Endothelial Cell APOE3 Regulates Neurovascular, Neuronal, and Behavioral Function.

BACKGROUND: Specialized brain endothelial cells and human APOE3 are independently important for neurovascular function, yet whether APOE3 expression by endothelial cells contributes to brain function is currently unknown. In the present study, we determined whether the loss of endothelial cell APOE3 impacts brain vascular and neural function. METHODS: We developed APOE3fl/fl/Cdh5(PAC)-CreERT2+/- (APOE3Cre+/-) and APOE3fl/fl/Cdh5(PAC)-CreERT2-/- (APOE3Cre-/-, control) mice and induced endothelial cell APOE3 knockdown with tamoxifen at ≈4 to 5 weeks of age. Neurovascular and neuronal function were evaluated by biochemistry, immunohistochemistry, behavioral testing, and electrophysiology at 9 months of age. RESULTS: We found that the loss of endothelial APOE3 expression was sufficient to cause neurovascular dysfunction including higher permeability and lower vessel coverage in tandem with deficits in spatial memory and fear memory extinction and a disruption of cortical excitatory/inhibitory balance. CONCLUSIONS: Our data collectively support the novel concept that endothelial APOE3 plays a critical role in the regulation of the neurovasculature, neural circuit function, and behavior.

Multi-parametric Z-spectral MRI may have a good performance for glioma stratification in clinical patients.

OBJECTIVES: To comprehensively and noninvasively risk-stratify glioma grade, isocitrate dehydrogenase (IDH) genotype, and 1p/19q codeletion status using multi-contrast Z-spectral magnetic resonance imaging (MRI). METHODS: One hundred and thirteen patients with glioma were retrospectively included. Multiple contrasts contributing to Z-spectra, including direct saturation of water (DSW), semi-solid magnetization transfer contrast (MTC), amide proton transfer (APT) effect, aliphatic nuclear Overhauser effect, and the 2-ppm chemical exchange saturation transfer peak (CEST@2ppm), were fitted with five individual Lorentzian functions. Z-spectral contrasts were compared according to the three most important risk stratifications: tumor grade, IDH genotype, and 1p/19q codeletion status. We further investigated the differentiation of 1p/19q codeletion status within IDH mutant gliomas. The stratification performance of individual Z-spectral contrasts and their combination was quantified using receiver operating characteristic (ROC) analyses. RESULTS: DSW was significantly different within grade, IDH genotypes, and 1p/19q codeletion status. APT was significantly different with grade and IDH mutation, but not with 1p/19q subtypes. CEST@2ppm was only significantly different with 1p/19q codeletion subtypes. DSW and CEST@2ppm were the two Z-spectral contrasts able to differentiate 1p/19q codeletion subtypes within IDH mutant gliomas. For differentiating glioma grades using ROC analyses, DSW achieved the largest AUC. For differentiating IDH genotypes, DSW and APT achieved comparable AUCs. DSW was the best metric for differentiating 1p/19q codeletion status within all patients and within the IDH mutant patients. Combining all Z-spectral contrasts improved sensitivity and specificity for all risk stratifications. CONCLUSIONS: Multi-parametric Z-spectral MRI serves as a useful, comprehensive, and noninvasive imaging technique for glioma stratification in clinical patients. KEY POINTS: • Multiple contrasts contributing to Z-spectra were separately fitted with Lorentzian functions. • Z-spectral contrasts were compared within the three most important and common tumor risk stratifications for gliomas: tumor grade, IDH genotype, and 1p/19q codeletion status. • The stratification performance of individual Z-spectral contrasts and their combination was quantified using receiver operating characteristic analyses, which found Z-spectral MRI to be a useful and comprehensive imaging biomarker for glioma stratification.

Non-Gaussian diffusion imaging with a fractional order calculus model to predict response of gastrointestinal stromal tumor to second-line sunitinib therapy.

