Rapamycin Perfluorocarbon Nanoparticle Mitigates Cisplatin-Induced Acute Kidney Injury.

For nearly five decades, cisplatin has played an important role as a standard chemotherapeutic agent and been prescribed to 10-20% of all cancer patients. Although nephrotoxicity associated with platinum-based agents is well recognized, treatment of cisplatin-induced acute kidney injury is mainly supportive and no specific mechanism-based prophylactic approach is available to date. Here, we postulated that systemically delivered rapamycin perfluorocarbon nanoparticles (PFC NP) could reach the injured kidneys at sufficient and sustained concentrations to mitigate cisplatin-induced acute kidney injury and preserve renal function. Using fluorescence microscopic imaging and fluorine magnetic resonance imaging/spectroscopy, we illustrated that rapamycin-loaded PFC NP permeated and were retained in injured kidneys. Histologic evaluation and blood urea nitrogen (BUN) confirmed that renal structure and function were preserved 48 h after cisplatin injury. Similarly, weight loss was slowed down. Using western blotting and immunofluorescence staining, mechanistic studies revealed that rapamycin PFC NP significantly enhanced autophagy in the kidney, reduced the expression of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), as well as decreased the expression of the apoptotic protein Bax, all of which contributed to the suppression of apoptosis that was confirmed with TUNEL staining. In summary, the delivery of an approved agent such as rapamycin in a PFC NP format enhances local delivery and offers a novel mechanism-based prophylactic therapy for cisplatin-induced acute kidney injury.

Comparison of hyperpolarized 13 C and non-hyperpolarized deuterium MRI approaches for imaging cerebral glucose metabolism at 4.7 T.

PURPOSE: The purpose of this study was to directly compare two isotopic metabolic imaging approaches, hyperpolarized (HP) 13 C MRI and deuterium metabolic imaging (DMI), for imaging specific closely related segments of cerebral glucose metabolism at 4.7 T. METHODS: Comparative HP-13 C and DMI neuroimaging experiments were conducted consecutively in normal rats during the same scanning session. Localized conversions of [1-13 C]pyruvate and [6,6-2 H2 ]glucose to their respective downstream metabolic products were measured by spectroscopic imaging, using an identical 2D-CSI sequence with parameters optimized for the respective experiments. To facilitate direct comparison, a pair of substantially equivalent 2.5-cm double-tuned X/1 H RF surface coils was developed. For improved results, multidimensional low-rank reconstruction was applied to denoise the raw DMI data. RESULTS: Localized conversion of HP [1-13 C]pyruvate to [1-13 C]lactate, and [6,6-2 H2 ]glucose to [3,3-2 H2 ]lactate and Glx-d (glutamate and glutamine), was detected in rat brain by spectroscopic imaging at 4.7 T. The SNR and spatial resolution of HP-13 C MRI was superior to DMI but limited to a short time window, whereas the lengthy DMI acquisition yielded maps of not only lactate, but also Glx production, albeit with relatively poor spectral discrimination between metabolites at this field strength. Across the individual rats, there was an apparent inverse correlation between cerebral production of HP [1-13 C]lactate and Glx-d, along with a trend toward increased [3,3-2 H2 ]lactate. CONCLUSION: The HP-13 C MRI and DMI methods are both feasible at 4.7 T and have significant potential for metabolic imaging of specific segments of glucose metabolism.

Validating in vivo hyperpolarized 129 Xe diffusion MRI and diffusion morphometry in the mouse lung.

PURPOSE: Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using 3 He, it has never been validated in mice for 129 Xe. Here, we examine the effect of cardiac motion on diffusion imaging and validate 129 Xe diffusion morphometry in mice. THEORY AND METHODS: Mice were imaged using gradient-echo-based diffusion imaging, and apparent diffusion-coefficient (ADC) maps were generated with and without cardiac gating. Diffusion-weighted images were fit to a previously developed theoretical model using Bayesian probability theory, producing morphometric parameters that were compared with conventional histology. RESULTS: Cardiac gating had no significant impact on ADC measurements (dual-gating: ADC = 0.020 cm2 /s, single-gating: ADC = 0.020 cm2 /s; P = .38). Diffusion-morphometry-generated maps of ADC (mean, 0.0165 ± 0.0001 cm2 /s) and acinar dimensions (alveolar sleeve depth [h] = 44 µm, acinar duct radii [R] = 99 µm, mean linear intercept [Lm ] = 74 µm) that agreed well with conventional histology (h = 45 µm, R = 108 µm, Lm = 63 µm). CONCLUSION: Cardiac motion has negligible impact on 129 Xe ADC measurements in mice, arguing its impact will be similarly minimal in humans, where relative cardiac motion is reduced. Hyperpolarized 129 Xe diffusion morphometry accurately and noninvasively maps the dimensions of lung microstructure, suggesting it can quantify the pulmonary microstructure in mouse models of lung disease.

