改进的同步迭代算法在光声血管成像中的应用

光声成像结合了光学成像和声学成像的优点，是一种高分辨率，高对比度的无损伤医学成像技术.一种改进的同步迭代算法应用于光声图像重建.仿真和模拟结果表明，与传统的代数迭代算法相比，在90°，135°，180°的有限场光声成像中，此算法对测量误差的校正和迭代次数的收敛上具有较大的优势，图像重建的速度和成像质量都有了明显的提高.实验中，一种圆形扫描结构的光声成像装置，用于180°的有限场扫描，利用改进的同步迭代算法，重建出了高对比度和高分辨率（60μm）的鸡胚胎光声血管图像.实验证明，这种算法的应用，大幅度减少了数据采集时间，为光声成像技术运用于实时监测血流灌注和肿瘤光动力治疗的血管损伤效应提供了潜在的应用价值. 关键词： 光声成像 有限角度 代数迭代算法 光声血管成像     

耗散环境下原子-库场相互作用系统中原子的偶极压缩特性

运用全量子理论并结合数值计算方法,研究了处于真空库和热库中原子系统的偶极压缩特性,讨论了原子的初态以及热库的平均光子数对原子偶极压缩特性的影响.研究表明:真空库中,初始处于基态和激发态的叠加态原子,当激发态的粒子布居概率少于基态时,原子的偶极压缩无限接近于零而永远不消失;反之,原子的偶极压缩将在有限的时间内消失;热库中,不管原子初始处于什么态,其偶极压缩都在有限的时间内消失,并且随着热库的平均光子数的增大而消失得越快。     

Photoacoustic Imaging of Animals with an Annular Transducer Array

A photoacoustic system with an annular transducer array is presented for rapid, high-resolution photoacoustic tomography of animals. An eight-channel data acquisition system is applied to capture the photoacoustic signals by using multiplexing and the total time of data acquisition and transferring is within 3 s. A limited-view filtered back projection algorithm is used to reconstruct the photoacoustic images. Experiments are performed on a mouse head and a rabbit head and clear photoacoustic images are obtained. The experimental results demonstrate that this imaging system holds the potential for imaging the human brain.     

基于探测超声的新型生物组织光声层析成像

利用一束单频探测超声穿过由脉冲激光照射产生的光声激发区域，使之与光致声场产生相互作用，光声信号将耦合到探测束上，再解调探测超声来重建光吸收区域的图像，可以得到丰富的组织信息.该信息不仅反映了组织中光吸收的特性，也反映了组织的声学特性.实验中，通过旋转超声探测器进行数据采集，并利用滤波反投影算法重建图像，可得到高信噪比的光声层析图像.由于激光的窄光谱线宽，其吸收是特征分子选择性的，所以此方法既是一种无损伤的结构层析成像方法，也可用于组织的功能成像.     

In Vivo Monitoring of Neovascularization in Tumour Angiogenesis by Photoacoustic Tomography

Photoacoustic tomography （PAT） is presented to in vivo monitor neovascularization in tumour angiogenesis with high resolution and high contrast images in a rat. With a circular scan system, the photoacoustic signal, generated by laser pulses at a wavelength of 532nm from a Q-switched Nd：YAG laser is captured by a hydrophone with a diameter of 1 mm and a sensitivity of 850nV/Pa. The vascular structure around the rat tumour is imaged clearly, with optimal contrast, because blood has strong absorption near this wavelength. Serial noninvasive photoacoustic images of neovascularization in tumour angiogenesis are also obtained consecutively from a growing tumour implanted under the skin of a rat over a period of two weeks. This work demonstrates that PAT can potentially provide a powerful tool for tumour angiogenesis detection in cancer research. It will bring us closer to clinical applications for tumour diagnosis and treatment monitoring.     

Fast Microwave-Induced Thermoacoustic Tomography Based on Multi-Element Phase-Controlled Focus Technique

We develop a fast microwave-induced thermoacoustic tomography system based on a 320-element phase-controlled focus linear transducer array. A 1.2-GHz microwave generator transmits microwave with a pulse width of 0.5 μs and an incident energy density of 0. 45 mJ/cm^2, and the microwave energy is delivered by a rectangular waveguide with a cross section of （80.01 ± 0.02） × 10^-4 m^2. Compared to single transducer collection, the system with the multi-element linear transducer array can eliminate the mechanical rotation of the transducer, hence can effectively reduce the image blurring and improve the image resolution. Using a phase-controlled focus technique to collect thermoacoustic signals, the data need not be averaged because of a high signal-to-noise ratio, resulting in a total data acquisition time of less than 5 s. The system thus provides a rapid and reliable approach to thermoacoustic imaging, which can potentially be developed as a powerful diagnostic tool for early-stage breast caners.     

A Combined Reconstruction Algorithm for Limited-View Multi-Element Photoacoustic Imaging

We present a photoacoustic imaging system with a linear transducer array scanning in limited-view felds and develop a combined reconstruction algorithm, which is a combination of the limited-field filtered back projection （LFBP） algorithm and the simultaneous iterative reconstruction technique （SIRT） algorithm, to reconstruct the optical absorption distribution. In this algorithm, the LFBP algorithm is exploited to reconstruct the original photoacoustic image, and then the SIRT algorithm is used to improve the quality of the final reconstructed photoacoustic image. Numerical simulations with calculated incomplete data validate the reliability of this algorithm and the reconstructed experimental results further demonstrate that the combined reconstruction algorithm effectively reduces the artifacts and blurs and yields better quality of reconstruction image than that with the LFBP algorithm.     

基于代数重建算法的有限角度扫描的光声成像

由于滤波反投影重建算法要求对成像区域进行全方位扫描以获取完全投影数据,它需要较长时间采集大量数据,使其在医学上的应用受到限制。研究了在有限角度下采用代数重建算法进行光声成像的方法,实验用的光源为YAG激光器,波长为1064nm,重复频率20Hz,脉宽为6ns,探测器为针状的磺化聚二氟乙烯(PVDF)膜水听器,接收面积的直径为1mm,从仿真和实验结果表明该方法适用于“非完备投影数据”的光声层析成像。从图像重建效果上与滤波反投影算法相比较,该成像算法提高了重建图像的分辨率和对比度。采用代数重建算法的有限角度的光声成像方法,对临床医学的无损伤检测,具有重要的意义。     

Plasmon resonance coupling in strongly coupled gold nanotube arrays with structural defects

We theoretically investigate the transmission spectra and the field distributions with different defects in the gold nanotube arrays by using the finite-difference time-domain method.It is found that the optical properties of the nanotube arrays are strongly influenced by different defects.When there are no defects in the central nanotube,the values of peaks located at both sides of the photonic band gap have their maxima.Based on the distributions of electric field component E x and the total energy distribution of the electric and the magnetic field,we show that mainly a dipole field distribution is exhibited for the plasmon mode at the long-wavelength edge of the band gap but higher order modes of the composite are excited at the short-wavelength edge of the band gap.The plasmon resonant modes can also be controlled by introducing defects.     

Unconventional geometric logic gate in a strong-driving-assisted multi-mode cavity

<正>We propose a scheme to implement an unconventional geometric logic gate separately in a two-mode cavity and a multi-mode cavity assisted by a strong classical driving field.The effect of the cavity decay is included in the investigation.The numerical calculation is carried out,and the result shows that our scheme is more tolerant to cavity decay than the previous one because the time consumed for finishing the logic gate is doubly reduced.