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The Different Modes 不同的模式

Bidimensional Mode 二维模式

Bidimensional (2D) echocardiography provides anatomic cross-sections of the heart via the emission of a wide ultrasound beam through the thorax and the reception of the echoes reflected by its different structures. This wide beam allows viewing of a large part of the organ. It is shaped in such a manner as to travel between the ribs and the pulmonary lobes. Several views or projections are used in order to observe all of the cardiac structures. 2D echocardiography allows real-time visualization of the movement and deformation of these structures in two dimensions. Bidimensional harmonic echocardiography integrates secondary harmonics of reflected echoes. This improves the visualization of structures with low levels of reflectivity, such as the myocardium.
二维 (2D) 超声心动图通过胸部发射宽超声波束并接收其不同结构反射的回声来提供心脏的解剖横截面。这种宽光束可以观察器官的大部分。它的形状是在肋骨和肺叶之间移动。使用多个视图或投影来观察所有心脏结构。二维超声心动图可以在二维空间中实时显示这些结构的运动和变形。二维谐波超声心动图集成了反射回波的二次谐波。这改善了反射率低的结构(例如心肌)的可视化。

Time-Motion Mode 时间运动模式

Historically, time-motion (TM) mode (or M-mode) was the first mode developed. A line is selected on the 2D ultrasound cone and a series of points moving in time can then be obtained. These points correspond to the echoes reflected by the different acoustic interfaces of each cardiac structure being penetrated. The point of origin and orientation of this line can be modified if the device is equipped with "anatomic" or "freeangle" M-mode capabilities. Because of the contraction and dilation of the heart, the position of these points will vary according to the cardiac cycle phases. This appears on the screen as undulating lines corresponding to the movement of the points over time. Due to high sampling frequency, TM mode enables the recording of very rapid cardiac movements such as valve motion . It also allows measurement of the dimensions of the heart (wall thickness and endocavitary diameters in systole and diastole) and analysis of the motion of different structures of the organ during the cardiac cycle.
从历史上看,时间运动(TM)模式(或M模式)是第一个开发的模式。在二维超声锥上选择一条线,然后可以获得一系列随时间移动的点。这些点对应于被穿透的每个心脏结构的不同声学界面反射的回声。如果设备配备了“解剖学”或“自由角度”M 模式功能,则可以修改该线的原点和方向。由于心脏的收缩和扩张,这些穴位的位置会根据心动周期阶段而变化。这在屏幕上显示为起伏的线条,对应于点随时间的移动。由于采样频率高,TM模式可以记录非常快速的心脏运动,例如瓣膜运动 。它还可以测量心脏的尺寸(收缩期和舒张期的壁厚和腔内直径),并分析心脏周期中器官不同结构的运动。

Spectral Doppler Mode 频谱多普勒模式

When an ultrasound beam of a particular frequency encounters a flow of erythrocytes moving at speed , part of these ultrasounds is reflected toward the transducer at a modified frequency. This is defined as the Doppler effect . This change in frequency, or shift, is proportional to the speed of the erythrocytes (i.e., the blood flow speed) and to the angle cosine (referred to as ) formed by the ultrasound beam and the blood flow axis of displacement according to the equation:
当特定频率的超声波束遇到高速 移动的红细胞流时,这些超声波的一部分会以改变的频率反射到换能器。这被定义为多普勒效应 。这种频率或位移的变化与红细胞的速度(即血流速度)和超声束形成的角余弦(称为 )成正比,根据公式:
where is the measured frequency shift, is the initial ultrasound speed in the soft tissue, and is the initial beam frequency [3]. The Doppler examination, by measuring this frequency shift, allows the determination of the blood flow velocity and its direction. To best measure real flow velocity without underestimating it, the angle must be as close to 0 degrees as possible. The ultrasound beam must then be aligned as much as possible to the axis of the flow movement.
其中 是测得的频移, 是软组织中的初始超声速度, 是初始束频[3]。多普勒检查通过测量这种 频移,可以确定血流速度及其方向。为了在不低估真实流速的情况下最好地测量它, 角度必须尽可能接近 0 度。然后,超声波束必须尽可能地与流动运动的轴对齐。
The Doppler examination allows the study of the characteristics of the intracardiac flows, the detection of abnormal flows, and the measurement of transvalvular or transorifice stroke volumes.
The spectral Doppler exam includes pulsed and continuous wave Doppler modes, which complement each other perfectly. In both cases, the frequency shift is analyzed and filtered by the cardiac ultrasound machine, which transforms it into acoustic and graphic signals. The graphic signal represents the spectral analysis through fast Fourier transform of all reported frequency shifts in the flow under study. A velocity "envelope" changing in time can thus be obtained. As a rule, when erythrocytes move toward the transducer, their velocities are coded as positive. Inversely, they are coded as negative when moving away from the transducer. Not all red cells within a blood flow move at the same velocity. The Doppler signal will indicate through its intensity the relative prevalence of these velocities. In a normal transvalvular flow, the erythrocytes move in the same direction and at the same speed. The flow is then considered to be "laminar."

