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When we want to extend the life of an actual infrastructure and improve its serviceability adjusting the change of environmental situation, we need to evaluate its structural integrity quantitatively by using an appropriate inspection procedure on it. It is, therefore, important for a civil engineer to set up an effective inspection procedure to get the quantitative integrity evaluation of an infrastructure. The procedure of inspection for an infrastructure in Japan is divided into two types, that is, a periodical inspection and occasional (eventwise) inspection just after an earthquake. Inspector is chosen to have his experience career as a civil engineer more than 5 years and inspects infrastructures to classify the integrity level by five ranks on the each part of the structure by using the visual inspection according to the inspection manual tentatively provided by the Public Works Research Institute, Ministry of Construction. In the case if an inspector found any important damage or defect by the visual inspection, the precise inspection will be done by using a nondestructive testing to evaluate the size, shape and location of the damage or defect on the infrastructure. And if we could identify the damage or defect with an accurate information, we can evaluate its remaining life time by means of fracture mechanics and fatigue analysis and decide whether the damage or defect will propagate further or not. Thus we can, eventually, evaluate the structural integrity of the infrastructure by using the analysis of quantification theory [3] to classify the structures into four groups of integrity as A (Keep Watching), B (Need Small Repair), C (Need Large Repair) and D (Need Replace or Reconstruction).

When we diagnose the structural integrity of a material in service and evaluate its remaining life time, we need to improve analyzing method to get the accurate information for a internal damage of a material. And by the recent demand for high level quality control of structural joint the accuracy improvement of detected image became essential in nondestructive evaluation (NDE)1. So far several methods like X-ray, EMAT and ultrasonics are used to detect an internal defect and 3D image of a damage is obtained only by CAT scan method of X-ray inspection.

When we diagnose the structural integrity of a steel member in service and evaluate its remaining life time, we need to improve analyzing method to get the accurate information of a internal defect of a member. And by the recent demand for high level quality control of welding of steel joint the accuracy improvement of defect detection in the image display became essential in nondestructive evaluation (NDE)[1][2][3]. So far the defect information obtained by an ultrasonic test is displayed in several ways and A-scan and B-scan displays are commonly used in a field inspection and C-scan display is used in laboratory test of the steel structural member[4][5].