曹 景文, 森村 晋哉, 伊藤 博巳, 伊藤 貴司, 小西 辰男

Jing-Wen TSAO, Shinya MORIMURA, Hiromi ITOH, Takashi ITOH, Tatsuo KONISHI

アロカ株式会社

Aloka Co., Ltd.

キーワード : Ultrasonic imaging, Texture analysis

The two new images derived from local frequency dependent attenuation (FDA) coefficient and frequency modality (FM) of pulse-echo signals are becoming available in medical ultrasound, in addition to the current amplitude-demodulated (AM) image and its log-compression version (AML). In this paper, FDA and FM images are formed using short-time spectral moments analysis, upon which the method of FDA estimation is based either on the rate of log-power decay or on the rate of mean frequency shift, while the FM is observed from mean frequency.
Comparisons of AM, AML, FM, and FDA images in views of the same uniform region and of the same cyst embedded area within a tissue-like phantom exhibit significant differences in texture, but in which FM and FDA images indicate the cyst with poor contrast. The texture features such as 1st & 2nd order histograms (1H & 2H), and 2D-autocovariance function (ACVF) of each image were extracted. Usually, the 1H of AM image obeys a Rayleigh function, whereas FM and FDA images both lead 1H close to a Gaussian distribution. The statistics (Table 1) of 2H and AVCF, which serve as measures, are utilized for texture coarseness and speckle size assessments in the literature.
Based on the correlation coefficients evaluation, we found that FDA image is in a sense dependent, it appears to be the result of performing a spatial differentiation on axial direction of AML image or of FM image depending on the abovementioned FDA estimation method being used. Thus, we conclude that it should expect the availability of FDA image particularly to its quantitative description of tissue states rather than to imaging itself, and that FM image which differs fundamentally from AM image, carries phase information of echo signals, could contribute to textural diagnosis.