Somatostatin-receptor scintigraphy in the management of gastroenteropancreatic tumors.

OBJECTIVE: This study evaluates the diagnostic and therapeutic implications of somatostatin-receptor scintigraphy in the management of patients with proven or high clinical suspicion of gastroenteropancreatic endocrine tumors. METHODS: Forty-one patients were studied by planar and tomographic imaging at 4 h and 24 h after 111In-pentetreotide injection. Scintigraphic findings were compared with computed tomography, and in several patients also with ultrasound, angiography, biopsy, and/or surgery, when performed. RESULTS: Among 23 patients with carcinoid tumor, three of nine primary tumors were initially identified by scintigraphy. Unsuspected mesenteric metastases found on scintigraphy in three patients led to octreotide treatment. Scintigraphic detection of multiple metastases in a patient with thyroid metastasis of bronchial carcinoid spared her an unnecessary total thyroidectomy. Among 18 patients with 19 islet-cell tumors, scintigraphy detected three of five insulinomas, whereas computed tomography identified only one. Receptor positivity in an islet-cell tumor (vipoma?) with no metastases on the scan led to surgical removal of the primary tumor. Receptor-positive metastases of gastrinoma (two of three patients), glucagonoma (two of three patients), and parathyroid hormone-related peptide-producing tumor (one patient) led to octreotide treatment. Nonvisualization of metastases of a glucovipoma led to chemotherapy. CONCLUSIONS: Somatostatin-receptor scintigraphy contributes to the management of patients with gastroenteropancreatic tumors in the following ways: 1) localization of a primary occult tumor, allowing surgical removal; 2) staging of the disease for optimal therapy-surgical excision or systemic treatment; and 3) identification of receptor status of the metastases for octreotide treatment or chemotherapy.

Gallbladder visualization with In-111 labeled octreotide.

In-111 DTPA octreotide, a labeled somatostatin analog, was reported to be superior to I-123 octreotide for detection of somatostatin-receptor-bearing tumors because of longer half-life and better labeling characteristics. In addition, renal rather than hepatobiliary clearance decreases intestinal interference and greatly reduces accumulation of the tracer in the gallbladder. Using the In-111 labeled octreotide, the authors noted distinct gallbladder visualization in one patient with an insulinoma who was studied following an overnight fast. In two additional patients scanned in the fasting state gallbladder uptake was also demonstrated. In all 3 patients, this uptake disappeared following a meal. The authors conclude that when using this imaging modality, abdominal scans should not be performed in the fasting state. Furthermore, if significant uptake is demonstrated in the gallbladder area, imaging should be repeated several hours later, following a fatty meal. Both false-positive and false-negative findings of pathologic uptake in this area will thus be avoided.

99mTc-MAG3: dynamic studies in patients with renal disease.

Animal studies have suggested that 99mTc-mercapto-acetylglycyl-glycyl-glycine (99mTc-MAG3) might be suitable for the determination of the renal plasma flow (RPF) because of its high renal clearance. In this study 131I-orthoiodohippurate (131I-OIH) and 99mTc-MAG3 (labeling always greater than 95%) were administered simultaneously in 11 patients (creatinine clearance ranging from 14 to 130 ml/min per 1.73 m2) to measure effective RPF(ERPF) using the standard technique (UV/P). Glomerular filtration rate (GFR; clearance of 125I-thalamate, 125I-OT) was also measured. The mean ratio of 99mTc-MAG3 clearance to 131I-IOH clearance was 0.55 +/- 0.02 (SEM), P less than 0.01, n = 16, and was independent of GFR and ERPF. To study this difference in renal handling of the radiopharmaceuticals, renal extractions by the right kidney were determined in another six patients after a single shot of the agents. Renal extraction of 99mTc-MAG3 was 0.60 +/- 0.03 after 5 min, and 0.41 +/- 0.08 after 30 min. Renal extraction of 131I-OIH amounted to 0.86 +/- 0.04 and 0.77 +/- 0.03, respectively. Using renal extractions of 0.41 and 0.77, respectively, it appeared that calculated renal plasma flows measured simultaneously with 99mTc-MAG3 and 131I-OIH were similar. Protein binding 30 min after the priming dose was 66% for 99mTc-MAG3 and 47% for 123I-OIH. We conclude that in spite of a high renal clearance (ratio to 125I-OT clearance 2.69 +/- 0.27), 99mTc-MAG3 seems unsuitable for an accurate determination of the RPF.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the renal scanning agent N-succinyldesferrioxamine B in dogs.

The mechanism of the excretion of 67 Ga-N-succinyldesferrioxamine B (SDF) was investigated in five healthy dogs. Comparison of the SDF clearance rates for whole blood and plasma as well as SDF renograms with those of 131 I-o-iodohippuric acid (OIH) and 111In-diethylenetriamine-pentaacetic acid (DTPA) revealed that SDF is cleared by glomerular filtration and not by an active tubular transport mechanism.

Gold-195m: a steady-state imaging agent for venography that gives blood velocity measurement.

Gold-195m has found applications in first-pass studies for investigating both right and left ventricular activity as well as lung transit. Owing to its reasonably short half-life of 30 sec we have found it particularly useful for imaging leg veins up to and including the inferior vena cava. Its short half-life prevents recirculation activity from appearing, so continuous perfusion into a superficial foot vein and application of ankle tourniquets yield a steady-state image of the deep veins, with particularly good resolution. Its decay pattern along a vessel is very sensitive to blood velocity, so measurement of activity at various points on a vein in a computer static image can give velocity values that reveal abnormalities due to partial or complete thrombosis. The radiation dosimetry of 195mAu used in this way is lower than contrast and technetium-99m macroaggregated albumin [( 99mTc]MAA) venography, making it particularly useful for investigating deep vein thrombosis (DVT) in pregnancy.