大矢 晃久¹, 油田 信一², 中島 真人¹

Akihisa OHYA¹, Shin'ichi YUTA², Masato NAKAJIMA¹

¹慶応義塾大学理工学部電気工学科, ²筑波大学電子情報工学系

¹Department of Electrical Engineering, Faculty of Science and Technology, Keio University, ²Institute of Information Science and Electronics, University of Tsukuba

キーワード : Speckle Region, Scatterers' Density, Point Spread Function

A random granular pattern called "speckle" appears on the B-mode images obtained with the ultrasonic diagnostic equipment. This speckle arises as a result of the random interference of the ultrasonic waves reflected or scattered at each point of the tissue, and it doesn't coincide with the micro structure of the tissue itself. There are a lot of indistinct facts concerning the characteristics of the ultrasonic speckle phenomena. And the purpose of this study is to clear them.
In this paper, the relationship between the outbreak of the speckle and the scatterers' density is investigated. In case the object is considered as a group of numerous scatterers gathered at random, the speckle becomes dominant in the image when the scatterer is dense to a certain degree. Such a region of the scatterers' density is called "speckle region". We examine quantitatively this speckle region, using the mutual correlation coefficient of the B-mode image and the reference image which is the distribution of the scatterers' density convoluted with the point spread function of the imaging system.
As the result of the 2-D computer simulations using an approximate model of the B-mode imaging system for the random scatterers, we come to a conclusion that the condition for the speckle region depends on each parameter of the imaging system and that the speckle region tends to be caused by 1: lower center frequency of the ultrasonic pulse wave, 2: longer pulse duration, 3: smaller aperture of the transducer. And by normalization of the scatterers' density using the size of the point spread function, it is found that the speckle region arises when more than about 10 scatterers exist in the size of it.