PURPOSE: To demonstrate the clinical value of a non-Gaussian diffusion model using fractional order calculus (FROC) for early prediction of the response of gastrointestinal stromal tumor to second-line sunitinib targeted therapy. METHODS: Fifteen patients underwent sunitinib treatment after imatinib resistance. Diffusion-weighted imaging with multiple b-values was performed before treatment (baseline) and 2 weeks (for early prediction of response) after initiating sunitinib treatment. Conventional MRI images at 12 weeks were used to determine the good and poor responders according to the modified Choi criteria for MRI. Diffusion coefficient D, fractional order parameter ß (which correlates to intravoxel tissue heterogeneity), and a microstructural quantity µ were calculated using the FROC model. The FROC parameters and the longest diameter of the lesion, as well as their changes after 2 weeks of treatment, were compared between the good and poor responders. Additionally, the pretreatment FROC parameters were individually combined with the change in D (ΔD) using a logistic regression model to evaluate response to sunitinib treatment with a receiver operating characteristic analysis. RESULTS: Forty-two good-responding and 32 poor-responding lesions were identified. Significant differences were detected in pretreatment ß (0.67 versus 0.74, P = 0.011) and ΔD (45.7% versus 12.4%, P = 0.001) between the two groups. The receiver operating characteristic analysis showed that ΔD had a significantly higher predictive power than the tumor size change (area under the curve: 0.725 versus 0.580; 0.95 confidence interval). When ΔD was combined with pretreatment ß, the area under the curve improved to 0.843 with a predictive accuracy of 75.7% (56 of 74). CONCLUSIONS: The non-Gaussian FROC diffusion model showed clinical value in early prediction of gastrointestinal stromal tumor response to second-line sunitinib targeted therapy. The pretreatment FROC parameter ß can increase the predictive accuracy when combined with the change in diffusion coefficient during treatment. Magn Reson Med 79:1399-1406, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Induced saturation transfer recovery steady states (iSTRESS) for proton exchange rate mapping with CEST MRI, a preliminary study.

Proton exchange underpins essential mechanisms in diverse MR imaging contrasts. Omega plots have proven effective in mapping proton exchange rates (kex) in live human brains, enabling the differentiation of MS lesion activities and characterization of ischemic stroke. However, Omega plots require extended saturation durations (typically 5 to 10 s), resulting in high specific absorption rates (SAR) that can hinder clinical feasibility. In this study, we introduce a novel kex mapping approach, named induced Saturation Transfer Recovery Steady-States (iSTRESS). iSTRESS integrates an excitation flip angle pulse prior to chemical exchange saturation transfer (CEST) saturation, effectively aligning the magnetization with its steady-state value. This innovation reduces saturation times and mitigates SAR concerns. The formula for iSTRESS-based kex quantification was derived theoretically, involving two measurements with distinct excitation flip angles and saturation B1 values. Bloch-McConnell simulations confirmed that iSTRESS-based kex values closely matched input values (R2 > 0.99). An iSTRESS MRI sequence was implemented on a 9.4 T preclinical MRI, imaging protein phantoms with pH values ranging from 6.2 to 7.4 (n = 4). Z-spectra were acquired using excitation flip angles of 30° and 60°, followed by CEST saturation at powers of 30 and 120 Hz respectively, with a total saturation time of <1 s, resulting in two iSTRESS states for kex mapping. kex maps derived from the phantom study exhibited a linear correlation (R2 > 0.99) with Omega plot results. The developed iSTRESS method allows for kex quantification with significantly reduced saturation times, effectively minimizing SAR concerns.

Role of histogram features on arterial spin labeling perfusion magnetic resonance imaging in identifying isocitrate dehydrogenase genotypes and glioma malignancies.

