Monitoramento em tempo real de High Intensity Focused Ultrasound (HIFU) Ablação de<em> In Vitro</em> Canine Fígados Usando Movimento Harmônico Imaging para ultra-som focalizado (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
Movimento Harmônico Imaging para ultra-som focalizado (HMIFU) é uma técnica que pode executar e monitorar de alta intensidade ultra-som focalizado (HIFU) ablação. Um movimento oscilatório é gerado no foco de um transdutor HIFU frequência central 93-elemento e 4,5 MHz através da aplicação de um sinal de modulação em amplitude de 25 Hz utilizando um gerador de função. Um transdutor de imagiologia de 64 elemento e 2,5 MHz com 68kPa pico de pressão é confocally colocado no centro do transdutor HIFU para adquirir os dados do canal de rádio-frequência (RF). Neste protocolo, monitoramento em tempo real da ablação térmica utilizando HIFU, com uma potência acústica de 7 W em fígados canino in vitro é descrita. HIFU tratamento é aplicada sobre o tecido durante 2 min e a região de ablação é digitalizado em tempo real utilizando imagiologia divergentes ou onda plana até 1.000 quadros / segundo. A matriz de dados do canal de RF é multiplicado por uma matriz esparsa para a reconstrução de imagem. O campo reconstruída de vista é de 90 ° para wa divergentesve e 20 mm para a imagem latente onda plana e os dados são amostrados a 80 MHz. A reconstrução é realizada numa unidade de processamento gráfico (GPU), a fim de imagem em tempo real com uma taxa de 4,5 visor. 1-D normalizado de correlação cruzada dos dados de RF reconstruído é utilizado para estimar deslocamentos axiais na região focal. A magnitude do deslocamento de pico a pico na profundidade focal diminui durante a ablação térmica, que indica a rigidez do tecido, devido à formação de uma lesão. A relação de deslocamento de sinal-ruído (SNR d) na área focal para a onda avião era 1,4 vezes maior do que para divergindo onda mostrando que a imagem de ondas planas parece produzir mapas de deslocamento melhor qualidade para HMIFU do que divergindo imagem onda.
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
Monitorização em tempo real de lesões HIFU é importante para assegurar a entrega adequada da lesão e eficiente. Como as formas de lesão, o tecido endurece e amplitude de movimento sob a sua excitação diminui. Aplicando HIFU numa região dos resultados de tecidos em uma força de radiação acústica que induz tecido deslocamento. A mudança relativa no deslocamento é um substituto da mudança relativa na rigidez tecidual. Esta técnica oferece a vantagem de monitorização lesão HIFU sem parar o tratamento, em…
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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