全息声谱显示

本文提出了一种全息声谱的编码和显示方法，全息声谱图是在二维屏幕上显示四维的声谱函数语图，它同时表征了语声的幅度谱和相位谱，在显示坐标上，除了时间轴和频率轴两维外，还分别用亮度来表示幅度谱，用色彩来表示相位谱，通过编码，我们成功地实现了这一显示系统。     

微型计算机在喉疾病声谱分析中的应用

通过应用微机和北京邮电大学通用信号谱分析系统，分别对喉病患者和同年龄健康人的嗓音信号进行声谱分析，探索正常嗓音和病态嗓音的声学特征与规律，检测方法无痛苦、精度高、可视性强、客观化程度较高，为医务工作者早期诊断某些喉疾病提供参考数据     

基于小波包的血栓超声多普勒信号检测

提出了基于小波包分解的血栓超声多普勒信号检测方法。利用小波包分解血栓多普勒信号,计算每一子带信号的时间散度,并从中提取与血栓敏感的特征参数进行分类。利用本方法对300例仿真多普勒信号和163例临床采集的大脑中动脉多普勒信号进行分析,得到的检测总误判率比用传统声谱分析方法降低约13％。表明:该方法有效克服了传统声谱分析法中短时傅里叶变换存在的时频分辨率矛盾,提高了血栓多普勒信号自动检测的准确性,可为临床检测血栓提供更为可靠的参数。     

聚丁二炔Langmuir—Blodgett薄膜的光声谱研究：（Ⅰ）结构表征与光声？…

本在用Ｘ－射线小角衍射聚合与转载先后次序不同的ＰＤＡ ＬＢ膜进行结构表征的基础上,不同厚度的ＰＤＡ ＬＢ膜的光声新斩波频率效应说明,随着ＰＤＡ ＬＢ膜厚度增加,ＬＢ膜的热学性质逐渐明显。此外,还探讨了如何从ＰＤＡ ＬＢ膜的光声谱求得光声吸收系数问题,本的研究结果表明,光声谱技术是研究ＬＢ膜热学特性的有效手段。     

聚丁二炔Langmuir-Blodgett薄膜的光声谱研究(Ⅰ)结构表征与光声吸收系数

本文在用Ｘ－射线小角衍射对聚合与转载先后次序不同的ＰＤＡＬＢ膜进行结构表征的基础上,不同厚度ＰＤＡＬＢ膜的光声斩波频率效应说明,随着ＰＤＡＬＢ膜厚度增加,ＬＢ膜的热学性质逐渐明显。此外,还探讨了如何从ＰＤＡＬＢ膜的光声谱求得光声吸收系数问题,本文的研究结果表明,光声谱技术是研究ＬＢ膜热学特性的有效手段。     

聚丁二炔Langmuir—BLodgett薄膜的光声谱研究（Ⅱ）光谱综合分析和荧 …

本文用光声谱结合光吸收谱,荧光光谱等对在工业上在潜在应用前景的聚十炔（ｐｏｌｙｄｉａｃｅｔｙｌｅｎｅ,ＰＤＡ）Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ（ＬＢ）薄膜进行了研究。     

NH3在Cu及其氧化表面物理吸附的光声振动谱研究

本工作采用激光光声谱对85K多晶Cu表面上NH₃分子的物理吸附进行了研究。通过监测NH₃分子伞形振动模(ν₂),发现在清洁和预吸附O的Cu表面上,相同物理吸附态NH₃分子振动谱的峰位频率和峰的半高宽度(FWHM)随覆盖度表现出不同的变化规律,对应着不同的物理吸附机理。实验结果同时表明高分辨率的光声谱在研究弱吸附体系细致结构和细微作用方面的潜力。 关键词：     

聚丁二炔Langmuir-Blodgett薄膜的光声谱研究(Ⅱ) 光谱综合分析和荧光量子效率

本文用光声谱（ｐｈｏｔｏａｃｏｕｓｔｉｃｓｐｅｃｔｒｏｓｃｏｐｙ,ＰＡＳ）结合光吸收谱、荧光光谱等对在工业上有潜在应用前景的聚丁二炔（ｐｏｌｙｄｉａｃｅｔｙｌｅｎｅ,ＰＤＡ）Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔ（ＬＢ）薄膜进行了研究。对经不同气体环境处理的ＰＤＡＬＢ膜的紫外－可见光声谱、光吸收谱和荧光光谱的综合分析表明,ＰＤＡＬＢ膜的激发态弛豫过程中激子和极化子形成的元激发性质。此外,还讨论了ＰＤＡＬＢ膜的荧光量子效率。本文的研究结果表明,用光声谱研究ＬＢ膜,可以获取仅用其他光谱得不到的信息。     

