Imaging and Quantification of the Area of Fast-Moving Microbubbles Using a High-Speed Camera and Image Analysis

High-speed imaging can be used to image fast processes, such as cavitation bubble dynamics. We demonstrate a method of imaging cavitation bubbles around a dental ultrasonic scaler tip. Cavitation around ultrasonic scalers is being researched for cleaning dental plaque, but the method shown here could be used for many different applications.

We've also developed an image analysis protocol using open source software which allows the user to calculate the area of cavitation bubbles to allow for comparisons between different experiments. To create the experimental setup, you will need a high-speed camera, a high intensity cold light source, two laboratory jacks, a micropositioning stage with rotation, a 3D micropositioning stage, a microscope zoom lens, and an ultrasonic scaler to generate cavitation microbubbles, or the object that you wish to image. To begin the procedure, attach a micropositioning stage with XYZ translation and rotation to a laboratory jack.

Fix the handpiece of the ultrasonic scaler in the micropositioning stage. Use a high-speed camera with the desired frame rate and resolution. Attach a micropositioning sliding plate to the high-speed camera body, and connect it to a tripod.

Use a lens with the desired resolution and focal lens and attach it to the high-speed camera body. Attach an XY micropositioning stage with rotation to another laboratory jack and place an optically transparent imaging tank on top of this. You will also need a high intensity cold light source with a fiber light guide.

Fill the imaging tank with water and immerse the tip of the instrument inside the tank. Connect the camera and load the live view in the imaging software. Use low magnification to focus on the tip of the ultrasonic scaler, repositioning the light source if necessary.

In this study, illumination was provided in bright field mode. Select the optimal frame rate and shutter speed for the high-speed camera. In this case, a short shutter speed of 262 nanoseconds was chosen to ensure the fast-moving cavitation bubbles were in focus.

Adjust the magnification of the zoom lens and the intensity of the light source, so the background is white without being overexposed. Record the rotation angle of the tip for reproducibility. To ensure the field of view is consistent for each repeat, choose a reference point and note down the coordinates.

In this case, the reference point was the tip of the ultrasonic scaler. If image analysis will be done, take an image of the instrument without any cavitation. This will be used to subtract the area of the instrument to calculate the area of the bubbles.

Then, image the cavitation around the instrument. These are high-speed videos of cavitation occurring around different ultrasonic scaler tips. In this study, image analysis was used to calculate the mean area of cavitation occurring, and these graphs show the comparison between different tips.

This technique is useful for imaging bubble patterns and their exact locations, which is useful for understanding how cavitation bubbles could be used for different applications, such as cleaning. These high-speed imaging experiments can also be validated with new medical simulations. We have used articles based on finite element modeling to simulate the three-dimensional, nonlinear, and transient interaction between the vibration and the formation of the scaler tip.

We also simulated the water flow around the scaler, and the cavitation formation and their dynamics. This protocol shows the relatively simple way to create a high-speed imaging setup, that when mastered correctly, can be useful for imaging cavitation bubbles around dental ultrasonic scalers, and also for imaging other types of instruments which produce cavitation microbubbles. After watching this video, you should have a good understanding of how to create a high-speed imaging set up to image fast-moving microbubbles.

The main advantage of this method is easy to set up, and the rapid image analysis can easily be applied to hundreds of images. This technique will help researchers to use high-speed imaging to image fast-moving microbubbles, and it can be easily adapted for various bubble imaging applications.