热声、光声双模态早期乳腺肿瘤成像系统

本文提出一种热声、光声双模态乳腺肿瘤检测成像系统。本装置中,脉冲微波和脉冲激光分别为热声、光声激发源,产生的热声、光声信号被同一个超声探测器、同一套数据采集装置接收,用同一种成像算法重建出图像。该系统可同时获取多种互补的诊断参数,提高检测早期乳腺肿瘤的准确率。     

褐飞虱求偶鸣声中有效声段及其特征

对褐飞虱Nilaparvata lugens (Stal) 雌、雄虫播放求偶鸣声信号的不同声段及其组合,结果表明在它们求偶识别过程中,由多个规则连续的声脉冲所组成的声段是有效的。播放不同声脉冲重复频率和主振频率组合的模拟信号,表明褐飞虱雌、雄虫求偶信号的声脉冲重复频率是它们识别异性的敏感声学特征参数,其敏感范围较窄,分别为70～90 Hz和22 Hz左右;而对主振频率的敏感范围较宽,分别为200 ～1 700 Hz和100～300 Hz。     

用光声技术测量生物组织粘弹特性的研究

报道了一种用光声技术测量生物组织粘弹特性的新方法,即用脉冲激光在生物组织中激发出光声信号（应力波）,从光声信号的振幅弛豫特性曲线中测量出应力波的弛豫时间,根据粘弹性理论,该弛豫时间就等于生物组织的粘弹比.用该方法测量Kelvin-Voigt模型的模拟生物组织的粘弹比,测量结果与用流变仪测量的结果完全一致,符合率达到97%.进而用光声方法测量出Maxwell模型的生物组织的粘弹比.理论分析与实验结果都表明：该方法只与被测物的声阻抗有关,而与它的状态无关,因此可用于任意状态的生物组织粘弹特性的测量.光声测量方法具有实时、快速、测量灵敏度高和重复性好的优点,因此在生物医学领域具有潜在的应用前景.     

调频声调制方向选择性与其前掩蔽的关系:小鼠下丘细胞内记录研究北大核心CSCD

细胞外记录研究报道听中枢神经元的调制方向选择性和前掩蔽均与神经抑制有关,但由于未能获得抑制性突触输入作用的直接证据,尚存有争议。本研究在20只昆明小鼠(Mus musculus Km)上进行在体细胞内记录,研究了下丘神经元调频声的调制方向选择性或偏好与其前掩蔽之间的关系。共获得93个下丘神经元,对其中37个产生动作电位(action potential,AP)发放且数据完整的神经元做了分析和讨论。在上扫选择性神经元(n=12)频率调谐的高频边存在抑制性突触后电位构成的抑制区,而在下扫选择性神经元(n=8)的低频边存在抑制区,在不具有调制方向选择性的神经元(n=17)频率调谐的高、低频边均未观察到有明显的抑制区,表明这些抑制区是调频声调制方向选择性形成的重要原因。比较上扫和下扫调频声对上、下扫选择性和非选择性神经元的前掩蔽效应,结果显示具有调制方向选择性的神经元,其所偏好方向的调频声对最佳频率(best frequency,BF)声产生的前掩蔽强于非偏好的调频声;而无调制方向选择性神经元,上、下扫调频声的掩蔽效应无差异。以上结果提示,AP后跟随的强抑制性突触后电位可能是调制方向选择性神经元前掩蔽产生的机制。     

基于直线电机的大视场快速光声显微成像系统

光声成像技术是近年来发展的一种新型的无损医学成像技术,它是以脉冲激光作为激发源,以检测的声信号为信息载体,通过相应的图像重建算法重建组织内部结构和功能信息的成像方法。该方法结合了光学成像和声学成像的特点,可提供深层组织高分辨率和高对比度的组织层析图像,在生物医学临床诊断以及在体成像领域具有广泛的应用前景。目前光声成像的扫描方式主要有基于步进电机扫描方式和基于振镜的扫描方式,本文针对目前步进电机扫描速度慢(10 mm×10 mm;0.001帧/s),振镜扫描范围小(1 mm2)的不足,发展了基于直线电机扫描的大视场快速光声显微成像系统。同一条扫描线过程中直线电机速度最高可达200 mm/s。该技术采用逐线采集光声信号的方式,比逐点采集光声信号的步进电机快800倍。该系统对10 mm×10 mm全场扫描的扫描速度为0.8帧/s。最大可扫描视场范围可以达到50 mm×50 mm。大视场快速光声显微成像系统的发展将为生物医学提供新的成像工具。     

