Physics in Medicine最新文献

In this manuscript, we explore the use of the Heat-Transfer Method (HTM) for the real-time analysis of microbial growth using Saccharomyces cerevisiae as a model organism. The thermal responses of gold electrodes upon exposure to suspensions of S. cerevisiae (wild type strain DLY640) concentrations were monitored, demonstrating an increase in thermal resistance at the solid-liquid interface with higher concentrations of the microorganism. Flow cells were manufactured using 3D-printing to facilitate longitudinal experiments.

We can clearly discriminate between the growth of S. cerevisiae under optimal conditions and under the influence of factors that inhibit the replication process, such as the use of nutrient depleted growth medium, elevated temperature, and the presence of toxic compounds. In addition, it is possible to determine the kinetics of the growth process and quantify yeast replication which was demonstrated by measuring a mutant temperature sensitive strain.

This is the first time HTM has been used for the real-time determination of factors that impact microbial growth. Thermal sensing is low-cost, offers straightforward analysis and measurements can be performed on-site. Due to the versatility of this method, this platform can be extended to monitor other microorganisms and in particular to study the response of bacteria to selected antibiotics.

The aim of this study is the assessment of the Geant4 capabilities in accurately modeling of dose distribution in a heterogeneous water phantom. In this purpose, a Geant4 user code has been designed and developed to enable an accurate modeling of cross beam profiles in a heterogeneous water phantom deposited by a 12 MV photon beam emitted by a Saturne 43 Linac head and configuring a 10 × 10 cm² radiation field. The calculated cross beam profiles at two distinct depths (22 cm and 25 cm), were compared to the ones obtained with MCNPX code. Our findings show that the shapes of dosimetric curves at two distinct depths calculated with Geant4 code and the ones obtained by MCNPX code are in a very good agreement. However, the Geant4 code seems painfully slow when calculating those dosimetric curves and its associated statistical uncertainties don't seem to reach 1% after two weeks of calculations. To deal with this issue, we suggest that a new variance reduction technique specially addressed for dose calculation in a heterogeneous medium must be developed by the Geant4 collaboration, in order to decrease the required computing time and to improve the statistical of calculations.

Organometallic halide perovskite materials are attracting considerable interest for high performance photovoltaic and photodetector applications due to their exceptional opto-electronic properties and easy processing capability. The high atomic numbers (Z) of their constituents also make these materials suitable for X-ray detection. Here we report on the direct detection of X-ray induced photocurrents in flexible organolead halide perovskite based detectors. The electrical response of the detectors was found to be linear with the radiation dosage. These perovskite based radiation detectors were about 550% more sensitive than commonly used amorphous silicon solar devices. The high sensitivity to the X-rays could be attributed to the high Z constituents and large charge carrier mobility. Our results indicate that the perovskite materials are promising candidates for direct X-ray detectors.

Objective

The purpose of this study is to assess the validity of Bioelectrical Impedance Analysis (BIA) to characterize the regional fat distribution among female and its correlation with anthropometric indices.

Materials and methods

The following indices were carried out: weight, height, body mass index (BMI), waist circumference (WC), hip circumference (HC), waist hip index (WC + HC) of random samples (209) of women (age, 32–85 years). The segmental body fat percentages were assessed by bioelectrical impedance analysis. Hand-to-Hand and Foot-to-Foot Body Analyzer devices were used to estimate upper and lower body fat percent (BF %), respectively. Upper and lower body fat measurements were used to calculate total body fat. Agreement between the variables was assessed by scatter plots.

Results

The plots of upper and lower percent body fat (BF %) against waist and hip circumferences revealed significant correlation values of (r = 0.949) and (r = 0.942), respectively. The total of upper and lower body fat ratios showed a stronger correlation with the BMI than those of severally. Weak to fear correlations between upper and lower body fat percent, with BMI were observed.

Conclusion

The results indicated that the BIA technique of estimating segmental body fat percent associated with the anthropometrical indices (WC, HC) has the potential to determine adiposity risk available for use in large epidemiological studies.

Generalized epilepsy is accompanied by large-amplitude synchronized spike-wave discharges on electroencephalography. The condition rapidly and synchronously involves most regions of the brain, but the mechanism underlying this global involvement remains unclear. Here I attempt to clarify this phenomenon by hypothesizing a series resonance in an equivalent electric circuit for the white matter. This hypothesis is based on the ideas that the electric conduction along an axon is due to the displacement current, and the unit structure composed of a node of Ranvier and the next node can be regarded as a capacitor or an inductor, depending on the geometry and the substance around the nodes. The flash-visual evoked potentials at various flash repetition rates were measured in generalized epilepsy patients, and compared with those for healthy controls and focal epilepsy patients. The P₁₀₀ amplitude plotted against the flash repetition rate had a maximum peak at a certain flash repetition rate only for each of the generalized epilepsy patients. The observation of a peak in the P₁₀₀ amplitude was inferred to reflect the series resonance phenomenon in the white matter. I speculate that patients with generalized epilepsy have large regions of white matter with similar resonance frequencies.