15 N-carnitine, a novel endogenous hyperpolarized MRI probe with long signal lifetime.

PURPOSE: The purpose of this study was to investigate hyperpolarization and in vivo imaging of [15 N]carnitine, a novel endogenous MRI probe with long signal lifetime. METHODS: L-[15 N]carnitine-d9 was hyperpolarized by the method of dynamic nuclear polarization followed by rapid dissolution. The T1 signal lifetimes were estimated in aqueous solution and in vivo following intravenous injection in rats, using a custom-built dual-tuned 15 N/1 H RF coil at 4.7 T. 15 N chemical shift imaging and 15 N fast spin-echo images of rat abdomen were acquired 3 minutes after [15 N]carnitine injection. RESULTS: Estimated T1 times of [15 N]carnitine at 4.7 T were 210 seconds (in H2 O) and 160 seconds (in vivo), with an estimated polarization level of 10%. Remarkably, the [15 N]carnitine coherence was detectable in rat abdomen for 5 minutes after injection for the nonlocalized acquisition. No downstream metabolites were detected on localized or nonlocalized 15 N spectra. Diffuse liver enhancement was detected on 15 N fast spin-echo imaging 3 minutes after injection, with mean hepatic SNR of 18 ± 5 at a spatial resolution of 4 × 4 mm. CONCLUSION: This study showed the feasibility of hyperpolarizing and imaging the biodistribution of HP [15 N]carnitine.

Single-Session Bronchial Thermoplasty Guided by 129Xe Magnetic Resonance Imaging. A Pilot Randomized Controlled Clinical Trial.

Rationale: Adverse events have limited the use of bronchial thermoplasty (BT) in severe asthma.Objectives: We sought to evaluate the effectiveness and safety of using 129Xe magnetic resonance imaging (129Xe MRI) to prioritize the most involved airways for guided BT.Methods: Thirty subjects with severe asthma were imaged with volumetric computed tomography and 129Xe MRI to quantitate segmental ventilation defects. Subjects were randomized to treatment of the six most involved airways in the first session (guided group) or a standard three-session BT (unguided). The primary outcome was the change in Asthma Quality of Life Questionnaire score from baseline to 12 weeks after the first BT for the guided group compared with after three treatments for the unguided group.Measurements and Main Results: There was no significant difference in quality of life after one guided compared with three unguided BTs (change in Asthma Quality of Life Questionnaire guided = 0.91 [95% confidence interval, 0.28-1.53]; unguided = 1.49 [95% confidence interval, 0.84-2.14]; P = 0.201). After one BT, the guided group had a greater reduction in the percentage of poorly and nonventilated lung from baseline when compared with unguided (-17.2%; P = 0.009). Thirty-three percent experienced asthma exacerbations after one guided BT compared with 73% after three unguided BTs (P = 0.028).Conclusions: Results of this pilot study suggest that similar short-term improvements can be achieved with one BT treatment guided by 129Xe MRI when compared with standard three-treatment-session BT with fewer periprocedure adverse events.

Toward noninvasive quantification of adipose tissue oxygenation with MRI.

