (QSM) with paramagnetic and diamagnetic susceptibility source separation has the potential to distinguish neuropathological alterations in a transgenic mouse model of tauopathy. 3D multi-echo gradient echo data were acquired from fixed brains of PS19 (Tau) transgenic mice and age-matched wild-type (WT) mice (n = 5 each) at 11.7 T. The multi-echo data were fit to a 3-pool complex signal model to derive maps of paramagnetic component susceptibility (PCS) and diamagnetic component susceptibility (DCS). Group-averaged signal fraction and composite susceptibility maps showed significant region-specific differences between the WT and Tau mouse brains. Significant bilateral increases in PCS and |DCS| were observed in specific hippocampal and cortical sub-regions of the Tau mice relative to WT controls. Comparison with immunohistological staining for microglia (Iba1) and phosphorylated-tau (AT8) further indicated that the PCS and DCS differences corresponded to regional microgliosis and tau deposition in the PS19 mouse brains, respectively. The results demonstrate that quantitative susceptibility source separation may provide sensitive imaging markers to detect distinct pathological alterations in tauopathies.

Senolytic therapy preserves blood-brain barrier integrity and promotes microglia homeostasis in a tauopathy model

Cellular senescence, characterized by expressing the cell cycle inhibitory protein p21/CDKN1A, is evident in driving age-related diseases. Senescent cells play a crucial role in the initiation and progression of tau-mediated pathology, suggesting that targeting cell senescence offers a therapeutic potential for treating tauopathy associated diseases. This study focuses on identifying non-invasive biomarkers and validating their responses to a well-characterized senolytic therapy combining dasatinib and quercetin (D+Q), in a widely used tauopathy mouse model, PS19. We employed human-translatable MRI measures, including water extraction with phase-contrast arterial spin tagging (WEPCAST) MRI, T2 relaxation under spin tagging (TRUST), and structural MRI, and longitudinally assessed brain physiology and regional volumes in PS19 mice. Our data reveal increased BBB permeability, decreased oxygen extraction fraction, and brain atrophy in 9-month-old PS19 mice compared to their littermate controls. (D+Q) treatment effectively preserves BBB integrity, rescues cerebral oxygen hypometabolism, attenuates brain atrophy, and alleviates tau hyperphosphorylation in PS19 mice. Mechanistically, D+Q treatment induces a shift of microglia from a disease-associated to a homeostatic state, reducing a senescence-like microglial phenotype marked by increased p21/CDKN1A. D+Q-treated PS19 mice exhibit enhanced cue-associated cognitive performance in the tracing fear conditioning test compared to the vehicle-treated littermates, implying improved cognitive function by D+Q treatment. Our results pave the way for application of senolytic treatment as well as these noninvasive MRI biomarkers in clinical trials in tauopathy associated neurological disorders.

Routine sterile glove and instrument change at the time of abdominal wound closure to prevent surgical site infection (ChEETAh): a model-based cost-effectiveness analysis of a pragmatic, cluster-randomised trial in seven low-income and middle-income countries

BACKGROUND

Surgical site infection (SSI) is a major burden on patients and health systems. This study assessed the cost-effectiveness of routine change of sterile gloves and instruments before abdominal wall closure to prevent SSI.

METHODS

A decision-analytic model was built to estimate average costs and outcomes of changing gloves and instruments before abdominal wall closure compared with current practice. Clinical data were obtained from the ChEETAh trial, a multicentre, cluster-randomised trial in seven low-income and middle-income countries (LMICs), and costs were obtained from a study (KIWI) that assessed costs associated with SSIs in LMICs. Outcomes were measured as the percentage of surgeries resulting in SSIs. Costs were measured from a health-care provider perspective and were reported in 2021 US$. The economic analysis used a partially split single-country costing approach, with pooled outcomes data from all seven countries in the ChEETAh trial, and data for resource use and unit costs from India (KIWI); secondary analyses used resource use and costs from Mexico and Ghana (KIWI).

FINDINGS

In the base case, the average cost of the intervention was $259∙92 compared with $261∙10 for current practice (cost difference -$1∙18, 95% CI -4∙08 to 1∙33). In the intervention group, an estimated 17∙6% of patients had an SSI compared with 19∙7% of patients in the current practice group (absolute risk reduction 2∙10%, 95% CI 2∙07-2∙84). At all cost-effectiveness thresholds assumed ($0 to $14 000), the intervention had a higher likelihood of being cost-effective compared with current practice, indicating that the intervention was cost-effective. Similar results were obtained when the analysis using data from India was repeated using resource use and unit cost data from Mexico and Ghana.

INTERPRETATION

Routine sterile glove and instrument change before abdominal wall closure is effective and the costs are similar to those for current practice. Routine change of gloves and instruments before abdominal wall closure should be rolled out in LMICs.

FUNDING

National Institute for Health and Care Research (NIHR) Clinician Scientist Award, NIHR Global Health Research Unit Grant, and Mölnlycke Healthcare.

Accuracy of the Wound Healing Questionnaire in the diagnosis of surgical-site infection after abdominal surgery in low- and middle-income countries

INTRODUCTION

Telemedicine is being adopted for postoperative surveillance but requires evaluation for efficacy. This study tested a telephone Wound Healing Questionnaire (WHQ) to diagnose surgical site infection (SSI) after abdominal surgery in low- and middle-income countries.