AIM: Background: Accurate preoperative grading and isocitrate dehydrogenase (IDH) identification is highly important for proper treatment planning and prognosis evaluation in glioma patients. Purpose To explore the applicability of histogram features from non-invasive arterial spin labeling (ASL)-weighted MRI in differentiating isocitrate dehydrogenase mutant (IDH-mut) and wild type (IDH-wt), and separating lower-grade gliomas (LGGs) from glioblastoma multiforme (GBM). MATERIAL AND METHODS: Methods One hundred thirty-one patients scanned with ASL-weighted and anatomic MRI were retrospectively included. Cerebral blood flow (CBF) maps were calculated, from which 10 histogram features describing the CBF distribution were extracted within the tumor region. Correlation analysis was used to determine correlations between histogram features, and tumor grades and IDH genotypes. Independent t-tests and Fisher\'s exact tests were used to determine the differences in extracted histogram features, age at diagnosis, and gender among different glioma subtypes. Binary logistic regression was used to combine multivariates, and the diagnostic performances were evaluated with receiver operating characteristic curves. RESULTS: Results CBF histogram features were significantly correlated with tumor grades and IDH genotypes, and facilitate the efficacious differentiation of LGGs from GBM, and IDH-mut from IDH-wt gliomas. A model combining the CBF 30th percentile and age at diagnosis resulted in an area under the receiving operating characteristic curve (AUC) of 0.73 in judging LGGs from GBM. Integrating age at the time of diagnosis and CBF 10th percentile allows more comprehensive differentiation of IDH-mut and IDH-wt gliomas, and the combined model achieved an improved AUC of 0.856 (sensitivity, 84.4%; and specificity, 82.9%). CONCLUSION: Conclusion Histogram features from non-invasive ASL-weighted MRI were significantly correlated with tumor grade and IDH genotypes, and facilitated efficacious differentiation of glioma subtypes. Combining age at the time of diagnosis and perfusion histogram features resulted in a more comprehensive identification of tumor subtypes, which indicated that ASL-weighted MRI can serve as non-invasive tool for the pre-surgical evaluation of gliomas.

A cell-penetrating PHLPP peptide improves cardiac arrest survival in murine and swine models.

Out-of-hospital cardiac arrest is a leading cause of death in the US, with a mortality rate over 90%. Preclinical studies demonstrate that cooling during cardiopulmonary resuscitation (CPR) is highly beneficial, but can be challenging to implement clinically. No medications exist for improving long-term cardiac arrest survival. We have developed a 20-amino acid peptide, TAT-PHLPP9c, that mimics cooling protection by enhancing AKT activation via PH domain leucine-rich repeat phosphatase 1 (PHLPP1) inhibition. Complementary studies were conducted in mouse and swine. C57BL/6 mice were randomized into blinded saline control and peptide-treatment groups. Following a 12-minute asystolic arrest, TAT-PHLPP9c was administered intravenously during CPR and significantly improved the return of spontaneous circulation, mean arterial blood pressure and cerebral blood flow, cardiac and neurological function, and survival (4 hour and 5 day). It inhibited PHLPP-NHERF1 binding, enhanced AKT but not PKC phosphorylation, decreased pyruvate dehydrogenase phosphorylation and sorbitol production, and increased ATP generation in heart and brain. TAT-PHLPP9c treatment also reduced plasma taurine and glutamate concentrations after resuscitation. The protective benefit of TAT-PHLPP9c was validated in a swine cardiac arrest model of ventricular fibrillation. In conclusion, TAT-PHLPP9c may improve neurologically intact cardiac arrest survival without the need for physical cooling.

Quantitative sodium imaging with a flexible twisted projection pulse sequence.

The quantification of sodium MR images from an arbitrary intensity scale into a bioscale fosters image interpretation in terms of the spatially resolved biochemical process of sodium ion homeostasis. A methodology for quantifying tissue sodium concentration using a flexible twisted projection imaging sequence is proposed that allows for optimization of tradeoffs between readout time, signal-to-noise ratio efficiency, and sensitivity to static field susceptibility artifacts. The gradient amplitude supported by the slew rate at each k-space radius regularizes the readout gradient waveform design to avoid slew rate violation. Static field inhomogeneity artifacts are corrected using a frequency-segmented conjugate phase reconstruction approach, with field maps obtained quickly from coregistered proton imaging. High-quality quantitative sodium images have been achieved in phantom and volunteer studies with real isotropic spatial resolution of 7.5 x 7.5 x 7.5 mm(3) for the slow T(2) component in approximately 8 min on a clinical 3-T scanner. After correcting for coil sensitivity inhomogeneity and water fraction, the tissue sodium concentration in gray matter and white matter was measured to be 36.6 +/- 0.6 micromol/g wet weight and 27.6 +/- 1.2 micromol/g wet weight, respectively.

