Results 1 - 10 of 6437
Results 1 - 10 of 6437. Search took: 0.031 seconds
|Sort by: date | relevance|
[en] A new chemical-shift-sensitive NMR imaging technique is presented. The basic idea of the suggested method consists in the utilization of suitable pulses (hard pulse sequences of specially designed amplitude modulated pulses) to excite only distinct parts of the spectrum under investigation. THis excitation can be used to suppress unwanted resonances of a multi-line spectrum leading to a spectrum simplification. (author). 3 refs.; 3 figs
[en] Highlights: • Chemical shift imaging or Dixon-based fat suppression techniques are very useful in the domain of musculoskeletal MR imaging. • Differentiation of benign from malignant marrow lesions is possible on chemical shift imaging. • Bone lesion conspicuity e.g. granuloma, fracture and sclerosis is enhanced on opposed phase imaging. • Bone marrow lesion healing can be identified as loss of signal on opposed phase imaging. • Hemosiderin detection in areas of hemorrhage or pigmented villonodular synovitis is conspicuous on in-phase imaging. - Abstract: Fat suppression technique is a valuable resource in musculoskeletal magnetic resonance (MR) imaging that is helpful in the diagnosis and differentiation of various pathologies. Multiple different techniques are available for fat suppression, including frequency selective pulse sequence, inversion recovery, hybrid technique, chemical shift imaging (CSI) and the related Dixon based approach. The utility of CSI and Dixon approach is not well recognized in the domain of musculoskeletal MR imaging. The aim of this article is to review the various options for fat suppression and present focused discussion of the role of CSI and Dixon techniques for musculoskeletal MR imaging.
[en] Purpose: To introduce a new radiologic classification of renal angiomyolipoma (AML). Materials and methods: Between 1995 and 2014, CT or MR images in 98 patients with histologically proven 98 AMLs were reviewed independently by a radiologist and a resident. The lesions were classified as (a) 53 fat-rich AML (≤−10HU), (b) 22 fat-poor AML (>−10HU) with tumor-to-spleen ratio (TSR) <0.71 or signal intensity index (SII) >16.5%, and (c) 23 fat-invisible AML (>−10HU) with TSR ≥0.71 and SII ≤16.5%. Inter-reader agreement was assessed with a weighted kappa value. Fat-poor and fat-invisible AMLs were compared in terms of attenuation value, TSR, and SII using unpaired t-test. Results: The weighted kappa value was 0.956 (95% confidence interval, 92.0–99.1%). When a region of interest (ROI) was placed within the most hypodense area on unenhanced CT or within the most signal-dropped area on chemical shift image, the mean attenuation values, TSRs, and SIIs of fat-poor versus fat-invisible AMLs were 19.5 ± 8.1 HU versus 38.1 ± 9.9 HU, 0.59 ± 0.19 versus 0.96 ± 0.01, and 43.7 ± 16.9% versus −5.4 ± 21.1%, respectively (p < 0.0001). When a ROI was placed within the other area on CT or chemical shift images, 90.1% (48/53) of fat-rich AMLs were mis-classified as fat-poor or fat-invisible AML and 50% (11/22) of fat-poor AMLs as fat-invisible AML. Conclusion: The new radiologic classification of renal AML is feasible for clinical practice. ROI location is important in differentiating the types of AMLs.
[en] Sclerosing liposarcoma of epididymis is a rare extratesticular scrotal tumor with variable prognosis. Ultrasonography is the initial imaging modality of choice for the evaluation of scrotal mass and helps to differentiate testicular and extratesticular masses, thereby narrowing down the differential diagnosis. Magnetic resonance imaging with its excellent soft tissue resolution can help in the further characterization of the nature of the tumor. In this case report, we highlight the role of chemical shift imaging in making a confident preoperative diagnosis of liposarcoma thereby guiding optimal and timely management.
