I am a nuclear medicine specialist. In terms of diagnosis of a carcinoid
tumour, pathological examination is the definite test. If you have sample of the tissue then a pathological examination will provide all the details of the nature of disease. Close to pathological examination, an Octreotide
scan is the next best thing. MRI
can detect tumors but octreotide scan goes a step further and charecterizes the lesion with respect to expression of somatostatin receptors which other wise can only be commented on a pathological examination.
There is another type of scanning called the DOTATATE PET scan. This is not approved in US if you are residing there, but the rest of the world has been doing this procedure for more than half a decade now and it produced wonderful results. It is highly sensitive form of octreotide scanning with the advantage of added CT images.
You can try that modality. It also gives information of staging of the disease as well.
Hope this was helpful.