Pulsed Wave Spectral Doppler

The unique transducer crystal emits at a certain frequency (known as recurrence frequency), then listens between each ultrasound blast. Knowing the ultrasound propagation speed through soft tissue ( 1540 ), it becomes possible to set the emission and reception so as to record only frequencies reflected from a certain depth of the beam [3]. The pulsed wave Doppler examination requires selecting a small zone, called sample volume, on the Doppler cursor line positioned on the 2D echocardiographic image. This sample volume contains erythrocytes whose velocities
独特的换能器晶体以特定频率(称为递归频率)发射,然后在每次超声波爆炸之间进行监听。知道超声波通过软组织的传播速度(1540 ),就可以设置发射和接收,以便仅记录从光束一定深度反射的频率[3]。脉冲波多普勒检查需要在位于 2D 超声心动图图像上的多普勒光标线上选择一个小区域,称为样本体积。该样品体积包含速度

are to be analyzed. Thus this examination enables the analysis of the blood flow characteristics in a specific area of the heart or great arteries [3]. The time allocated to reception of the reflected waves limits the measurable maximum velocities. The maximum recordable frequency shift (known as the Nyquist limit) is equal to half of the recurrent frequency of the wave train emitted by the transducer. Frequency shifts that go beyond this limit lead to an artifact known as "aliasing" or "ambiguous velocity." When this artifact is produced, the part of the Doppler envelope exceeding this limit is truncated and appears at the opposite edge of the screen. When this phenomenon becomes very pronounced, it can interfere with the measurement of maximum velocities and even prevent the determination of flow direction. To increase the Nyquist limit, one can modify the baseline, use a lower frequency transducer, increase the recurrence frequency by purposefully selecting a sample volume very close to the transducer, or even use a high pulse repetition frequency (PRF) technique known as a high PRF. The latter involves setting the transducer in a nearly continuous emission and reception mode, allowing the capture of the entirety of the Doppler signals encountered along the beam without the interference of a now very high Nyquist limit. However, high PRF mode does not allow one to know the exact depth at which the measured velocities were recorded (ambiguous range). This becomes extremely close to continuous Doppler (see below) [3-5].

Continuous Wave Spectral Doppler

Continuous wave spectral Doppler is characterized by the use of two crystals working in a simultaneous and continuous manner, one emitting and one receiving. This continuous work by both crystals abolishes the Nyquist limit and allows the recording of any velocity value. However, with all velocities along the beam being recorded, it becomes impossible to pinpoint the exact location of the origin of the flow. Pairing the pulsed wave and continuous wave modes allows one to locate the flows and to record the highest velocities without any artifacts, respectively.

Color Doppler Mode 彩色多普勒模式

In color Doppler mode, the cardiac flow is directly visible in color on the 2D image. As a rule, flows moving toward the transducer appear in red whereas those moving away from it appear in blue. This color representation is obtained through the velocity spectrum obtained by fast Fourier transform. The different velocities recorded by the device are represented by a series of small colored squares (vertical axis) moving in time (horizontal axis). The greater the quantity of erythrocytes moving at the same speed at the same time, the more the Doppler signals will coincide (i.e., in the same square), leading to greater square color intensity. This type of representation is known as "amplitude analysis" because the different intensity amplitudes are displayed. If the Nyquist limit is reached, as in the case of pulsed wave spectral Doppler, an aliasing phenomenon will appear. It is characterized by a change in color: red becoming blue and vice versa. Another important concept is variance. Variance expresses the degree of difference between the varying velocities within a sample volume and the average velocity. In a normal laminar flow, variance is very low and maximum velocities are generally lower than the Nyquist frequency limit. The flow then is coded in a homogeneous red or blue color. On the other hand, turbulent flows are characterized by a widened velocity spectrum-in other words, by a wide variance. This leads to multiple colors that cover the spectrum between red and blue (known as a mosaic aspect) . Color Doppler mode is very useful for locating flows and is able to accurately determine their extent within the cardiac cavities (colorimetric extent). The measurement of flow velocities is performed using spectral modes (pulsed wave or continuous wave Doppler).
在彩色多普勒模式下,心流在 2D 图像上以彩色直接可见。通常,流向换能器的气流显示为红色,而远离传感器的气流显示为蓝色。这种颜色表示是通过快速傅里叶变换获得的速度光谱获得的。设备记录的不同速度由一系列随时间移动的小彩色方块(垂直轴)表示(水平轴)。同时以相同速度移动的红细胞数量越多,多普勒信号重合的程度就越高(即在同一方块中),从而导致更大的方形颜色强度。这种类型的表示称为“振幅分析”,因为显示了不同的强度振幅。如果达到奈奎斯特极限,如脉冲波谱多普勒的情况,将出现混叠现象。它的特点是颜色变化:红色变成蓝色,反之亦然。另一个重要概念是方差。方差表示样品体积内变化速度与平均速度之间的差异程度。在正常层流中,方差非常小,最大速度通常低于奈奎斯特频率极限。然后将流程编码为均匀的红色或蓝色。另一方面,湍流的特征是速度谱变宽,换句话说,变化很大。这导致了覆盖红色和蓝色之间的光谱的多种颜色(称为马赛克方面)。 彩色多普勒模式对于定位血流非常有用,并且能够准确确定它们在心腔内的范围(比色范围)。 使用频谱模式(脉冲波或连续波多普勒)进行流速测量。