BACKGROUND: Molecular oxygen (O2) plays a key role in normal and pathological adipose tissue function, yet technologies to measure its role in adipose tissue function are limited. O2 is paramagnetic and, in principle, directly influences the magnetic resonance (MR) 1H longitudinal relaxation rate constant of lipids, R1; thus, we hypothesize that MR imaging (MRI) can directly measure adipose O2 via a simple measure of R1. METHODS: R1 was measured in a 4.7T preclinical MRI system at discrete oxygen partial pressure (pO2) levels. These measures were made in vitro in an idealized system and in vivo in subcutaneous and visceral white adipose of rodents. pO2 was determined using an invasive fiber-optic oxygen monitor. From the MRI and fiber optic data we determined the "relaxivity" of O2 in lipid, a critical parameter in converting the MRI-based R1 measurement into pO2. We used breathing gas challenge to estimate the changes in lipid pO2 (ΔpO2). RESULTS: The relaxivity of O2 in lipid was determined to be 1.7·10-3 ± 4·10-4 mmHg-1s-1 at 4.7T and 37 °C, and was consistent between in vitro and in vivo adipose tissue. There was a strong, significant correlation between MRI- and gold standard OxyLite-based measurements of lipid ΔpO2 for in vivo visceral and subcutaneous fat depots in rodents. CONCLUSION: This study lays the foundation for a direct, noninvasive measure of adipose pO2 using MRI and will allow for noninvasive measurement of O2 flux in adipose tissue. The proposed approach would be of particular importance in the interrogation of the pathogenesis of type 2 diabetes, where it has been suggested that adipose tissue hypoxia is an independent driver of insulin resistance pathway.

Direct comparison of 129 Xe diffusion measurements with quantitative histology in human lungs.

PURPOSE: Chronic obstructive pulmonary disease (COPD) is an irreversible lung disease characterized by small-airway obstruction and alveolar-airspace destruction. Hyperpolarized 129 Xe diffusion MRI of lung is a promising biomarker for assessing airspace enlargement, but has yet to be validated by direct comparison to lung histology. Here we have compared diffusion measurements of hyperpolarized (HP) 129 Xe in explanted lungs to regionally matched morphological measures of airspace size. METHODS: Explanted lungs from five COPD patients and two idiopathic pulmonary fibrosis (IPF) patients were imaged using MRI with hyperpolarized 129 Xe using a two-b-value gradient-echo diffusion sequence, and 34 histological samples were taken from these lungs for quantitative histology. Mean-linear-intercept (Lm ) was compared with spatially matched measures of apparent diffusion coefficient (ADC) from 129 Xe MRI. RESULTS: The mean ADC from COPD lung samples was 0.071 ± 0.011 cm2 /s, and for IPF lungs was 0.033 ± 0.001 cm2 /s (P < 10-15 between groups). The mean Lm in COPD samples was 0.076 ± 0.027 cm and 0.041 ± 0.004 cm in IPF (P = 2.7 × 10-7 between groups). The Pearson-correlation between ADC and Lm measurements was r = 0.59. CONCLUSIONS: Diffusion MRI of HP 129 Xe quantifies regional airspace enlargement in COPD. 129 Xe ADC showed much less overlap between groups than quantitative histology, consistent with our past experience with 3 He diffusion MRI in COPD. Magn Reson Med 77:265-272, 2017. © 2016 Wiley Periodicals, Inc.

Diffusion lung imaging with hyperpolarized gas MRI.

Lung imaging using conventional 1 H MRI presents great challenges because of the low density of lung tissue, lung motion and very fast lung tissue transverse relaxation (typical T2 * is about 1-2 ms). MRI with hyperpolarized gases (3 He and 129 Xe) provides a valuable alternative because of the very strong signal originating from inhaled gas residing in the lung airspaces and relatively slow gas T2 * relaxation (typical T2 * is about 20-30 ms). However, in vivo human experiments should be performed very rapidly - usually during a single breath-hold. In this review, we describe the recent developments in diffusion lung MRI with hyperpolarized gases. We show that a combination of the results of modeling of gas diffusion in lung airspaces and diffusion measurements with variable diffusion-sensitizing gradients allows the extraction of quantitative information on the lung microstructure at the alveolar level. From an MRI scan of less than 15 s, this approach, called in vivo lung morphometry, allows the provision of quantitative values and spatial distributions of the same physiological parameters as measured by means of 'standard' invasive stereology (mean linear intercept, surface-to-volume ratio, density of alveoli, etc.). In addition, the approach makes it possible to evaluate some advanced Weibel parameters characterizing lung microstructure: average radii of alveolar sacs and ducts, as well as the depth of their alveolar sleeves. Such measurements, providing in vivo information on the integrity of pulmonary acinar airways and their changes in different diseases, are of great importance and interest to a broad range of physiologists and clinicians. We also discuss a new type of experiment based on the in vivo lung morphometry technique combined with quantitative computed tomography measurements, as well as with gradient echo MRI measurements of hyperpolarized gas transverse relaxation in the lung airspaces. Such experiments provide additional information on the blood vessel volume fraction, specific gas volume and length of the acinar airways, and allow the evaluation of lung parenchymal and non-parenchymal tissue. Copyright © 2015 John Wiley & Sons, Ltd.

