使用統計參數與衰減發展參數化
超音波影像之可行性

超音波B-mode影像容易因不同系統之訊號、影像處理技術與使用者操作的不一致，使影像只能顯示定值化的組織結構而無法提供特性定量化之訊息。有鑑於此，本研究嘗試用超音波參數來發展定量化影像。以往許多研究已證實超音波散射訊號的包封機率密度函數 (probability density function, PDF)，是取決於介質內散射子的濃度、大小、分佈狀況以及散射橫斷面 (scattering cross-section) 的均勻程度等因素，所以使用包括non-Rayleigh、K與Nakagami等分佈可描述散射訊號的PDF分佈。這些分佈以Nakagami PDF最能廣泛的描述不同生理組織特性所造成的散射訊號包封值，Nakagami參數因此是一個可被用來定量組織之特性的重要參數。此外，超音波衰減在以往研究中也已被應用於發展定量化影像，諸如肝、乳房以及腦等器官的影像都已被探討。本研究結合一階統計模型與超音波衰減的量測結果，來發展多參數之定量化超音波影像。使用中心頻率為4.54 MHz的非聚焦式換能器來量取假體與肝組織的超音波回波訊號，再計算此散射訊號包封值之Nakagami、Scaling及衰減係數等參數，將局部組織所計算之統計參數結果以虛擬色彩 (pseudo-color) 或灰階值來成像。定量參數都經由軟體模擬與假體實驗來驗證。研究結果已證實Nakagami與Scaling參數可用來描述組織中散射子濃度以及其均勻程度，衰減係數也能夠由逆散射訊號中被測量出，並可初步產生定量化之假體及肝影像。

關鍵字

Scaling參數； Nakagami分佈；定量化影像；衰減係數

並列摘要

The gray-scale of ultrasonic B-mode images is easily adjusted due to different system characteristics and user operation. B-mode images are able to display the structure of tissue, which on the other hand could not provide the quantitative information for tissues. For these reasons, current study attempts to develop the quantitative images using ultrasonic parameters. Previous studies have verified that the probability density function (PDF) of the envelope of backscattered signals depends on the homogeneity of concentration, size, distribution, and scattering cross section of scatterers. Typical PDF distributions to describe backscattered signals include non-Rayleigh, K, and Nakagami distributions. The Nakagami PDF is especially a PDF to better describe the envelope of backscattered signals resulting from various physiological tissues. The Nakagami is an important parameter to quantify properties of the tissue. In addition to those statistical parameters, ultrasonic attenuation has been applied to develop the quantitative images from organs of the liver, breast, and brain, etc. This study is to develop a multi-parametric ultrasonic image by combing results of both the first-order statistical model and ultrasonic attenuation measurements. A non-focused transducer with central frequency of 4.5 MHz was used to measure ultrasonic echo signals from tissue-mimicking phantoms and liver tissues. Parameters of Nakagami, Scaling, and attenuation coefficient were calculated from backscattered signals. Subsequently, a gray-scale or a pseudo-color ultrasonic image was obtained based on calculation of statistical parameters from a local tissue. Results of this study has validated that both parameters of Nakagami and Scaling could be used to describe the concentration and the homogeneity of scatterers in tissues. The attenuation coefficient was measured from backscattered signals. These results could be used to form quantitative image for a phantom and the liver.

並列關鍵字

Quantitative image ； Attenuation coefficient ； Scaling parameter ； Nakagami distribution

參考文獻

[52] 蔡富全, 超音波逆散射訊號之統計模型與應用, 私立中原大學碩士論文, 中壢, 2001.

[1] K.K. Shung, and G.A. Thieme, Ultrasonic Scattering in Biological Tissues, CRC Press, Boca Raton, 1993.

[3] D.A. Knapik, B. Starkoski, C.J. Pavlin, and F.S. Foster, “A Real-time 200 MHz Ultrasound B-Scan Imager ,” IEEE Ultrasonics Symposium, 1997.

[4] D.A. Christensen, Ultrasonic Bioinstrumentation, Wiley, New York, 1988.

[5] G.R. Lockwood, D.H. Turnbull, D.A. Christopher, and F.S. Foster, “Beyond 30 MHz ,” IEEE Engineering in Med. and Biol., 1996.

國際替代計量

使用統計參數與衰減發展參數化超音波影像之可行性

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