气体栓子超声多普勒信号的仿真研究

通过分析研究气体栓子的超声多普勒信号的特征及其成因,建立气体栓子的超声多普勒仿真模型,为后续的气体栓子与固体栓子的分类提供理论基础。先利用超声辐射力和液体黏滞阻力的模型计算气体栓子所受的超声辐射力和黏滞阻力,然后计算气体栓子在血管内的径向加速度和轴向加速度,并从加速度得到气体栓子在血管内的运动轨迹,最后建立气体栓子的计算机仿真模型。实验中仿真合成气体栓子和固体栓子的超声多普勒信号,对信号的分析结果表明,相比于固体栓子,仿真的气体栓子信号受到作用力而产生的加速度将导致气栓信号在多普勒声谱图上频域的展宽,当气体栓子由低速区域加速到高速区域再由高速区减速至低速区将会在声谱图上体现为"V"型,若只有单一的加速或减速运动将只表现为斜线型。将仿真的气栓信号与临床采集的气栓信号进行比较,发现两者的特征是吻合的,说明气栓超声多普勒信号的仿真方法是合理的。      

时域光声谱技术及其在生物组织检测中的应用

当强度调制的光束照射于吸收物质,周期性热流使周围的介质热胀冷缩而激发声波,这种将光能转化为声能的现象称为光声效应。基于光声效应的时域光声谱技术将光学和声学有机地结合,为生物组织的无损检测技术提供了新的检测手段。该技术能够实现类似光学技术的高对比度和近似于声学技术的高精度和穿透深度,在生物医学检测中具有广阔的应用前景。文章介绍时域光声谱技术的原理及其在生物组织成分检测和层析成像检测中的应用。     

改进的经验模态分解法分离超声多普勒血流与管壁信号

超声多普勒血流信号常包含管壁信号的干扰,准确分离二者对提高血流检测的精度具有重要作用。本文提出两种改进的经验模态分解(EMD)方法,先将含管壁信号的超声多普勒信号分解成多层本征模态函数(IMF),然后根据血流信号与管壁信号的不同特性,对既含管壁信号又含血流信号的IMF分量进行分离处理,最后将各层IMF分量中的管壁成分叠加得到管壁信号的估计,而血流信号可通过原信号减去估计的管壁信号而得到。将本方法用于计算机仿真信号和人体实测的超声多普勒信号,并与高通滤波器法、空间选择性降噪法和原EMD法进行比较,结果表明:本文提出的两种方法能在较大的管壁搏动速度范围内准确地分离血流信号和管壁信号,其平均相对误差比高通滤波器的结果降低了约52%和57%。可见,本文提出的两种方法有望用于血流信号与管壁信号的准确分离。      

Doppler angle and flow velocity mapping by combined Doppler shift and Doppler bandwidth measurements in optical Doppler tomography

Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information.     

Higher-order cross-correlation-based Doppler optical coherence tomography

A method based on higher-order cross-correlation is proposed to fetch the Doppler information on flow velocity within areas under low signal-to-noise ratio (SNR) by spectral domain optical coherence tomography. The proposed method is theoretically developed and validated by measurement of a moving mirror with known velocities. Standard deviations of flow velocities of the mirror under different SNRs are determined by the proposed method and compared with those by the modified phase-resolved method. Measurement of flowing particles within a glass capillary is also conducted, and Doppler flow velocity maps of the glass capillary are reconstructed by both methods. All experimental results demonstrate that the proposed method can significantly suppress noise, thus rendering it suitable for flow measurement under low SNR cases.     

Simultaneous measurement of flow velocity and Doppler angle by the use of Doppler optical coherence tomography

Monitoring blood flow velocity could have great value for biomedical research and clinical diagnostics. One of current restrictions to determine flow velocity by the use of Doppler optical coherence tomography (Doppler OCT) is that the Doppler angle should be predefined. However, from a practical point of view, it is not easy to predetermine Doppler angle for a flow beneath the tissue surface. In this work, a novel method for measuring both flow velocity and Doppler angle simultaneously by the use of Doppler OCT is proposed and demonstrated. Based on Doppler spectrum analysis, this technique measures both longitudinal and transverse components of flow velocity by detecting its Doppler shift and Doppler bandwidth to determine velocity and Doppler angle simultaneously. Such a technique extends flow velocity measurement into a broadening practical use of Doppler OCT where Doppler angle would not need to be predefined, for example, blood flow beneath the tissue surface. Therefore, with this technique, Doppler OCT could be applied to more practical diagnoses of microcirculation.     

Real-time measurement of in vitro flow by Fourier-domain color Doppler optical coherence tomography

The possibility of measuring a full Doppler flow depth profile in parallel by use of frequency-domain optical coherence tomography is demonstrated. The method is based on a local phase analysis of the backscattered signal and allows for imaging of bidirectional Doppler flow. The Doppler frequency limit is 5 kHz for the presented measurements and is set by half of the frame rate of the CCD detector array. We measured the flow of 0.3-microm microspheres suspended in distilled water at controlled flow rates and in vitro human blood flow through a 200-microm capillary with a real-time color-encoded Doppler tomogram rate of 2-3/s.     