What makes a good pediatric transplant lung: Insights from in vivo lung morphometry with hyperpolarized 3 He magnetic resonance imaging.

Obtaining information on transplanted lung microstructure is an important part of the current care for monitoring transplant recipients. However, until now this information was only available from invasive lung biopsy. The objective of this study was to evaluate the use of an innovative non-invasive technique, in vivo lung morphometry with hyperpolarized ³He MRI-to characterize lung microstructure in the pediatric lung transplant population. This technique yields quantitative measurements of acinar airways' (alveolar ducts and sacs) parameters, such as acinar airway radii and alveolar depth. Six pediatric lung transplant recipients with cystic fibrosis underwent in vivo lung morphometry MRI, pulmonary function testing, and quantitative CT. We found a strong correlation between lung lifespan and alveolar depth-patients with more shallow alveoli were likely to have a negative outcome sooner than those with larger alveolar depth. Combining morphometric results with CT, we also determined mean alveolar wall thickness and found substantial increases in this parameter in some patients that negatively correlated with DLCO. In vivo lung morphometry uniquely provides previously unavailable information on lung microstructure that may be predictive of a negative outcome and has a potential to aid in lung selection for transplantation.

Regional ventilation changes in severe asthma after bronchial thermoplasty with (3)He MR imaging and CT.

PURPOSE: To quantify regional lung ventilation in healthy volunteers and patients with severe asthma (both before and after thermoplasty) by using a combination of helium 3 ((3)He) magnetic resonance (MR) imaging and computed tomography (CT), with the intention of developing more effective image-guided treatments for obstructive lung diseases. MATERIALS AND METHODS: With approval of the local institutional review board, informed consent, and an Investigational New Drug Exemption, six healthy volunteers and 10 patients with severe asthma were imaged in compliance with HIPAA regulations by using both multidetector CT and (3)He MR imaging. Individual bronchopulmonary segments were labeled voxel by voxel from the CT images and then registered to the (3)He MR images by using custom software. The (3)He signal intensity was then analyzed by evaluating the volume-weighted fraction of total-lung signal intensity present in each segment (segmental ventilation percentage [ SVP segmental ventilation percentage ]) and by identifying the whole-lung defect percentage and the segmental defect percentage. Of the 10 patients with asthma, seven received treatment with bronchial thermoplasty and were imaged with (3)He MR a second time. Changes in segmental defect percentages and whole-lung defect percentages are presented. RESULTS: Ventilation measures for healthy volunteers yielded smaller segment-to-segment variation (mean SVP segmental ventilation percentage , 100% ± 18 [standard deviation]) than did the measures for patients with severe asthma (mean SVP segmental ventilation percentage , 97% ± 23). Patients with asthma also demonstrated larger segmental defect percentages (median, 13.5%; interquartile range, 8.9%-17.8%) than healthy volunteers (median, 6%; interquartile range, 5.6%-6.3%). These quantitative results confirm what is visually observed on the (3)He images. A Spearman correlation of r = -0.82 was found between the change in whole-lung defect percentage and the number of days between final treatment and second (3)He imaging. CONCLUSION: Regional quantification of lung ventilation is indeed feasible and may be a useful technique for image-guided treatment of obstructive lung diseases, such as bronchial thermoplasty for severe asthma. In these patients, ventilation defects decreased as a function of time after treatment.

In vivo lung morphometry with accelerated hyperpolarized (3) He diffusion MRI: a preliminary study.

