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1.
Biomed Res Int ; 2020: 6418343, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32509865

RESUMO

Purpose: To evaluate the performance of amide proton transfer-weighted (APTw) imaging against the reference standard of gadolinium-enhanced T1-weighted imaging (Gd-T1w) in children with intracranial infection. Materials and Methods: Twenty-eight pediatric patients (15 males and 13 females; age range 1-163 months) with intracranial infection were recruited in this study. 2D APTw imaging and conventional MR sequences were conducted using a 3 T MRI scanner. Kappa (κ) statistics and the McNemar test were performed to determine whether the hyperintensity on APTw was related to the enhancement on Gd-T1w. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of APTw imaging to predict lesion enhancement were calculated. Result: In twelve patients with brain abscesses, the enhancing rim of the abscesses on the Gd-T1w images was consistently hyperintense on the APTw images. In eight patients with viral encephalitis, three showed slight spotted gadolinium enhancement, while the APTw image also showed a slight spotted high signal. Five of these patients showed no enhancement on Gd-T1w and isointensity on the APTw image. In eleven patients with meningitis, increased APTw signal intensities were clearly visible in gadolinium-enhancing meninges. Sixty infectious lesions (71%) showed enhancement on Gd-T1w images. The sensitivity and specificity of APTw were 93.3% (56/60) and 91.7% (22/24). APTw demonstrated excellent agreement (κ = 0.83) with Gd-T1w, with no significant difference (P = 0.69) in detection of infectious lesions. Conclusions: These initial data show that APTw MRI is a noninvasive technique for the detection and characterization of intracranial infectious lesions. APTw MRI enabled similar detection of infectious lesions to Gd-T1w and may provide an injection-free means of evaluation of intracranial infection.

2.
Nanoscale ; 2020 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-32400835

RESUMO

Engineering coordination compounds, e.g., prussian blue (PB) and its analogues (PBAs), with designable complex nanostructures via chemical etching holds great opportunities for improving energy storage performances by adjusting topological geometry, selectively exposing active sites, tuning electronic properties and enhancing accessible surface area. Unfortunately, it remains ambiguous particularly on site-selective and anisotropic etching behaviors. Herein, for the first time, we propose that two distinct regions are formed inside NiCo PBA (NCP) cubes due to the competition between classical ion-by-ion crystallization and non-classical crystallization based on aggregation. Such a unique structure ultimately determines not only the etching position but also the anisotropic pathway by selectively exposing unprotected Ni sites. According to this principle, complex PBA architectures, including nanocages, open nanocubes (constructed by six cones sharing the same apex), nanocones, and chamfer nanocubes can be intentionally obtained. After thermal annealing, NCP nanocones are converted to morning glory-like porous architectures composed of NiO/NiCo2O4 heterostructures with a mean particle size of 5 nm, which show improved rate performance and cycling stability.

3.
Small ; : e2000653, 2020 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-32432831

RESUMO

Fiber-based supercapacitors (FSCs) possess great potential as an ideal type of power source for future weaveable/wearable electronics and electronic-textiles. The performance of FSCs is, without doubt, primarily determined by the properties of fibrous electrodes. Carbonaceous fibers, e.g., commercial carbon fibers, newly developed graphene fibers, and carbon nanotube fibers, are deemed as promising materials for weaveable/wearable supercapacitors owing to their exotic properties including high tensile strength and robustness, excellent electrical conductivity, good flexibility, and environmental stability. Nevertheless, bare carbonaceous fiber normally exhibits low capacitance originating from electric double-layer capacitance, which remains unsatisfactory for efficiently powering wearable and portable devices. Numerous efforts have been devoted to tailoring fiber properties by hybridizing pseudocapacitive materials, and impressive progress has been achieved thus far. Herein, the microstructures of pristine carbonaceous fibers are introduced in detail, and the recent advances in rational nano/microstructure design of their hybrids, which provides the feasibility to achieve the synergistic interaction between conductive agents and pseudocapacitive nanomaterials but are normally overlooked, are comprehensively reviewed. Besides, the challenges in developing high-performance fibrous electrodes are also elaborately discussed.

