The Model 523 and 523A Doppler Cardiac Flow Phantoms are quality assurance tissue mimicking flow phantoms used to evaluate the flow rate, sensitivity, and depth of penetration of doppler ultrasound imaging systems. The phantoms are contained in a protective 1cm Acrylic housing to provide strength and permanence. Contain four flow channels. 2.0, 4.0, 6.0, and 8.0mm (±5%). Also select attenuation of either 0.5 db/cm/mHz or 0.7 db/cm/mHz. Each phantom provided with 2 gallons of fluid (5-micron sand version). The Model 523 differs from the 523A only in the angle of the fixed scanning surface and overall dimensions.