Evaluating bonding integrity of piezoceramic transducer

Currently I am working on a Structural Health Monitoring system utilizing piezoceramic transducers. The proof of concepts have worked very well. But we are in the process of working small scale manufacturing. We have observed inconsistency in the electrical response and trying to root cause the issues. In our design the piezoceramic transducer is attached to a host structure with cyanoacrylate adhesive. One of our concerns is the integrity of the adhesive. What are the possible non invasive methods to evaluate the integrity of the bonding?

Note 1: We are looking at X-ray as an option.

Note 2: This questions is related to How to measure electro-mechanical coupling?