Nuclear imaging. 67Gallium, 201thallium, 18F-labeled fluoro-2-deoxy-D-glucose positron emission tomography

67Gallium scan has been used for years in sarcoidosis as a marker of activity, a determiner of the extent and distribution of the disease, a diagnostic support, and an aid in therapeutic management. Because of its limited sensitivity and specificity for sarcoidosis, however, it is currently used mainly to assist in diagnosis in difficult cases, particularly in those with isolated extrathoracic sarcoidosis. The finding of the typical lambda or panda patterns supports the diagnosis and reinforces the indication to perform an appropriate biopsy or Kveim-Siltzbach test. In addition, the detection of clinically silent extrathoracic uptake may provide sites for biopsy. 67Gallium scans' routine use in the follow-up of pulmonary sarcoidosis under treatment has decreased because that is best accomplished by means of serial chest radiographs and PFT. 201Thallium scintigraphy studies the myocardial perfusion and is complementary to echocardiography and 24-hour electrocardiographic monitoring in the assessment of sarcoid cardiac involvement. It typically shows segmental areas of decreased uptake in the ventricular myocardium that disappear or decrease in size during stress or after intravenous administration of dipyridamole. That reverse distribution is not specific for cardiac sarcoidosis, however, because it may also occur in other cardiomyopathies. PET is based on the increase of glucose metabolism in inflamed tissues. It may have great potential to assess sarcoidosis activity, but it is still largely experimental and is not routinely employed.