Comparison of labeled MIBG and somatostatin analogs in imaging neuroendocrine tumors.

In 10 patients with histologically proven neuroendocrine tumors (4 carcinoids, 4 pheochromocytomas, 1 medullary thyroid cancer and 1 Merkel tumor) the results of radiolabeled metaiodobenzylguanidine (MIBG) and somatostatin analogs were compared. A total of 24 tumor lesions was detected on standard imaging studies. MIBG scintigraphy correctly localized 12 (50%) of these lesions which were observed in 5 patients (4 with pheochromocytoma and 1 with carcinoid tumor). Scintigraphy using labeled somatostatin analogs correctly localized 21 (87%) lesions which occurred in 8 patients (4 with carcinoid, 2 with pheochromocytoma, 1 with medullary thyroid cancer and 1 with Merkel tumor). Concordant scintigraphic results were obtained in 1 patient with carcinoid and 2 with pheochromocytoma. In conclusion, although this series was limited, our results suggest that MIBG is more accurate than somatostatin analogs in imaging pheochromocytoma. Conversely, somatostatin analogs are more accurate than MIBG in detecting other neuroendocrine tumors such as carcinoids.

Detecting deep venous thrombosis with technetium-99m-labeled synthetic peptide P280.

UNLABELLED: Scintigraphy, using small, thrombus-avid, synthetic peptides labeled with gamma-emitting nuclides is an innovative approach to the noninvasive detection of acute deep venous thrombosis (DVT). The goal of this study was to evaluate clinically 99mTc-P280 for imaging DVT. The peptide P280 is a 26 amino acid dimer that binds with high affinity to the GPIIb/IIIa receptor expressed on activated platelets and can be labeled with 99mTc. METHODS: Scintigraphy with 99mTc-P280 (10-22 mCi) was performed in nine patients with clinical suspicion and diagnostic evidence of DVT. Planar and tomographic images of the legs, abdomen/pelvis, chest and head were obtained immediately, 1, 2, 4 and 24 hr after injection. RESULTS: No adverse effects were noted after 99mTc-P280 administration in any patient. Positive visualization of thrombi occurred in eight of nine cases with confirmed DVT within 1 hr of tracer injection. The majority of the patients had recent onset of DVT symptoms (less than 3 wk), while the only negative case was diagnosed 42 days earlier and was likely related to an accident 7 mo earlier. Thrombi-to-background ratios were essentially constant over the study. Technetium-99m-P280 accumulation was also discernible in two patients with pulmonary embolism, while in a third patient the radiotracer concentrated in a cerebellar hemangioblastoma. CONCLUSION: These human studies indicate that 99mTc-P280 is a potentially safe and sensitive procedure for diagnosing DVT and pulmonary embolism. It also may have substantial utility in monitoring active venous thrombosis.