1,4-苯二硫醇分子的表面增强共振拉曼散射的化学增强

利用密度泛函和含时密度泛函理论方法研究了1,4-苯二硫醇分子在两个金团簇之间的表面增强拉曼散射及表面增强共振拉曼散射光谱. 采用对应四种不同形式的电荷转移激发态能量的入射光,计算了表面增强共振拉曼光谱. 结果显示,光谱增强的效果与电荷转移的形式密切相关. 不同的电荷转移形式对增强因子的贡献是有差异的.     

Theoretical study on SERRS of rhodamine 6G adsorbed on Ag2 cluster: chemical mechanism via intermolecular or intramolecular charge transfer

The problem of the chemical enhancement of rhodamine 6G (R6G) adsorbed on silver cluster has been theoretically investigated by charge difference densities (CDDs) to show the direct charge transfer (CT) evidence. For surface‐enhanced resonance Raman scattering (SERRS) of R6G excited at 514.5 nm, the enhancements of v(151) and v(154) result from weak intermolecular (from Ag to R6G) CT and the strong intramolecular CT [similar to that of resonance Raman scattering (RRS) of R6G], respectively. The possibility of the SERRS of R6G contributed from pure intermolecular CT is also discussed, when the incident light is close to the new metal–R6G CT excited state at 1571.4 nm. Meanwhile compared with the absorption process the fluorescence yield of R6G is investigated by transition densities and CCDs. Copyright © 2008 John Wiley & Sons, Ltd.     

MR imaging of multiple hepatic cysts in a patient with polycystic liver disease

We report a case of a 55-year-old woman with polycystic liver disease that we examined with magnetic resonance (MR) imaging, CT and ultrasound. The MR images demonstrated varying intensities in the cyst contents which we believe is due to different degrees and age of hemorrhage. Such variability among the cysts was not seen on the CT or ultrasound images.     

Comparison of in vitro breast cancer visibility in analyser‐based computed tomography with histopathology,mammography, computed tomography and magnetic resonance imaging

High‐resolution analyser‐based X‐ray imaging computed tomography (HR ABI‐CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI‐CT images provided significantly better low‐contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12–13 mGy in CT and ABI‐CT. The excellent visibility of in vitro breast cancer suggests that HR ABI‐CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.     

CT and MR appearance of subureteric Teflon and periuretral Teflon migration: a case report.

We present the computed tomography (CT) and magnetic resonance (MR) findings of a case in which an adult patient underwent subureteric injection of polytetrafluoroethylene (PTFE; Teflon) (STING) to correct vesicoureteral reflux. We report the appearance of periureteral PTFE migration mimicking cystic pathology.     

Formation of multifunctional Fe_3O_4/Au composite nanoparticles for dual-mode MR/CT imaging applications

Recent advances with iron oxide/gold(Fe3O4/Au) composite nanoparticles(CNPs) in dual-modality magnetic resonance(MR) and computed tomography(CT) imaging applications are reviewed. The synthesis and assembly of "dumbbelllike" and "core/shell" Fe3O4/Au CNPs is introduced. Potential applications of some developed Fe3O4/Au CNPs as contrast agents for dual-mode MR/CT imaging applications are described in detail.     

Observer reliability in CT and MRI of the abdomen/pelvis

The purpose of this research was to evaluate two sources of error in the performance of computerized tomography (CT) and magnetic resonance imaging (MRI) of the abdomen/pelvis. The sources of error assessed were inter- and intra-observer reliability. Thirty abdomen/pelvis CT scans were randomly selected from each of three hospitals (university, VA, military) with different CT scanners. Two radiologists were recruited from each site to be CT observers. Forty-five abdomen/pelvis MRI scans were randomly selected from two institutions with different MRI scanners. Four observers were recruited to read the MRI scans. All scans were read blind without clinical information or patient identification. Overall inter-observer and intra-observer diagnostic agreement was significantly higher for MRI compared to CT. Inter-observer diagnostic agreement rates were also significantly higher for MRI when the etiologies of neoplastic vascular and metabolic/toxic were assigned. Observer experience in CT (range: 5-9 yr) or MRI (range: 2-4 yr) was not statistically associated with improved diagnostic agreement. This research addresses many of the criticisms of the MRI literature and compares MRI favorably to CT.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Magnetic resonance imaging of soft tissue masses: an evaluation of fifty-three histologically proven tumors

Fifty-three histologically confirmed soft tissue masses in 48 patients were evaluated by magnetic resonance imaging (MR) and computerized tomography (CT). Twenty-three of these were malignant, twenty-three benign and seven of intermediate malignancy (all aggressive fibromatosis). The two procedures were compared for sensitivity and delineation of masses, their relationship to important neurovascular structures, their potential for histological diagnoses, their relative roles in influencing the surgical approach and the preferred modality in the follow-up for detection of tumor recurrence. Both modalities have their relative strengths and weaknesses. However, the superior contrast resolution of magnetic resonance imaging, its demonstration of lesions not clearly identified by CT, its pluridirectional capabilities and its ability to demonstrate large soft tissue tumors in a single coronal or sagittal plane makes it the preferred initial modality for evaluation of the soft tissue tumor of uncertain etiology and also in the follow-up of these patients. Despite MR's superiority in anatomically staging soft tissue tumors it, like CT, is of limited value in characterizing soft tissue sarcomas.     

