Sanntidsovervåking av High Intensity fokusert ultralyd (HIFU) Ablation av<em> In Vitro</em> Canine Livers Bruke Harmonic Motion Imaging for fokusert ultralyd (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 for fokusert ultralyd (HMIFU) er en teknikk som kan utføre og overvåke høy intensitet fokusert ultralyd (HIFU) ablasjon. En oscillerende bevegelse blir generert i fokus for en 93-element og 4,5 MHz senterfrekvens hifu transduktor ved å anvende en 25 Hz amplitude-modulerte signal ved hjelp av en funksjonsgenerator. En 64-element og 2,5 MHz bildebehandling svinger med 68kPa topptrykket er confocally plassert i sentrum av HIFU svinger til å overta radio-frekvens (RF) kanaldata. I denne protokollen, er sanntids overvåking av termisk ablasjon bruker HIFU med en akustisk kraft av 7 W på canine lever i vitro beskrevet. HIFU behandling anvendes på vevet i løpet av 2 minutter og ablateres region er avbildet i sanntid ved hjelp av avvikende eller plan bølge avbildning opp til 1000 bilder / sekund. Matrisen til kanaldata RF multipliseres med en glissen matrise for bilde gjenoppbygging. Den rekonstruerte synsfelt er på 90 ° for divergerende wave og 20 mm for plan bølge avbilding og dataene er samplet på 80 MHz. Rekonstruksjonen er utført på en grafisk Processing Unit (GPU) for å bildet i sanntid på en 4,5 skjerm frame rate. 1-D normalisert krysskorrelasjon av den rekonstruerte RF informasjonen blir brukt til å estimere aksielle forskyvninger i fokalområdet. Størrelsen av den spiss-til-spiss forskyvningen ved brenn dybde avtar under den termiske ablasjon som betegner avstivning av vevet som følge av dannelsen av en lesjon. Forskyvningen signal-til-støy-forhold (SNR d) ved fokusområdet for planbølge var 1,4 ganger høyere enn for avvikende bølge som viser at plan bølge avbildning som synes å gi bedre forskyvning kart kvalitet for HMIFU enn divergerende bølge imaging.
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
Sanntidsovervåking av HIFU lesjoner er viktig for å sikre riktig og effektiv lesjon levering. Som lesjon former, stivner vevet og dens bevegelse amplitude etter eksitasjon avtar. Påføring HIFU i en region av vev resulterer i en akustisk stråling kraft som induserer vev forskyvning. Den relative endringen i forskyvning er et surrogat for relativ endring i vev stivhet. Denne teknikken har den fordelen av å overvåke hifu lesjon uten å stoppe behandling, i motsetning til andre ultralydbaserte metoder. Den tidsmessig…
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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