The defect detection using ultrasonic imaging with frequency-domain SAFT (F-SAFT) is discussed. The F-SAFT provides an accurate and time-efficient algorithm for 3-D reconstruction. F-SAFT allows data processing in the 3-D Fourier space using angular spectrum method. It facilitates synchronization of ultrasonic signals scattered back in the different directions. F-SAFT when combined with ultrasonic imaging is found to be efficient in detecting inclusion in steel slabs.