PURPOSE: Parallel imaging can be used to reduce imaging time and to increase the spatial coverage in hyperpolarized gas magnetic resonance imaging of the lung. In this proof-of-concept study, we investigate the effects of parallel imaging on the morphometric measurement of lung microstructure using diffusion magnetic resonance imaging with hyperpolarized (3) He. METHODS: Fully sampled and under-sampled multi-b diffusion data were acquired from human subjects using an 8-channel (3) He receive coil. A parallel imaging reconstruction technique (generalized autocalibrating partially parallel acquisitions [GRAPPA]) was used to reconstruct under-sampled k-space data. The morphometric results of the generalized autocalibrating partially parallel acquisitions-reconstructed data were compared with the results of fully sampled data for three types of subjects: healthy volunteers, mild, and moderate chronic obstructive pulmonary disease patients. RESULTS: Morphometric measurements varied only slightly at mild acceleration factors. The results were largely well preserved compared to fully sampled data for different lung conditions. CONCLUSION: Parallel imaging, given sufficient signal-to-noise ratio, provides a reliable means to accelerate hyperpolarized-gas magnetic resonance imaging with no significant difference in the measurement of lung morphometry from the fully sampled images. GRAPPA is a promising technique to significantly reduce imaging time and/or to improve the spatial coverage for the morphometric measurement with hyperpolarized gases.

In vivo lung morphometry with hyperpolarized (3) He diffusion MRI: reproducibility and the role of diffusion-sensitizing gradient direction.

PURPOSE: Lung morphometry with hyperpolarized gas diffusion MRI is a highly sensitive technique for the noninvasive measurement of acinar microstructural parameters traditionally only accessible by histology. The goal of this work is to establish the reproducibility of these measurements in healthy volunteers and their dependence on the direction of the applied diffusion-sensitizing gradient. METHODS: Hyperpolarized helium-3 ((3) He) lung morphometry MRI was performed on a total of five healthy subjects. Two subjects received duplicate imaging on the same day and three subjects received duplicate imaging after a 4-month or 27-month delay to assess reproducibility. Four subjects repeated the measurement during the same session with different diffusion-sensitizing gradient directions to determine the effect on the parameter estimates. RESULTS: The (3) He lung morphometry measurements were reproducible over the short term and long term (e.g., % coefficient of variation [CV] of mean chord length, Lm = 2.1% and 2.9%, respectively) and across different diffusion gradient directions (Lm % CV = 2.6%). Results also show independence of field inhomogeneity effects at 1.5T. CONCLUSION: (3) He lung morphometry is a reproducible technique for measuring acinar microstructure and is effectively independent of the choice of diffusion gradient direction. This provides confidence for the use of this technique to compare populations and treatment efficacy.

Assessment of regional lung function with multivolume (1)H MR imaging in health and obstructive lung disease: comparison with (3)He MR imaging.

PURPOSE: To introduce a method based on multivolume proton (hydrogen [(1)H]) magnetic resonance (MR) imaging for the regional assessment of lung ventilatory function, investigating its use in healthy volunteers and patients with obstructive lung disease and comparing the outcome with the outcome of the research standard helium 3 ((3)He) MR imaging. MATERIALS AND METHODS: The institutional review board approved the HIPAA-compliant protocol, and informed written consent was obtained from each subject. Twenty-six subjects, including healthy volunteers (n = 6) and patients with severe asthma (n = 11) and mild (n = 6) and severe (n = 3) emphysema, were imaged with a 1.5-T whole-body MR unit at four lung volumes (residual volume [ RV residual volume ], functional residual capacity [ FRC functional residual capacity ], 1 L above FRC functional residual capacity [ FRC+1 L 1 L above FRC ], total lung capacity [ TLC total lung capacity ]) with breath holds of 10-11 seconds, by using volumetric interpolated breath-hold examination. Each pair of volumes were registered, resulting in maps of (1)H signal change between the two lung volumes. (3)He MR imaging was performed at FRC+1 L 1 L above FRC by using a two-dimensional gradient-echo sequence. (1)H signal change and (3)He signal were measured and compared in corresponding regions of interest selected in ventral, intermediate, and dorsal areas. RESULTS: In all volunteers and patients combined, proton signal difference between TLC total lung capacity and RV residual volume correlated positively with (3)He signal (correlation coefficient R(2) = 0.64, P < .001). Lower (P < .001) but positive correlation results from (1)H signal difference between FRC functional residual capacity and FRC+1 L 1 L above FRC (R(2) = 0.44, P < .001). In healthy volunteers, (1)H signal changes show a higher median and interquartile range compared with patients with obstructive disease and significant differences between nondependent and dependent regions. CONCLUSION: Findings in this study demonstrate that multivolume (1)H MR imaging, without contrast material, can be used as a biomarker for regional ventilation, both in healthy volunteers and patients with obstructive lung disease.

Probing lung microstructure with hyperpolarized noble gas diffusion MRI: theoretical models and experimental results.