Evaluation of B0-correction of relative CBF maps using tagging distance dependent Z-spectrum (TADDZ).

Arterial spin labeling (ASL) MRI, based on endogenous contrast from blood water, is used in research and diagnosis of cerebral vascular conditions. However, artifacts due to imperfect imaging conditions such as B0-inhomogeneity (ΔB0) could lead to variations in the quantification of relative cerebral blood flow (CBF). In this study, we evaluate a new approach using tagging distance dependent Z-spectrum (TADDZ) data, similar to the ΔB0 corrections in the chemical exchange saturation transfer (CEST) experiments, to remove the imaging plane B0 inhomogeneity induced CBF artifacts in ASL MRI. Our results indicate that imaging-plane B0-inhomogeneity can lead to variations and errors in the relative CBF maps especially under small tagging distances. Along with an acquired B0 map, TADDZ data helps to eliminate B0-inhomogeneity induced artifacts in the resulting relative CBF maps. We demonstrated the effective use of TADDZ data to reduce variation while subjected to systematic changes in ΔB0. In addition, TADDZ corrected ASL MRI, with improved consistency, was shown to outperform conventional ASL MRI by differentiating the subtle CBF difference in Alzheimer's disease (AD) mice brains with different APOE genotypes.

Epidermal growth factor treatment of female mice that express APOE4 at an age of advanced pathology mitigates behavioral and cerebrovascular dysfunction.

APOE4 is a major genetic risk factor for Alzheimer's disease and high amyloid-ß (Aß) levels in the brain are a pathological hallmark of the disease. However, the contribution of specific APOE-modulated Aß-dependent and Aß-independent functions to cognitive decline remain unclear. Increasing evidence supports a role of APOE in modulating cerebrovascular function, however whether ameliorating this dysfunction can improve behavioral function is still under debate. We have previously demonstrated that systemic epidermal growth factor (EGF) treatment, which is important for vascular function, at early stages of pathology (treatment from 6 to 8 months) is beneficial for recognition and spatial memory and cerebrovascular function in female mice that express APOE4. These data raise the important question of whether EGF can improve APOE4-associated cerebrovascular and behavioral dysfunction when treatment is initiated at an age of advanced pathology. Positive findings would support the development of therapies that target cerebrovascular dysfunction associated with APOE4 in aging and AD in individuals with advanced cognitive impairment. Therefore, in this study female mice that express APOE4 in the absence (E4FAD- mice) or presence (E4FAD+ mice) of Aß overproduction were treated from 8 to 10 months of age systemically with EGF. EGF treatment mitigated behavioral dysfunction in recognition memory and spatial learning and improved hippocampal neuronal function in both E4FAD+ and E4FAD- mice, suggesting that EGF treatment improves Aß-independent APOE4-associated deficits. The beneficial effects of EGF treatment on behavior occurred in tandem with improved markers of cerebrovascular function, including lower levels of fibrinogen, lower permeability when assessed by MRI and higher percent area coverage of laminin and CD31 in the hippocampus. These data suggest a mechanistic link among EGF signaling, cerebrovascular function and APOE4-associated behavioral deficits in mice with advanced AD-relevant pathology.

B1- non-uniformity correction of phased-array coils without measuring coil sensitivity.

