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Objective: Patients with thyroid cancer may require detailed anatomic imaging before ^sup 131^I therapy. Imaging by contrastenhanced CT is contraindicated because it may result in saturation of tissues with iodine, decreasing the avidity of thyroid or thyroid cancer cells to subsequent radioiodine for extended intervals. Gadolinium-enhanced MRI offers an alternative to CT for detailed anatomic imaging. However, it is not known whether gadolinium contrast affects uptake of iodine by the thyroid gland since lanthanides affect ion transport in a variety of ways. The objective of this project was to determine whether the gadolinium MRI contrast injection alters thyroid uptake of radioiodine.
Methods: Radioiodine uptake by the thyroid gland was measured at 6 h and 24 h after the oral administration of 100 (mu)Ci ^sup 123^I-Na-I. Three to seven days later, a standard dose (20 mL) of Magnevist (gadolinium DTPA) was administered intravenously. Another capsule of 100 (mu)Ci ^sup 123^I Na-I immediately was given orally, and 6-h and 24-h radioiodine uptake by the thyroid gland was again measured and compared to baseline values.
Results: There was no statistically significant difference in uptake of radioiodine uptake by the thyroid gland between baseline values and those acquired immediately after the administration of Magnevist.
Conclusion: Contrast-enhanced MRI may be safely performed before contemplated determinations of thyroid uptake of radioiodine, ^sup 131^I therapy for hyperthyroidism, and postsurgical ^sup 131^I imaging and therapy for well-differentiated thyroid cancer.
Key Words: radioiodine uptake; thyroid; gadolinium contrast
J Nucl Med Technol 2000, 28.41-44
Well-differentiated thyroid carcinoma can be highly treatable, with long-term survival rates well in excess of 90%. Prognosis depends on patient age, gender, histology, stage of disease, and appropriate surgical and medical management (1). The classic therapeutic triad for managing well-differentiated thyroid cancer consists of surgical removal of the thyroid, ablation of residual thyroid tissue with ^sup 131^I, and subsequent long-term suppression of TSH levels with exogenous thyroxine.
Patients with well-differentiated thyroid cancer often require detailed anatomic imaging for surgery planning, assessment of recurrence, and definition of the spatial relationship of tumor-to-- critical structures. Imaging may be required in the weeks before contemplated ^sup 131^I therapy. Imaging by contrast-enhanced CT is contraindicated in these situations because it may result in saturation of tissues with iodine, thereby decreasing the avidity of...