4.
ACS Appl Mater Interfaces ; 12(10): 12155-12164, 2020 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-32053344

RESUMO

Wearable strain sensors are emerging rapidly for their promising applications in human motion detection for diagnosis, healthcare, training instruction, and rehabilitation exercise assessment. However, it remains a bottleneck in gaining comfortable and breathable devices with the features of high sensitivity, linear response, and tunable detection range. Textiles possess fascinating advantages of good breathability, aesthetic property, tailorability, and excellent mechanical compliance to conformably attach to human body. As the meandering loops in a textile can be extended in different directions, it provides plenty of room for exploring ideal sensors by tuning a twisting structure with rationally selected yarn materials. Herein, textile sensors with twisting architecture are designed via a solution-based process by using a stable water-based conductive ink that is composed of polypyrrole/polyvinyl alcohol nanoparticles with a mean diameter of 50 nm. Depending on the predesigned twisting models, the thus-fabricated textile sensors show adjustable performances, exhibiting a high sensitivity of 38.9 with good linearity and a broad detection range of 200%. Such sensors can be integrated into fabrics and conformably attached to skin for monitoring subtle (facial expressions, breathing, and speaking) and large (stretching, jumping, running and jogging, and sign language) human motions. As a proof-of-concept application, by integrating with a wireless transmitter, the signals detected by our sensors during exercise (e.g., running) can be remotely received and displayed on a smartphone. It is believed that the integration of our textile sensors with selected twisting models into a cloth promises full-range motion detection for wearable electronics and human-machine interfaces.

5.
Neuroimage Clin ; 25: 102153, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31901792

RESUMO

Amide proton transfer-weighted (APTw) MRI is a novel molecular imaging technique that can noninvasively detect endogenous cellular proteins and peptides in tissue. Here, we demonstrate the feasibility of protein-based APTw MRI in characterizing amnestic mild cognitive impairment (aMCI). Eighteen patients with confirmed aMCI and 18 matched normal controls were scanned at 3 Tesla. The APTw, as well as conventional magnetization transfer ratio (MTR), signal differences between aMCI and normal groups were assessed by the independent samples t-test, and the receiver-operator-characteristic analysis was used to assess the diagnostic performance of APTw. When comparing the normal control group, aMCI brains typically had relatively higher APTw signals. Quantitatively, APTw intensity values were significantly higher in nine of 12 regions of interest in aMCI patients than in normal controls. The largest areas under the receiver-operator-characteristic curves were 0.88 (gray matter in occipital lobe) and 0.82 (gray matter in temporal lobe, white matter in occipital lobe) in diagnosing aMCI patients. On the contrary, MTR intensity values were significantly higher in only three of 12 regions of interest in the aMCI group. Additionally, the age dependency analyses revealed that these cross-sectional APTw/MTR signals had an increasing trend with age in most brain regions for normal controls, but a decreasing trend with age in most brain regions for aMCI patients. Our early results show the potential of the APTw signal as a new imaging biomarker for the noninvasive molecular diagnosis of aMCI.

7.
Mol Imaging Biol ; 22(1): 218, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31808030

RESUMO

This article is about head and neck tumor MR imaging and is not within the scope of two National Institutes of Health grants (R0ICA166171, ROICA228188) erroneously listed. Thus, the authors would like to remove the reference to the NIH grants R01CA166171 and R01CA228188 in this article.

8.
Quant Imaging Med Surg ; 9(10): 1641-1651, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31728308

RESUMO

Background: Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver, preoperative grading of HCC is of great clinical significance. Amide proton transfer-weighted (APTw) imaging, as a novel contrast mechanism in the field of molecular imaging, provided new diagnostic ideas for the grading of HCC. Methods: Between May 2017 and April 2018, 32 consecutive patients with pathologically confirmed HCC were enrolled, including 19 high-grade HCCs and 13 low-grade HCCs. DWI and APTw scanning was performed on a 3T MRI scanner. Two observers drew regions of interest independently by referring to the axial T2-weighted imaging, and APTw and apparent diffusion coefficient (ADC) values were obtained. Inter- and intra-observer agreements were assessed with the intraclass correlation coefficients (ICCs). The independent sample t test was used to compare the APTw and ADC values between the high- and low-grade HCC tumor parenchyma. The receiver operating characteristic curve was used to analyze the diagnostic efficacy of high- from low-grade HCC tumors. Spearman correlation analysis was used to assess the relationship between APTw and ADC values and HCC histological grades. Results: There were significant differences between the APTw or ADC values for the high- and low-grade HCCs (P=0.034 and 0.010). Both APTw and DWI had good diagnostic performance in differentiating the high- from the low-grade HCCs, with areas under the curves of 0.814 and 0.745, respectively. Moderate correlations existed between APTw values and histological grades (r=0.534; P=0.002), as well as ADC values and histological grades (r=-0.417; P=0.018). Conclusions: The APTw imaging is a useful imaging biomarker that complements DWI for the more accurate and comprehensive HCC characterization.

