Printable Perovskite Diodes for Broad-Spectrum Multienergy X-Ray Detection.

Multienergy X-ray detection is critical to effectively differentiate materials in a variety of diagnostic radiology and nondestructive testing applications. Silicon and selenium X-ray detectors are the most common for multienergy detection; however, these present poor energy discrimination across the broad X-ray spectrum and exhibit limited spatial resolution due to the high thicknesses required for radiation attenuation. Here, an X-ray detector based on solution-processed thin-film metal halide perovskite that overcomes these challenges is introduced. By harnessing an optimized n-i-p diode configuration, operation is achieved across a broad range of soft and hard X-ray energies stemming from 0.1 to 10's of keV. Through detailed experimental and simulation work, it is shown that optimized Cs0.1 FA0.9 PbI3 perovskites effectively attenuate soft and hard X-rays, while also possessing excellent electrical properties to result in X-ray detectors with high sensitivity factors that exceed 5 × 103 µ C G y Vac - 1 cm - 2 $\mu {\rm{C}}\;{{\bf Gy}}_{{\rm{Vac}}}^{ - 1}\;{\rm{c}}{{\rm{m}}^{ - 2}}$ and 6 × 104 µC Gy-1 cm-2 within soft and hard X-ray regimes, respectively. Harnessing the solution-processable nature of the perovskites, roll-to-roll printable X-ray detectors on flexible substrates are also demonstrated.

Alcohol use among young men who have sex with men.

This study reveals associations between alcohol use and demographic variables, as well as the relation between alcohol use and sexual activity, using episodic data. Data were obtained during summer and fall 2008 from a sample of 558 gay, bisexual, and other young men who have sex with men (YMSM), ages of 13-29 years in New York City. Recruitment strategies targeted potential participants at gay-related venues and public spaces often frequented by YMSM. Alcohol use varied by race/ethnicity, with White YMSM consuming significantly more alcohol than other races/ethnicities. Participants over the age of 21 drank significantly more alcohol than participants ages 13-20. Alcohol use was not found to be associated with sexual risk-taking activity. Our findings are enriched by a large, diverse sample of urban YMSM. Study limitations are noted.

Spectral propagation-based x-ray phase-contrast computed tomography.

Purpose: Propagation-based x-ray imaging (PBI) is a phase-contrast technique that is employed in high-resolution imaging by introducing some distance between sample and detector. PBI causes characteristic intensity fringes that have to be processed with appropriate phase-retrieval algorithms, which has historically been a difficult task for objects composed of several different materials. Spectral x-ray imaging has been introduced to PBI to overcome this issue and to potentially utilize the spectral nature of the data for material-specific imaging. We aim to explore the potential of spectral PBI in three-dimensional computed tomography (CT) imaging in this work. Approach: We demonstrate phase-retrieval for experimental high-resolution spectral propagation-based CT data of a simple two-component sample, as well as a multimaterial capacitor test sample. Phase-retrieval was performed using an algorithm based on the Alvarez-Macovski model. Virtual monochromatic (VMI) and effective atomic number images were calculated after phase-retrieval. Results: Phase-retrieval results from the spectral data set show a distinct gray-level for each material with no residual phase-contrast fringes. Several representations of the phase-retrieved data are provided. The VMI is used to display an attenuation-equivalent image at a chosen display energy of 80 keV, to provide good separation of materials with minimal noise. The effective atomic number image shows the material composition of the sample. Conclusions: Spectral photon-counting detector technology has already been shown to be compatible with spectral PBI, and there is a foreseeable need for robust phase-retrieval in high-resolution, spectral x-ray CT in the future. Our results demonstrate the feasibility of phase-retrieval for spectral PBI CT.

Precise phase retrieval for propagation-based images using discrete mathematics.

