Том 47, № 2 (2016)

Temperature dependences of ¹H nuclear magnetic resonance (NMR) splitting signals of 2,6-lutidine aqueous solutions were studied in the vicinity of lower critical solution temperatures. The splitting of ¹H NMR signals was considered as an order parameter at “liquid–liquid” phase transition. It was discovered that critical indices to determine the behavior of the order parameter are different (i.e., demonstrate heterogeneity) for structurally non-equivalent hydrogen atoms of the 2,6-lutidine molecule. An isotope effect associated with van der Waals interactions was registered in the obtained ¹H NMR spectra.

Magnetic resonance imaging (MRI) has emerged as the method of choice for in vivo quantification of lipids. The MRI methods originally proposed for lipid quantification did not take into account for the loss of signal due to T2*. In the last decade, a number of algorithms has been introduced for the T2* correction. These algorithms assumed that the T2* of the water protons (T2_w*) is the same as the T2* of lipid protons (T2_L*). More recent algorithms have proposed a more sophisticated model (dual T2* correction), which consider different values for T2_w* and T2_L*. However, no reference values exist for validating the values of T2_w* and T2_L* obtained by these algorithms in tissues or phantoms where water and lipid protons co-exist. In the current work, we propose a direct measurement of T2_w* and T2_L* in phantoms consisting of water–lipid mixtures. MR multi-gradient-echo images were acquired with a low receiver bandwidth/pixel with the aim of separating the water and lipid signals. In all phantoms, T2_L* (range 7.6–10.7 ms) was significantly shorter than T2_w* (range 48.9–57.4 ms). The proposed method provides the ground truth values of T2_w* and T2_L* for development, validation, and optimization of lipid quantification methods based on dual T2* correction.

This research aimed to study the influence of the geometrical configuration of a translucent fiberglass post on the dual cure resin cement polymerization by electron paramagnetic resonance (EPR) spectroscopy. A 20-mm long, White Post DC no. 1 fiberglass post (FGM, Joinvile, SC, Brazil) was sectioned in half to obtain two different groups of posts: cylindrical and conical. Each post was cemented with AllCem A1 dual cure resin cement (FGM, Joinvile, SC, Brazil) using a root canal model and light cured for 40 s. Following cementation, the post was removed and sectioned to obtain 2 mm samples at different depth of cementation. EPR spectra were obtained 10 min and 24 h after cementation to determine the concentration of free radicals (FR) in the surrounding hardened (cured) dental cement, once the concentration of FR is proportional to the light intensity at the restoration point. No significant decrease was observed in light transmission through the cylindrical post that affected the FR concentration, at depths up to 5.5 mm. In contrast, a decrease was verified for all samples conical geometry. The light conduction was effective up to 5.5 mm of curing depth when a cylindrical post was used. The cylindrical configuration was more efficient at conducting light to the deepest points of the restoration compared with the conical configuration.

The aim of this study was to determine the optimal k-space sampling distribution at a compressed sensing (CS) technique for imaging small blood vessels. First, we calculated the energy spectrum of the target vessel and then used this spectral information and the incoherence of undersampling artifacts by polynomial probability density with a power of decay (p) to determine the k-space sampling distribution for CS undersampling. The optimal p was calculated based on the energy spectra of different target vessels having different diameters which were described with full widths at half maximums (FWHMs). The optimized p together with its randomly sampled k-space was then applied to the data previously obtained with conventional magnetic resonance angiography (MRA) at 7.0 Tesla (T) MRI. Two acceleration factors of CS, such as ×3 and ×5 (33 and 20 %), were reconstructed from the conventional MRA data. The lower p was well fitted to the energy spectra of smaller vessels, in that the sampling density distribution of the lower p was closest to these spectra. However, with the higher acceleration (i.e., 20 %), two p values for small FWHMs, such as 0.56 and 0.84 mm, were not distinguishable because the undersampling of the DC point in k-space for the lower p was infeasible. With an acceleration of 33 %, the optimal p was obtained with the smallest vessels, and it most clearly discriminated the smaller vessels on the MRA images, as compared with other values of p. This study optimized the k-space sampling distribution for small vessels at CS technique. The results suggest that the lower p is suitable for the effective visualization of small vessels. Future studies are needed to appropriately adjust the acceleration factor and optimized p concurrently, since too high acceleration could restrict the applicable range of p and make it difficult to clearly depict smaller vessels.

To evaluate whether metabolic profiles obtained using high-resolution magic angle spinning magnetic resonance spectroscopy (HR MAS MRS) and total choline-containing compound (tCho) on in vivo MRS could predict indolent tumors based on highly favorable prognostic factors. We analyzed 50 frozen tissue samples from 50 patients (mean 46.4 years, range 29–72 years) with breast cancer using HR MAS MRS. In vivo single-voxel MRS analyses were also performed on these patients preoperatively. We defined estrogen receptor (ER)-positive tumors with a low histological grade, low Ki-67-positivity (<14 %), and negative lymph node metastases as an indolent tumor. By univariate analysis, metabolic profiles on HR MAS MRS and tCho on in vivo MRS were compared according to dichotomized pathological parameters using the Mann–Whitney test. By multivariate analysis, orthogonal projections to latent structure-discriminant analysis (OPLS-DA) were performed to differentiate groups with different prognostic pathological parameters. A total of 6 indolent tumors (12 %) and 44 non-indolent tumors (88 %) were studied. By univariate analysis, tumors without recurrence showed significantly higher Tau and Cr values than those with recurrence (P = 0.041, respectively). By multivariate analysis, an OPLS-DA model showed sensitivities of 100, 77, and 82 % and specificities of 68, 100, and 96 % for the prediction of indolent tumors, tumors with recurrence, and tumors with lymph node metastases, respectively. By univariate analysis of in vivo MRS, tumors without recurrence showed significantly higher values of tCho than those with recurrence (P = 0.043 and 0.035). Several metabolites of Gly, Lac, Tau, Cr, GPC, and Cho on HR MAS MRS could be potential candidate biomarkers for predicting indolent tumors, tumors with early recurrence, and lymph node metastases. Metabolite profiling using HR MAS MRS might enable the prediction of breast cancer prognoses, especially for ER-positive tumors.