METHOD

A multi-centre, international, prospective study was embedded in the FALCON trial; a factorial RCT testing measures to reduce SSI in seven low- and middle-income countries (NCT03700749). It was conducted according to a pre-registered protocol (SWAT126) and reported according to STARD guidelines. The reference test was in-person review by a trained clinician at 30 postoperative days according to US Centres for Disease Control criteria. The index test was telephone administration of an adapted WHQ at 27 to 30 postoperative days by a researcher blinded to the outcome of in-person review. The sum of item response scores generated an overall score between 0 and 29. The primary outcome was the diagnostic accuracy of the WHQ, defined as the proportion of SSI correctly identified by the telephone WHQ, and summarized using the area under the receiving operator characteristic curve (AUROC) and diagnostic test accuracy statistics.

RESULTS

Patients were included from three upper-middle income (396 patients, 13 hospitals), three lower-middle income (746 patients, 19 hospitals), and one low-income country (54 patients, 4 hospitals). 90.3% (1088 of 1196) patients were successfully contacted. Those with non-midline incisions (adjusted odds ratio: 0.36, 95% c.i. 0.17 to 0.73, P=0.005) or a confirmed diagnosis of SSI on in-person assessment (odds ratio: 0.42, 95% c.i. 0.20 to 0.92, P=0.006) were harder to reach. The questionnaire correctly discriminated between most patients with and without SSI (AUROC 0.869, 95% c.i. 0.824 to 0.914), which was consistent across subgroups. A representative cut-off score of ≥4 displayed a sensitivity of 0.701 (0.610-0.792), specificity of 0.911 (0.878-0.943), positive predictive value of 0.723 (0.633-0.814) and negative predictive value of 0.901 (0.867-0.935).

CONCLUSION

SSI can be diagnosed using a telephone questionnaire (obviating in-person assessment) in low resource settings.

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

BACKGROUND

Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks.

METHODS

The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned.

RESULTS

A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31).

CONCLUSION

Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov).

Collision Tumour of Combined Neuroendocrine and Squamous Cell Carcinoma of Nasal Cavity and Paranasal Sinus- Case Report and Review of Literature

Background

There have been many disputes about the definition, diagnosis, therapy, and prognosis of collision tumours.

Case Summary

We describe a rare patient with a collision tumour consisting of high-grade neuroendocrine carcinoma (NEC) and squamous cell carcinoma (SCC) in the right nasal cavity and paranasal sinus. She received surgery, concurrent chemoradiotherapy, and then two cycles of palliative chemotherapy. Follow-up at 26 months after diagnosis showed that this patient experienced a complete response with no signs of recurrence or metastasis. A literature review of previous 27 cases diagnosed with collision tumour of NEC and SCC in the head and neck was also undertaken.

Conclusion

It is highly challenging to manage collision tumours because these are two morphologically and etiologically distinct tumours. Well-designed multimodality therapy including surgery and chemoradiotherapy might lead to a long survival in these patients.

A Case of Myoepithelioma of Nasal Cavity and Short Review of Literature

Introduction: Myoepithelioma is a rare neoplasm of the salivary glands and accounts for less than 1% of salivary gland neoplasms. Only 7 cases of myoepithelioma in the nasal cavity have been reported till date in literature. Case Report: A 61 year old male presented to us with epistaxis. There was a pinkish fleshy mass occupying the right nasal cavity. Biopsy showed evidence of an epithelial tumor of intermediate aggressiveness. We did an endoscopic complete excision of nasal cavity mass. Histopathological examination of the resected tumor was consistent with myoepithelioma. Due to its rarity, the nature of the tumor is not known and regular follow-ups are needed for early detection of recurrence and malignancy. There has been no evidence of tumor recurrence in the 18 months following surgery.

Diagnostic Efficacy of New Xpert Ultra for Extrapulmonary Tuberculosis Using Culture and Composite Reference Standard

Introduction

Xpert Ultra (Cepheid, USA) is recently introduced with an extra category of trace-positive results and higher sensitivity for tuberculosis (TB) diagnosis.

Objective

The objective of the study was to assess the diagnostic accuracy of Xpert Ultra for extrapulmonary samples using culture and composite reference standard (CRS) as the gold standard.

Materials and Methods

In a 1-year (March 2021-22) prospective observational study, samples of suspected extrapulmonary TB (EPTB) patients were subjected to Ziehl-Neelsen staining, culture, and Xpert Ultra (Cepheid, Sunnyvale, CA) tests. Relevant clinical and treatment information was noted. The diagnostic accuracy of Xpert Ultra compared with culture and CRS was calculated.

Results

Out of 1720 suspected patients of EPTB, 223 (13%), predominantly males 135 (60%), with a mean age of 41.46 ± 19.81 years, were diagnosed as TB positive following CRS criteria. The maximum cases were of pleural TB (35.4%), followed by central nervous system TB (17.9%), gastrointestinal TB (17.5%), and lymph node TB (12.1%). Of all samples, 150 (8.7%) were microbiologically confirmed, including 141 detected by Xpert ultra, 67 culture positive, and only 16 smear positive. Among the Xpert Ultra-positive samples, 35 showed trace results, including six false-positive results. Considering culture and CRS as the gold standard, the sensitivity (86.57%, 59.64%) and specificity (94.98%, 99.47%) of Xpert Ultra were calculated, respectively. Rifampicin resistance was detected in 1 (0.70%) sample.

