Optimal Imaging Time for Diagnostic I-123 Whole Body Scan in the Follow-up of Patients with Differentiated Thyroid Cancer: Comparison between 6- and 24-Hour Images of the Same Subjects / 핵의학분자영상

PURPOSE: To determine optimal imaging time for diagnostic I-123 whole body scan in the follow-up of patients with differentiated thyroid cancer (DTC), we compared the image quality of 6- and 24-hour images of the same subjects. MATERIALS AND METHODS: Four hundred ninety-eight patients (M:F=55:443, Age 47.6+/-12.9 years) with DTC who had undergone total thyroidectomy and I-131 ablation therapy underwent diagnostic whole body scanning 6 hour and 24 hour after oral ingestion of 185 MBq (5 mCi) of I-123. Serum thyroglobulin measurement and ultrasonography of the neck were performed at the time of imaging. In 40 patients underwent additional I-131 therapy, post-therapy I-131 images were obtained and compared with diagnostic I-123 images. RESULTS: In 440 patients (88.4%), 6- and 24-hour diagnostic I-123 images were concordant, and 58 patients (11.6%) showed discordant findings. Among 58 discordant patients, 31 patients showed abnormal tracer uptake on only 6-hour image, which turned out false-positive findings in all cases. In 12 patients with positive findings on only 24-hour image, remnant thyroid tissue (4 patients) and cervical lymph node metastasis (3 patients) were presented. Among 40 patients underwent additional I-131 therapy, 6-hour and 24-hour images were discordant in 13 patients. All 5 patients with abnormal uptake on only 6-hour image revealed false-positive results, whereas most of 24-hour images were concordant with post-therapy I-131 images. CONCLUSION: I-123 imaging at 24-hour could reduce false-positive findings and improve diagnostic accuracy, compared with 6-hour image in the follow-up of patient with DTC.

False-positive I-131 Scan by Contaminated Muffler in a Patient with Thyroid Carcinoma / 핵의학분자영상

A 39-year-old female patient who had undergone a total thyroidectomy for a papillary thyroid carcinoma underwent a whole body scan with I-131. The I-131 scan was performed 72 hours after administering 185 MBq (5 mCi) of an I-131 solution. The anterior image of the head, neck, and upper chest showed multiple areas of increased uptake in the mediastinal area considering of functional metastasis. However, radioactivity was not evident in the image taken after removing her clothes and muffler. The image obtained after placing the muffler on the pallet showed that the radioactivity was still present. It is well known that artifacts on an I-131 scan can be produced by styling hair sputum, drooling during sleep, chewing gum, and paper or a cloth handkerchief that is contaminated with the radioactive iodine from either perspiration or saliva. This activity might be mistaken for a functional metastasis. Therefore, it is essential that an image be obtained after removing the patient's clothes. In this study, artifacts due to a contaminated muffler on the I-131 scan were found. These mimicked a functional metastasis of the mediastinal area in a patient with a papillary thyroid carcinoma.

Clinical Applications of 18-FDG PET in Recurred Differentiated Thyroid Cancer with Negative 131I Whole Body Scintigraphy: A Comparative Analysis with 99mTc-MIBI Scintigraphy / 대한내분비학회지

BACKGROUND: In patients with differentiated thyroid cancer treated by surgery and radioactive iodine ablation, serum thyroglobulin(Tg) and 131I whole body scan(WBS) are recognized as being the best cooperative indicators for detection of recurrence or metastasis. However, in some cases, 131I WBS shows no specific lesions despite elevated serum Tg. Therefore, 18-Fluorine-fluorodeoxyglucose (FDG) positron emission tomography(PET) has emerged as a useful method for the detection of 131I WBS negative thyroid cancers. The aims of the present study are to evaluate the clinical usefulness of this technique in detection and to compare the results with 99mTc-MIBI scintigraphy(MIBI) in cases of final results being confirmed by histologic diagnosis and other imaging methods. METHODS: We conducted a retrospective analysis amon 131I WBS negative recurred papillary thyroid carcinoma patients(male: female ratio=9:22, median age=42 yr). FDG PET was performed in 28 patients and MIBI 28 patients, 25 of whom were common to both groups. All patients had histologically proven recurrence/metastasis and negative 131I WBS results but persistently elevated serum Tg levels. In each case overall clinical evaluations were performed including histology, cytology, thyroglobulin level, other imaging methods, posttherapy 131I WBS and subsequent clinical course, to allow comparison with the results of FDG PET. RESULTS: In 19 cases of patients with negative 131I WBS, proven recurrence/metastasis lesions were detected in FDG PET. Compared with MIBI, FDG PET was found to be superior in 8 cases(including 2 patients with distant metastases). No FDG-negative/MIBI-positive tumor was observed. One FDG PET negative and MIBI negative case was proven 3 months later to be metastatic cervical lymph nodes, Sensitivities were 94.7% in the FDG PET group and 52.6% in MIBI. Diagnostic accuracy of FDG PET was superior to that of MIBI(93% vs. 62%, respectively, p=0.003). CONCLUSION: Our results confirmed the clinical usefulness of FDG PET for detection of 131I negative differentiated thyroid cancers and suggested the value of FDG PET as an initial diagnostic step, rather than MIBI, in these cases.

Usefulness of Tc-99m MIBI Scan in the Postoperative Follow Up Of Well-Differentiated Thyroid Cancer / 대한핵의학회잡지

To evaluate the clinical utility of Tc-99m MIBI scan in the detection of residual thyroid tissue or metastatic lesion in postoperative thyroid cancer patients, we compared Tc-99m MIBI scan with I-131 diagnostic and therapeutic scan in 30 postoperative well-differentiated thyroid cancer patients. Thyroglobulin levels of both on and off thyroid hormone medication and antithyroglobulin antibody were tested [Tg(on), Tg(off)l Positive rates for I-131 diagnostic and Tc-99m MIBI scan were 81% and 68% respectively. Concordance between I-131 diagnostic and Tc-99m MIBI scan was observed in 15 cases; 12 positive and 3 negative respectively Among the 6 cases with negative I-131 diagnostic scan and positive Tc-99m MIBI scan, 4 were positive in the therapeutic I-131 scan. We concluded that Tc-99m MIBI scan maybe a useful complementary modality to the currently established method of I131 scan and serum thyroglobulin level in the detection of recurrent or metastatic thyroid cancer, especially in the case of negative I-131 diagnostic scan.