Echtzeit-Überwachung von hochintensiven fokussierten Ultraschall (HIFU) Ablation<em> In-vitro-</em> Canine Livers Verwendung harmonische Bewegung Imaging für fokussierten Ultraschall (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
Harmonic Motion-Imaging für fokussierten Ultraschall (HMIFU) ist eine Technik, durchzuführen und zu überwachen hochintensiven fokussierten Ultraschall (HIFU) Ablation kann. Eine oszillierende Bewegung an dem Mittelpunkt einer 93-Element und 4,5 MHz Mittelfrequenz HIFU Wandlers durch Anlegen einer 25 Hz amplitudenmodulierten Signals über einen Funktionsgenerator erzeugt wird. Ein 64-Element und 2,5 MHz Bildwandler mit 68kPa Spitzendruck konfokal in der Mitte des HIFU Wandler an die Hochfrequenz (HF) Kanaldaten erwerben wird. In diesem Protokoll wird die Echtzeitüberwachung der thermischen Ablation mit HIFU mit einer akustischen Leistung von 7 W auf Hunde- Leber in vitro beschrieben. HIFU-Behandlung basiert auf dem Gewebe während 2 min aufgetragen und die abgetragenen Bereichs wird in Echtzeit unter Verwendung von divergierenden oder ebene Welle Bildgebung bis zu 1.000 Bilder / Sekunde abgebildet. Die Matrix der HF-Kanaldaten durch eine Dünnmatrix für die Bildrekonstruktion multipliziert. Das rekonstruierte Sichtfeld von 90 ° zum Ablenken waVE und 20 mm für die ebene Welle Bildgebung und die Daten bei 80 MHz abgetastet. Die Rekonstruktion basiert auf einer Graphical Processing Unit (GPU), um Bild in Echtzeit an einem 4,5-Anzeige Bildrate durchgeführt. 1-D normierte Kreuzkorrelation der rekonstruierten HF-Daten können verwendet werden, um axiale Verschiebungen im Fokusbereich zu schätzen. Der Betrag des Spitzen-zu-Spitzen-Verschiebung am Fokustiefe bei der thermischen Ablation die Versteifung des Gewebes aufgrund der Bildung einer Läsion zeigt abnimmt. Die Verschiebung Signal-zu-Rausch-Verhältnis (SNR d) im Schwerpunktbereich für die ebene Welle war 1,4-mal höher als bei divergierenden Wellen zeigen, dass die ebene Welle Bildgebung scheint besser Displacement-Maps Qualität für HMIFU als divergierende Wellen Bildgebung in der Herstellung.
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
Echtzeit-Überwachung von HIFU Läsionen ist wichtig, die richtige und effiziente Läsion Lieferung. Da die Läsion Formen, versteift sich das Gewebe und dessen Bewegungsamplitude unter Anregung ab. Aufbringen HIFU in einem Bereich des Gewebes führt zu einer Schallstrahlungskraft, die Gewebeverschiebung induziert. Die relative Änderung der Verschiebung ein Surrogat relative Änderung der Gewebesteifigkeit. Diese Technik bietet den Vorteil der Überwachung HIFU Läsion ohne Anhalten der Behandlung im Gegensatz zu ander…
Divulgazioni
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 |
Riferimenti
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