The ill-posed problem of phase retrieval in optics, using one or more intensity measurements, has a multitude of applications using electromagnetic or matter waves. Many phase retrieval algorithms are computed on pixel arrays using discrete Fourier transforms due to their high computational efficiency. However, the mathematics underpinning these algorithms is typically formulated using continuous mathematics, which can result in a loss of spatial resolution in the reconstructed images. Herein we investigate how phase retrieval algorithms for propagation-based phase-contrast X-ray imaging can be rederived using discrete mathematics and result in more precise retrieval for single- and multi-material objects and for spectral image decomposition. We validate this theory through experimental measurements of spatial resolution using computed tomography (CT) reconstructions of plastic phantoms and biological tissues, using detectors with a range of imaging system point spread functions (PSFs). We demonstrate that if the PSF substantially suppresses high spatial frequencies, the potential improvement from utilising the discrete derivation is limited. However, with detectors characterised by a single pixel PSF (e.g. direct, photon-counting X-ray detectors), a significant improvement in spatial resolution can be obtained, demonstrated here at up to 17%.

Full Field X-Ray Scatter Tomography.

In X-ray imaging, photons are transmitted through and absorbed by the target object, but are also scattered in significant quantities. Previous attempts to use scattered X-ray photons for imaging applications used pencil or fan beam illumination. Here we present 3D X-ray Scatter Tomography using full-field illumination for small-animal imaging. Synchrotron imaging experiments were performed on a phantom and the chest of a juvenile rat. Transmitted and scattered photons were simultaneously imaged with separate cameras; a scientific camera directly downstream of the sample stage, and a pixelated detector with a pinhole imaging system placed at 45° to the beam axis. We obtained scatter tomogram feature fidelity sufficient for segmentation of the lungs and major airways in the rat. The image contrast in the scatter tomogram slices approached that of transmission imaging, indicating robustness to the amount of multiple scattering present in our case. This opens the possibility of augmenting full-field 2D imaging systems with additional scatter detectors to obtain complementary modes or to improve the fidelity of existing images without additional dose, potentially leading to single-shot or reduced-angle tomography or overall dose reduction for live animal studies.

Quantifying lung aeration in neonatal lambs at birth using lung ultrasound.

Background: Lung ultrasound (LUS) is a safe and non-invasive tool that can potentially assess regional lung aeration in newborn infants and reduce the need for X-ray imaging. LUS produces images with characteristic artifacts caused by the presence of air in the lung, but it is unknown if LUS can accurately detect changes in lung air volumes after birth. This study compared LUS images with lung volume measurements from high-resolution computed tomography (CT) scans to determine if LUS can accurately provide relative measures of lung aeration. Methods: Deceased near-term newborn lambs (139 days gestation, term ∼148 days) were intubated and the chest imaged using LUS (bilaterally) and phase contrast x-ray CT scans at increasing static airway pressures (0-50 cmH2O). CT scans were analyzed to calculate regional air volumes and correlated with measures from LUS images. These measures included (i) LUS grade; (ii) brightness (mean and coefficient of variation); and (iii) area under the Fourier power spectra within defined frequency ranges. Results: All LUS image analysis techniques correlated strongly with air volumes measured by CT (p < 0.01). When imaging statistics were combined in a multivariate linear regression model, LUS predicted the proportion of air in the underlying lung with moderate accuracy (95% prediction interval ± 22.15%, r 2 = 0.71). Conclusion: LUS can provide relative measures of lung aeration after birth in neonatal lambs. Future studies are needed to determine if LUS can also provide a simple means to assess air volumes and individualize aeration strategies for critically ill newborns in real time.

Substance use in the MSM population of New York City during the era of HIV/AIDS.

This literature review considers the historical significance, emergence of, and interplay between the HIV and illicit drug use epidemics among gay, bisexual, and other men who have sex with men (MSM) in New York City (NYC). The continual rise in HIV infections in recent years among MSM, particularly among young MSM (YMSM), commands a need for the examination of the effectiveness of current HIV prevention strategies and a more comprehensive understanding of the complex biopsychosocial influences that place YMSM at risk. A chronological perspective of both the HIV and illicit drug use epidemics affecting NYC MSM is presented, followed by a review of the existing research on the synergistic relation between the two. Special consideration is given to the patterns and interconnectivity between HIV, substance use, and housing instability specific to YMSM, as they represent the demographic currently at greatest risk for HIV transmission in NYC. Thereafter, an overview of treatment research is provided. We conclude by offering recommendations for future research and best practices as we move forward in an attempt to reduce the incidence of HIV transmission.

Material Decomposition Using Spectral Propagation-Based Phase-Contrast X-Ray Imaging.