Parallel imaging can be used to increase SNR and shorten acquisition times, albeit, at the cost of image non-uniformity. B1- non-uniformity correction techniques are confounded by signal that varies not only due to coil induced B1- sensitivity variation, but also the object's own intrinsic signal. Herein, we propose a method that makes minimal assumptions and uses only the coil images themselves to produce a single combined B1- non-uniformity-corrected complex image with the highest available SNR. A novel background noise classifier is used to select voxels of sufficient quality to avoid the need for regularization. Unique properties of the magnitude and phase were used to reduce the B1- sensitivity to two joint additive models for estimation of the B1- inhomogeneity. The complementary corruption of the imaged object across the coil images is used to abate individual coil correction imperfections. Results are presented from two anatomical cases: (a) an abdominal image that is challenging in both extreme B1- sensitivity and intrinsic tissue signal variation, and (b) a brain image with moderate B1- sensitivity and intrinsic tissue signal variation. A new relative Signal-to-Noise Ratio (rSNR) quality metric is proposed to evaluate the performance of the proposed method and the RF receiving coil array. The proposed method has been shown to be robust to imaged objects with widely inhomogeneous intrinsic signal, and resilient to poorly performing coil elements.

Creatine CEST MRI for Differentiating Gliomas with Different Degrees of Aggressiveness.

PURPOSE: Creatine (Cr) is a major metabolite in the bioenergetic system. Measurement of Cr using conventional MR spectroscopy (MRS) suffers from low spatial resolution and relatively long acquisition times. Creatine chemical exchange saturation transfer (CrCEST) magnetic resonance imaging (MRI) is an emerging molecular imaging method for tissue Cr measurements. Our previous study showed that the CrCEST contrast, obtained through multicomponent Z-spectral fitting, was lower in tumors compared to normal brain, which further reduced with tumor progression. The current study was aimed to investigate if CrCEST MRI can also be useful for differentiating gliomas with different degrees of aggressiveness. PROCEDURES: Intracranial 9L gliosarcoma and F98 glioma bearing rats with matched tumor size were scanned with a 9.4 T MRI scanner at two time points. CEST Z-spectra were collected using a customized sequence with a frequency-selective rectangular saturation pulse (B1 = 50 Hz, duration = 3 s) followed by a single-shot readout. Z spectral data were fitted pixel-wise with five Lorentzian functions, and maps of CrCEST peak amplitude, linewidth, and integral were produced. For comparison, single-voxel proton MR spectroscopy (1H-MRS) was performed to quantify and compare the total Cr concentration in the tumor. RESULTS: CrCEST contrasts decreased with tumor progression from weeks 3 to 4 in both 9L and F98 phenotypes. More importantly, F98 tumors had significantly lower CrCEST integral compared to 9L tumors. On the other hand, integrals of other Z-spectral components were unable to differentiate both tumor progression and phenotype with limited sample size. CONCLUSIONS: Given that F98 is a more aggressive tumor than 9L, this study suggests that CrCEST MRI may help differentiate gliomas with different aggressiveness.

The feasibility of quantitative MRI of perivascular spaces at 7T.

BACKGROUND: Dilated brain perivascular spaces (PVSs) are found to be associated with many conditions, including aging, dementia, and Alzheimer's disease (AD). Conventionally, PVS assessment is mainly based on subjective observations of the number, size and shape of PVSs in MR images collected at clinical field strengths (≤3T). This study tests the feasibility of imaging and quantifying brain PVS with an ultra-high 7T whole-body MRI scanner. NEW METHOD: 3D high resolution T2-weighted brain images from healthy subjects (n=3) and AD patients (n=5) were acquired on a 7T whole-body MRI scanner. To automatically segment the small hyperintensive fluid-filling PVS structures, we also developed a quantitative program based on algorithms for spatial gradient, component connectivity, edge-detection, k-means clustering, etc., producing quantitative results of white matter PVS volume densities. RESULTS: The 3D maps of automatically segmented PVS show an apparent increase in PVS density in AD patients compared to age-matched healthy controls due to the PVS dilation (8.0±2.1 v/v% in AD vs. 4.9±1.3 v/v% in controls, p<0.05). COMPARISON WITH EXISTING METHOD: We demonstrated that 7T provides sufficient SNR and resolution for quantitatively measuring PVSs in deep white matter that is challenging with clinical MRI systems (≤3T). Compared to the conventional visual counting and rating for the PVS assessment, the quantitation method we developed is automatic and objective. CONCLUSIONS: Quantitative PVS MRI at 7T may serve as a non-invasive and endogenous imaging biomarker for diseases with PVS dilation.