1-23I-MIBG thyroid uptake: Implications for MIBG imaging of the heart.

BACKGROUND: 123I-MIBG has been widely used in patients with heart failure and neurological disorders. The patients are pre-treated with Lugol's oral solution or potassium perchlorate to prevent thyroid uptake of unlabeled 123I to limit the thyroid radiation exposure. However, despite the inhibition of the iodide pump, the thyroid is frequently visualized. The aim of this study was to study the pattern of thyroid uptake. METHODS: We reviewed the 123I-MIBG images of 57 patients studied in three different centers in Italy for cardiac (n = 42) or neurological (n = 15) indications. They were imaged at 15 minutes and 4 hours after injection and in all patients, the thyroid was included in the imaging field of view. In 2 of the 3 centers, the patients were pre-treated with Lugol's oral solution and/or potassium perchlorate (group 1) but in the third center, they were not (group 2). The following imaging parameters were evaluated: heart-to-mediastinum ratio (H/M), thyroid-to-mediastinum ratio (T/M) at 4 hours, and tracer wash out from the heart (HWO) and from the thyroid (TWO). RESULTS: In the cardiac patients, the HWO was 22.98 ± 7.16% and TWO was 11.4 ± 11.86% (P < .0001). The TWO was 12.2 ± 13.1% in group 1 and 10.05 ± 8.97% in group 2 (P = NS). In the neurological patients the HWO was 26 ± 8.1% and the TWO was 20.32 ± 6.41 (P < .05). The difference in TWO was statistically significant (P < .01) between cardiac and neurological patients, whereas the HWO was not. The 4-hour H/M was 1.49 ± 0.23 in cardiac patients vs 1.4 ± 0.39 in neurological patients (P = NS). The 4-hour T/M was 1.33 ± 0.3 in cardiac patients vs 1.15 ± 0.13 in neurological patients (P < 0.05). CONCLUSION: The thyroid visualization in MIBG imaging is likely an expression of thyroid sympathetic innervation. The differences in TWO and T/M ratio in cardiac and neurological patients probably express differences in thyroid dopaminergic receptors. Thus, pre-treatment with potassium perchlorate or Lugol's solution may not be justified in patients undergoing 123I-MIBG imaging in whom the risk of side effects due to pre-treatment could be higher than the risk due to thyroid radiation exposure.

Multicentre study of 18F-FDG-PET/CT prostate incidental uptake.

AIM: The purpose of our study was to establish the prevalence and pathological nature of fluorine-18-fluorodeoxyglucose (18F-FDG) prostate incidental uptake (PIU) among patients studied for non-prostate-malignant purposes in three nuclear medicine centres. METHODS: We retrospectively evaluated 20,422 scans performed on male patients; all patients underwent 18F-FDG-PET/CT for purposes not related to prostate disease. RESULTS: Among 20,422 patients PIU was identified for 280 (1.4 %) with an average age of 70 ± 10.7 years. Sixty-three of the 280 patients with PIU (22.5 %) underwent PSA dosage and biopsy to determine the nature of the incidental uptake. Thirty-five of the 63 (55.5 %) PIU were malignant whereas 28/63 (44.5 %) were benign. The average value of PSA for patients with benign PIU was 3.7 ± 2.8 ng/ml whereas it was 7.8 ± 8.2 ng/ml in patients with malignant PIU; this difference was statistically significant. For malignant lesions, the average lesion-to-liver SUVmax ratio was 2.9 ± 2.5 and the average lesion-to-blood-pool SUVmax ratio was 3.7 ± 2.5. For benign lesions, the average lesion-to-liver SUVmax ratio was 2.5 ± 1.7 and the average lesion-to-blood-pool SUVmax ratio was 3.5 ± 2.4; there was no statistically significant difference between lesion-to-liver and lesion-to-blood-pool SUVmax ratios for benign and malignant lesions. CONCLUSION: Because PIU values are indicative of malignancy for a substantial percentage of patients, further investigation is required.