9.
J Mater Chem B ; 7(40): 6232-6237, 2019 10 16.
Artigo em Inglês | MEDLINE | ID: mdl-31566630

RESUMO

Nanozymes have been extensively investigated to imitate protein enzymes in biomimetic chemistry and the identification of the active site is believed to be the pre-requisite before one can effectively regulate their activity. Herein, ultrathin NiCo LDH nanosheets are synthesized via a fast co-precipitation at room temperature and can be stably dispersed in water without any additives of surfactants or organic solvents. By tuning the ratio between Ni and Co in LDH nanosheets, the activity is tuned and their peroxidase-like activity is determined by Co sites that show higher affinity to both 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) due to the strong Lewis acidity of Co3+ and the low redox potential of Co3+/Co2+. Together with their small crystallite size, ultra-thin thickness and tunable composition, NiCo LDH is used as a nanozyme for highly sensitive colorimetric detection of H2O2 and the limit of detection (LOD) reaches 0.48 µM.

10.
Small ; 15(47): e1904255, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31588685

RESUMO

As an essential member of 2D materials, MXene (e.g., Ti3 C2 Tx ) is highly preferred for energy storage owing to a high surface-to-volume ratio, shortened ion diffusion pathway, superior electronic conductivity, and neglectable volume change, which are beneficial for electrochemical kinetics. However, the low theoretical capacitance and restacking issues of MXene severely limit its practical application in lithium-ion batteries (LIBs). Herein, a facile and controllable method is developed to engineer 2D nanosheets of negatively charged MXene and positively charged layered double hydroxides derived from ZIF-67 polyhedrons into 3D hollow frameworks via electrostatic self-assembling. After thermal annealing, transition metal oxides (TMOs)@MXene (CoO/Co2 Mo3 O8 @MXene) hollow frameworks are obtained and used as anode materials for LIBs. CoO/Co2 Mo3 O8 nanosheets prevent MXene from aggregation and contribute remarkable lithium storage capacity, while MXene nanosheets provide a 3D conductive network and mechanical robustness to facilitate rapid charge transfer at the interface, and accommodate the volume expansion of the internal CoO/Co2 Mo3 O8 . Such hollow frameworks present a high reversible capacity of 947.4 mAh g-1 at 0.1 A g-1 , an impressive rate behavior with 435.8 mAh g-1 retained at 5 A g-1 , and good stability over 1200 cycles (545 mAh g-1 at 2 A g-1 ).

11.
Magn Reson Med ; 82(6): 2046-2061, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31264278

RESUMO

PURPOSE: To extend the variably-accelerated sensitivity encoding (vSENSE) method from 2D to 3D for fast chemical exchange saturation transfer (CEST) imaging, and prospectively implement it for clinical MRI. METHODS: The CEST scans were acquired from 7 normal volunteers and 15 brain tumor patients using a 3T clinical scanner. The 2D and 3D "artifact suppression" (AS) vSENSE algorithms were applied to generate sensitivity maps from a first scan acquired with conventional SENSE-accelerated 2D and 3D CEST data. The AS sensitivity maps were then applied to reconstruct the other CEST frames at higher acceleration factors. Both retrospective and prospective acceleration in phase-encoding and slice-encoding dimensions were implemented. RESULTS: Applying the 2D AS vSENSE algorithm to a 2-fold undersampled 3.5-ppm CEST frame halved the scan time of conventional SENSE, while generating essentially identical reconstruction errors (p ≈ 1.0). The 3D AS vSENSE algorithm permitted prospective acceleration by up to 8-fold, in total, from phase-encoding and slice-encoding directions for individual source CEST images, and an overall speed-up in scan time of 5-fold. The resulting vSENSE-accelerated amide proton transfer-weighted images agreed with conventional 2-fold-accelerated SENSE CEST results in brain tumor patients and healthy volunteers. Importantly, the vSENSE method eliminated unfolding artifacts in the slice-encoding direction that compromised conventional SENSE CEST scans. CONCLUSION: The vSENSE method can be extended to 3D CEST imaging to provide higher acceleration factors than conventional SENSE without compromising accuracy.

