I don’t believe it’s possible to diagnose something on a radiograph that has no radiographically evident findings. No do I believe we can be reasonably held to the standard of seeing something that cannot be seen. 

It’s doubtful this wording would be an effective medicolegal hedge. If you say “not radiographically evident”, but 100 other people see a pulmonary nodule, then it is radiographically evident regardless of your statement to the contrary. Would be in no worse a defense position saying “No cardiopulmonary disease”  or “Normal study” and missing the same nodule.