Assessment of magnetic field interactions and heating for cerebral aneurysm flow diverters during 7T MRI.

Flow diverters (FDs) are utilized for a wide range of aneurysms, but show safety issues such as adverse interactions with static magnetic fields (displacement force and torque) and radiofrequency-induced heating during magnetic resonance imaging (MRI). The present study aimed to assess these adverse interactions in a 7-tesla (7T) static magnetic field and radiofrequency-induced heating during a 7T MRI for two types of FD. Displacement force and magnetically induced torque were assessed using the deflection angle method and low friction surface method, respectively. To assess heating, each FD was set in a phantom filled with gelled-saline mixed with polyacrylic acid and underwent a 7T MRI using a three-dimensional fast spin echo method. Displacement force and magnetically induced torque in the 7T static magnetic field were undetectable, and radiofrequency-induced heating during 7T MRI remained ≤ 0.6 °C for both types of FD, suggesting that magnetic field interactions and heating on FDs during a 7T MRI are acceptable from a safety perspective.

Using Phase Difference Information to Detect Errors in the Flip Angle Measured with Actual Flip Angle Imaging at 7T.

Flip angle (FA) measurements using the actual flip angle imaging (AFI) method may induce significant errors in ultrahigh fields. We aimed to develop a method for detecting errors in FA measurements using phase information at 7 tesla. We performed computer simulations to elucidate the relationship between the FA calculation errors and the phase difference between the two AFI source images. We then examined whether a method based on the phase difference could detect FA calculation errors and determine the prescribed nominal FA of the scanner for accurate measurements in phantoms and healthy volunteers. The simulations confirmed that the calculated FA values erroneously decreased when the longitudinal magnetization and phase in one of the source images were inverted. Tests on phantoms and human subjects demonstrated that the phase difference information between the source images with a cut-off of 90° could readily detect FA calculation errors in the AFI method.

Whole cancer-region enhancement using meglumine-gadopentetate-glucose solution and 7.0-T magnetic resonance imaging.

To visualize whole cancerous region including hypoxic cancer without radiation exposure, we developed meglumine-gadopentetate-glucose solution for 7.0-T magnetic resonance imaging. The infusion solution consists of meglumine-gadopentetate and glucose solutions, and these solutions are mixed before the vein drip infusion. We used readily available solutions, and the concentrations of the meglumine-gadopentetate and glucose solutions were 37.14 and 5.0%, respectively. In the first and second experiments, vein infusions were conducted from a rabbit ear using meglumine-gadopentetate-saline and meglumine-gadopentetate-glucose solutions, and T1 weighted imaging was performed to visualize cancerous region. Using the meglumine-gadopentetate saline, it was not difficult to image cancer-growth regions with new blood vessels. Using the meglumine-gadopentetate-glucose solution, the signal intensity of whole cancerous region including hypoxic cancer substantially increased. The visualizing duration for the meglumine gadopentetate glucose was beyond 90 min, and the rabbit survived after the infusion. The signal intensity in the hypoxic cancer was increasing until 90 min using the meglumine-gadopentetate-glucose solution, since the meglumine-gadopentetate molecules were absorbed into almost the whole cancerous region along with glucose-molecule flows.

Analysis of Arabidopsis TPK2 and KCO3 reveals structural properties required for K+ channel function.

Arabidopsis thaliana contains five tandem-pore domain potassium channels, TPK1-TPK5 and the related one-pore domain potassium channel, KCO3. Although KCO3 is unlikely to be an active channel, it still has a physiological role in plant cells. TPK2 is most similar to KCO3 and both are localized to the tonoplast. However, their function remains poorly understood. Here, taking advantage of the similarities between TPK2 and KCO3, we evaluated Ca2+ binding to the EF hands in TPK2, and the elements of KCO3 required for K+ channel activity. Presence of both EF-hand motifs in TPK2 resulted in Ca2+ binding, but EF1 or EF2 alone failed to interact with Ca2+. The EF hands were not required for K+ transport activity. EF1 contains two cysteines separated by two amino acids. Replacement of both cysteines with serines in TPK2 increased Ca2+ binding. We generated a two-pore domain chimeric K+ channel by replacing the missing pore region in KCO3 with a pore domain of TPK2. Alternatively, we generated two versions of simple one-pore domain K+ channels by removal of an extra region from KCO3. The chimera and one of the simple one-pore variants were functional channels. This strongly suggests that KCO3 is not a pseudogene and KCO3 retains components required for the formation of a functional K+ channel and oligomerization. Our results contribute to our understanding of the structural properties required for K+ channel activity.

Reduction of Spermidine Content Resulting from Inactivation of Two Arginine Decarboxylases Increases Biofilm Formation in Synechocystis sp. Strain PCC 6803.

The phototropic bacterium Synechocystis sp. strain PCC 6803 is able to adapt its morphology in order to survive in a wide range of harsh environments. Under conditions of high salinity, planktonic cells formed cell aggregates in culture. Further observations using crystal violet staining, confocal laser scanning microscopy, and field emission-scanning electron microscopy confirmed that these aggregates were Synechocystis biofilms. Polyamines have been implicated in playing a role in biofilm formation, and during salt stress the content of spermidine, the major polyamine in Synechocystis, was reduced. Two putative arginine decarboxylases, Adc1 and Adc2, in Synechocystis were heterologously expressed in Escherichia coli and purified. Adc2 had high arginine decarboxylase activity, whereas Adc1 was much less active. Disruption of the adc genes in Synechocystis resulted in decreased spermidine content and formation of biofilms even under nonstress conditions. Based on the characterization of the adc mutants, Adc2 was the major arginine decarboxylase whose activity led to inhibition of biofilm formation, and Adc1 contributed only minimally to the process of polyamine synthesis. Taken together, in Synechocystis the shift from planktonic lifestyle to biofilm formation was correlated with a decrease in intracellular polyamine content, which is the inverse relationship of what was previously reported in heterotroph bacteria.IMPORTANCE There are many reports concerning biofilm formation in heterotrophic bacteria. In contrast, studies on biofilm formation in cyanobacteria are scarce. Here, we report on the induction of biofilm formation by salt stress in the model phototrophic bacterium Synechocystis sp. strain PCC 6803. Two arginine decarboxylases (Adc1 and Adc2) possess function in the polyamine synthesis pathway. Inactivation of the adc1 and adc2 genes leads to biofilm formation even in the absence of salt. The shift from planktonic culture to biofilm formation is regulated by a decrease in spermidine content in Synechocystis This negative correlation between biofilm formation and polyamine content, which is the opposite of the relationship reported in other bacteria, is important not only in autotrophic but also in heterotrophic bacteria.