12.
Magn Reson Med ; 82(5): 1812-1821, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31209938

RESUMO

PURPOSE: To develop prospectively accelerated 3D CEST imaging using compressed sensing (CS), combined with a saturation scheme based on time-interleaved parallel transmission. METHODS: A variable density pseudo-random sampling pattern with a centric elliptical k-space ordering was used for CS acceleration in 3D. Retrospective CS studies were performed with CEST phantoms to test the reconstruction scheme. Prospectively CS-accelerated 3D-CEST images were acquired in 10 healthy volunteers and 6 brain tumor patients with an acceleration factor (RCS ) of 4 and compared with conventional SENSE reconstructed images. Amide proton transfer weighted (APTw) signals under varied RF saturation powers were compared with varied acceleration factors. RESULTS: The APTw signals obtained from the CS with acceleration factor of 4 were well-preserved as compared with the reference image (SENSE R = 2) both in retrospective phantom and prospective healthy volunteer studies. In the patient study, the APTw signals were significantly higher in the tumor region (gadolinium [Gd]-enhancing tumor core) than in the normal tissue (p < .001). There was no significant APTw difference between the CS-accelerated images and the reference image. The scan time of CS-accelerated 3D APTw imaging was dramatically reduced to 2:10 minutes (in-plane spatial resolution of 1.8 × 1.8 mm2 ; 15 slices with 4-mm slice thickness) as compared with SENSE (4:07 minutes). CONCLUSION: Compressed sensing acceleration was successfully extended to 3D-CEST imaging without compromising CEST image quality and quantification. The CS-based CEST imaging can easily be integrated into clinical protocols and would be beneficial for a wide range of applications.

13.
Front Neurosci ; 13: 520, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31178687

RESUMO

Objectives: To define normal signal intensity values of amide proton transfer-weighted (APTw) magnetic resonance (MR) imaging in different brain regions. Materials and Methods: Twenty healthy subjects (9 females, mean age 29 years, range 19 - 37 years) underwent MR imaging at 3 Tesla. 3D APTw (RF saturation B1,rms = 2 µT, duration 2 s, 100% duty cycle) and 2D T2-weighted turbo spin echo (TSE) images were acquired. Postprocessing (image fusion, ROI measurements of APTw intensity values in 22 different brain regions) was performed and controlled by two independent neuroradiologists. Values were measured separately for each brain hemisphere. A subject was scanned both in prone and supine position to investigate differences between hemispheres. A mixed model on a 5% significance level was used to assess the effect of gender, brain region and side on APTw intensity values. Results: Mean APTw intensity values in the hippocampus and amygdala varied between 1.13 and 1.57%, in the deep subcortical nuclei (putamen, globus pallidus, head of caudate nucleus, thalamus, red nucleus, substantia nigra) between 0.73 and 1.84%, in the frontal, occipital and parietal cortex between 0.56 and 1.03%; in the insular cortex between 1.11 and 1.15%, in the temporal cortex between 1.22 and 1.37%, in the frontal, occipital and parietal white matter between 0.32 and 0.54% and in the temporal white matter between 0.83 and 0.89%. APTw intensity values were significantly impacted both by brain region (p < 0.001) and by side (p < 0.001), whereby overall values on the left side were higher than on the right side (1.13 vs. 0.9%). Gender did not significantly impact APTw intensity values (p = 0.24). APTw intensity values between the left and the right side were partially reversed after changing the position of one subject from supine to prone. Conclusion: We determined normal baseline APTw intensity values in different anatomical localizations in healthy subjects. APTw intensity values differed both between anatomical regions and between left and right brain hemisphere.

