高強度のリアルタイムモニタリングの超音波（HIFU）アブレーションを重視しました<em>インビトロ</em集束超音波のための調和運動イメージングの使用>犬の肝臓（HMIFU）
Summary
This article describes real-time monitoring of HIFU ablation in canine liver with high frame rate ultrasound imaging using diverging and plane wave imaging. Harmonic Motion Imaging for Focused Ultrasound is used to image the decrease of acoustic radiation force induced displacement in the ablated region.
Abstract
集束超音波（HMIFU）のための調和運動イメージングは、高強度の超音波（HIFU）アブレーションを集中実行し、監視することができる技術です。振動運動は、関数発生器を用いて、25 Hzの振幅変調信号を印加することにより、93素子と4.5 MHzの中心周波数HIFUトランスデューサの焦点で生成されます。 68kPaのピーク圧力で、64素子と2.5 MHzの撮像トランスデューサは、共焦点無線周波数（RF）チャネルのデータを取得するためにHIFUトランスデューサの中心に配置されています。このプロトコルでは、 インビトロでのイヌの肝臓に7 Wの音響パワーとHIFUを用いた熱アブレーションのリアルタイム監視が記載されています。 HIFU治療は、2分の間に組織に適用され、アブレーション領域1000フレーム/秒に発散または平面波イメージングを使用してリアルタイムで画像化されます。 RFチャネルデータの行列は、画像再構成のための疎行列乗算されます。ビューの再構築されたフィールドは、WAを発散するために90°でありますVEの平面波イメージングのための20ミリ、データが80 MHzでサンプリングされます。再構成は、4.5の表示フレームレートでリアルタイムに画像化するためにグラフィック処理装置（GPU）上で実行されます。再構成されたRFデータの1次元の正規化相互相関は、焦点領域内の軸方向の変位を推定するために使用されます。焦点深度でのピーク・ツー・ピーク変位の大きさが原因病変の形成組織の硬化を意味熱アブレーションの間に減少します。平面波のための焦点領域における変位信号対雑音比（SNR d）はその平面波イメージングは波撮像発散よりHMIFUための優れた変位マップの品質を生成するために表示される表示波発散よりも1.4倍高かったです。
Introduction
High Intensity Focused Ultrasound (HIFU) is a technique that generates temperature elevation at the focal region and can be used to ablate cancerous tissue 1. Temperature elevation at the focus causes thermal lesions in the tissue 2. In order to avoid overtreating a region and to reduce treatment duration, it is imperative to reliably monitor the ablation. Magnetic resonance-guided focused ultrasound (MRgFUS) is the main technique used in clinic to guide and monitor HIFU treatment 3. MRI provides high spatial resolution images of the treated region with tissue displacement or thermal dose but has a frame rate of 0.1-1 Hz and is costly. Several ultrasound-based techniques such as B-mode imaging 4, passive acoustic mapping 5, shear wave imaging 6 and acoustic radiation force impulse 7 have been developed to guide and monitor thermal ablation. However, B-mode imaging and passive acoustic mapping do not provide imaging of mechanical properties of the ablated region which is useful to the operator to improve lesion delivery.
Shear wave imaging and acoustic radiation force impulse can both characterize the elasticity of the tissue by measuring acoustic radiation force-induced displacements 7,8. However, in both methods, the HIFU treatment is typically interrupted to monitor the ablation. Our group has developed a technique called Harmonic Motion Imaging for Focus Ultrasound (HMIFU) which can monitor the HIFU treatment with ultrasound without stopping the ablation9,10. Briefly, a HIFU transducer sends an amplitude-modulated wave to the region to ablate while simultaneously generating an oscillatory motion in the focal region. A co-axially aligned ultrasound transducer is used to image this oscillation. The magnitude of the induced motion is related to the stiffness of the tissue.
To ensure proper lesion delivery, the temporal resolution of real-time monitoring is of key interest in ablation guidance. Recently, our group has shown real-time streaming of displacement at a frame rate up to 15 Hz, imaged with diverging waves in a narrow field of view and using a fast image reconstruction method 11. Several beamforming techniques can be used to image the displacements. A large field of view can be obtained with diverging wave imaging by changing the delay profile but the axial direction is not aligned with the HIFU beam on the lateral regions and the wave is attenuated due to geometric spreading in the lateral direction, which can affect the quality of the displacement estimation. In contrast, the lateral field of view for plane wave is upper bounded by the active aperture but the axial direction is aligned with the HIFU beam at the focus and there is no geometric spreading in the lateral direction. Depending on the type of application, one or the other imaging method can be selected. The objectives of this protocol are to show how plane wave imaging can provide real-time streaming of displacements images using HMIFU during ablation and to compare the quality of the motion estimation between diverging and plane wave imaging.
Protocol
Representative Results
Discussion
HIFU病変のリアルタイムモニタリングは、適切かつ効率的な病変の配信を保証することが重要です。病変の形態としては、組織が硬直し、励起下での運動の振幅は減少します。組織変位を誘発する音響放射力で組織の結果の領域にHIFUを適用します。変位の相対的な変化は、組織の剛性の相対的な変化の代理です。この技術は、他の超音波ベースの方法とは対照的に治療を停止することなく、H…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by the National Institutes of Health (R01-EB014496). The authors would like to thank Iason Apostolakis for his contribution to the experiments.
Materials
| P4-2 Phased array | ATL | ||
| H-178 HIFU transducer | Sonic Concepts | ||
| 3-D positioner | Velmex Inc. | ||
| AT33522A function generator | Agilent Technologies | ||
| V-1 ultrasound system | Verasonics | ||
| 3100L RF amplifier | ENI | ||
| Matching network | Sonic Concepts | ||
| Degasing system | Sonic Concepts | ||
| Programming software | Matlab | ||
| Jacket software package | Accelereyes |
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