The concept of a modular imaging system with interchangeable components will be presented. The modular concept provides greater flexibility in integration of custom-designed elements of the system with standard commercially available units deployed by operators. The ultrasonic techniques have been developed to satisfy flaw detection and imaging criteria as well as ultrasonic equipment capabilities. Application of the modular imaging system to characterize internal cracks in multilayered airplane structures and fracture critical components of steel bridges will be discussed.