超声波流速测量的多普勒频移提取方法研究

为了提高超声波多普勒法测量复杂流体流量的精度,针对流体的超声回波频率的复杂性,本文研究多普勒流速测量中的频偏提取方法。以傅里叶分析为理论基础,设计了硬件电路并获得代表回波平均频率的信号,然后以该信号作为输入,以数字鉴频法获得回波多普勒频移。基于该方法设计了一种超声多普勒流量测量系统,实验结果显示:油水混合流体流量的测量误差在3%以内,从而证实了此频偏提取方法的有效性。     

A wavelet space based approach for Doppler ultrasound blood signals separation

In medical Doppler ultrasound systems, a high-pass filter which is usually employed to filter wall clutter components, will remove the information of the low velocity blood flow. To extract intact Doppler ultrasound blood signals, a novel approach is proposed based on the spatially selective noise filtration. The wall signals are firstly estimated by the spatially selective noise filtration from wavelet spatial correlation property. Then the wall clutters are exactly obtained by a wavelet threshold de-noising technique which eliminates the residual blood flow signals. Finally the intact blood flow signals are achieved by subtracting the wall signals from the mixed signals. This approach is applied to both computer simulated and in vivo carotid Doppler ultrasound signals. The experiment results show that the wavelet space based approach can exactly extract the blood flow signals, and achieve about 45% lower results in the mean absolute error than that of the high-pass filtering. This approach is expected to be an effective method to remove the wall clutters in Doppler ultrasound systems.     

The effect of blood acceleration on the ultrasound power Doppler spectrum

The purpose of the present work was to study the influence of blood acceleration and time window length on the power Doppler spectrum for Gaussian ultrasound beams. The work has been carried out on the basis of continuum model of the ultrasound scattering from inhomogeneities in fluid flow. Correlation function of fluctuations has been considered for uniformly accelerated scatterers, and the resulting power Doppler spectra have been calculated. It is shown that within the initial phase of systole uniformly accelerated slow blood flow in pulmonary artery and aorta tends to make the correlation function about 4.89 and 7.83 times wider, respectively, than the sensitivity function of typical probing system. Given peak flow velocities, the sensitivity function becomes, vice versa, about 4.34 and 3.84 times wider, respectively, then the correlation function. In these limiting cases, the resulting spectra can be considered as Gaussian. The optimal time window duration decreases with increasing acceleration of blood flow and equals to 11.62 and 7.54 ms for pulmonary artery and aorta, respectively. The width of the resulting power Doppler spectrum is shown to be defined mostly by the wave vector of the incident field, the duration of signal and the acceleration of scatterers in the case of low flow velocities. In the opposite case geometrical properties of probing field and the average velocity itself are more essential. In the sense of signal–noise ratio, the optimal duration of time window can be found. Abovementioned results may contribute to the improved techniques of Doppler ultrasound diagnostics of cardiovascular system.     

Flow spectra from spectral power density calculations for pulsed Doppler

Range gated pulsed Doppler can be used to make localized velocity measurements within a blood vessel. Both the transducer and the sample volume are of finite size, and this prohibits the measurement of velocity at a point. A spectral flow profile can be created by stepping a sufficiently small sample volume across the lumen of a vessel. However no such set of spectra will correspond directly to the true velocity profile. In this study we developed a systematic theoretical treatment which allows Doppler spectral power density (SPD) functions to be calculated under a very wide range of conditions. Simulated flow spectra were created from sets of these spectra. The model is based on the beam intensity weighted volume method and incorporates, through the idea of a spread function, Guidi's individual flow line spectrum. Our method can be applied for different spread functions; with beam profiles which are uniform, Gaussian or arbitrarily narrow (needle beam); with range gated sample volumes which can be maximal (CW-type) or minimal (PW-type); and for beams which intersect the flow tube axis, or are off centre. Under all conditions we find the spread function parameter k, equal to the ratio of the central Doppler shift to half the bandwidth, plays a key role. After formulating the model analytically, we sought simplifications to allow results to be obtained from simple, practical formulae. Spread and unspread SPD functions are in most cases given as single integrals which contain measurable physical parameters and can be easily evaluated numerically. Model results are presented for flow spectra of parabolic flow, illustrating the interplay between different factors in determining the appearance of spectral flow profiles.     

The flow velocity distribution from the doppler information on a plane in three-dimensional flow

In order to observe and estimate the flow of fluid in three-dimensional space, the pulsed Doppler method has been used widely. However, the velocity information acquired is only the velocity component in the beam direction of the wave even if an observation plane is formed by beam scanning. Accordingly, it is difficult to know the velocity distribution in the observation plane in tree-dimensional flow. In this paper, the new idea for processing the velocity distribution in the beam direction on an observation plane for transposing to flux distribution (flow function method) has been introduced. Further, the flow in an observation domain is divided into two kinds of flows, viz., the base flow which indicates the directivity of the flow in the observation domain and the vortex which is considered a two-dimensional flow. By applying the theory of a stream function to the two-dimensional flow, and by using the physical feature of a streamline to the base flow, the velocity component v which intersects perpendicularly to the beam direction is estimated. The flow velocity distribution in a scanning plane (observation plane) can be known from these two components of velocity, viz., beam direction componentu and perpendicular component to the beam directionv. The principle was explained by an example of the blood flow measurement in normal and abnormal heart chamber, by the ultrasonic Doppler method.