超音波(Ultrasound)成像因為具有高時間解析度和相對低的成本，常被用於導引高能量聚焦超音波(HIFU)的治療手術。然而，HIFU的回音信號振幅通常遠大於成像信號，造成超音波影像上出現許多高回音的干擾圖案，導致難以使用即時超音波影像監測HIFU的治療過程。在本研究中提出了一種格雷編碼(Golay-encoded)脈衝反相相減(Pulse-inversion subtraction)的HIFU干擾消除方法，脈衝反相相減是將接收到的成像回音信號中的正脈衝減去負脈衝以消除HIFU干擾分量，此外成像採用格雷編碼激發，因此經過脈衝反相相減後的成像回波可藉由匹配濾波器(Matched filters)進行脈衝壓縮，能在有效地消除HIFU干擾的同時增強成像信號以改善信號干擾比(Signal-to-interference ratio)，就能更清楚地觀察HIFU治療期間目標對象的變化。我們透過PVA仿體與離體豬肝的實驗評估了所提出方法的效能，研究結果顯示未使用脈衝反相相減的4位元格雷編碼發射，能將SIR從未編碼單一脈衝的-15.0 dB提高到3.5 dB，在使用脈衝反相相減的四位元格雷編碼發射，更進一步將SIR提升至15.9 dB，此外分析人體呼吸引起的組織運動在脈衝反相相減中對HIFU抑制效果與超音波影像品質的影響也顯示可忽略不計。

Ultrasound (US) imaging is often used for guidance of high-intensity focused ultrasound (HIFU) treatment due to its high temporal resolution and relatively low cost. However, real-time US monitoring is often hindered when the strong HIFU interference overwhelms the imaging echoes. In this study, a method of Golay-encoded pulse-inversion subtraction (PIS) is proposed to better visualize the change of imaged object during the HIFU treatment. It effectively eliminates HIFU interference patterns in real-time US imaging and also improves the signal-to-interference ratio (SIR). In PIS method, the received imaging echo of positive transmit is subtracted from that of negative transmit to cancel the HIFU component. When Golay excitation is adopted, imaging echo after PIS is further decoded by matched filters for pulse compression. The performance of the proposed method was evaluated through experiments with both PVA phantom and ex-vivo swine liver. Results show that 4-bit Golay transmit can improve the SIR from -15.0 dB of un-coded transmit to 3.5 dB. With PIS, the SIR of 4-bit Golay further increases to 15.9 dB. Moreover, the effect of tissue motion due to breathing are also shown to be negligible on HIFU suppression and decoded image resolution.

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