Biomedical microwave-induced thermoacoustic imaging

Microwave induced thermoacoustic imaging(MTAI)has emerged as a potential biomedical imaging modality with over 20-year growth.MTAI typically employs pulsed microwave as the pumping source,and detects the microwave-induced ultrasound wave via acoustic transducers.Therefore,it features high acoustic resolution,rich elect romagnetic contrast,and large imaging depth.Benefiting from these unique advantages,MTAI has been extensively applied to various fields including pathology,biology,material and medicine.Till now,MTAI has been deployed for a wide range of biomedical applications,including cancer diagnosis,joint evaluation,brain in-vestigation and endoscopy.This paper provides a comprehensive review on(1)essential physics(endogenous/exogenous contrast mechanisms,penetration depth and resolution),(2)hardware configurations and software implementations(excit ation source,antenna,ultrasound detector and image recovery algorithm),(3)animal studies and clinical applications,and(4)future directions.

Investigation of artifacts by mapping SAR in thermoacoustic imaging

Microwave-induced thermoacoustic imaging(MI-TAI)remains one of the focus of attention among biomedical imaging modalities over the last decade.However,the transmission and dis-tribution of microwave inside bio-tissues are complicated,thus result in severe artifacts.In this study,to reveal the underlying mechanisms of artifacts,we deeply investigate the distribution of specific absorption rate(SAR)inside tissue-mimicking phantoms with varied morphological features using both mathematical simulations and corresponding experiments.Our simulated results,which are confirmed by the associated experimental results,show that the SAR distri-bution highly depends on the geometries of the imaging targets and the polarizing features of the microwave.In addition,we propose the potential mechanisms including Mie-scattering,Fabry-Perot-feature,small curvature effect to interpret the diffraction effect in different scenarios,which may provide basic guidance to predict and distinguish the artifacts for TAI in both fundamental and clinical studies.

Electron-beam-driven anomalous Doppler effects in Smith–Purcell radiation

The interaction between electrons and matter is an effective means of light emission,through mechanisms including Cherenkov radiation and Smith–Purcell radiation(SPR).In this study,we show that the superlight inverse Doppler effects can be realized in reverse Smith–Purcell radiation excited by a free electron beam with a homogeneous substrate.In particular,we find that two types of anomalous SPR exist in the homogenous substrate:special SPR and reverse SPR.Our results reveal that the electron velocity can be tuned to simultaneously excite different combinations of normal SPR,special SPR,and reverse SPR.The proposed manifold light radiation mechanism can offer greater versatility in controlling and shaping SPR.

肌内法瓦病的MRI表现及病理对照分析

目的探讨肌内法瓦病(FAVA)的MRI表现及其病理特征。方法回顾性分析2012年12月至2021年3月于河南省人民医院就诊的44例经病理证实的肌肉内FAVA的临床及影像资料,女25例、男19例,年龄5~29(15±6)岁。总结其临床及MRI特征,包括分型、部位、边界、信号强度、强化方式及程度、病变内有无血管流空,并与病理结果对照。结果 1例患者大腿及小腿肌肉同时受累,43例患者病变累及1个部位,包括小腿肌肉20例、大腿肌肉15例、前臂肌肉5例、上臂肌肉1例、臀肌1例、肩部肌肉1例。小腿腓肠肌受累最多见(13/44),其次为比目鱼肌(10/44)、股四头肌(9/44)。MRI示病变均为实性病变,其中局灶肿块型24例、弥漫浸润型15例、局部浸润型5例。病变的长轴均与肌肉长轴一致。T1WI及T2WI均呈不均匀中等高信号,脂肪抑制T2WI呈显著高信号,所有病变均可见迂曲扩张的畸形血管,其中18例可见流空血管影。增强后呈中等至明显不均匀强化。病理学上,病变的骨骼肌被纤维组织、脂肪成分、不规则的畸形静脉血管等多种成分浸润,导致MRI信号的不均匀。7例接受人类PIK3CA基因突变检测者中6例为突变型。结论肌内FAVA在临床、MRI影像以及组织病理学上均具有一定的特征性,其MRI信号特征可反映其复杂的病理成分。

THz trapped ion model and THz spectroscopy detection of potassium channels

Advanced molecular dynamics(MD)simulation and infrared(IR)spectroscopy have been widely adopted to reveal the detailed dynamic process of high-speed selective permeability of potassium channels.Yet these MD simulations cannot avoid the choice of empirical molecular force fields and high transmembrane voltages(as driving electric fields for ions)far exceeding physiological levels.Moreover,the IR spectroscopy method usually requires isotope labels for carbonyl groups of the channels,which may change the original permeation process.Here,we build the terahertz(THz)trapped ion model for the selectivity filter(SF)of potassium channels KcsA based on the density functional theory(DFT)calculation of ion potentials.In this model,the zero-point energy of trapped ions and quantum tunneling effect provide the physical basis for near diffusion limited permeation rates of ions and explain the high driving electric field in MD simulations.Quantitative calculations of zero-point energy and tunneling probability show that the quantum effect assisted knock-on mechanism may help to realize the physiological functions of potassium channels.Furthermore,based on the trapped ion model,we calculated the ion decoherence timescale under the influence of protein environmental noise.We use the quantum optics method to describe the interaction between THz waves and the trapped ion.Then the novel THz spectroscopy approaches through the THz resonance fluorescence and the intense field non-resonant effect are presented theoretically.These are expected to be isotope label-free detective methods of the rapid ion permeation dynamics.

Tunable optical topological transition of Cherenkov radiation

Approaches to generate and manipulate Cherenkov radiation(CR)are challenging yet meaningful.Optical topological transition(OTT)in novel materials and metamaterials is also promising for modern photonics.We study the OTT of CR in graphene-based hyperbolic metamaterials(GHMs)for the first time.In GHMs,conventional and hyperbolic CR can be switched when crossing the topological transition frequency.This frequency can be altered by metamaterial components and external optical elements.For instance,external ultrafast optical pumps cause an ultrafast OTT from the elliptical to the hyperbolic state.Then,hyperbolic CR can be excited by lowenergy electrons by leveraging the excellent photothermal properties of graphene.Hyperbolic CR vanishes when the GHM returns to its original state.Furthermore,graphene nonlocality occurs when the electron velocity is low enough,corresponding to a large wave vector.Concretely,when the electron velocity approaches the Fermi velocity of graphene,a nonlocality-induced OTT modifies the plasmonic properties of the GHM and brings a new lower velocity threshold of hyperbolic CR.Therefore,hyperbolic CR can only be induced in a limited velocity range.These findings pave the way for understanding CR properties in active plasmonic metamaterials and may be applied to complex photonic and polaritonic systems.