I-STMAS,a new high-resolution solid-state NMR method for half-integer quadrupolar nuclei

In complement to the previously proposed multiple-quantum magic-angle-spinning (MQMAS) and satellite transition MAS (STMAS) sequences, we describe a new two-dimensional high-resolution method, inverse-STMAS (I-STMAS) that allows second-order quadrupolar averaging. Like STMAS, I-STMAS correlates second-order quadrupole dephasing occurring on coherences related to the central transition (CT) and satellite transitions (STs), but does it in a reverse manner: CT evolves during the t₁ period while STs are detected during t₂. Although STMAS and I-STMAS are symmetric, there are some interesting and useful differences between the two methods. For example, we show that during the acquisition time t₂, it is possible to over-sample the data and then to process them to suppress the CT–CT correlation resonance.     

Applications of magnetic resonance imaging in diseases of the pediatric central nervous system

Magnetic resonance imaging (MRI) is rapidly becoming the initial diagnostic step in the evaluation of gross abnormalities involving the brain or spinal cord in the pediatric patient. Control of patient motion and support of vital functions are critical if future utilization of MRI is to progress beyond its current outpatient diagnostic role. Currently, MRI's noninvasiveness, sensitivity and multiplanar graphic depiction of the disease process are supplanting the more traditional diagnostic modalities of CT, metrizamide CT, and myelography.     

Hepatic angiomyolipoma: Value of proton (fat/water) chemical shift fast low angle shot (FLASH) MR imaging technique in detecting fatty tissue content

A case of angiomyolipoma of the liver in a 43-yr-old woman is reported. Findings on ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging techniques are presented and the usefulness of proton (fat/water) chemical shift FLASH imaging to confirm the presence of intratumoral fat is pointed out.     

Raman scattering from the molecular charge transfer crystal anthracene-PMDA

The Raman spectrum of the mixed stack charge transfer (CT) crystal anthracene-PMDA, has been measured in the wavelength region near the lowest CT transition at 5458 Å. Six low frequency modes are observed below 140 cm^?1, the mode at 130 cm^?1 showing strong resonance enhancement. These modes are assigned as librational motion of the anthracene and PMDA molecules by rigid body analysis of X-ray structural data.     

Economic impact of replacing CT with MR imaging for refractory epilepsy

Purpose: To evaluate the economic costs of using computed tomography (CT) vs. magnetic resonance (MR) imaging in the preoperative evaluation of refractory epilepsy patients. Methods: Preoperative CT and MR imaging findings from 117 patients who underwent surgery for medically refractory epilepsy during a 3.5-year period were reviewed. Cost savings were based on the paradigm that intracranial electroencephalogram monitoring (costing about $50,000) would have been necessary for preoperative localization of the epileptogenic zone in those patients without positive imaging findings. Savings attributed to replacing CT with MR were based on patients with positive MR and normal CT. A similar paradigm was used to calculate savings for replacing MR with CT. National savings were based solely on patients with neoplasms or vascular lesions because paradigms for other lesions vary considerable depending on institutional philosophy. Results: Replacing CT with MR imaging would have eliminated preoperative intracranial electrode procedures in 29 of 117 patients, with potential savings of $1,450,000 at our institution. In the 37 patients with neoplastic or vascular substrates, MR would have eliminated 10 invasive electrode procedures with estimated savings of $0.5 million institutionally and $3 to $4 million per year nationally. There were no cases to support replacing MR with CT. Conclusion: Replacing CT with MR decreases health costs associated with preoperative evaluation of intractable epilepsy requiring surgical amelioration.     

Direct visual evidence for chemical mechanisms of SERRS via charge transfer in Au20–pyrazine–Au20 junction

The essence of the chemical mechanism for surface‐enhanced resonance Raman scattering (SERRS) is the charge transfer (CT) between the metal and the molecule at the resonant electronic transition, which results in the mode‐selective enhancement in the SERRS spectrum. The site‐orientated CT can directly interpret the mode‐selective chemical enhancement in SERRS. However, it is a great challenge to intutively visualize the orientation and site of the CT. In this paper, for the pyrazine–Au₂ complex, a three‐dimensional (3D) cubic representation is built to provide direct visual evidence for chemical mechanisms of SERRS via CT from the Au₂ cluster to pyrazine at the resonant electronic transition. The relationship between the mode‐selective enhancements in SERRS and the site‐orientated CT was clearly revealed. The intracluster excitation (analog of plasmon excitation in large naonoparticles) was also visualized by the 3D cubic presentation, which provided the direct evidence of local electromagnetic field enhancement of SERRS. To study the quantum size effect and the coupling effect of the nanoparticles, the photoexcitation mechanisms of the Au₂₀–pyrazine complex and the Au₂₀–pyrazine–Au₂₀ junction were also investigated. The tunneling charge transfer from one Au₂₀ cluster to another Au₂₀ cluster outside the pyrazine in Au₂₀–pyrazine–Au₂₀ junction was also revealed visually. The calculated normalized extinction spectra of Au nanoparticles using the generalized Mie theory reveal that the resonance peak is red‐shifted due to the coupling between particles. Copyright © 2009 John Wiley & Sons, Ltd.     

