Abstract: A schlieren imaging system provides quantitative images suitable for testing medical equipment. One embodiment includes precision optics which form an image of a volume of a medium through which an ultrasonic acoustic wave propagates. A spatial filter passes diffracted light but blocks other light. A camera forms an image of the medium from the diffracted light so that regions of the medium which diffract light have higher light intensity in the image. From image intensities, a processor determines acoustic pressures or intensities, typically as a value indicating an integral of the acoustic pressure or intensity along an optical path through the volume. Integrated pressure is determined from a look-up table which relates predicted light intensity to pressure values which cause the predicted light intensity. The system is calibrated by forming an image of a reference ultrasonic acoustic wave and determining a relation between the image intensities and predicted intensities.