One of the causes of false positivity in I-131 whole-body scans is contamination with body secretions and awareness of the possibility of contamination would be obligatory in reporting whole-body I-131 scans.
Radioiodine accumulation because of local contamination reported in the literature includes sites such as hair, skin, and clothes. The aim of this study was to provide detailed information and case samples of radioiodine contamination artifacts and non-physiological, non-metastatic extra-thyroidal I-131 accumulation in whole-body I-131 imaging.
Thyroxin therapy was stopped for four weeks to obtain a serum TSH level above 30 µ-IU/mL. As a matter of routine, we advised patients to adhere to a low iodine diet for ten days prior to radioiodine scanning. The low iodine diet was advised to be continued 24 hours after the radioiodine administration too. We documented negative serum pregnancy test before administration of radioiodine in all women of child bearing age. Diagnostic whole-body scans were performed 48 hours after the administration of 185 MBq I-131 and 2 to 10 days after the administration of therapeutic dose of radioiodine. Radioiodine scans were performed with a dual-head gamma camera equipped with high energy collimators (Siemens, E-cam, IL, USA). Both anterior and posterior whole-body scans and spot views of neck and chest were performed, as routine. Delayed scans were obtained if necessary.
2.2. Case 1
A 57-year-old women underwent total thyroidectomy and radioiodine ablation therapy two years ago. Pathology report demonstrated widely invasive follicular thyroid carcinoma. Whole-body scan findings at day 5 after the administration of 100 mCi radioiodine therapy demonstrated intense accumulation of radioiodine in thyroid bed. Additionally, bilateral physiological breast iodine uptake (black arrows in
Figure 1 A) and colon activity (white arrow in Figure 1 A) were seen. A diagnostic scan was performed after withholding thyroxin therapy for four weeks on follow-up two years after the therapy. Her serum TSH and Tg levels were 115 µ-IU/mL and > 0.2 ng/mL, respectively when the diagnostic scan was acquired. The diagnostic whole-body scan was performed 48 hours after administration of 185 MBq I-131 and showed accumulation of radioiodine in her left humerus mimicking metastatic disease ( Figure 2 A and 2 B). There was no evidence of metastatic disease after 72 hours ( Figure 2 C and 2 D).
Figure 1. Anterior and Posterior Whole-body Scan Images 5 Days after Therapy Demonstrating Intense Accumulation of Radioiodine at Thyroid Bed with Physiological Bilateral Breast and Colon Activity
Teaching point: Physiological bilateral breast and colon activity may be seen in radioiodine scan.
Figure 2. Anterior and Posterior Whole-body Scan Images on Follow-up Scan After Two Years of I-131 Therapy
A and B show intense accumulation of I-131 in left humerus mimicking metastatic disease. There was no uptake in thyroid bed demonstrating successful ablation of the remnant. C, Anterior and D, Posterior show that whole-body scan images were normal after having a bath and removing head scarf. There was physiological activity in the bowel and stomach in both scans.
2.3. Case 2
The patient was a 74-year-old man on follow-up with papillary thyroid cancer for 11 years. A diagnostic radioiodine scan was performed after withholding thyroxin therapy for four weeks. His serum TSH and Tg levels were 100 µ-IU/mL and < 0.1 ng/mL, respectively when the diagnostic scan was acquired. The diagnostic whole-body scan was acquired 48 hours after administration of 185 MBq I-131 and showed accumulation of radioiodine in his right shoulder mimicking metastatic disease (white arrows in
Figures 3A and 3C) and intense bowel activity (black arrows in Figures 3A and 3B). There was no evidence of metastatic disease after self-cleaning after 72 hours (white arrow in Figure 3 D). Although radioiodine uptake due to contamination is usually outside the body contours, superposition with body structures may lead to misinterpretation. Radioiodine scans should be interpreted carefully. Delayed images after self-cleaning and changing clothes are extremely useful.
Figure 3. Anterior and Posterior Whole-body Scan Images on Follow-up Scan Eleven Years After the Diagnosis
2.4. Case 3
A 48-year-old woman was referred to our clinic for follow-up of her papillary thyroid cancer. Diagnostic radioiodine scan was performed after withholding thyroxin therapy with a serum TSH level of > 150 µ-IU/mL and serum Tg level of < 0.2 ng/mL and demonstrated a focal accumulation of radioiodine in her right maxillary region belonged to a dental inflamation and physiological nasal radioiodine activity (
Figure 4. Anterior Neck Spot View
Uptake in thyroid bed is demonstrated with white arrows. Additionally, focal accumulation of radioiodine is seen in right maxillary region (black arrow) that belonged to a dental inflamation. See physiological nasal activity.
2.5. Case 4
A 66-year-old woman was referred to our clinic for follow-up of her papillary thyroid cancer. Diagnostic radioiodine scan was performed after withholding thyroxin therapy with a serum TSH level of > 30 µ-IU/mL and serum Tg level of < 0.2 ng/mL and demonstrated a focal accumulation of radioiodine belonged to oesophageal activity (
Figure 5A). After drinking water there was not any activity ( Figure 5B).
Figure 5. Anterior Neck Spot View
A, Uptake inferior to left thyroid bed that belonged to oesophageal activity is shown with white arrows. B, Uptake is cleaned with a drink of water.
Teaching point: Although oesophageal activity usually appears as a linear midline region of increased I-131 uptake that can be reduced by drinking fluids, focal radioiodine accumulation in neck should be kept in mind to be a physiological oesophageal activity. Contamination artifacts may always occur as a result of radioactive sweat, saliva, or urine. Contaminations can easily be prevented by taking simple precautions.
2.6. Case 5
The patient was a 64-year-old woman whom was followed-up because of papillary thyroid cancer and endometrial carcinoma. She had undergone lympadenectomy. After withholding thyroxin therapy, her serum TSH and Tg levels were 75 µIU/mL < 0.2 ng/mL, respectively. There was no pathological radioiodine uptake in whole-body scan images except for physiological uptake in bowel and stomach. There was diffuse uptake in left lump because of lymphedema.
2.7. Case 6
A 15-year-old girl was referred to our clinic for ablation therapy of follicular thyroid carcinoma after total thyroidectomy. While her serum TSH and Tg levels were 229 µIU/mL and 0.2 ng/mL, respectively after radioiodine therapy, radioiodine scan was performed. There was a focal accumulation of radioiodine in thyroid bed. Additionally, less intense accumulations of radioiodine were detected in left maxillary and upper mediastinal regions.