Somatostatin Receptor-PET/CT/MRI of Head and Neck Neuroendocrine Tumors.

BACKGROUND AND PURPOSE: Due to its high sensitivity, somatostatin receptor-PET may detect smaller lesions and more extensive disease than contrast-enhanced MR imaging, while the superior spatial resolution of MR imaging enables lesions to be accurately localized. We compared results of somatostatin receptor-PET/MRI with those of MR imaging alone and assessed the added value of vertex-to-thigh imaging for head and neck neuroendocrine tumors. MATERIALS AND METHODS: Somatostatin receptor-PET/CT was acquired as limited brain or head and neck imaging, with optional vertex-to-thigh imaging, following administration of 64CU/68GA DOTATATE. Somatostatin receptor-PET was fused with separately acquired contrast-enhanced MR imaging. DOTATATE activity was classified as comparable, more extensive, and/or showing additional lesions compared with MR imaging. Vertex-to-thigh findings were classified as positive or negative for metastatic disease or incidental. RESULTS: Thirty patients (with 13 meningiomas, 11 paragangliomas, 1 metastatic papillary thyroid carcinoma, 1 middle ear neuroendocrine adenoma, 1 external auditory canal mass, 1 pituitary carcinoma, 1 olfactory neuroblastoma, 1 orbital mass) were imaged. Five had no evidence of somatostatin receptor-positive lesions and were excluded. In 11/25, somatostatin receptor-PET/MRI and MR imaging were comparable. In 7/25, somatostatin receptor-PET/MRI showed more extensive disease, while in 9/25, somatostatin receptor-PET/MRI identified additional lesions. On vertex-to-thigh imaging, 1 of 17 patients was positive for metastatic disease, 8 of 17 were negative, and 8 of 17 demonstrated incidental findings. CONCLUSIONS: Somatostatin receptor-PET detected additional lesions and more extensive disease than contrast-enhanced MR imaging alone, while vertex-to-thigh imaging showed a low incidence of metastatic disease. Somatostatin receptor-PET/MRI enabled superior anatomic delineation of tumor burden, while any discrepancies were readily addressed. Somatostatin receptor-PET/MRI has the potential to play an important role in presurgical and radiation therapy planning of head and neck neuroendocrine tumors.

Imaging of infection and inflammation with 18F-FDG-labeled leukocytes.

Conventional scintigraphic imaging with (67)Ga citrate and in vitro labeled leukocytes is routinely used to evaluate infectious and inflammatory conditions. Recent studies suggest that positron emission tomography (PET) with [(18)F]fluorodeoxyglucose (FDG) also may be useful in this setting. Both (67)Ga citrate and [(18)F]FDG are highly sensitive tracers, but their specificity for detecting infection is lower than that of in vitro labeled leukocytes, which is the radionuclide gold standard for imaging most infections. PET has several advantages over conventional scintigraphic techniques, including higher spatial resolution and faster imaging times. In vitro [(18)F]FDG labeled leukocytes represent an initial attempt to develop an infection-specific, positron-emitting tracer. The experience to date with PET imaging of [(18)F]FDG labeled leukocytes is reviewed in this article.

[Correlation of hematologic parameters with bone marrow and spleen uptake in FDG PET]. / Correlación de los parámetros hematológicos con la captación de FDG en médula ósea y bazo en la PET.

OBJECTIVE: To assess the relationship between various hematologic parameters and bone marrow (BM) and splenic uptake of FDG in PET imaging. MATERIAL AND METHODS: 29 patients with Hodgkin's disease (HD) referred for baseline FDG PET imaging before treatment and without evidence of bone marrow (BM) involvement were included in the study. Splenic uptake also was analyzed in 18 patients without splenic involvement. BM and splenic activity were visually graded on a 3 point scale. Activity pattern was classified as homogeneous or heterogeneous. Semi-quantitative analysis was also performed by drawing regions of interest (ROI) over the spine and spleen. ROIs also were drawn over right lung and liver. FDG uptake ratios for the spine and spleen in comparison with the lung and liver were generated. Visual scoring of marrow and splenic uptake, and the various ratios were correlated with hemoglobin (Hb), white blood cell (WBC), and platelet counts, and correlation coefficients were calculated. RESULTS: In 27/29 patients (93 %) BM and in 18/18 patients (100 %) spleen uptake was diffuse. There was a direct correlation between BM and spleen uptake of FDG with increasing WBC, which was stronger than the inverse correlation seen with Hb (the lower the Hb the greater the uptake). Correlation with platelet counts was weaker. CONCLUSION: There is a correlation between hematologic parameters such as Hb, WBC and platelet counts and the uptake of FDG in BM and spleen in PET imaging. Knowledge of this correlation should help to better interpret and understand PET imaging.

Thyroid uptake of liquid versus capsule 131I tracers in hyperthyroid patients treated with liquid 131I.

The amount of 131I used to treat hyperthyroid patients is based in part on the 24-hour thyroid uptake of a diagnostic amount of radioiodine (tracer). We compared the 24-hour uptake of an 131I tracer administered in liquid or capsule form to the 24-hour uptake of 131I therapy administered as liquid. Sixty-five hyperthyroid patients with Graves' disease were evaluated and subsequently treated with radioiodine. The liquid group (45 patients) received a liquid 131I tracer (1.85 MBq [0.05 mCi]) and the capsule group (20 patients) received a capsule 131I tracer (1.63 MBq [0.044 mCi]). Probe calibration factors were the same for the liquid and capsule 131I standards. All patients received therapeutic amounts of 131I [114.7-1106.3 MBq [3.1-29.9 mCi]) in liquid form. Therapy uptakes were obtained using the same collimated uptake probe modified with a calibrated lead shield to attenuate the high photon flux. The mean therapeutic uptake was the same for both groups (58%). The mean diagnostic uptake for the capsule group, however, was less than the mean diagnostic uptake for the liquid group (44% vs. 63%). The mean diagnostic uptake for the capsule group was significantly lower than the mean therapeutic uptake for this group (44% vs. 58%), whereas the mean diagnostic and therapeutic uptakes were similar for the group receiving a liquid tracer (63% vs. 58%). In conclusion, diagnostic uptakes performed with a liquid tracer more accurately predicted liquid therapy uptakes than diagnostic uptakes performed with a capsule tracer. This raises concern about the bioavailability of 131I in capsule form and has implications for determining the amount of 131I to administer for therapy. Patients whose 131I therapy was based on the uptake of a capsule tracer received a higher than intended amount of radiation to the thyroid gland.