Schlieren imaging

Schlieren imaging is a method to visualize density variations in transparent media.^[1]

The term "schlieren imaging" is commonly used as a synonym for schlieren photography, though this article particularly treats visualization of the pressure field produced by ultrasonic transducers, generally in water or tissue-mimicking media. The method provides a two-dimensional (2D) projection image of the acoustic beam in real-time ("live video"). The unique properties of the method enable the investigation of specific features of the acoustic field (e.g. focal point in HIFU transducers), detection of acoustic beam-profile irregularities (e.g. due to defects in transducer) and on-line identification of time-dependent phenomena ^[2] (e.g. in phased array transducers). Some researchers^[who?] say that schlieren imaging is equivalent to an X-ray radiograph of the acoustic field.^{[citation needed]}