Real-time Monitoring of High Intensity Focused Ultrasound (HIFU) Ablation of In Vitro Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)

The overall goal of this procedure is to use plain wave imaging to stream displacement images in real time during liver ablation through the use of harmonic motion imaging for focused ultrasound or haifu. This is accomplished by first generating oscillatory motion in a liver sample with a high intensity focused ultrasound transducer. A thermal ablation is made using an amplitude modulated signal while radio frequency signals are acquired by a confocal aligned phased array using plain or diverging wave imaging.

These signals are beam formed using a delay in some method implemented with a sparse matrix multiplication and estimated into displacement images using normalized 1D cross correlation that are viewable in real time. Ultimately, FU is used to show a decrease of peak to peak displacement at the focal region during thermal ablation, which denotes stiffening of the tissue due to the formation of the lesion. The main advantage of this technique of existing methods is that high full lesion is monitored in will time at high temporal resolution and without interrupting the treatment, which reduces the treatment duration and helps prevent over treatment.

Now this method can provide insight into treatment and monitoring of liver tumors. It can also be applied to other organs such as breast and pancreas. In preparation, DGAs and ex vivo canine liver sample for 90 minutes in a tank of DGAs PBS secure the tissue on an acoustic absorber using needles to make the required transducers obtain a 64 element 0.32 millimeter pitch, 2.5 megahertz, center frequency phased array, and a 93 element hemispherical array.

Hy Fu transducer assembly begins with inserting the phased array into the center hole of the FU transducer. Then align the two transducers coaxially and secure the central imaging transducer with the adjustment screws. Next, the therapeutic FU transducer must be covered by a volume controlled polyurethane membrane loaded with flowing degas water.

Now mount the assembly on a computer controlled arm. Then connect the therapeutic transducer to a 50 decibels RF amplifier, and connect the amplifier to a function generator from the function generator. Send a 25 hertz sine wave with a maximum amplitude to 500 millivolts.

Next, connect the imaging transducer to an ultrasound system controlled by software in a MATLAB environment. Then apply a command that creates a reconstruction matrix associated with a standard delay in some algorithm. For each grid, enter the command for diverging wave imaging or for plane wave imaging.

See the text for details of the commands. Next, cast the reconstruction matrix to A GPU matrix and create a setup file for the ultrasound channel data acquisition. This is done by entering the appropriate command name in the MATLAB command window.

Enter a name for the setup file. Next, set up an external trigger to synchronize the ultrasound system with the function generator so that the data acquisition is timed to the beginning of the fu. Now place the tank of DGAs PBS with the liver under the transducers and proceed with imaging and anding in the software.

Run the setup script provided by the ultrasound system manufacturer for B mode imaging. Then name the created setup file and use the VSX command to load it. Now move both transducers and use the B mode display on the computer screen to position them in the targeted region of the liver to ablate.

Target a region about one centimeter under the surface of the liver to avoid high ultrasound attenuation due to absorption. Then save a conventional B mode image of the liver on the computer. Data acquisition is done through use of the VSX command.

This applies haifu for two minutes to the targeted region and saves the data. Details on this command are provided in the text protocol for displacement imaging. Define the region of interest as the focal region at negative six decibels 70 millimeters from the transducer surface.

Extract the displacement data in this region. MATLAB can also be used to convert the temporal displacement signal at the focus into audible sound so that the operator can appreciate the decrease in volume of the audible sound, which indicates the formation of the lesion real-time display of acoustic radiation, force induced displacement using plain wave imaging in in vitro canine livers during haifu ablation was performed. Positive displacement are shown in red and negative displacement are shown in blue.

Lesions were successfully delivered using FU ablation. A decrease of HMI peak negative displacement amplitude during FU ablation could be imaged with both diverging and plain wave imaging. A B mode interlay shows the targeted region in the liver.

The 50 hertz HMI displacement sound corresponding to the ablation monitored with plane wave was incorporated to the video. The decrease of HMI displacement amplitude due to the ablation could be heard, which provided an additional monitoring tool HMI displacement at the focal region. During ablation were obtained for diverging and plain wave imaging.

Peak tope displacement decreased for all the targeted locations in the liver. This was assessed by both diverging and plane wave imaging. In comparison, plane wave imaging was found to have a higher displacement signal to noise ratio at the focus than diverging wave imaging.

After watching this video, you should have a good understanding of how to monitor high flu ablation using am motion imaging with plain or diverging waste. While attempting this procedure, it is important to remember to process the data with a time effective method in order to achieve real time monitoring of the ablation Following this procedure. Other methods like cavitation mapping can be performed in order to answer additional questions like, are there any mechanical effects such as cavitation that contribute to the lesion.