Diagnostics is among the current hot jobs in the Army Medical Corps, and it includes different types of radiologists, or physicians who have specialized training in obtaining and interpreting medical images.
On the other hand, a nuclear medicine officer works with radioactive materials, called radiopharmaceuticals. Those materials are introduced to the body, then this radiologist uses cameras and computers to detect and map the radioactive drug in a patient's body to create diagnostic images.
Nuclear diagnostics is used for examining organs and regions within organs that can't be seen using common diagnostics, such as X-rays. Nuclear diagnostics can be used for checking for injuries, but it's especially useful for finding tumors and other abnormalities.