基于样品及点源光声信号逆卷积的光声成像方法

光声成像是一种新的生物组织成像方法,在目前的光声成像中,都是通过样品光声信号和超声探测器的脉冲响应来计算样品光吸收的投影,但是由于无法获得超声探测器较准确的脉冲响应,影响重建图像质量。提出一种新的计算样品光吸收投影的方法,从理论上给出了样品光吸收投影和样品及点源光声信号的关系,由样品及点源光声信号的逆卷积可直接计算样品光吸收的投影,点源光声信号通过聚焦入射激光直接测得。试验结果显示,重建图像和样品的相对位置、形状及尺寸完全吻合,成像系统空间分辨率达到0．3mm,证明这是一种有效的光声成像方法。     

声聚焦层析增强的三维微波热声成像

本文提出了一种提高微波热声断层成像层析能力的方法和装置.基于热声成像原理和声聚焦理论,搭建了由超短脉冲微波源、384阵元环形探测器、声聚焦透镜、384-64通道采集切换系统、精密扫描位移平台构成的微波热声三维成像系统,并实现了模拟样品的断层成像.实验结果表明该系统能够实现亚毫米级分辨率的热声成像,通过声聚焦方法成倍地提高了其层析分辨率.这对推动微波热声CT技术走向临床具有重要的意义.     

超短脉冲微波高效激发的高分辨率热声成像

微波热声成像综合了微波成像和超声成像的优点,具有很好的穿透深度及较高的图像分辨率。热声成像的激发源通常为基于脉冲调制的亚微秒级脉冲微波,激发能量密度约为几mJ/cm2,激发出的热声信号主频通常为2 MHz,成像分辨率约为500μm。随着热声成像向着临床应用方向发展,能否有效的减小辐射剂量并提高成像分辨率,是热声成像系统设计成败的一个关键因素。为了有效改善微波热声成像中热损伤及分辨率,设计开发了超短脉冲微波热声成像系统,实验结果表明该系统提高了热声转化效率约两个数量级,成像分辨率达到105μm,为热声成像的临床应用铺平了道路。     

光声结构与功能成像技术研究进展

光声成像技术利用短脉冲激光激发产生光声信号,可重建出组织的光吸收分布图像,它结合了纯光学成像的高对比度和纯声学成像的高分辨率特性.光声成像技术不仅能够有效的刻画生物组织结构,还能够精确实现无损功能成像,为研究生物组织的形态结构,生理、病理特征,代谢功能等提供了全新手段.本文简要分析了光声信号产生的机理,总结报道了目前实验室几套典型的成像系统及其最新应用进展,指出光声成像作为一种新型的生物医学成像方法,可望引发生物医学影像领域的一次革新.     

听觉中枢神经元对声信号的识别和处理

人类听觉的基本特性和机制与其他哺乳动物相似,因此,利用动物所作的听觉研究和获得的结果,有助于认识人类自身的听觉.围绕听觉中枢神经元对不同模式的声信号的识别和处理,简要综述了这方面的研究.声信号和声模式识别在听觉中枢对声信号的感受和加工中具有重要意义.听神经元作为声模式识别的结构和功能基础,对不同的声刺激模式产生不同反应,甚至是在同一声刺激模式下,改变其中的某个声参数,神经元的反应也会发生相应改变,而其反应的特性和机制均需要更多研究来解答.另外,声信号作为声信息的载体,不同的声信息寓于不同的声参数和声特征之中,研究发现,听觉中枢神经元存在相应的声信息甄别和选择的神经基础,能对动态变化的声频率、幅度和时程等进行反应和编码,并且,在不同种类动物上获得的研究结果极为相似,表明听觉中枢对不同声信号和声刺激模式的识别、分析和加工,具有共同性和普遍性.     

COMPARATIVE ANALYSIS OF SWIMBLADDER (DRUMMING) AND PECTORAL (STRIDULATION) SOUNDS IN THREE FAMILIES OF CATFISHES

ABSTRACT

Among teleosts, only representatives of several tropical catfish families have evolved two sonic organs: pectoral spines for stridulation and swimbladder drumming muscles. Pectoral mechanisms differ in relative size between pimelodids, mochokids and doradids, whereas swimbladder mechanisms exhibit differences in origin and insertion of extrinsic muscles. Differences in vocalization among families were investigated by comparing distress calls in air and underwater. High frequency broad-band pulsed sounds of similar duration were emitted during abduction of pectoral spines in all three families. Adduction sounds were similar to abduction signals in doradids, shorter and of lower sound pressure in mochokids, and totally lacking in pimelodids. Simultaneously or successively with pectoral sounds, low frequency harmonic drumming sounds were produced by representatives of two families. Drumming sounds were of similar intensity as stridulatory sounds in pimelodids, fainter in doradids, and not present in mochokids. Swimbladder sounds were frequency modulated and the fundamental frequency was similar in pimelodids and doradids. The ratio of stridulatory to drumming sound amplitude was higher in air than underwater in both doradids and one of the pimelodids. Also, overall duration of pectoral sounds, compared to swimbladder sounds, was longer in air than underwater in one doradid and pimelodid species. This first comparison of vocalization within one major teleost order demonstrates a wide variation in occurrence, duration, intensity and spectral content of sounds and indicates family- and species-specific as well as context- (receiver-) dependent patterns of vocalization.     