The pathogenesis of the Ebola virus which leads to a severe hemorrhagic fever in hosts is a very complex process which is not completely understood. Glycoproteins of the viral envelope are believed to play a crucial role in receptor binding and subsequently in fusion of the virus with the target cells of the host. As a result, the virus enters the cells and replicates. This process causes further cytopathic, and pathological reactions in the host's body. To gain further insights into the fusogenic interactions of the virus with cell membranes, we used well-controlled simple biomimetic systems, consisting of solid-supported phospholipid layers together with a small sequence of the viral glycoprotein (EBO17), which is believed to be the most important part responsible for viral pathogenesis. We monitor the real-time interaction of a EBO17 peptide sequence from the Ebola virus with dipalmitoylphosphatidylcholine (DMPC) phospholipid membranes using quartz crystal microbalance with dissipation monitoring (QCM-D) as a label-free method. In particular, we focus on the influence of the concentration of the peptide and the lipid layer geometry on the disrupting mechanism of the EBO17 peptide. Results indicate that for 2D supported lipid bilayers, low peptide concentrations induce a small, but detectable change in layer stability due to the presence of an α-helix configuration of the peptide. With large peptide concentrations, the peptide acquires a β-sheet configuration and no significant layer changes can be observed. A different mechanism is responsible for the interaction of the EBO17 peptides with the more complex 3D supported vesicle layers, for which a concentration-dependent trend can be observed leading to thicker lipid layers. Complementary analysis of the lipids' main phase transition evidences the differences induced in layer organization on the two layer geometries. These results confirm the importance of the interplay between lipid layer geometry and related peptide organization as an essential marker in peptide activity.

Therapeutic ultrasound is a widely used application in clinics. The response to ultrasound is tissue specific and the parameters of ultrasonic treatments are decisive. Here, the responses of primary enteric (ENS) and central nervous system (CNS) neural stem cells were investigated to different frequency – energy density – combination treatments between 510 kHz–3 W s/cm² and 4.36 MHz–25 W s/cm². Responses to ultrasonic treatments were both frequency and energy density dependent. Ultrasound enhanced the expansion and showed enlarged neurospheres for both ENS and CNS neural stem cell cultures. Differentiation was not impaired in regard to neuronal and glial cell number as well as neurite and glial fiber outgrowth. Ultrasound is a promising tool to expand neural stem cells in vitro neither influencing neurogenesis nor gliogenesis by applying specific frequency – energy density – combinations.

Acute Ischemic Stroke (AIS) is the major type of stroke occurring in patients. Aspiration thrombectomy, which uses suction to remove the thrombosis, is a promising technique in the clinical treatment of AIS patients. In this research a computational fluid dynamics (CFD) analysis was conducted to model the blood flow dynamics in a simplified cerebral model during an aspiration thrombectomy procedure. The flow system being analysed was a typical in vitro cerebral flow model, and the system parameters were set based on the clinical and in vitro data reported in open literature. The simulated flow field features showed good correlation with the in vitro response as reported in literature. The CFD study provides detailed technical data including the peak velocity occurring at the catheter tip and the suction force-suction distance relation during the aspiration thrombectomy procedure, which are useful new knowledge and have the potential to influence future catheter design as well as clinical operational protocols used during thrombectomy intervention.

A highly experienced versatile female professional singer displaying no apparent vocal complaint, developed inhaling singing, an innovative approach to reverse phonation. Although there are some reports in literature that describe the characteristics of ingressive phonation and sounds, to the best of our knowledge, no reports on actual inhaling singing are available in literature. This paper reports a case study on the acoustical analysis of inhaling singing, comparing this innovative technique with traditional exhaling singing. As this is rather undiscovered territory, we have decided to address several questions: is it possible to match the same pitches using inhaling singing compared to exhaling singing? Is the harmonic structure and energy distribution similar? Is it possible to maintain the same phonation duration in both techniques? Are there differences in volume and tessitura (vocal range)? This paper, reporting on the experience of one individual, demonstrates that a tessitura can be mastered in inhaling singing. Spectral analysis reveals a similar frequency distribution in both conditions. However, in inhaling singing the energy of the harmonics is significantly lower for the first 3 overtones, while the maximum phonation time is larger, than in exhaling singing. The singer reports that less effort is required for inhaling singing in the high register. As such, inhaling singing offers new possibilities for vocal performance.

The mechanism of mammalian hearing has intrigued scientists for decades. It is widely assumed that the process of hearing begins when sound reaches the inner ear and causes the basilar membrane (BM) to vibrate. These vibrations are then detected and consequently amplified by the outer hair cells (OHCs). We question this sequence of events and the inauguration of sound-induced motility, i.e. transformation of sound pressure wave into directional vibrations. Based on the morphology of the mammalian cochlea, we suggest that motility of the OHCs could be due to the synchronized action of hundreds of thousands of nanometric acoustic sensors-actuators in the OHC’s lateral wall. We propose that stochastic resonance in these nanometric units can account for all of the major features of mammalian hearing: a wide dynamic range; sharp frequency selectivity; generation of spontaneous otoacoustic emissions; and the ability to process relatively high frequencies. The proposed model might inspire the design of hypersensitive sensors and actuators, which potentially could be incorporated into new types of hearing aids.