[en] Substituent chemical shifts were examined for the 2- and 3-thiophene derivatives of chalcone and compared to the thiophene series of derivatives with the phenyl series. The chemical shift values for the α-carbons of the enones showed and inverse correlation with the Hammett σ values, but the correlation coefficients were moderate (r = 0.836 - 0.878). On the other hand, the β-carbons showed a normal correlation with excellent correlation coefficients (r = 0.994). The absolute magnitude of the ρ values for the α-carbon are about half of those of the β-carbon. The observation may be the result of a through-space transition of the electronic effect of the substituents in addition to the through bond transition
[en] Cysteines possess a unique property among the 20 naturally occurring amino acids: it can be present in proteins in either the reduced or oxidized form, and can regulate the activity of some proteins. Consequently, to augment our previous treatment of the other types of residues, the 13Cα and 13Cβ chemical shifts of 837 cysteines in disulfide-bonded cystine from a set of seven non-redundant proteins, determined by X-ray crystallography and NMR spectroscopy, were computed at the DFT level of theory. Our results indicate that the errors between observed and computed 13Cα chemical shifts of such oxidized cysteines can be attributed to several effects such as: (a) the quality of the NMR-determined models, as evaluated by the conformational-average (ca) rmsd value; (b) the existence of high B-factor or crystal-packing effects for the X-ray-determined structures; (c) the dynamics of the disulfide bonds in solution; and (d) the differences in the experimental conditions under which the observed 13Cα chemical shifts and the protein models were determined by either X-ray crystallography or NMR-spectroscopy. These quantum-chemical-based calculations indicate the existence of two, almost non-overlapped, basins for the oxidized and reduced -SH 13Cβ, but not for the 13Cα, chemical shifts, in good agreement with the observation of 375 13Cα and 337 13Cβ resonances from 132 proteins by Sharma and Rajarathnam (2000). Overall, our results indicate that explicit consideration of the disulfide bonds is a necessary condition for an accurate prediction of 13Cα and 13Cβ chemical shifts of cysteines in cystines.
[en] A continuum model for the calculation of chemical shift solvent effect is presented. The model allows the calculation of solvent effects of non-polar solutes, dissolved in solvents which are magnetically isotropic or at least nearly so but which otherwise may be polar or non polar. The agreement between experimental solvent shifts and the solvent shifts predicted by this new model is shown to be usually good, and to be in all cases considerably better than with other existing continuum models. It is also shown that where the agreement between theory and experimental is less satisfactory, the deviation can be qualitatively explained by the absence in the present theory of a site factor which relates the location of the measured nucleus to the centers of mass of the solute and solvent molecules
[fr]Fondee sur la notion du champ de reaction, une theorie macroscopique (c'est-a-dire basee sur un modele de milieu continu) a ete developpee pour permettre le calcul des deplacements chimiques dus aux effets de milieu, dans le cas des solutes non polaires. Les solvants consideres sont soit polaires, soit non polaires; ils sont de plus magnetiquement isotropes (ou presentent une anisotropie magnetique tres faible donc negligeable). L'accord entre les resultats experimentaux et ceux calcules a l'aide de cette nouvelle theorie est generalement bon et en tout cas considerablement meilleur qu'avec aucune des autres theories macroscopiques developpees anterieurement. Quelques ecarts sont neanmoins observes; ils peuvent s'expliquer qualitativement par l'absence dans la theorie d'un facteur de site qui tiendrait compte de la position du noyau considere par rapport aux centres de gravite des molecules de solute et de solvant
[en] The materials are constituted by chelates of paramagnetic metals of valency IV with beta-diketones. This can be applied to the study of organic molecules having basic properties according to Lewis
[fr]Les materiaux sont constitues par des chelates de metaux paramagnetiques a la valence IV avec des β-dicetones. Ceci est applicable a l'etude de molecules organiques presentant des proprietes basiques au sens de Lewis
[en] Although 15N- and 13C-based chemical exchange saturation transfer (CEST) experiments have assumed an important role in studies of biomolecular conformational exchange, 1H CEST experiments are only beginning to emerge. We present a methyl-TROSY 1H CEST experiment that eliminates deleterious 1H–1H NOE dips so that CEST profiles can be analyzed robustly to extract methyl proton chemical shifts of rare protein conformers. The utility of the experiment, along with a version that is optimized for 13CHD2 labeled proteins, is established through studies of exchanging protein systems. A comparison between methyl 1H CEST and methyl 1H CPMG approaches is presented to highlight the complementarity of the two experiments.