Initial experiences with the Verasonics ultrasound research platform Lucy Lin and Matthew A. Lewis

Department of Radiology, UT Southwestern Medical Center, Dallas, Texas

Goals The goals were to do a 3-dimensional scan in B-mode, acquire radio frequency (RF) data, and save images in sequence for both B-mode and RF.

1. Test the Doppler signal in the King/Rosenblatt setup (see if the ultrasound can detect movement and direction).

2. Coordinate with Chatzinoff’s robot program to do a scan of the breast tissue phantom; save both B-mode images and RF data. It should be able to locate tumors in the breast.

3. Image the HIFU “cooking” of Hinshaw’s phantom using an orthogonal orientation of the transducer; save both B-mode images and RF data. This will demonstrate the effects of HIFU on tissue and illustrate the process of burning a lesion into the gel.

References Brubaker, Jon. “Current Status of Automated Breast Ultrasound (ABUS) Market: What Does the Future

Hold?” MD Buyline. MD Buyline, 26 Mar. 2013. Web. 23 July 2013.

"Fundamentals of Ultrasound Imaging." Dynamic Ultrasound Group. Dynamic Ultrasound Group, n.d. Web. 24 June 2013.

Jefferson, Erica. “FDA Approves First Breast Ultrasound Imaging System for Dense Breast Tissue.” FDA. Federal Drug Administration, 18 Sept. 2012. Web. 23 July 2013.

Li, Sheng, and Pei-Hong Wu. "Comparison of Magnetic Resonance and Ultrasound-guided High-intensity." Chinese Journal of Cancer (2012): n. pag. 7 Dec. 2012. Web. 23 July 2013.

Acknowledgements Thank you to the STARS program, Stuart Ravnik, and Lynn Tam, for giving me the chance to engage in interesting research, make many new friends, and have such a wonderful experience. Thank you to my mentor, Matthew Lewis, for making everything so interesting and wonderful. I really appreciate his enthusiasm and patience with me. Also, I enjoyed working with my fellow lab-mates: Rajiv Chopra, Trevor Hinshaw, Anna Rosenblatt, Yonatan Chatzinoff, and Forrest Johnson. Their excitement toward science really inspires and encourages me. Finally, I would like to recognize Lamar High School. In particular, I want to thank the science department for building the foundation of my academic interests and my chemistry teacher, Meg Young, for introducing me to various research opportunities.

Funding for the project was provided by a CPRIT Operating grant R1308.

Future directions 1. Currently, FDA has only approved one ABUS for breast cancer screening, the Somo-v by U-Systems. Since mammograms are not reliable cancer indications for 40% of the female population, it is likely that the ABUS will rise in the market. It is important to increase the availability of this product in order to diagnose more women correctly.

2. It would be useful to be able to guide ultrasound ablation with ultrasound instead of MRI because of the lower cost and wider availability of ultrasounds. Right now, ultrasound cannot detect the heat emissions from the HIFU treatment or produce images as clear as MRI scans. If these areas can be improved, ultrasound image guidance could make ablations and different HIFU treatments more convenient and safe.

3. In our initial experiments, it is unclear if the observations in the B-mode image were due to tissue heating or cavitation, where bubbles are actually formed in the tissue. By analyzing the received RF signals using Fourier analysis to look for harmonics, it may be possible to identify cavitation.

Results (1)

Figure 1. The Doppler test with the King/Rosenblatt setup. The L7-4 transducer uses B-mode imaging to image the movement of air bubbles through a small tube that was placed in a tank. The lines are the walls of the tubing, and the blue spots indicate that the bubble is moving from left to right. If the movement was in the opposite direction, the spots would be red. The rest of the image shows the particles of dust and dirt in the surrounding water.

Conclusion 1.  Doppler sonography uses the Doppler effect to assess the movement and direction of structures. Generally, it detects high-frequency sound waves scattered off of blood cells to measure blood flow. It can also be used to diagnose conditions like blood clots, blocked arteries, venous insufficiency, etc. The VDAS showed movement and direction but did not include velocity or pressure.

2.  Breast cancer is the second leading cause of death among women, and according to the National Cancer Institute, about 40% of the women who get mammograms have dense breasts. Dense breasts are an issue because they can hide tumors on a mammogram. Thus, I replicated a form of an automated breast ultrasound (ABUS). It takes a series of images of the breast phantom to form a three-dimensional scan, which can be used to locate tumors in breasts with dense tissue.

3.  In the third experiment, the ultrasound imaged in real-time the process of ultrasound ablation, which is the heating and coagulation of tissue by HIFU. Image guidance is really beneficial because it can ensure that the HIFU is damaging the targeted cells and not the intervening tissue. Although MRI is currently used for image guidance with HIFU, the Verasonics system is sensitive to treatments in phantoms.

Results (2)

Figure 2. B-mode images from the automated three-dimensional scan of the breast tissue phantom. The circular structures that appear in the

images are tumor-mimicking structures located in the phantom.

. Figure 3. The setup of Chatzinoff’s robot and the L7-4 transducer. Ultrasound transmission gel was used as the medium to produce the images. Our programs coordinated with each other to make an automated scan of the breast. This is an example of a simple automated breast ultrasound, or ABUS.

Results (3)

Figure 5. The process of a lesion (indicated by the red circle) forming in the gel through HIFU cooking. The upper part of each image is the water

environment, and the lower part is the gel phantom.

Figure 6 and 7. Crosstalk from the HIFU that was accidentally received by the L7-4 transducer. On figure 6, the gel and the lesion can still be seen; on figure 7, the HIFU transmissions blocked the image formation. However, these images also show how the HIFU beams focused on the point where the lesion formed.

Figure 4. Setup for cooking the gel with HIFU. The HIFU transducer cooked the gel from the top, while the L7-4 transducer imaged the fo rming o f the l e s ion orthogonally from the side. Water was used as the contact medium.

Time

Voltage (mV)

Figure 8. The plot profile of a specular reflection from an RF image.

Frequency (MHz)

Arbitrary Units

Figure 9. The Fourier transform of the plot above. The fractional bandwidth was about 4 3 . 7 % w i t h a standard deviation of 2.83.

Introduction The Verasonics Data Acquisition System (VDAS) is a research ultrasound that can be programmed within the MATLAB computing environment. The UT Southwestern VDAS was received and installed in June 2013. The VDAS can process signals using a technique called beamforming, which uses an array of sensors to transmit and receive sound waves. An image is constructed by using a transducer to transmit sound waves into tissue or structure and then to interpret the intensity of the reflected waves.

This ultrasound also has HIFU capabilities, or high intensity focused ultrasound. Its intensity can essentially “cook” tissue. Therefore, it has been used for prostate cancer, uterine fibroids, and other tumors. By raising the temperature to about 85 degrees Celsius, HIFU destroys the targeted cells through a noninvasive and nonsurgical approach.

The L7-4 transducer is a probe that does a rectilinear scan. Therefore, it uses B-mode imaging, in which a linear array of sensors simultaneously scans a plane through an object. For the experiments, we often use ultrasound phantoms with similar acoustic properties to tissue.

delayed transmit pulses

converging wavefront

focal point

expanding wavefront

scattering volume

received echoes

delayed and summed echo