14.
Eur Radiol ; 29(12): 6643-6652, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31175415

RESUMO

OBJECTIVES: To assess the utility of amide proton transfer (APT) imaging as an imaging biomarker to predict prognosis and molecular marker status in high-grade glioma (HGG, WHO grade III/IV). METHODS: We included 71 patients with pathologically diagnosed HGG who underwent preoperative MRI with APT imaging. Overall survival (OS) and progression-free survival (PFS) according to APT signal, clinical factors, MGMT methylation status, and IDH mutation status were analyzed. Multivariate Cox regression models with and without APT signal data were constructed. Model performance was compared using the integrated AUC (iAUC). Associations between APT signals and molecular markers were assessed using the Mann-Whitney test. RESULTS: High APT signal was a significant predictor for poor OS (HR = 3.21, 95% CI = 1.62-6.34) and PFS (HR = 2.22, 95% CI = 1.33-3.72) on univariate analysis. On multivariate analysis, high APT signals were an independent predictor of poor OS and PFS when clinical factors alone (OS: HR = 2.89; PFS: HR = 2.13), or in combination with molecular markers (OS: HR = 2.85; PFS: HR = 2.00), were included as covariates. The incremental prognostic value of APT signals was significant for OS and PFS. IDH-wild type was significantly associated with high APT signals (p = 0.001) when compared to IDH-mutant; however, there was no difference based on MGMT methylation status (p = 0.208). CONCLUSION: High APT signal was a significant predictor of poor prognosis in HGG. APT data showed significant incremental prognostic value over clinical prognostic factors and molecular markers and may also predict IDH mutation status. KEY POINTS: • Amide proton transfer (APT) imaging is a promising prognostic marker of high-grade glioma. • APT signals were significantly higher in IDH-wild type compared to IDH-mutant high-grade glioma. • APT imaging may be valuable for preoperative screening and treatment guidance.


Assuntos
Neoplasias Encefálicas/genética , DNA/genética , Glioma/genética , Isocitrato Desidrogenase/genética , Imagem por Ressonância Magnética/métodos , Mutação , Amidas , Neoplasias Encefálicas/diagnóstico , Neoplasias Encefálicas/mortalidade , Análise Mutacional de DNA , Feminino , Seguimentos , Glioma/diagnóstico , Glioma/mortalidade , Humanos , Isocitrato Desidrogenase/metabolismo , Masculino , Pessoa de Meia-Idade , Prognóstico , Prótons , República da Coreia/epidemiologia , Taxa de Sobrevida/tendências , Fatores de Tempo
15.
Eur Radiol ; 29(10): 5298-5306, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30887206

RESUMO

OBJECTIVES: To determine the utility of the amide proton transfer-weighted MR imaging in differentiating the WHO grade and predict proliferative activity of meningioma. METHODS: Fifty-three patients with WHO grade I meningiomas and 26 patients with WHO grade II meningiomas underwent conventional and APT-weighted sequences on a 3.0 Tesla MR before clinical intervention. The APT-weighted (APTw) parameters in the solid tumor region were obtained and compared between two grades using the t test; the receiver operating characteristic (ROC) curve was used to assess the best parameter for predicting the grade of meningiomas. Pearson's correlation coefficient was calculated between the APTwmax and Ki-67 labeling index in meningiomas. RESULTS: The APTwmax and APTwmean values were not significantly different between WHO grade I and grade II meningiomas (p = 0.103 and p = 0.318). The APTwmin value was higher and the APTwmax-min value was lower in WHO grade II meningiomas than in WHO grade I tumors (p = 0.027 and p = 0.019). But the APTwmin was higher and the APTwmax-min was lower in microcystic meningiomas than in WHO grade II meningiomas (p = 0.001 and p = 0.006). The APTwmin combined with APTwmax-min showed the best diagnostic performance in predicting the grade of meningiomas with an AUC of 0.772. The APTwmax value was positively correlated with Ki-67 labeling index (r = 0.817, p < 0.001) in meningiomas; the regression equation for the Ki-67 labeling index (%) (Y) and APTwmax (%) (X) was Y = 4.9 × X - 12.4 (R2 = 0.667, p < 0.001). CONCLUSION: As a noninvasive imaging method, the ability of APTw-MR imaging in differentiating the grade of meningiomas is limited, but the technology can be used to predict the proliferative activity of meningioma. KEY POINTS: • The APTw min value was higher and the APTw max-min value was lower in WHO grade II meningioma than in grade I tumors. • The APTw min value was higher and the APTw max-min value was lower in microcystic meningiomas than in WHO grade II meningiomas. • The APTw max value was positively correlated with meningioma proliferation index.


