Nuclear medicine tests tend to take longer than other imaging modalities.  There are two big reasons for this.  To minimize radiation exposure to your patient, we use a small amount of the radioactive tracer.  This means that we have to take longer pictures to see it well.  The other reason is that we are often watching organ systems perform a function.  While we would like for this to happen instantaneously, it can often take an hour or more for the body to do the things needed for the test.  Some tests - like a GI Bleed - may even require your patient to come back later to see if things changed overnight.