A Method of Reducing Speckle Noises Appeared in Ultrasound Tomographic Image

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  • 超音波断層画像におけるスペックルノイズの低減法
  • チョウオンパ ダンソウ ガゾウ ニ オケル スペックル ノイズ ノ テイゲンホ

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In the field of clinical medicine the ultrasound tomographic image employing the ultrasound diagnostic equipment has been widely used. A speckle noise appearing on the image, however, becomes a major factor of the image degradation. The speckle noise is caused by the interference between echoes from one point on the biological tissues and those from a neighboring point and exhibits a granular pattern similar to a structure of the biological tissues. The resulting tomographic image includes the structure of the biological tissues as well as the speckle noise. Therefore, to reduce the speckle noise is most important. In general the speckle noise reduction is achieved by averaging a number of images with different speckle pattern. To obtain these images, two methods have been proposed; one is scanning of a transducer and the other is changing of ultrasonic pulse frequency. Although these two methods have experimentally been employed, they are not practically used. This comes from the fact that the generating time of image is too long and the frequency hand of commercially available transducers is limited. A new method developed for improving those problems is described in this paper. This method reduces the speckle noise by averaging the randomly phase modulated images from an original image. The numerical proressing of the practical ultrasonic image was conducted and the reduction of speckle noise were studied.

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