Framework for evaluating photon-counting detectors under pile-up conditions.

Purpose: While X-ray photon-counting detectors (PCDs) promise to revolutionize medical imaging, theoretical frameworks to evaluate them are commonly limited to incident fluence rates sufficiently low that the detector response can be considered linear. However, typical clinical operating conditions lead to a significant level of pile-up, invalidating this assumption of a linear response. Here, we present a framework that aims to evaluate PCDs, taking into account their non-linear behavior. Approach: We employ small-signal analysis to study the behavior of PCDs under pile-up conditions. The response is approximated as linear around a given operating point, determined by the incident spectrum and fluence rate. The detector response is subsequently described by the proposed perturbation point spread function (pPSF). We demonstrate this approach using Monte-Carlo simulations of idealized direct- and indirect-conversion PCDs. Results: The pPSFs of two PCDs are calculated. It is then shown how the pPSF allows to determine the sensitivity of the detector signal to an arbitrary lesion. This example illustrates the detrimental influence of pile-up, which may cause non-intuitive effects such as contrast/contrast-to-noise ratio inversion or cancellation between/within energy bins. Conclusions: The proposed framework permits quantifying the spectral and spatial performance of PCDs under clinically realistic conditions at a given operating point. The presented example illustrates why PCDs should not be analyzed assuming that they are linear systems. The framework can, for example, be used to guide the development of PCDs and PCD-based systems. Furthermore, it can be applied to adapt commonly used measures, such as the modulation transfer function, to non-linear PCDs.

Triptycene-Bis(aroyleneimidazole)s as Non-Fullerene Acceptors: The Missing Links.

The syntheses of four triptycene-bis(aroyleneimidazole)s-the missing links with respect to the previously reported triptycene-mono(aroyleneimidazole)s and triptycene-tris(aroyleneimidazole)s-are presented. Their optoelectronic properties and use as non-fullerene acceptors in organic photovoltaics with poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}[3-fluoro-2-(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl) (PTB7) as a donor are described; these systems reach a maximum power conversion efficiency of 2 %. Furthermore, the effect of molecular symmetry on the photovoltaic device performance is discussed.

Vascular lesions of the maxillofacial region: a case report and review of the literature.

There is frequently lack of understanding and apprehension among dental practitioners treating patients with vascular lesions of the oral and maxillofacial region. Arteriovenous malformations are rare lesions which can easily be misdiagnosed yet produce the very dramatic clinical presentation of severe life threatening oral bleeding. Much of this apprehension likely stems from a lack of understanding of these anomalies, including lesion behavior/ characteristics, clinical work-up, and treatment paradigms. A comprehensive, in depth review of the full spectrum of vascular lesions of the maxillofacial complex is beyond the scope of this review. The purpose of this article is to provide a comprehensive review of the diagnosis, treatment, and risks associated with these complex vascular anomalies and provide a case report. In 1982, Mulliken and Glowacki published a landmark article proposing characterization of vascular defects based on biologic and pathologic differences. Their work differentiated between two major categories of vascular lesions: hemangiomas and vascular malformations. Different categories, names, and treatment options have been advocated over the years with multiple outcomes. They can occur in various areas throughout the body, with 60 percent being located in the head and neck. The true mechanism of pathogenesis of vascular anomalies is still unclear. Embolization and surgery is often combined for extended cases to improve their facial contour and oral function. We present the case of a 29-year-old female that is 36 weeks pregnant and presented to University Hospital after having significant bleeding from her oral cavity. She was found to have a gingival lesion associated with a radiolucency in the right posterior mandible. During her stay she had an episode of acute bleeding that required an emergent exploration, embolization, and resection secondary to an Arteriovenous Malformation associated with the Inferior Alveolar Artery. We will discuss the presentation, treatment provided, and outcome of this patient. We will also cover the diverse group of congenital vascular malformations, and their pathologic, clinical, and radiologic diagnosis and management.