The introduction of hyperpolarized gases ((3)He and (129)Xe) has opened the door to applications for which gaseous agents are uniquely suited-lung MRI. One of the pulmonary applications, diffusion MRI, relies on measuring Brownian motion of inhaled hyperpolarized gas atoms diffusing in lung airspaces. In this article we provide an overview of the theoretical ideas behind hyperpolarized gas diffusion MRI and the results obtained over the decade-long research. We describe a simple technique based on measuring gas apparent diffusion coefficient (ADC) and an advanced technique, in vivo lung morphometry, that quantifies lung microstructure both in terms of Weibel parameters (acinar airways radii and alveolar depth) and standard metrics (mean linear intercept, surface-to-volume ratio, and alveolar density) that are widely used by lung researchers but were previously available only from invasive lung biopsy. This technique has the ability to provide unique three-dimensional tomographic information on lung microstructure from a less than 15 s MRI scan with results that are in good agreement with direct histological measurements. These safe and sensitive diffusion measurements improve our understanding of lung structure and functioning in health and disease, providing a platform for monitoring the efficacy of therapeutic interventions in clinical trials.

Quantification of human lung structure and physiology using hyperpolarized 129Xe.

PURPOSE: To present in vivo, human validation of a previously proposed method to measure key pulmonary parameters related to lung microstructure and physiology. Some parameters, such as blood-air barrier thickness, cannot be measured readily by any other noninvasive modality. METHODS: Healthy volunteers (n = 12) were studied in 1.5T and 3T whole body human scanners using hyperpolarized xenon. Xenon uptake by lung parenchyma and blood was measured using a chemical shift saturation recovery sequence. Both dissolved-xenon peaks at 197 ppm and 217-218 ppm were fitted against a model of xenon exchange (MOXE) as functions of exchange time. Parameters related to lung function and structure can be obtained by fitting to this model. RESULTS: The following results were obtained from xenon uptake (averaged over all healthy volunteers): surface-area-to-volume ratio = 210 ± 50 cm(-1) ; total septal wall thickness = 9.2 ± 6.5 µm; blood-air barrier thickness = 1.0 ± 0.3 µm; hematocrit = 27 ± 4%; pulmonary capillary blood transit time = 1.3 ± 0.3 s, in good agreement with literature values from invasive experiments. More detailed fitting results are listed in the text. CONCLUSION: The initial in vivo human results demonstrate that our proposed methods can be used to noninvasively determine lung physiology by simultaneous quantification of a few important pulmonary parameters. This method is highly promising to become a versatile screening method for lung diseases.

Probing lung microstructure with hyperpolarized 3He gradient echo MRI.

In this paper we demonstrate that gradient echo MRI with hyperpolarized (3)He gas can be used for simultaneously extracting in vivo information about lung ventilation properties, alveolar geometrical parameters, and blood vessel network structure. This new approach is based on multi-gradient-echo experimental measurements of hyperpolarized (3)He gas MRI signal from human lungs and a proposed theoretical model of this signal. Based on computer simulations of (3)He atoms diffusing in the acinar airway tree in the presence of an inhomogeneous magnetic field induced by the susceptibility differences between lung tissue (alveolar septa, blood vessels) and lung airspaces, we derive analytical expressions relating the time-dependent MR signal to the geometrical parameters of acinar airways and the blood vessel network. Data obtained on eight healthy volunteers are in good agreement with literature values. This information is complementary to the information obtained by means of the in vivo lung morphometry technique with hyperpolarized 3He diffusion MRI previously developed by our group, and opens new opportunities to study lung microstructure in health and disease.

Development and Validation of a Prechiasmatic Mouse Model of Subarachnoid Hemorrhage to Measure Long-Term Cognitive Deficits.

Controllable and reproducible animal models of aneurysmal subarachnoid hemorrhage (SAH) are crucial for the systematic study of the pathophysiology and treatment of this debilitating condition. However, current animal models have not been successful in replicating the pathology and disabilities seen in SAH patients, especially the long-term neurocognitive deficits that affect the survivor's quality of life. Therefore, there is an unmet need to develop experimental models that reliably replicate the long-term clinical ramifications of SAH - especially in mice where genetic manipulations are straightforward and readily available. To address this need, a standardized mouse SAH model is developed that reproducibly produced significant and trackable long-term cognitive deficits. SAH is induced by performing double blood injections into the prechiasmatic cistern - a simple modification to the well-characterized single prechiasmatic injection mouse model of SAH. Following SAH, mice recapitulated key characteristics of SAH patients, including cerebral edema measured by MRI - an indicator of early brain injury (EBI), neuroinflammation, apoptosis, and long-term cognitive impairment. This newly developed SAH mouse model is considered an ideal paradigm for investigating the complex SAH pathophysiology and identifying novel druggable therapeutic targets for treating SAH severity and SAH-associated long-term neurocognitive deficits in patients.