Assuntos
Amidas , Neoplasias Meníngeas/patologia , Meningioma/patologia , Prótons , Adulto , Idoso , Proliferação de Células/fisiologia , Feminino , Humanos , Antígeno Ki-67/metabolismo , Imagem por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-Idade , Gradação de Tumores , Curva ROC
16.
Front Neurol ; 10: 104, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30853932

RESUMO

Background: Amide proton transfer (APT) MR imaging has shown great potential in the evaluation of stroke severity because of its sensitivity to acid environments. However, this promising MRI technique has not been used to assess treatment efficacy with regard to stroke recovery. Purpose: To assess the therapeutic effect of supportive treatment in ischemic stroke patients using the pH-sensitive APT MRI technique. Material and Methods: Forty-three ischemic stroke patients at an early stage were recruited and scanned with conventional and APT MRI sequences at 3T before treatment. After treatment, 26 patients underwent a follow-up MRI scan (one to three times on different days). The magnetization-transfer-ratio asymmetry at 3.5 ppm, usually called the APT-weighted (APTW) signal, was measured. The APTW signal changes following treatment were analyzed. Results: Baseline APTW signal intensities in the infarcted lesions inversely correlated with baseline stroke severity. Lesion APTW values gradually increased with time in 24 cases (92.3%) with a follow-up MRI scan, showing clinical symptom improvements. Two cases (7.7%) showed further decreased APTW signal in the follow-up scan, accompanied by clinical symptom aggravation. Compared to the baseline, significant APTW signal increases were found for all post-treatment patients (efficacious), whether based on post-treatment or on stroke onset times. The increase in APTW signal in the ischemic stroke lesion after treatment was associated with an improvement in clinical symptoms. Conclusion: The APTW signal would be a useful imaging biomarker by which to assess the therapeutic efficacy of ischemic stroke treatment.

17.
Neuroimage ; 189: 202-213, 2019 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-30654175

RESUMO

Current chemical exchange saturation transfer (CEST) neuroimaging protocols typically acquire CEST-weighted images, and, as such, do not essentially provide quantitative proton-specific exchange rates (or brain pH) and concentrations. We developed a dictionary-free MR fingerprinting (MRF) technique to allow CEST parameter quantification with a reduced data set. This was accomplished by subgrouping proton exchange models (SPEM), taking amide proton transfer (APT) as an example, into two-pool (water and semisolid macromolecules) and three-pool (water, semisolid macromolecules, and amide protons) models. A variable radiofrequency saturation scheme was used to generate unique signal evolutions for different tissues, reflecting their CEST parameters. The proposed MRF-SPEM method was validated using Bloch-McConnell equation-based digital phantoms with known ground-truth, which showed that MRF-SPEM can achieve a high degree of accuracy and precision for absolute CEST parameter quantification and CEST phantoms. For in-vivo studies at 3 T, using the same model as in the simulations, synthetic Z-spectra were generated using rates and concentrations estimated from the MRF-SPEM reconstruction and compared with experimentally measured Z-spectra as the standard for optimization. The MRF-SPEM technique can provide rapid and quantitative human brain CEST mapping.