Conclusion

Diagnosis of EPTB is a challenge and Xpert Ultra may detect TB at a very early stage. However, it is essential to rule out false-positive results. Additional studies are needed on Xpert Ultra to interpret trace results better.

Extremely Rare Case of Extra Skeletal Soft Tissue Chondroma of Masseteric Space: a Diagnostic Challengel

Benign soft tissue chondroma is a rare type of extraskeletal chondrocytic tumour. It usually can be found in skeletal system in extremities. Head and neck region is one of the most uncommon sites for extraskeletal chondroma .Most common site is tongue and there has been paucity of cases arising from the other subsites .We present a case of 56 years gentleman who came to our OPD with a right masticator space swelling. It was nonmalignant on FNAC. He underwent wide local excision through a transparotid approach. Final biopsy & IHC report showed presence of benign chondrocytic neoplasm- soft tissue chondroma (extraskeletal). No further therapy was used and he has been in follow up since then. To our knowledge ,this is the third reported case of masseteric space chondroma.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-023-03705-5.

Strategies to minimise and monitor biases and imbalances by arm in surgical cluster randomised trials: evidence from ChEETAh, a trial in seven low- and middle-income countries

BACKGROUND

Cluster randomised controlled trials (cRCT) present challenges regarding risks of bias and chance imbalances by arm. This paper reports strategies to minimise and monitor biases and imbalances in the ChEETAh cRCT.

METHODS

ChEETAh was an international cRCT (hospitals as clusters) evaluating whether changing sterile gloves and instruments prior to abdominal wound closure reduces surgical site infection at 30 days postoperative. ChEETAh planned to recruit 12,800 consecutive patients from 64 hospitals in seven low-middle income countries. Eight strategies to minimise and monitor bias were pre-specified: (1) minimum of 4 hospitals per country; (2) pre-randomisation identification of units of exposure (operating theatres, lists, teams or sessions) within clusters; (3) minimisation of randomisation by country and hospital type; (4) site training delivered after randomisation; (5) dedicated 'warm-up week' to train teams; (6) trial specific sticker and patient register to monitor consecutive patient identification; (7) monitoring characteristics of patients and units of exposure; and (8) low-burden outcome-assessment.

RESULTS

This analysis includes 10,686 patients from 70 clusters. The results aligned to the eight strategies were (1) 6 out of 7 countries included ≥ 4 hospitals; (2) 87.1% (61/70) of hospitals maintained their planned operating theatres (82% [27/33] and 92% [34/37] in the intervention and control arms); (3) minimisation maintained balance of key factors in both arms; (4) post-randomisation training was conducted for all hospitals; (5) the 'warm-up week' was conducted at all sites, and feedback used to refine processes; (6) the sticker and trial register were maintained, with an overall inclusion of 98.1% (10,686/10,894) of eligible patients; (7) monitoring allowed swift identification of problems in patient inclusion and key patient characteristics were reported: malignancy (20.3% intervention vs 12.6% control), midline incisions (68.4% vs 58.9%) and elective surgery (52.4% vs 42.6%); and (8) 0.4% (41/9187) of patients refused consent for outcome assessment.

CONCLUSION

cRCTs in surgery have several potential sources of bias that include varying units of exposure and the need for consecutive inclusion of all eligible patients across complex settings. We report a system that monitored and minimised the risks of bias and imbalances by arm, with important lessons for future cRCTs within hospitals.

Antibiotic point prevalence survey at a tertiary healthcare hospital in India: Identifying strategies to improve the antibiotic stewardship program immediately after a COVID-19 wave

Background

The COVID-19 pandemic has substantially affected the antibiotic stewardship activities in most hospitals of India.

Aims

We conducted an antibiotic point prevalence survey (PPS) immediately after the decline of a major COVID-19 wave at a dedicated COVID-19 hospital. By doing so we aimed to identify the antibiotic prescription patterns, identify factors influencing the choice of antibiotics, and identify/develop strategies to improve the antibiotic stewardship program in such setups.

Methods

The PPS was single-centred, cross-sectional, and retrospective in nature. Patients admitted in various wards and intensive care units (ICUs) between September 2021 to October 2021 were included in our PPS.

Results

Of the included 460 patients, 192 were prescribed antibiotics. Of these 192 patients, ICU-admitted patients had the highest number of antibiotics prescribed i.e. 2.09 ± 0.92. Only a minor fraction (7.92 %) of antibiotics prescriptions were on the basis of culture reports. Most of the antibiotics were prescribed empirically by the parenteral route. The most common group of antibiotics prescribed were third-generation cephalosporins. Carbapenems were the most common designated antibiotics prescribed. A large number of patients (22.40 %) were prescribed a double anaerobic coverage.

