適用於可攜式高速超音波系統之低複雜度位移補償波束成像引擎與VLSI架構設計

超音波影像系統可以提供生理組織，血流等診療資訊。相比於其他醫用影像系統如Ｘ光、電腦斷層掃描和核磁共振成像等，超音波影像系統具有非侵入性、無放射性、成本較低、高顯像速率（Frame Rate）以及可攜式等特性。相關研究已經進行多時，並且大量應用於臨床診斷及治療上。波束成像是超音波影像系統最主要的子模組之一，功能為產生影像。由於波束成像需要相當大的硬體資源以及運算時間，因此如何在維持一定影像品質前提下有效減少系統的成本與提升顯像速率，便成為高速超音波成像系統一個重要的研究趨勢。波束成像方法可概括分類為真實孔徑（Real Aperture）以及合成孔徑（Synthetic Aperture）。相較起真實孔徑，合成孔徑擁有較低的複雜度和成本，因此適用於可攜式高速超音波成像系統。合成孔徑的輸出影像是疊加處理多次探頭激發的影像資料而成。若是過程中目標物體有位移現象，會在影像資料間產生非同調現象（Inhomogeneous）。在正常診療情況下，受測者可藉由短時間閉氣而減少位移現象，或是經由現存的離線（Off-line）系統位移補償演算法來進行修正。然而當應用在救護車，戰場或是孩童身上時，位移現象將會難以避免而影響影像品質甚鉅。針對以上問題，本文將提出一個即時二維位移補償演算法。此演算法運用合成發射孔徑的空間特性，大幅降低其運算複雜度，並讓系統產生高品質的影像。此外，本文針對架構設計提出一個適用於線性陣列（Linear Array）的低複雜度延遲加總（Delay-and Sum）架構。以上特點經過整合並利用晶片實現，可開發出一套具有高影像品質以及位移補償功能的即時可攜式超音波成像系統。高影像品質和即時成像可以幫助醫師即時掌握病患病況，提升醫療效率及品質；可攜式的裝置配合本文提出的位移補償演算法，可讓此研究的成像系統運用在救護車、戰場或是偏遠地區的醫療推廣，為醫學影像領域提供嶄新的應用面向。

關鍵字

超音波影像；波束成像；合成孔徑成像；位移補償；硬體架構設計

並列摘要

Ultrasonic imaging system provide diagnostic information like tissue images and blood velocity. Compared to other medical imaging systems such as X-ray, computed tomography and magnetic resonance imaging, ultrasonic imaging system has features like non-invasive, non-radioactive, low cost, high frame rate and portable. Related researches have been carried out for long time and widely applied in clinical diagnosis and treatments. Beamforming is one of the most important sub-modules in ultrasound imaging system which could generate B-mode images. It requires considerable hardware resources and computational time. Hence, reducing system cost and increasing the frame rate while keeping good image quality become an important research issue in high frame rate ultrasound imaging system. Beamforming could be roughly classified into real aperture (RA) and synthetic aperture (SA). Compared to RA, SA is more suitable in high frame rate ultrasound imaging system due to lower complexity and cost. The output image of SA is formed with series of low resolution images (LRIs). It is susceptible to motion, which will cause the inhomogeneous LRIs. In the normal clinics, motion can be reduced by holding breath or compensated by existing off-line algorithm. However, when the system is used on the ambulance, battlefield, or children, motion is difficult to avoid and it will degrade the image quality severely. To solve above problems, a real time two-dimensional motion compensation algorithm is proposed. Proposed method could reduce computational complexity significantly by geometry characteristics of synthetic transmit aperture, and generate high quality images. Besides, a low-complexity linear array delay-and-sum architecture is proposed. Integrating above features with chip implementation, we have developed a high image quality and motion compensated real-time portable ultrasound imaging system. Real-time and high image quality characteristics are helpful for physicians to immediately evaluate patients, which could improve the healthcare efficiency and quality. The portable and motion compensated characteristics could let the proposed imaging system be used in the ambulance, battlefield or medical promotion in remote areas, and provide a new application-oriented field in medical imaging.

並列關鍵字

Ultrasound Image ； Beamforming ； Synthetic Aperture Imaging ； Motion Compensation ； VLSI Design

參考文獻

[1] J. Y. Lu, H. Zou, and J. F. Greenleaf, “Biomedical ultrasound beam forming,” Ultrasound Med. Biol., vol. 20, pp. 403-28, 1994.

[4] GE Healthcare, http://www.gehealthcare.com.

[5] P. C. Li, “Principles of Medical Ultrasound,” Class Notes, National Taiwan University, 2006.

[6] M. C. Tsai, A. Y. Wu , “Low-Complexity Adaptive Beamformer Engine in High Frame Rate Ultrasound Image System,” Master Thesis, National Taiwan University, 2010.

[8] S.-L. Wang and P.-C. Li, “High Frame Rate Adaptive Imaging Using Coherence Factor Weighting and the MVDR Method,” 2008 IEEE Ultrasonics Symposium, Beijing, China, Nov. 2008

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適用於可攜式高速超音波系統之低複雜度位移補償波束成像引擎與VLSI架構設計

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