General Considerations 一般注意事项

Choice of Transducer 换能器的选择

The choice of a transducer depends on the size of the animal. In general, a 10 or transducer is adequate for cats and dogs weighing less than is adequate for medium-size dogs, and 3.5 or is adequate for large or giant breeds (Doberman, Great Dane, Bull Mastiff, etc.). Most current transducers are multifrequency. The transducer must be covered in gel and, if necessary, the animal's skin should be shaved to ensure contact without any kind of air interference, which could block the ultrasounds.
换能器的选择取决于动物的大小。一般来说,10 或 换能器对于体重小 于中型犬的猫和狗来说就足够了,而 3.5 或 对于大型或巨型品种(杜宾犬、大丹犬、公牛獒等)就足够了。目前大多数传感器都是多频的。换能器必须用凝胶覆盖,如有必要,应剃掉动物的皮肤,以确保接触时没有任何空气干扰,这可能会阻挡超声波。

Positioning the Animal 定位动物

There are two possible positions for the animal: lying down or standing against a support. In the first option, the animal is placed in a lateral position on a table with a side hole, which allows for the placement of the transducer against the
  • Fig. 1-1 Animal positioned on the imaging table to perform an ultrasound. See Video 1-1 for the standing position. (Photo credit: Éric de Madron.)
    图1-1 动物被放置在成像台上进行超声检查。站立姿势见视频1-1。(图片来源:Éric de Madron。
thorax on the lateral side (Figure 1-1). Right-sided views are thus obtained with the animal in right lateral recumbency and vice versa. The standing position is often better tolerated by very large breed dogs and also by stressed or dyspneic animals (Video 1-1). A trained operator can obtain similar and repeatable measurements from these two positions [8].
胸部在外侧(图1-1)。因此,当动物处于右侧卧位时,可以获得右侧视图,反之亦然。非常大的犬以及压力大或呼吸困难的动物通常更能忍受站立姿势(视频 1-1)。训练有素的操作员可以从这两个位置获得相似且可重复的测量结果[8]。

Settings 设置

The depth must be set so that the cardiac image occupies the entire screen. The ultrasound beam gradually loses its energy as it progresses through the thorax and reflects off the successive interfaces. Echoes from the deep structures are thus weak whereas those from structures near the transducer are very intense. To compensate for this phenomenon, the proximal echo signals must be attenuated and the distant ones amplified. This compensation can be set in a progressive fashion [2,9]. Also, the ultrasound beam energy is set using total gain so as to clearly visualize all structures, including those with low reflectivity such as the myocardium, while avoiding image saturation by overly bright echoes. There are many settings to choose from, including the focal position, endocardial echo amplification, erythrocyte echo attenuation, beam width, and sweep frequency repetition.

Normal Bidimensional Views

These views have been well described in dogs and in cats [12]. Videos 1-2 to 1-7 demonstrate how to obtain these views with the animal in a standing position. Videos 1-9 to 1-15 show views with the animal in a recumbent position.
这些观点在狗 和猫身上得到了很好的描述[12]。视频 1-2 至 1-7 演示了如何在动物站立的情况下获得这些视图。视频 1-9 至 1-15 显示了动物处于卧位的视图。

Right Parasternal Long Axis Views Long Axis 4 Chambers View: Optimized for Viewing the Atria
右胸骨旁长轴视图 长轴 4 腔室视图:针对观察心房进行了优化

The beam is aligned with the long axis of the heart and angulated to view both ventricles and both atria (Figure 1-2, ; see also Video 1-8). This is the best view to observe the interatrial septum.
光束与心脏的长轴对齐并成角度以观察两个心室和两个心房(图 1-2; 另见视频 1-8)。这是观察房间隔的最佳视图。