適用於高頻超音波影像系統之可重組化的彩色都卜勒數位信號處理引擎

Reconfigurable Color Doppler DSP Engine Design for High-Frequency Ultrasonic Imaging Systems

俞子豪(Tzu-Hao Yu)

指導教授 ： 吳安宇

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.10528

摘要

超音波影像（ultrasonic imaging）是一種被廣泛使用的造影方式，它具有低成本、非侵入性（non-invasiveness）、即時成像、與儀器較方便攜帶等特性。在1980年代，高頻段的超音波影像（high-frequency ultrasonic imaging）已被發展用作工業上的檢測用途。同時，醫用的超音波成像也正蓬勃發展。雖然傳統上低頻率的超音波影像（2~10 MHz）已經能夠符合大部分應用的需求，高頻超音波還是以其極佳的空間解析度（spatial resolution）而變得日趨重要。這種良好的空間解析度對於眼科學或皮膚醫學等表淺性的觀察是不可或缺的。
隨著高速電子技術與高頻探頭（transducer）製作上的進步，高頻超音波的研究方向已漸漸由傳統上探頭的製作與模擬轉變為信號與影像處理、諧波影像（harmonic imaging）、都卜勒血流量測（Doppler blood flow estimation）與顯影劑（contrast agent）的發展等。醫用高頻超音波雖然已發展了二十餘年，仍然有許多應用與問題是我們必須去發掘與解決的。以現今電子與生物技術進步的速度，我們可以預見在不久的將來，高頻超音波在眼科學、皮膚醫學、血管內造影、小動物影像與基因生物學上都會扮演極其重要的角色。
彩色都卜勒（Color Doppler）影像是一種在醫學界被廣泛使用的超音波成像模式。其主要的價值在於它可以即時（real-time）地呈現出體內流速的二維影像，應用的對象包含血流及心搏等。然而，為了即時成像的需求，其運算與資料處理量卻是相當龐大的。因此，為了節省成本與降低功率的消耗，在硬體設計上就必須謹慎地考量，才能在合理的成本下提供即時性的寶貴資訊。
目前為止，還沒有任何一套高頻超音波影像系統能支援彩色都卜勒的模式。並且，現今高頻超音波系統的可攜性仍明顯不足，這在未來將會是愈來愈不可接受的。因為這不但會使病人必須親自到醫院才能作檢查，造成病人的痛苦，且使這樣的醫療資源難以普及化，尤其在一些需要第一線診斷的情況如救護車或戰場等，大型的醫療設備更無法提供立即的救助。
本論文的研究主題是針對我們正在發展的一套高頻超音波影像系統，設計並實現一顆彩色都卜勒的數位訊號處理引擎（Color Doppler DSP engine）。由於此超音波系統的目標為高攜帶性、功能的全面性、及良好的影像品質，因此本設計也依循著這三個目標前進。首先，本設計是由特製化的專用積體電路（application-specific integrated circuit, ASIC）作實現，相較於目前一般處理器的架構而言，能大大地減少成本與功率的消耗。其次，本設計具有多種可變化的參數，能方便使用者對各種不同的目標環境都能夠掌握到實用的資訊。最後，本設計良好的抗雜訊能力更展現了令人滿意的影像品質。本設計以TSMC 0.18 μm CMOS technology作晶片的實現，同時利用了Altera Stratix II FPGA作為驗證的工具。本設計扮演了高頻超音波影像系統的高效能都卜勒運算核心，不論在臨床上或是研究上皆有其前瞻性的價值。

關鍵字

超音波影像 ； 高頻 ； 都卜勒 ； 數位訊號處理引擎

並列摘要

Ultrasonic imaging is a well-established imaging modality that has the advantages of cost-effectiveness, non-invasiveness, rapid imaging, and portability. In the 1980’s, high-frequency ultrasound had been developed for the detection in industrial applications. Meanwhile, the development of medical ultrasonic imaging was flourishing. Although traditional low-frequency (2~10 MHz) ultrasonic imaging system can meet most clinical applications, high-frequency medical ultrasound has become increasingly important for its good spatial resolution which can be utilized by some specific applications such as ophthalmology and dermatology.
With the evolution of high-speed electronics and high-frequency transducer fabrication, the research direction has gradually changed from transducer fabrication and modeling to signal and image processing or even harmonic imaging, Doppler flow estimation, and contrast agent. Although high-frequency medical ultrasound has been developed for about 20 years, there are many applications to be developed and problems to be solved. In the near future, with the fast progress of electronics and biotechnology, high-frequency ultrasound will be more and more important in ophthalmology, dermatology, intravascular imaging, small animal imaging, and genetics development.
Color Doppler imaging is a well-established Doppler ultrasound mode and very valuable for visualizing in real time the distribution of blood flow in a specific region of interest. However, it is computationally quite expensive. To meet the large computational and data bandwidth needs in Color Doppler imaging, dedicated hardware design is required to reduce the area and power consumption while provide valuable information in real time.
To the best of our knowledge, there is no high-frequency (> 20 MHz) ultrasonic imaging system supporting Color Doppler mode ever published. Also, the portability of current high-frequency ultrasonic imaging systems is insufficient. This will be more and more unacceptable since it is inconvenient and sometimes harmful for patients to go to the hospital for diagnoses. The high cost also reduces the popularity of such medical devices. Moreover, in ambulances or battlefields, portable devices supporting immediate diagnosis can greatly increase the survival rate.
In this thesis, the research topic is to design and implement a Color Doppler DSP engine optimized for the high-frequency ultrasonic imaging system under our development. The major goals of our imaging system are good portability, flexibility, and image quality. Hence, the presented Color Doppler DSP engine is guided to have three features. First, it is implemented with customized ASIC design for low power and low cost considerations. Second, the reconfigurable system parameters of the proposed DSP engine enable users to acquire sufficient information as needed. Finally, its strong de-noising ability results in satisfying image quality. The proposed Color Doppler DSP engine is implemented with TSMC 0.18 μm CMOS technology and also emulated by Altera Stratix-II FPGA. Acting as the computation kernel of our developing high-frequency ultrasonic imaging system, the proposed Color Doppler DSP engine is significant to the clinical and research field.

並列關鍵字

Ultrasonic imaging ； high-frequency ； Doppler ； DSP engine

參考文獻

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