Conclusion

The strategies that we identified to improve the antibiotic stewardship program at our institute included reviving the culture of sending culture reports to prescribe antibiotics, improving surgical prophylaxis guidelines, training resident doctors to categorize antibiotic prescriptions appropriately, closely monitoring prescriptions providing double anaerobic coverage, and improving the electronic medical record system for improving prescription auditing.

Routine sterile glove and instrument change at the time of abdominal wound closure to prevent surgical site infection (ChEETAh): a pragmatic, cluster-randomised trial in seven low-income and middle-income countries

BACKGROUND

Surgical site infection (SSI) remains the most common complication of surgery around the world. WHO does not make recommendations for changing gloves and instruments before wound closure owing to a lack of evidence. This study aimed to test whether a routine change of gloves and instruments before wound closure reduced abdominal SSI.

METHODS

ChEETAh was a multicentre, cluster randomised trial in seven low-income and middle-income countries (Benin, Ghana, India, Mexico, Nigeria, Rwanda, South Africa). Any hospitals (clusters) doing abdominal surgery in participating countries were eligible. Clusters were randomly assigned to current practice (42) versus intervention (39; routine change of gloves and instruments before wound closure for the whole scrub team). Consecutive adults and children undergoing emergency or elective abdominal surgery (excluding caesarean section) for a clean-contaminated, contaminated, or dirty operation within each cluster were identified and included. It was not possible to mask the site investigators, nor the outcome assessors, but patients were masked to the treatment allocation. The primary outcome was SSI within 30 days after surgery (participant-level), assessed by US Centers for Disease Control and Prevention criteria and on the basis of the intention-to-treat principle. The trial has 90% power to detect a minimum reduction in the primary outcome from 16% to 12%, requiring 12 800 participants from at least 64 clusters. The trial was registered with ClinicalTrials.gov, NCT03700749.

FINDINGS

Between June 24, 2020 and March 31, 2022, 81 clusters were randomly assigned, which included a total of 13 301 consecutive patients (7157 to current practice and 6144 to intervention group). Overall, 11 825 (88·9%) of 13 301 patients were adults, 6125 (46·0%) of 13 301 underwent elective surgery, and 8086 (60·8%) of 13 301 underwent surgery that was clean-contaminated or 5215 (39·2%) of 13 301 underwent surgery that was contaminated-dirty. Glove and instrument change took place in 58 (0·8%) of 7157 patients in the current practice group and 6044 (98·3%) of 6144 patients in the intervention group. The SSI rate was 1280 (18·9%) of 6768 in the current practice group versus 931 (16·0%) of 5789 in the intervention group (adjusted risk ratio: 0·87, 95% CI 0·79-0·95; p=0·0032). There was no evidence to suggest heterogeneity of effect across any of the prespecified subgroup analyses. We did not anticipate or collect any specific data on serious adverse events.

INTERPRETATION

This trial showed a robust benefit to routinely changing gloves and instruments before abdominal wound closure. We suggest that it should be widely implemented into surgical practice around the world.

FUNDING

National Institute for Health Research (NIHR) Clinician Scientist Award, NIHR Global Health Research Unit Grant, Mölnlycke Healthcare.

A multiscale tissue assessment in a rat model of mild traumatic brain injury

Diffusion tensor imaging (DTI) has demonstrated the potential to assess the pathophysiology of mild traumatic brain injury (mTBI) but correlations of DTI findings and pathological changes in mTBI are unclear. We evaluated the potential of ex vivo DTI to detect tissue damage in a mild mTBI rat model by exploiting multiscale imaging methods, histology and scanning micro-X-ray diffraction (SμXRD) 35 days after sham-operation (n = 2) or mTBI (n = 3). There were changes in DTI parameters rostral to the injury site. When examined by histology and SμXRD, there was evidence of axonal damage, reduced myelin density, gliosis, and ultrastructural alterations in myelin that were ongoing at the experimental time point of 35 days postinjury. We assessed the relationship between the 3 imaging modalities by multiple linear regression analysis. In this analysis, DTI and histological parameters were moderately related, whereas SμXRD parameters correlated weakly with DTI and histology. These findings suggest that while DTI appears to distinguish tissue changes at the microstructural level related to the loss of myelinated axons and gliosis, its ability to visualize alterations in myelin ultrastructure is limited. The use of several imaging techniques represents a novel approach to reveal tissue damage and provides new insights into mTBI detection.

Post mortem mapping of connectional anatomy for the validation of diffusion MRI

Diffusion MRI (dMRI) is a unique tool for the study of brain circuitry, as it allows us to image both the macroscopic trajectories and the microstructural properties of axon bundles in vivo. The Human Connectome Project ushered in an era of impressive advances in dMRI acquisition and analysis. As a result of these efforts, the quality of dMRI data that could be acquired in vivo improved substantially, and large collections of such data became widely available. Despite this progress, the main limitation of dMRI remains: it does not image axons directly, but only provides indirect measurements based on the diffusion of water molecules. Thus, it must be validated by methods that allow direct visualization of axons but that can only be performed in post mortem brain tissue. In this review, we discuss methods for validating the various features of connectional anatomy that are extracted from dMRI, both at the macro-scale (trajectories of axon bundles), and at micro-scale (axonal orientations and other microstructural properties). We present a range of validation tools, including anatomic tracer studies, Klingler's dissection, myelin stains, label-free optical imaging techniques, and others. We provide an overview of the basic principles of each technique, its limitations, and what it has taught us so far about the accuracy of different dMRI acquisition and analysis approaches.