Oxytocin-induced birth causes sex-specific behavioral and brain connectivity changes in developing rat offspring.

Despite six decades of the use of exogenous oxytocin for management of labor, little is known about its effects on the developing brain. Motivated by controversial reports suggesting a link between oxytocin use during labor and autism spectrum disorders (ASDs), we employed our recently validated rat model for labor induction with oxytocin to address this important concern. Using a combination of molecular biological, behavioral, and neuroimaging assays, we show that induced birth with oxytocin leads to sex-specific disruption of oxytocinergic signaling in the developing brain, decreased communicative ability of pups, reduced empathy-like behaviors especially in male offspring, and widespread sex-dependent changes in functional cortical connectivity. Contrary to our hypothesis, social behavior, typically impaired in ASDs, was largely preserved. Collectively, our foundational studies provide nuanced insights into the neurodevelopmental impact of birth induction with oxytocin and set the stage for mechanistic investigations in animal models and prospective longitudinal clinical studies.

Evaluation of Apparent Diffusion Coefficient Repeatability and Reproducibility for Preclinical MRIs Using Standardized Procedures and a Diffusion-Weighted Imaging Phantom.

Relevant to co-clinical trials, the goal of this work was to assess repeatability, reproducibility, and bias of the apparent diffusion coefficient (ADC) for preclinical MRIs using standardized procedures for comparison to performance of clinical MRIs. A temperature-controlled phantom provided an absolute reference standard to measure spatial uniformity of these performance metrics. Seven institutions participated in the study, wherein diffusion-weighted imaging (DWI) data were acquired over multiple days on 10 preclinical scanners, from 3 vendors, at 6 field strengths. Centralized versus site-based analysis was compared to illustrate incremental variance due to processing workflow. At magnet isocenter, short-term (intra-exam) and long-term (multiday) repeatability were excellent at within-system coefficient of variance, wCV [±CI] = 0.73% [0.54%, 1.12%] and 1.26% [0.94%, 1.89%], respectively. The cross-system reproducibility coefficient, RDC [±CI] = 0.188 [0.129, 0.343] µm2/ms, corresponded to 17% [12%, 31%] relative to the reference standard. Absolute bias at isocenter was low (within 4%) for 8 of 10 systems, whereas two high-bias (>10%) scanners were primary contributors to the relatively high RDC. Significant additional variance (>2%) due to site-specific analysis was observed for 2 of 10 systems. Base-level technical bias, repeatability, reproducibility, and spatial uniformity patterns were consistent with human MRIs (scaled for bore size). Well-calibrated preclinical MRI systems are capable of highly repeatable and reproducible ADC measurements.

Gold nanoparticle-enhanced X-ray microtomography of the rodent reveals region-specific cerebrospinal fluid circulation in the brain.

Cerebrospinal fluid (CSF) is essential for the development and function of the central nervous system (CNS). However, the brain and its interstitium have largely been thought of as a single entity through which CSF circulates, and it is not known whether specific cell populations within the CNS preferentially interact with the CSF. Here, we develop a technique for CSF tracking, gold nanoparticle-enhanced X-ray microtomography, to achieve micrometer-scale resolution visualization of CSF circulation patterns during development. Using this method and subsequent histological analysis in rodents, we identify previously uncharacterized CSF pathways from the subarachnoid space (particularly the basal cisterns) that mediate CSF-parenchymal interactions involving 24 functional-anatomic cell groupings in the brain and spinal cord. CSF distribution to these areas is largely restricted to early development and is altered in posthemorrhagic hydrocephalus. Our study also presents particle size-dependent CSF circulation patterns through the CNS including interaction between neurons and small CSF tracers, but not large CSF tracers. These findings have implications for understanding the biological basis of normal brain development and the pathogenesis of a broad range of disease states, including hydrocephalus.