Detection of low‐frequency tones and whale predator sounds by the American sand lance Ammodytes americanus

Auditory evoked potentials (AEP) were used to measure the hearing range and auditory sensitivity of the American sand lance Ammodytes americanus. Responses to amplitude‐modulated tone pips indicated that the hearing range extended from 50 to 400 Hz. Sound pressure thresholds were lowest between 200 and 400 Hz. Particle acceleration thresholds showed an improved sensitivity notch at 200 Hz but not substantial differences between frequencies and only a slight improvement in hearing abilities at lower frequencies. The hearing range was similar to Pacific sand lance Ammodytes personatus and variations between species may be due to differences in threshold evaluation methods. AEPs were also recorded in response to pulsed sounds simulating humpback whale Megaptera novaeangliae foraging vocalizations termed megapclicks. Responses were generated with pulses containing significant energy below 400 Hz. No responses were recorded using pulses with peak energy above 400 Hz. These results show that A. americanus can detect the particle motion component of low‐frequency tones and pulse sounds, including those similar to the low‐frequency components of megapclicks. Ammodytes americanus hearing may be used to detect environmental cues and the pulsed signals of mysticete predators.     

A basic study on universal design of auditory signals in automobiles

In this paper, the impression of various kinds of auditory signals currently used in automobiles and a comprehensive evaluation were measured by a semantic differential method. The desirable acoustic characteristic was examined for each type of auditory signal. Sharp sounds with dominant high-frequency components were not suitable for auditory signals in automobiles. This trend is expedient for the aged whose auditory sensitivity in the high frequency region is lower. When intermittent sounds were used, a longer OFF time was suitable. Generally, "dull (not sharp)" and "calm" sounds were appropriate for auditory signals. Furthermore, the comparison between the frequency spectrum of interior noise in automobiles and that of suitable sounds for various auditory signals indicates that the suitable sounds are not easily masked. The suitable auditory signals for various purposes is a good solution from the viewpoint of universal design.     

Encoding properties of auditory neurons in the brain of a soniferous damselfish: response to simple tones and complex conspecific signals

The fish auditory system encodes important acoustic stimuli used in social communication, but few studies have examined response properties of central auditory neurons to natural signals. We determined the features and responses of single hindbrain and midbrain auditory neurons to tone bursts and playbacks of conspecific sounds in the soniferous damselfish, Abudefduf abdominalis. Most auditory neurons were either silent or had slow irregular resting discharge rates <20 spikes s⁻¹. Average best frequency for neurons to tone stimuli was ~130 Hz but ranged from 80 to 400 Hz with strong phase-locking. This low-frequency sensitivity matches the frequency band of natural sounds. Auditory neurons were also modulated by playbacks of conspecific sounds with thresholds similar to 100 Hz tones, but these thresholds were lower than that of tones at other test frequencies. Thresholds of neurons to natural sounds were lower in the midbrain than the hindbrain. This is the first study to compare response properties of auditory neurons to both simple tones and complex stimuli in the brain of a recently derived soniferous perciform that lacks accessory auditory structures. These data demonstrate that the auditory fish brain is most sensitive to the frequency and temporal components of natural pulsed sounds that provide important signals for conspecific communication.     

A Quantitative Analysis of the Sounds of Hector's Dolphin

We developed an automatic, computer-based system in which digital signal processing techniques were used to measure 31 variables from digitized Hector's dolphin (Cephalorhynchus hectori) sounds. Principal component analyses of these data were used to investigate the relationships between sounds. Hector's dolphins make only a very few types of pulsed “clicks”, most of which are centred around 125 kHz. None of these had an average frequency of less than 82 kHz, and the only audible sounds were made up of high-frequency clicks repeated at such high rates that the repetition rate was audible to us as a tonal “cry” or “squeal”. In comparison to signal levels recorded from other cetaceans, all the Hector's dolphin signals were low-level; the maximum received sound pressure level was 163 dB (re 1μPa).     