VascuViz: a multimodality and multiscale imaging and visualization pipeline for vascular systems biology

Despite advances in imaging, image-based vascular systems biology has remained challenging because blood vessel data are often available only from a single modality or at a given spatial scale, and cross-modality data are difficult to integrate. Therefore, there is an exigent need for a multimodality pipeline that enables ex vivo vascular imaging with magnetic resonance imaging, computed tomography and optical microscopy of the same sample, while permitting imaging with complementary contrast mechanisms from the whole-organ to endothelial cell spatial scales. To achieve this, we developed 'VascuViz'-an easy-to-use method for simultaneous three-dimensional imaging and visualization of the vascular microenvironment using magnetic resonance imaging, computed tomography and optical microscopy in the same intact, unsectioned tissue. The VascuViz workflow permits multimodal imaging with a single labeling step using commercial reagents and is compatible with diverse tissue types and protocols. VascuViz's interdisciplinary utility in conjunction with new data visualization approaches opens up new vistas in image-based vascular systems biology.

Microstructural Tissue Changes in a Rat Model of Mild Traumatic Brain Injury

Our study investigates the potential of diffusion MRI (dMRI), including diffusion tensor imaging (DTI), fixel-based analysis (FBA) and neurite orientation dispersion and density imaging (NODDI), to detect microstructural tissue abnormalities in rats after mild traumatic brain injury (mTBI). The brains of sham-operated and mTBI rats 35 days after lateral fluid percussion injury were imaged ex vivo in a 11.7-T scanner. Voxel-based analyses of DTI-, fixel- and NODDI-based metrics detected extensive tissue changes in directly affected brain areas close to the primary injury, and more importantly, also in distal areas connected to primary injury and indirectly affected by the secondary injury mechanisms. Histology revealed ongoing axonal abnormalities and inflammation, 35 days after the injury, in the brain areas highlighted in the group analyses. Fractional anisotropy (FA), fiber density (FD) and fiber density and fiber bundle cross-section (FDC) showed similar pattern of significant areas throughout the brain; however, FA showed more significant voxels in gray matter areas, while FD and FDC in white matter areas, and orientation dispersion index (ODI) in areas most damage based on histology. Region-of-interest (ROI)-based analyses on dMRI maps and histology in selected brain regions revealed that the changes in MRI parameters could be attributed to both alterations in myelinated fiber bundles and increased cellularity. This study demonstrates that the combination of dMRI methods can provide a more complete insight into the microstructural alterations in white and gray matter after mTBI, which may aid diagnosis and prognosis following a mild brain injury.

Fractional anisotropy from diffusion tensor imaging correlates with acute astrocyte and myelin swelling in neonatal swine models of excitotoxic and hypoxic-ischemic brain injury

The specific cytopathology that causes abnormal fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging (DTI) after neonatal hypoxia-ischemia (HI) is not completely understood. The panoply of cell types in the brain might contribute differentially to changes in DTI metrics. Because glia are the predominant cell type in brain, we hypothesized that changes in FA and MD would signify perturbations in glial microstructure. Using a 3-Tesla clinical scanner, we conducted in vivo DTI MRI in nine neonatal piglets at 20-96 h after excitotoxic brain injury from striatal quinolinic acid injection or global HI. FA and MD from putamen, caudate, and internal capsule in toto were correlated with astrocyte swelling, neuronal excitotoxicity, and white matter injury. Low FA correlated with more swollen astrocytes immunophenotyped by aquaporin-4 (AQP4), glial fibrillary acidic protein (GFAP), and glutamate transporter-1 (GLT-1). Low FA was also related to the loss of neurons with perineuronal GLT-1+ astrocyte decorations, large myelin swellings, lower myelin density, and oligodendrocyte cell death identified by 2',3'-cyclic nucleotide 3'-phosphodiesterase, bridging integrator-1, and nuclear morphology. MD correlated with degenerating oligodendrocytes and depletion of normal GFAP+ astrocytes but not with astrocyte or myelin swelling. We conclude that FA is associated with cytotoxic edema in astrocytes and oligodendrocyte processes as well as myelin injury at the cellular level. MD can detect glial cell death and loss, but it may not discern subtle pathology in swollen astrocytes, oligodendrocytes, or myelin. This study provides a cytopathologic basis for interpreting DTI in the neonatal brain after HI.

Developmental, cellular, and behavioral phenotypes in a mouse model of congenital hypoplasia of the dentate gyrus

In the hippocampus, a widely accepted model posits that the dentate gyrus improves learning and memory by enhancing discrimination between inputs. To test this model, we studied conditional knockout mice in which the vast majority of dentate granule cells (DGCs) fail to develop – including nearly all DGCs in the dorsal hippocampus – secondary to eliminating Wntless (Wls) in a subset of cortical progenitors with Gfap-Cre. Other cells in the Wls^fl/-;Gfap-Cre hippocampus were minimally affected, as determined by single nucleus RNA sequencing. CA3 pyramidal cells, the targets of DGC-derived mossy fibers, exhibited normal morphologies with a small reduction in the numbers of synaptic spines. Wls^fl/-;Gfap-Cre mice have a modest performance decrement in several complex spatial tasks, including active place avoidance. They were also modestly impaired in one simpler spatial task, finding a visible platform in the Morris water maze. These experiments support a role for DGCs in enhancing spatial learning and memory.

