Thyroid Remnant Estimation by Diagnostic Dose (131)I Scintigraphy or (99m)TcO4(-) Scintigraphy after Thyroidectomy: A Comparison with Therapeutic Dose (131)I Imaging.

In this clinical study, we have compared routine diagnostic dose (131)I scan and (99m)TcO4(-) thyroid scintigraphy with therapeutic dose (131)I imaging for accurate thyroid remnant estimation after total thyroidectomy. We conducted a retrospective review of the patients undergoing total thyroidectomy for differentiated thyroid carcinoma (DTC) and subsequently receiving radioactive iodine (RAI) treatment to ablate remnant thyroid tissue. All patients had therapeutic dose RAI whole body scan, which was compared with that of diagnostic dose RAI, (99m)TcO4(-) thyroid scan, and ultrasound examination. We concluded that therapeutic dose RAI scan reveals some extent thyroid remnant in all DTC patients following total thyroidectomy. Diagnostic RAI scan is much superior to ultrasound and (99m)TcO4(-) thyroid scan for the postoperative estimation of thyroid remnant. Ultrasound and (99m)TcO4(-) thyroid scan provide little information for thyroid remnant estimation and, therefore, would not replace diagnostic RAI scan.