Monitoreo en tiempo real de Ultrasonido de alta intensidad (HIFU) Ablación de<em> In Vitro</em> Canine hígados Uso Movimiento armónico Imaging para Ultrasonido 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
Movimiento armónico Imaging para Ultrasonido Focalizado (HMIFU) es una técnica que puede realizar y supervisar ultrasonido focalizado de alta intensidad (HIFU) ablación. Un movimiento oscilatorio se genera en el foco de un transductor de HIFU frecuencia central 93-elemento y 4,5 MHz mediante la aplicación de una señal modulada en amplitud 25 Hz utilizando un generador de funciones. Un transductor de formación de imágenes 64-elemento y 2,5 MHz con pico de presión 68kPa se coloca confocal en el centro del transductor HIFU para adquirir los datos del canal de radiofrecuencia (RF). En este protocolo, se describe la monitorización en tiempo real de la ablación térmica mediante HIFU con una potencia acústica de 7 W en hígados caninos in vitro. El tratamiento con HIFU se aplica sobre el tejido durante 2 min y la región de ablación se forma la imagen en tiempo real utilizando imágenes divergentes o onda plana hasta 1000 fotogramas / segundo. La matriz de datos del canal de RF se multiplica por una matriz escasa para la reconstrucción de la imagen. El campo reconstruida de vista es de 90 ° para divergente wacinco y 20 mm para formación de imágenes de onda plana y los datos se muestrean a 80 MHz. La reconstrucción se realiza en una unidad de procesamiento gráfico (GPU) con el fin de imagen en tiempo real a una velocidad 4,5 pantalla. 1-D correlación cruzada normalizada de los datos RF reconstruido se utiliza para estimar desplazamientos axiales en la región focal. La magnitud del desplazamiento de pico a pico en la profundidad focal disminuye durante la ablación térmica que denota rigidez del tejido debido a la formación de una lesión. La relación de desplazamiento de señal a ruido (SNR d) en la esfera de actividad de onda plana era 1,4 veces mayor que para divergentes de onda que muestra que las imágenes de onda plana parece producir un mejor desplazamiento de los mapas de calidad para HMIFU que diverge de imágenes de 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
Monitoreo en tiempo real de las lesiones HIFU es importante para asegurar la entrega adecuada y eficiente de la lesión. Como las formas de lesión, el tejido se pone rígido y su amplitud de movimiento bajo excitación disminuye. La aplicación de HIFU en una región de los resultados de tejido en una fuerza de radiación acústica que induce el desplazamiento del tejido. El cambio relativo en el desplazamiento es un sustituto de cambio relativo en la rigidez del tejido. Esta técnica ofrece la ventaja de seguimiento d…
Divulgations
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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