High intensity focused ultrasound (HIFU) is a noninvasive treatment technique to induce thermal or mechanical bioeffects. Characterising the wave field is essential for reliable and reproducible transducer operation in clinical use. This paper presents a schlieren technique to visualise and quantify transducer wave fields. https://www.roneverhart.com/Macallan-Cask-Strength-Red-Label-Gift-Set-With-Luxury-Hip-Flask-750ml/