Realtid Övervakning av hög intensitet fokuserat ultraljud (HIFU) ablation av<em> In Vitro</em> Canine Lever Använda Harmonic Motion Imaging för fokuserat ultraljud (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 för fokuserat ultraljud (HMIFU) är en teknik som kan utföra och övervaka högintensivt fokuserat ultraljud (HIFU) ablation. En oscillerande rörelse alstras vid fokus för en 93-elementet och 4,5 MHz centerfrekvens HIFU-omvandlare genom att applicera en 25 Hz amplitud-modulerad signal under användning av en funktionsgenerator. En 64-elementet och 2,5 MHz imaging omvandlare med 68kPa topptryck confocally placeras i centrum av HIFU givaren att förvärva radiofrekvens (RF) kanaldata. I detta protokoll är realtidsövervakning av värme ablation med användning av HIFU med en akustisk effekt 7 W på hund lever in vitro beskrivs. HIFU behandling appliceras på vävnaden under 2 min och avlägsnade regionen avbildas i realtid med hjälp av divergerande eller plan våg avbildning upp till 1000 bilder / sekund. Matrisen av kanaldata RF multipliceras med en gles matris för bildrekonstruktion. Den rekonstruerade synfält är 90 ° för divergerande wave och 20 mm för plan våg avbildning och data samlas vid 80 MHz. Ombyggnaden utförs på ett grafiskt Processing Unit (GPU) för att bilden i realtid på en 4,5 visningsbildhastighet. 1-D normaliserad korskorrelation av den rekonstruerade RF-data används för att uppskatta axiella förskjutningar i fokalområdet. Storleken av topp-till-topp-förskjutning vid bränn djupet minskar under den termiska ablation som betecknar förstyvning av vävnaden på grund av bildandet av en lesion. Förskjutningen signal-brusförhållande (SNR d) vid fokalområdet för plan våg var 1,4 gånger högre än för divergerande våg visar att plan våg avbildning tycks producera bättre förskjutning kartor kvalitet för HMIFU än divergerande våg avbildning.
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
Realtidsövervakning av HIFU lesioner är viktigt att säkerställa korrekt och effektiv skada leverans. När skadeformer stelnar vävnaden och dess rörelse amplitud enligt excitation minskar. Tillämpa HIFU i en region av vävnadsresulterar i en akustisk strålningskraft som inducerar vävnadsförskjutning. Den relativa förändringen av förskjutning är en surrogat av relativ förändring i vävnads styvhet. Denna teknik erbjuder fördelen att övervaka HIFU lesionen utan att stoppa behandlingen i motsats till andra…
Declarações
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 |
Referências
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