Learned Proximal Networks for Quantitative Susceptibility Mapping

Quantitative Susceptibility Mapping (QSM) estimates tissue magnetic susceptibility distributions from Magnetic Resonance (MR) phase measurements by solving an ill-posed dipole inversion problem. Conventional single orientation QSM methods usually employ regularization strategies to stabilize such inversion, but may suffer from streaking artifacts or over-smoothing. Multiple orientation QSM such as calculation of susceptibility through multiple orientation sampling (COSMOS) can give well-conditioned inversion and an artifact free solution but has expensive acquisition costs. On the other hand, Convolutional Neural Networks (CNN) show great potential for medical image reconstruction, albeit often with limited interpretability. Here, we present a Learned Proximal Convolutional Neural Network (LP-CNN) for solving the ill-posed QSM dipole inversion problem in an iterative proximal gradient descent fashion. This approach combines the strengths of data-driven restoration priors and the clear interpretability of iterative solvers that can take into account the physical model of dipole convolution. During training, our LP-CNN learns an implicit regularizer via its proximal, enabling the decoupling between the forward operator and the data-driven parameters in the reconstruction algorithm. More importantly, this framework is believed to be the first deep learning QSM approach that can naturally handle an arbitrary number of phase input measurements without the need for any ad-hoc rotation or re-training. We demonstrate that the LP-CNN provides state-of-the-art reconstruction results compared to both traditional and deep learning methods while allowing for more flexibility in the reconstruction process.

Diffusion-time dependence of diffusional kurtosis in the mouse brain

PURPOSE

To investigate diffusion-time dependency of diffusional kurtosis in the mouse brain using pulsed-gradient spin-echo (PGSE) and oscillating-gradient spin-echo (OGSE) sequences.

METHODS

3D PGSE and OGSE kurtosis tensor data were acquired from ex vivo brains of adult, cuprizone-treated, and age-matched control mice with diffusion-time (t_D ) ~ 20 ms and frequency (f) = 70 Hz, respectively. Further, 2D acquisitions were performed at multiple times/frequencies ranging from f = 140 Hz to t_D = 30 ms with b-values up to 4000 s/mm² . Monte Carlo simulations were used to investigate the coupled effects of varying restriction size and permeability on time/frequency-dependence of kurtosis with both diffusion-encoding schemes. Simulations and experiments were further performed to investigate the effect of varying number of cycles in OGSE waveforms.

RESULTS

Kurtosis and diffusivity maps exhibited significant region-specific changes with diffusion time/frequency across both gray and white matter areas. PGSE- and OGSE-based kurtosis maps showed reversed contrast between gray matter regions in the cerebellar and cerebral cortex. Localized time/frequency-dependent changes in kurtosis tensor metrics were found in the splenium of the corpus callosum in cuprizone-treated mouse brains, corresponding to regional demyelination seen with histological assessment. Monte Carlo simulations showed that kurtosis estimates with pulsed- and oscillating-gradient waveforms differ in their sensitivity to exchange. Both simulations and experiments showed dependence of kurtosis on number of cycles in OGSE waveforms for non-zero permeability.

CONCLUSION

The results show significant time/frequency-dependency of diffusional kurtosis in the mouse brain, which can provide sensitivity to probe intrinsic cellular heterogeneity and pathological alterations in gray and white matter.

Ex vivo diffusion MRI of the human brain: Technical challenges and recent advances

This review discusses ex vivo diffusion magnetic resonance imaging (dMRI) as an important research tool for neuroanatomical investigations and the validation of in vivo dMRI techniques, with a focus on the human brain. We review the challenges posed by the properties of post-mortem tissue, and discuss state-of-the-art tissue preparation methods and recent advances in pulse sequences and acquisition techniques to tackle these. We then review recent ex vivo dMRI studies of the human brain, highlighting the validation of white matter orientation estimates and the atlasing and mapping of large subcortical structures. We also give particular emphasis to the delineation of layered gray matter structure with ex vivo dMRI, as this application illustrates the strength of its mesoscale resolution over large fields of view. We end with a discussion and outlook on future and potential directions of the field.

Nuclei-specific deposits of iron and calcium in the rat thalamus after status epilepticus revealed with quantitative susceptibility mapping (QSM)

PURPOSE

To investigate pathological changes in the rat brain after pilocarpine-induced status epilepticus using quantitative susceptibility mapping (QSM).

MATERIALS AND METHODS

3D multiecho gradient-echo (GRE) data were acquired from ex vivo brains of pilocarpine-injected and age-matched control rats at 11.7T. Maps of R2* and quantitative susceptibility were calculated from the acquired 3D GRE magnitude and phase data, respectively. QSM and R2* maps were compared with Perls' (iron) and Alizarin-red-S (calcium) stainings in the same brains to investigate the pathophysiological basis of susceptibility contrast.

