Visualization of therapeutic ultrasound beams using horizontal fringe patterns-based background oriented Schlieren imaging and digital image correlation

In medicals, use of ultrasound wave requires a safe treatment with no human effects. The uncontrolled intenities of the ultrasound sources leads to potential risk of thermal and cause ineffective treatment to the patient. This intensity is a main physical parameter used, therefore this parameter must be set and controlled accurately. So far, the hydrophone probe method is considered to become a gold standard in ultrasound intensity beams visualization. Unfortunately, the method is time-consuming, intrusive, and off-axis measurements. Nowadays, an optical method called background-oriented schlieren (BOS) imaging has been developed as an alternative to the probe method. This optical method strongly depends on the background patterns that currently use the random dot patterns and the digital image correlation (DIC) algorithm as a background. The interesting one is this algorithm can also be used to analyze the image of regular pattern background and being developed in this researched especially in the visualization of ultrasound intensity beams. This paper reports that new technique of development of BOS imaging to visualize the ultrasound beams (field) produced by a 1-MHz frequency therapeutic transducer operated in continuous-wave mode. The results show that the developed BOS imaging can visualize and distinguish the ultrasound beams even with the various intensities. This results are promising to be used for ultrasound beams calibration or accuracy assessment to ensure patient safety in medical applications.