Multi-echo investigations of positive and negative CBF and concomitant BOLD changes.

Unlike the positive blood oxygenation level-dependent (BOLD) response (PBR), commonly taken as an indication of an 'activated' brain region, the physiological origin of negative BOLD signal changes (i.e. a negative BOLD response, NBR), also referred to as 'deactivation' is still being debated. In this work, an attempt was made to gain a better understanding of the underlying mechanism by obtaining a comprehensive measure of the contributing cerebral blood flow (CBF) and its relationship to the NBR in the human visual cortex, in comparison to a simultaneously induced PBR in surrounding visual regions. To overcome the low signal-to-noise ratio (SNR) of CBF measurements, a newly developed multi-echo version of a center-out echo planar-imaging (EPI) readout was employed with pseudo-continuous arterial spin labeling (pCASL). It achieved very short echo and inter-echo times and facilitated a simultaneous detection of functional CBF and BOLD changes at 3 T with improved sensitivity. Evaluations of the absolute and relative changes of CBF and the effective transverse relaxation rate, R2*, the coupling ratios, and their dependence on CBF at rest, CBFrest, indicated differences between activated and deactivated regions. Analysis of the shape of the respective functional responses also revealed faster negative responses with more pronounced post-stimulus transients. Resulting differences in the flow-metabolism coupling ratios were further examined for potential distinctions in the underlying neuronal contributions.

Characterization of pseudo-continuous arterial spin labeling: Simulations and experimental validation.

PURPOSE: To characterize pseudo-continuous arterial spin labeling (pCASL) through simulations of spin inversion and to discuss suitable parameter settings for measuring cerebral perfusion. METHODS: Simulations of arterial spin inversion in pCASL were performed based on the Bloch equation. Both the labeling and the control condition of pCASL were analyzed separately, and the labeling efficiency, α, was calculated depending on the averages of both, the radiofrequency (RF) field amplitude and labeling gradient strength. The influence of additional parameters characterizing the pCASL pulse sequence, such as the interpulse interval, the RF duty cycle, and the labeling gradient, also were studied. An echo-planar imaging protocol utilizing a short repetition time was developed for experimental validation by estimating α in the internal carotid artery. RESULTS: The effectiveness of the control condition of balanced pCASL crucially depends on both the labeling gradient amplitude and the RF duty cycle. The use of large values for both quantities improves the insensitivity to off-resonance gradients caused by magnetic field inhomogeneities. In addition, balanced and unbalanced pCASL become comparably effective. CONCLUSION: By use of appropriate parameter settings, labeling efficiencies of around 90% are feasible, independent of expected off-resonance gradients at 3T. Magn Reson Med 79:1638-1649, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Anodic TiO2 nanotube layers electrochemically filled with MoO3 and their antimicrobial properties.

In the present work, the authors produce a Ti surface with a TiO2 nanotube coating and investigate the electrochemical filling of these layers with MoO3. The authors demonstrate that using a potential cycling technique, a homogenous MoO3 coating can be generated. Controllable and variable coating thicknesses are achieved by a variation of the number of cycles. Thicknesses from a few nanometers to complete filling of the nanotube layers can be obtained. A thermal treatment is used to convert the as-deposited amorphous MoO(x) phases into MoO3. These MoO3 loaded nanotube layers were then investigated regarding their antimicrobial properties using strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The authors found that the combination of crystalline MoO3 on TiO2 nanotubes shows excellent antimicrobial properties.

Mechanisms of laser-induced dissection and transport of histologic specimens.

Rapid contact- and contamination-free procurement of histologic material for proteomic and genomic analysis can be achieved by laser microdissection of the sample of interest followed by laser-induced transport (laser pressure catapulting). The dynamics of laser microdissection and laser pressure catapulting of histologic samples of 80 mum diameter was investigated by means of time-resolved photography. The working mechanism of microdissection was found to be plasma-mediated ablation initiated by linear absorption. Catapulting was driven by plasma formation when tightly focused pulses were used, and by photothermal ablation at the bottom of the sample when defocused pulses producing laser spot diameters larger than 35 microm were used. With focused pulses, driving pressures of several hundred MPa accelerated the specimen to initial velocities of 100-300 m/s before they were rapidly slowed down by air friction. When the laser spot was increased to a size comparable to or larger than the sample diameter, both driving pressure and flight velocity decreased considerably. Based on a characterization of the thermal and optical properties of the histologic specimens and supporting materials used, we calculated the evolution of the heat distribution in the sample. Selected catapulted samples were examined by scanning electron microscopy or analyzed by real-time reverse-transcriptase polymerase chain reaction. We found that catapulting of dissected samples results in little collateral damage when the laser pulses are either tightly focused or when the laser spot size is comparable to the specimen size. By contrast, moderate defocusing with spot sizes up to one-third of the specimen diameter may involve significant heat and ultraviolet exposure. Potential side effects are maximal when samples are catapulted directly from a glass slide without a supporting polymer foil.

Principles of laser microdissection and catapulting of histologic specimens and live cells.

Rapid contact- and contamination-free procurement of specific samples of histologic material for proteomic and genomic analysis as well as separation and transport of living cells can be achieved by laser microdissection (LMD) of the sample of interest followed by a laser-induced forward transport process [laser pressure "catapulting," (LPC)] of the dissected material. We investigated the dynamics of LMD and LPC with focused and defocused laser pulses by means of time-resolved photography. The working mechanism of microdissection was found to be plasma-mediated ablation. Catapulting is driven by plasma formation, when tightly focused pulses are used, and by ablation at the bottom of the sample for moderate and strong defocusing. Driving pressures of several hundred megapascals accelerate the specimen to initial velocities of 100-300 m/s before it is rapidly slowed down by air friction. With strong defocusing, driving pressure and initial flight velocity decrease considerably. On the basis of a characterization of the thermal and optical properties of the histologic specimens and supporting materials used, we calculated the temporal evolution of the heat distribution in the sample. After laser microdissection and laser pressure catapulting (LMPC), the samples were inspected by scanning electron microscopy. Catapulting with tightly focused or strongly defocused pulses results in very little collateral damage, while slight defocusing involves significant heat and UV exposure of up to about 10% of the specimen volume, especially if samples are catapulted directly from a glass slide. Time-resolved photography of live-cell catapulting revealed that in defocused catapulting strong shear forces originate from the flow of the thin layer of culture medium covering the cells. By contrast, pulses focused at the periphery of the specimen cause a fast rotational movement that makes the specimen wind its way out of the culture medium, thereby undergoing much less shear stresses. Therefore, the recultivation rate of catapulted cells was much higher when focused pulses were used.