Assuntos
Encéfalo/diagnóstico por imagem , Interpretação de Imagem Assistida por Computador/métodos , Processamento de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética/métodos , Imagem Molecular/métodos , Neuroimagem/métodos , Adulto , Amidas , Humanos , Interpretação de Imagem Assistida por Computador/normas , Processamento de Imagem Assistida por Computador/normas , Imagem por Ressonância Magnética/normas , Imagem Molecular/normas , Neuroimagem/normas , Prótons , Reprodutibilidade dos Testes
18.
J Magn Reson Imaging ; 50(2): 347-364, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-30663162

RESUMO

Amide proton transfer-weighted (APTw) imaging is a molecular MRI technique that generates image contrast based predominantly on the amide protons in mobile cellular proteins and peptides that are endogenous in tissue. This technique, the most studied type of chemical exchange saturation transfer imaging, has been used successfully for imaging of protein content and pH, the latter being possible due to the strong dependence of the amide proton exchange rate on pH. In this article we briefly review the basic principles and recent technical advances of APTw imaging, which is showing promise clinically, especially for characterizing brain tumors and distinguishing recurrent tumor from treatment effects. Early applications of this approach to stroke, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and traumatic brain injury are also illustrated. Finally, we outline the technical challenges for clinical APT-based imaging and discuss several controversies regarding the origin of APTw imaging signals in vivo. Level of Evidence: 3 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:347-364.

19.
Nanoscale ; 11(5): 2492-2500, 2019 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-30672555

RESUMO

Heteroatom-doped carbon nanostructures with uniform size and morphology, well-designed architectures, and minimized interfacial resistance have been recognized as promising electrode materials for energy storage, but remain a crucial challenge. Herein, we develop a general approach of polarity-induced decoration of a monolayer sheath of metal-organic framework (MOF) particles with excellent uniformity in size and morphology on electrospun polymer nanofibers. These hybrid nanofibers are facilely converted into nitrogen-doped nanofibrous carbon (denoted as N-NFC) during pyrolysis. The thus-obtained N-NFC features (1) a one-dimensional nanofibrous structure with a highly conductive core, (2) a monolayer sheath of hollow carbon-frames with uniform size and morphology, (3) plenty of micro/mesopores with a highly accessible surface area, and (4) a high N-doping level, all of which guarantee its good electrochemical performance with a high capacitance of 387.3 F g-1 at 1 A g-1. In a solid-state supercapacitor, it delivers excellent rate capability (78.0 F g-1 at 0.2 A g-1 and 64.0 F g-1 at 1 A g-1), an enhanced energy density of 7.9 W h kg-1 at a power density of 219 W kg-1, and outstanding cycling stability with 90% capacity retained over 10 000 cycles at 1 A g-1.

20.
Magn Reson Med ; 81(5): 2915-2923, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30697813

RESUMO

PURPOSE: To investigate the effects of frequency drift on chemical exchange saturation transfer (CEST) imaging at 3T, and to propose a new sequence for correcting artifacts attributed to B0 drift in real time. THEORY AND METHODS: A frequency-stabilized CEST (FS-CEST) imaging sequence was proposed by adding a frequency stabilization module to the conventional non-frequency-stabilized CEST (NFS-CEST) sequence, which consisted of a small tip angle radiofrequency excitation pulse and readout of three non-phase-encoded k-space lines. Experiments were performed on an egg white phantom and 26 human subjects on a heavy-duty clinical scanner, in order to compare the difference of FS-CEST and NFS-CEST sequences for generating the z-spectrum, magnetization transfer ratio asymmetry (MTRasym ) spectrum, and amide proton transfer weighted (APTw) image. RESULTS: The B0 drift in CEST imaging, if not corrected, would cause APTw images and MTRasym spectra from both the phantom and volunteers to be either significantly higher or lower than the true values, depending on the status of the scanner. The FS-CEST sequence generated substantially more stable MTRasym spectra and APTw images than the conventional NFS-CEST sequence. Quantitatively, the compartmental-average APTw signals (mean ± standard deviation) from frontal white matter regions of all 26 human subjects were -0.32% ± 2.32% for the NFS-CEST sequence and -0.14% ± 0.37% for the FS-CEST sequence. CONCLUSIONS: The proposed FS-CEST sequence provides an effective approach for B0 drift correction without additional scan time and should be adopted on heavy-duty MRI scanners.


Assuntos
Clara de Ovo/química , Processamento de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética , Convulsões Febris/diagnóstico por imagem , Algoritmos , Animais , Artefatos , Galinhas , Criança , Pré-Escolar , Tontura/diagnóstico por imagem , Feminino , Cefaleia/diagnóstico por imagem , Humanos , Masculino , Imagens de Fantasmas , Ondas de Rádio
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