Hozumi T, Yoshida K, Abe Y, Kanda R, Akasaka T, Takagi T, Yagi T, Ogata Y, Yoshikawa J
Division of Cardiology, Kobe General Hospital, Japan.
J Am Soc Echocardiogr. 1998 Jun;11(6):660-7. doi: 10.1016/s0894-7317(98)70043-4.
With transthoracic echocardiography, it is sometimes difficult to obtain a clear image of the apical portion of the heart because of noise near the transducer. To reduce this artifact, we have developed a new technique (near field noise reduction, NFNR) based on the digital filtering by using radiofrequency signals. This technique may be useful for the accurate measurement of the wall thickness of the myocardium in the near field. The objectives of these studies were (1) to determine the accuracy of this new technique for the measurement of wall thickness in the experimental study and (2) to determine whether the improvement in the image quality in the apical portion can be obtained in the clinical setting by using the NFNR technique.
By using the NFNR technique, we measured wall thickness of three kinds of phantoms (wall thickness 9.0, 14.0, and 21.0 mm) moving at various velocities (5 to 80 mm/sec) in the water bath with artifact produced by a single probe. It was difficult to obtain clear echocardiographic images of the phantom and measure its wall thickness because of the artifact. By using the NFNR technique, on the other hand, the same phantom was clearly imaged. It was possible to measure the wall thickness of each phantom at each moving velocity with the NFNR technique. Mean differences between the echocardiographic measurement and actual value of wall thickness in each phantom model (9.0, 14.0, and 21.0 mm) were 0.04 +/- 0.58 mm, 0.09 +/- 0.58 mm, and -0.02 +/- 0.24 mm, respectively.
We studied 25 initial patients in whom the near field was not clearly imaged in apical views by conventional echocardiography because of near field noise. Apical four-chamber or two-chamber views were obtained with and without the NFNR technique. Two observers independently graded endocardial visualization for the 50 segments by using a three-point scale (0 = endocardium not seen, 1 = seen in part but not all of the segment, 2 = endocardium seen along entire segment). The mean segment score in the imaging with the NFNR technique was significantly higher than that without the NFNR technique (observer 1: 1.8 +/- 0.7 vs 1.2 +/- 0.8, p < 0.01; observer 2: 1.6 +/- 0.7 vs 1.2 +/- 0.8, p < 0.01).
The newly developed NFNR technique provides clear echocardiographic images and accurate wall thickness measurement in the experimental model even when it is difficult to obtain clear images because of the artifact. This new technique will be useful in the reduction of near field noise in the clinical setting.
使用经胸超声心动图时，由于换能器附近的噪声，有时很难获得心脏心尖部的清晰图像。为减少这种伪像，我们开发了一种基于射频信号数字滤波的新技术（近场噪声降低，NFNR）。该技术可能有助于准确测量近场心肌壁厚度。这些研究的目的是：（1）在实验研究中确定这种新技术测量壁厚度的准确性；（2）确定在临床环境中使用NFNR技术是否能改善心尖部的图像质量。
我们使用NFNR技术，在水浴中，对三种以不同速度（5至80毫米/秒）移动的模拟体模（壁厚度分别为9.0、14.0和21.0毫米）进行壁厚度测量，该模拟体模由单个探头产生伪像。由于伪像，很难获得模拟体模的清晰超声心动图图像并测量其壁厚度。另一方面，使用NFNR技术时，同一模拟体模能被清晰成像。使用NFNR技术可以测量每个模拟体模在每个移动速度下的壁厚度。每个模拟体模模型（9.0、14.0和21.0毫米）的超声心动图测量值与实际壁厚度值之间的平均差异分别为0.04±0.58毫米、0.09±0.58毫米和 -0.02±0.24毫米。
我们研究了25例初始患者，这些患者由于近场噪声，在传统超声心动图的心尖视图中近场成像不清晰。分别在使用和不使用NFNR技术的情况下获取心尖四腔或两腔视图。两名观察者使用三点量表（0 = 未看到心内膜，1 = 部分看到但不是整个节段，2 = 沿整个节段看到心内膜）对50个节段的心内膜可视化进行独立分级。使用NFNR技术成像时的平均节段评分显著高于不使用NFNR技术时（观察者1：1.8±0.7对1.2±0.8，p < 0.01；观察者2：1.6±0.7对1.2±0.8，p < 0.01）。
新开发的NFNR技术在实验模型中即使因伪像难以获得清晰图像时，也能提供清晰的超声心动图图像和准确的壁厚度测量。这项新技术将有助于在临床环境中减少近场噪声。