Hearing in honeybees: the mechanical response of the bee's antenna to near field sound

In the dance language, honeybees use airborne near field sound signals to inform their nestmates of the location of food sources. In behavioral experiments it has recently been shown that Johnston's organ, a chordotonal organ located in the pedicel of the antenna, is used to perceive these sound signals. In the present study the mechanical response of the antennal flagellum to stimulation with near field sound signals was investigated using laser vibrometry. The absolute amplitudes of antennal deflection with acoustical stimulation, the response to sounds of different displacement and velocity amplitudes, the shape of movement of the flagellum, the mechanical frequency response and the mechanical directional sensitivity of the auditory sense organ of the honeybee are described. Using pulsed stimuli simulating the dance sounds it is shown that the temporal pattern of the dance sound is resolved on the level of antennal vibrations.     

Evaluation of a technique for the measurement of chlorophyll fluorescence from leaves exposed to continuous white light

Abstract An instrument for the generation and measurement of modulated chlorophyll fluorescence signals from leaves exposed to continuous, highintensity white light is described. Modulated fluorescence is generated in the leaf by pulsed diodes emitting low-intensity yellow radiation and is detected with a photodiode whose output is fed to an amplifier locked in to the frequency of the lightemitting diodes. Comparisons are made between the modulated fluorescence signals measured with this instrument and the continuous fluorescence signals emitted from dark-adapted leaf tissue and isolated thylakoids when photosynthetic activity is induced by exposure to a range of intensities of continuous broad-band, blue-green light. The modulated fluorescence signals were similar to the continuous fluorescence signals, but they were not always identical. The small differences between the two signals are mainly attributable to differences in the populations of chloroplasts being monitored in the two measurements as a result of differential penetration of the modulated and actinic light sources into the sample.     

A method for computerized modification of certain natural animal sounds for communication study purposes

A new method for computerized modification of sound signals is presented. With digital signal processing in the time domain it is possible to alter the amplitude, the frequency and the time scale of natural sounds independently. The method can be applied to natural sounds with reasonably pure tonal quality.     

Segmentation of heart sounds based on dynamic clustering

The heart sound signal is first separated into cycles, where the cycle detection is based on an instantaneous cycle frequency. The heart sound data of one cardiac cycle can be decomposed into a number of atoms characterized by timing delay, frequency, amplitude, time width and phase. To segment heart sounds, we made a hypothesis that the atoms of a heart sound congregate as a cluster in time–frequency domains. We propose an atom density function to indicate clusters. To suppress clusters of murmurs and noise, weighted density function by atom energy is further proposed to improve the segmentation of heart sounds. Therefore, heart sounds are indicated by the hybrid analysis of clustering and medical knowledge. The segmentation scheme is automatic and no reference signal is needed. Twenty-six subjects, including 3 normal and 23 abnormal subjects, were tested for heart sound signals in various clinical cases. Our statistics show that the segmentation was successful for signals collected from normal subjects and patients with moderate murmurs.     

Finding your mate at a cocktail party: frequency separation promotes auditory stream segregation of concurrent voices in multi-species frog choruses

Vocal communication in crowded social environments is a difficult problem for both humans and nonhuman animals. Yet many important social behaviors require listeners to detect, recognize, and discriminate among signals in a complex acoustic milieu comprising the overlapping signals of multiple individuals, often of multiple species. Humans exploit a relatively small number of acoustic cues to segregate overlapping voices (as well as other mixtures of concurrent sounds, like polyphonic music). By comparison, we know little about how nonhuman animals are adapted to solve similar communication problems. One important cue enabling source segregation in human speech communication is that of frequency separation between concurrent voices: differences in frequency promote perceptual segregation of overlapping voices into separate “auditory streams” that can be followed through time. In this study, we show that frequency separation (ΔF) also enables frogs to segregate concurrent vocalizations, such as those routinely encountered in mixed-species breeding choruses. We presented female gray treefrogs (Hyla chrysoscelis) with a pulsed target signal (simulating an attractive conspecific call) in the presence of a continuous stream of distractor pulses (simulating an overlapping, unattractive heterospecific call). When the ΔF between target and distractor was small (e.g., ≤3 semitones), females exhibited low levels of responsiveness, indicating a failure to recognize the target as an attractive signal when the distractor had a similar frequency. Subjects became increasingly more responsive to the target, as indicated by shorter latencies for phonotaxis, as the ΔF between target and distractor increased (e.g., ΔF = 6–12 semitones). These results support the conclusion that gray treefrogs, like humans, can exploit frequency separation as a perceptual cue to segregate concurrent voices in noisy social environments. The ability of these frogs to segregate concurrent voices based on frequency separation may involve ancient hearing mechanisms for source segregation shared with humans and other vertebrates.