Material decomposition in X-ray imaging uses the energy-dependence of attenuation to digitally decompose an object into specific constituent materials, generally at the cost of enhanced image noise. Propagation-based X-ray phase-contrast imaging is a developing technique that can be used to reduce image noise, in particular from weakly attenuating objects. In this paper, we combine spectral phase-contrast imaging with material decomposition to both better visualize weakly attenuating features and separate them from overlying objects in radiography. We derive an algorithm that performs both tasks simultaneously and verify it against numerical simulations and experimental measurements of ideal two-component samples composed of pure aluminum and poly(methyl methacrylate). Additionally, we showcase first imaging results of a rabbit kitten's lung. The attenuation signal of a thorax, in particular, is dominated by the strongly attenuating bones of the ribcage. Combined with the weak soft tissue signal, this makes it difficult to visualize the fine anatomical structures across the whole lung. In all cases, clean material decomposition was achieved, without residual phase-contrast effects, from which we generate an un-obstructed image of the lung, free of bones. Spectral propagation-based phase-contrast imaging has the potential to be a valuable tool, not only in future lung research, but also in other systems for which phase-contrast imaging in combination with material decomposition proves to be advantageous.

Sexual practices of gay, bisexual, and other nonidentified MSM attending New York City gyms: patterns of serosorting, strategic positioning, and context selection.

This descriptive paper characterizes the sexual behaviors of a diverse sample (N=311) of gay, bisexual, and other nonidentified men who have sex with men (MSM) who regularly attended gyms in New York City. Approximately 50% of the sample indicated sex with primary male partners, while 88% of the men had sexual relations with male casual partners in the 6 months prior to assessment. The participants met their casual partners in a variety of different venues, including the Internet. Differences were noted along key demographic factors with regard to the contexts in which men met their partners. The data indicate that the men use serosorting, strategic positioning, and contexts in which they meet other men, to influence choices concerning sexual partners and practices as a form of health protection. It is proposed that these patterns of sexual behavior are representative of the totality of the lives of gay, bisexual, and other MSM, because despite engaging in gym behaviors, which might be considered health promoting, these men are simultaneously taking risks. Such findings point to varying motivations as to why gay, bisexual, and other MSM actually attend the gym.

When the emotions really started kicking in, which ended up being a problem: sex, HIV, and emotions among young gay and bisexual men.

Interviews from 10 young gay and bisexual men aged 18 to 29 were examined to explore how young gay and bisexual men make decisions regarding sexual behaviors in the age of AIDS. Three main themes emerged: (a) disconnections between what an individual knows about HIV, their motivations to remain HIV-negative, and their sexual behaviors; (b) a struggle to connect emotionally and intimately with another man; and (c) a power dynamic whereby the individual acts as an autonomous decider in the decision-making process. Participants indicated high levels of HIV knowledge, and were engaged in a struggle to balance emotional experiences with sexual partners in a complex gendered dynamic. Findings from this analysis indicate a need to reexamine the social-cognitive theoretical frameworks that have guided gay men's HIV-prevention efforts, as these frameworks have failed to account for the psychologically complex emotional experiences and gender dynamics that are part of sexual decision making.

Environmental factors in relation to unprotected sexual behavior among gay, bisexual, and other MSM.

This descriptive article illustrates the casual sexual behaviors of a diverse sample (N = 311) of gay, bisexual, and other men who have sex with men (MSM) regularly attending gyms in New York City. Approximately 88% of the sample noted sex with a casual partner in the previous 6 months. Participants reported the frequency of unprotected sexual acts, the perceived HIV status of their partners, and the contexts where they met their casual sex partners. The study findings suggest that the context in which MSM choose to meet casual sex partners has an effect on both the number of casual sex partners they meet and the number of casual sex partners with whom they engage in unprotected receptive anal intercourse and unprotected insertive anal intercourse. We found that the highest risk sexual behaviors took place at bareback sex parties, which are often held at private venues. Men who meet their sexual partners at bareback sex parties are also likely to frequent bathhouses/sex clubs and nonbareback sex parties, suggesting a varied exploration of sexual contexts, partners, and behaviors. We attempt to enhance individual-level models of understanding sexual behavior and risk by proposing that the individual is influenced by the physical context where he makes his decisions.