RESULTS

Bilaterally symmetric lesions were detected in reproducible thalamic regions of pilocarpine-treated rats, characterized by hyperintensity in R2* maps. In comparison, quantitative susceptibility maps demonstrated heterogeneous contrast within the lesions, with distinct hyperintense (paramagnetic) and hypointense (diamagnetic) areas. Comparison with histological assessment revealed localized deposits of iron- and calcium-positive granules in thalamic nuclei corresponding to paramagnetic and diamagnetic areas delineated in the susceptibility maps, respectively. Pronounced differences were observed in the lesions between background-corrected phase images and reconstructed susceptibility maps, indicating unreliable differentiation of iron and calcium deposits in phase maps. Multiple linear regression showed a significant association between susceptibility values and measured optical densities (ODs) of iron and calcium in the lesions (R2  = 0.42, P < 0.001), with a positive dependence on OD of iron and negative dependence on OD of calcium.

CONCLUSION

QSM can detect and differentiate pathological iron and calcium deposits with high sensitivity and improved spatial accuracy compared to R2* or GRE phase images, rendering it a promising technique for diagnosing thalamic lesions after status epilepticus.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:554-564.

Elucidation of White Matter Tracts of the Human Amygdala by Detailed Comparison between High-Resolution Postmortem Magnetic Resonance Imaging and Histology

The amygdala has attracted considerable research interest because of its potential involvement in various neuropsychiatric disorders. Recently, attempts have been made using magnetic resonance imaging (MRI) to evaluate the integrity of the axonal connections to and from the amygdala under pathological conditions. Although amygdalar pathways have been studied extensively in animal models, anatomical references for the human brain are limited to histology-based resources from a small number of slice locations, orientations and annotations. In the present study, we performed high-resolution (250 μm) MRI of postmortem human brains followed by serial histology sectioning. The histology data were used to identify amygdalar pathways, and the anatomical delineation of the assigned structures was extended into 3D using the MRI data. We were able to define the detailed anatomy of the stria terminalis and amygdalofugal pathway, as well as the anatomy of the nearby basal forebrain areas, including the substantia innominata. The present results will help us understand in detail the white matter structures associated with the amygdala, and will serve as an anatomical reference for the design of in vivo MRI studies and interpretation of their data.

Diffusion tensor imaging measures of white matter compared to myelin basic protein immunofluorescence in tissue cleared intact brains

We provide datasets from combined ex vivo diffusion tensor imaging (DTI) and Clear Lipid-exchanged, Anatomically Rigid, Imaging/immunostaining compatible, Tissue hYdrogel (CLARITY) performed on intact mouse brains. DTI-derived measures of fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD) were compared to antibody-based labeling of myelin basic protein (MBP), as measured by fluorescence microscopy. We used a customized CLARITY hydrogel solution to facilitate whole brain tissue clearing and subsequent immunolabeling. We describe how CLARITY was made compatible with magnetic resonance imaging with the intention of facilitating future multimodal imaging studies that may combine noninvasive imaging with 3D immunohistochemistry. These data and methods are related to the accompanying research article entitled, 'The role of myelination in measures of white matter integrity: Combination of diffusion tensor imaging and two-photon microscopy of CLARITY intact brains' (E.H. Chang, M. Argyelan, M. Aggarwal, T-S. Chandon, K.H. Karlsgodt, S. Mori, A.K. Malhotra, 2016) [1].

The role of myelination in measures of white matter integrity: Combination of diffusion tensor imaging and two-photon microscopy of CLARITY intact brains

Diffusion tensor imaging (DTI) is used extensively in neuroscience to noninvasively estimate white matter (WM) microarchitecture. However, the diffusion signal is inherently ambiguous because it infers WM structure from the orientation of water diffusion and cannot identify the biological sources of diffusion changes. To compare inferred WM estimates to directly labeled axonal elements, we performed a novel within-subjects combination of high-resolution ex vivo DTI with two-photon laser microscopy of intact mouse brains rendered optically transparent by Clear Lipid-exchanged, Anatomically Rigid, Imaging/immunostaining compatible, Tissue hYdrogel (CLARITY). We found that myelin basic protein (MBP) immunofluorescence significantly correlated with fractional anisotropy (FA), especially in WM regions with coherent fiber orientations and low fiber dispersion. Our results provide evidence that FA is particularly sensitive to myelination in WM regions with these characteristics. Furthermore, we found that radial diffusivity (RD) was only sensitive to myelination in a subset of WM tracts, suggesting that the association of RD with myelin should be used cautiously. This combined DTI-CLARITY approach illustrates, for the first time, a framework for using brain-wide immunolabeling of WM targets to elucidate the relationship between the diffusion signal and its biological underpinnings. This study also demonstrates the feasibility of a within-subject combination of noninvasive neuroimaging and tissue clearing techniques that has broader implications for neuroscience research.