Cardiac calcifications: difficult MRI diagnosis

Magnetic resonance imaging (MRI) and computed tomography (CT) were performed in 40 patients with a variety of cardiovascular diseases. These imaging modalities were compared to investigate their relative value in the assessment of cardiovascular diseases. Of these 40 patients, 7 were found by CT to have detectable cardiovascular calcifications. These patients included one calcified mitral stenosis, one calcified coronary artery, one calcified type B aortic dissection, two calcified myocardial infarctions, and two patients with calcific pericarditis. In several cases, MRI was misleading because of difficulty in detecting calcifications. We present a series of cases illustrating a limitation of MRI in identifying diagnostically and clinically important cardiovascular calcifications.     

Bremsstrahlung-induced Auger peaks

For highly-polar nitro-substituted aromatic compounds, characterization of the nitro-N 1s core-hole states from the standpoint of intramolecular charge-transfer (CT) interaction is obtained through analysis of the energy difference between the satellite and the main peak, and the relative intensity of the satellite compared to the main peak.Two-dimensional configuration interaction (CI) is considered between the no-bond (covalent) and the CT (ionic) structures in both the initial and the final states. The off-diagonal element between these two structures is given in terms of the core resonance integral between the ring carbon and the nitro nitrogen, and can therefore be reduced by steric hindrance, and is also closely related to the π-electron density at the adjacent carbon in the donor orbital. The absolute magnitude of the off-diagonal element and the ionization potential of the donor are important factors determining the relative intensity of the CT satellite.It was found that in the case of some nitro-N 1s core-hole ions the CT structure is located below the no-bond structure, and that two-dimensional CI calculations are valid as far as the ground and the CT states are concerned.     

Synthesis,spectroscopic, and computational studies of charge‐transfer complexation between benzidine with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone and chloronil

The solid charge transfer (CT) complexes that have been formed from the reactions of donor benzidine (BZ) and the π‐acceptors such as 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) and chloronil (CHL) have been studied and characterized experimentally and theoretically. The experimental work which includes the use of UV‐visible spectroscopy to identify the CT band of the CT‐complex. The composition of the complexes has been investigated successfully by using spectrophotometric titration and Job method of continuous variation to be 1:1. Furthermore, to calculate the formation constant and molar extinction coefficient, we have used the Benesi‐Hildebrand equation. Infrared and proton nuclear magnetic resonance spectral studies were used to characterize and confirm the formation of CT‐complex. The experimental studies were well supported by quantum chemical simulations by using density functional theory. The computational analysis of molecular geometry, Mulliken charges, and molecular electrostatic potential surfaces of reactants and complexes is very much helpful in assigning the CT route. The C═O bond length of DDQ and CHL increased upon complexation with BZ. We have also observed that the substantial amount of charge has been transferred from BZ to DDQ and CHL in the process of complexation. An excellent consistency has been achieved between experimental and theoretical results.     

Magnetic resonance imaging in the diagnosis of the cranio-cervical manifestations of the mucopolysaccharidoses

Sixteen magnetic resonance (MR) studies were performed in eight patients with mucopolysaccharidosis (MPS). In patients with Hunter, Hurler, and Scheie syndromes, multiple areas of increased signal intensity were noted in the periventricular white matter. Computerized tomography (CT) frequently failed to demonstrate these white matter lesions. Other findings included spinal cord compression, hydrocephalus and airway obstruction due to soft tissue thickening around pharynx. In patients with Morquio syndrome, cervical spine dislocation, spinal cord compression and hydrocephalus were diagnosed by MR. MR was superior compared to CT, plain films and plain tomography, as the narrowing caused by bone and soft tissue changes were better seen with MR. Our experience suggests that MR should be the primary imaging modality for the detection of cranial abnormalities in patients with MPS. High resolution surface coil imaging may be preferable to invasive procedures such as myelography and CT with intrathecal contrast agents for the evaluation of cervical spine disease.     

Theoretical Studies of Electron Paramagnetic Resonance Parameters for Cr4+ Ions in Ca2GeO4 Crystals

The electron paramagnetic resonance (EPR) parameters (zero-field splitting D and g factors g_||, g_⊥) of Cr⁴⁺ ions in Ca₂GeO₄ crystals have been calculated from the complete high-order perturbation formulas of EPR parameters for a 3d² ion in trigonal MX₄ clusters. In these formulas, in addition to the contributions to EPR parameters from the widely used crystal-field (CF) mechanism, the contributions from the charge-transfer (CT) mechanism (which are often neglected) are included. From the calculations, it is found that for the high valence state 3dⁿ ions in crystals, the reasonable explanation of EPR parameters (in particular, the g factors) should take both the CF and CT mechanisms into account.