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.lecoureures.shop/product-category/course-a-pied-accessoires-hydratation-sac-a-dos/