Reactivation of mutant p53 by a dietary-related compound phenethyl isothiocyanate inhibits tumor growth

Mutations in the p53 tumor-suppressor gene are prevalent in human cancers. The majority of p53 mutations are missense, which can be classified into contact mutations (that directly disrupts the DNA-binding activity of p53) and structural mutations (that disrupts the conformation of p53). Both of the mutations can disable the normal wild-type (WT) p53 activities. Nevertheless, it has been amply documented that small molecules can rescue activity from mutant p53 by restoring WT tumor-suppressive functions. These compounds hold promise for cancer therapy and have now entered clinical trials. In this study, we show that cruciferous-vegetable-derived phenethyl isothiocyanate (PEITC) can reactivate p53 mutant under in vitro and in vivo conditions, revealing a new mechanism of action for a dietary-related compound. PEITC exhibits growth-inhibitory activity in cells expressing p53 mutants with preferential activity toward p53^R175, one of the most frequent ‘hotspot' mutations within the p53 sequence. Mechanistic studies revealed that PEITC induces apoptosis in a p53^R175 mutant-dependent manner by restoring p53 WT conformation and transactivation functions. Accordingly, in PEITC-treated cells the reactivated p53^R175 mutant induces apoptosis by activating canonical WT p53 targets, inducing a delay in S and G2/M phase, and by phosphorylating ATM/CHK2. Interestingly, the growth-inhibitory effects of PEITC depend on the redox state of the cell. Further, PEITC treatments render the p53^R175 mutant sensitive to degradation by the proteasome and autophagy in a concentration-dependent manner. PEITC-induced reactivation of p53^R175 and its subsequent sensitivity to the degradation pathways likely contribute to its anticancer activities. We further show that dietary supplementation of PEITC is able to reactivate WT activity in vivo as well, inhibiting tumor growth in xenograft mouse model. These findings provide the first example of mutant p53 reactivation by a dietary compound and have important implications for cancer prevention and therapy.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

B0 -orientation dependent magnetic susceptibility-induced white matter contrast in the human brainstem at 11.7T

PURPOSE

To investigate B0 -field-orientation dependent white matter contrast in the human brainstem based on R2 * and frequency difference (Δf) mapping from gradient echo (GRE) imaging at 11.7T.

METHODS

Multi-echo GRE data were acquired from two fixed human brainstem specimens at multiple orientations with respect to the static B0 field. The B0 -orientation dependent modulation curves of R2 * and Δf measurements between short and long echo time regimes were used to reconstruct maps of three-dimensional (3D) white matter orientation vectors. The results were compared with maps from diffusion MRI, susceptibility tensor imaging, and histological staining of the same specimens.

RESULTS

R2 * and Δf maps demonstrated distinct and significant contrast modulation between the corticospinal tract (CST) and transverse pontine fibers (TPF) dependent on B0 orientation. Interleaved fiber orientations of the CST and TPF could be sensitively resolved based on field-orientation-dependent fitting of the R2 * and Δf measurements. The fitted 3D orientation vector maps and peak-to-peak amplitude of R2 * and Δf modulation exhibited close correspondence to primary eigenvector and anisotropy maps derived from diffusion MRI. The amplitude of B0 -orientation dependent R2 * modulation was significantly (P < 0.005) higher in the CST compared with TPF, while fractional anisotropies were comparable.

CONCLUSION

The findings of this study demonstrate the potential of B0 -orientation dependent susceptibility-induced R2 * and Δf contrasts to probe tract-specific orientation and microstructure in white matter. Magn Reson Med 75:2455-2463, 2016. © 2016 Wiley Periodicals, Inc.

Randomized double-blind comparison of ephedrine and phenylephrine for management of post-spinal hypotension in potential fetal compromise

BACKGROUND

Most studies comparing phenylephrine and ephedrine have been conducted during elective caesarean sections in healthy mothers with no fetal compromise. The effect of vasopressors on fetal outcome may differ between healthy and compromised fetuses. There has been little research into the effect of phenylephrine and ephedrine, when used for management of post-spinal hypotension in the presence of potential fetal compromise.

METHODS

Healthy women with a singleton pregnancy undergoing emergency caesarean section for fetal compromise under spinal anaesthesia were studied. One-hundred-and-six consecutive subjects, who developed hypotension after spinal anaesthesia, were randomly allocated to two groups of 53 each, to receive either phenylephrine (Group P) or ephedrine (Group E). For every systolic blood pressure reading <100mmHg patients received phenylephrine 100μg or ephedrine 8mg depending on group allocation. Umbilical blood gas parameters and Apgar scores were recorded.

RESULTS

There was no statistically significant difference in umbilical arterial pH (P=0.79), umbilical venous pH (P=0.98), other blood gas parameters, incidence of fetal acidosis (P=1.00) and Apgar scores. The number of hypotensive episodes, vasopressor doses for treatment of the first hypotensive episode and the total number of doses used during the study period were comparable. The median [IQR] total number of doses of phenylephrine and ephedrine used before delivery were 2 [1-2] and 2 [1-2], respectively (P=0.67). More patients receiving ephedrine (24.5%) developed tachycardia than those receiving phenylephrine (3.8%) (P=0.004). Bradycardia was more common with phenylephrine, with 39.6% of patients in Group P as compared to only 1.9% of patients in Group E developing a heart rate <60beats/min after vasopressor administration (P=0.001).

CONCLUSIONS

Both phenylephrine 100μg and ephedrine 8mg boluses are equally efficacious when treating post-spinal hypotension in the presence of potential fetal compromise. However, phenylephrine may be a better choice in the presence of maternal tachycardia.