Purpose: To assess the value of extending the routinely used base-of-skull (BOS) to upper-thigh field of view (FOV) to include the head on 18F-FDG PET/CT in cancer patients.Methods: We retrospectively reviewed 1000 consecutive top-of-head to foot PET/CT studies. Abnormalities above BOS were categorized as unsuspected or known and were correlated with pathology, MRI/CT, and clinical follow-up.Results: Of the 1000 patients, 102 (10.2%) had potentially significant findings above BOS. Of these, 70/102 (69%) were known and 32/102 (31%) were unsuspected. Of the patients with unsuspected findings, follow-up data was unavailable in 7/32 (22%) and abnormalities were confirmed in 25/32 (78%). Of the 25 confirmed unsuspected findings, 4/25 (16%) were false positives and 21/25 (84%) were true positives. Of these, 13/21 (62%) were confirmed metastatic, and 8/21 (38%) were benign. Unsuspected finding of brain metastasis changed the management in 11/13 (85%) and staging in 4/13 (31%).Conclusion: Including the head in PET/CT FOV incidentally detected clinically significant findings in 2.1% (21/1000) of patients. The detection of previously unsuspected metastasis had significant impact on patient management and provided more accurate staging.
Spleen shows a high physiological uptake on radionuclide somatostatin receptor (SSTR) imaging studies. Autoradiography and immunohistochemistry studies showed that SSTRs are mainly located in the red pulp of the spleen. In this review article we will summarize the significance of splenic uptake in SSTR imaging studies and will also present high resolution splenic images of Ga-68 DOTANOC PET in which splenic distribution of the radiotracer appears to be correlating with the distribution of red pulp.
Hyperparathyroidism is a condition caused by increased secretion of the parathyroid hormone, which plays an important role in calcium homeostasis. This condition has been diagnosed more frequently recently and can affect multiple organ systems resulting in a variety of signs and symptoms. Hyperparathyroidism can be classified as primary, secondary, or tertiary disease and can result from eutopic or ectopic parathyroid lesions. Parathyroid adenoma is the most common cause of primary hyperparathyroidism, accounting for more than 80% of cases. Parathyroid hyperplasia is the cause in about 20% of patients, while parathyroid carcinoma is rare and accounts for less than 1% of cases. Surgical removal of the abnormal gland(s) is the definite treatment for hyperparathyroidism. Bilateral neck exploration is the classical approach for parathyroidectomy. In recent years, minimally invasive parathyroidectomy is becoming more popular due to the fewer complications and shorter hospital stay. This new approach has placed a greater emphasis on the preoperative localization techniques. Multiple localization techniques have been used, including invasive techniques, anatomical, and scintigraphic imaging modalities. Thallium/pertechnetate subtraction method was introduced in 1980 and was the first method to gain widespread acceptance. It is not widely used now due to the suboptimal characteristics of thallium and the technical difficulties associated with subtraction and registration. The dual-phase method using Tc-99m sestamibi is currently the method of choice for parathyroid localization. It is based on the differential washout rate of sestamibi from the thyroid and abnormal parathyroid glands. The reported sensitivity of this method ranges from 80% to 90%. The addition of single-photon emission computed tomography (SPECT) and more recently SPECT/CT improves the anatomical localization and helps in the differentiation of the parathyroid from the thyroid lesions. Multiple factors can affect the sensitivity of the scan including the lesion size, cellularity, and the presence of P-glycoprotein. Modification of the imaging protocol may help to avoid false positive or false negative results in certain cases. Positron emission tomography has been recently investigated for possible role in parathyroid imaging and showed promising results with 11 C-methionine.
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At a time when reducing the radiation dose to patients and the public has become a major focus, we assessed the radiation exposure rate from patients after an 18 F-FDG PET/CT scan and evaluated different interventions to reduce it. Methods: We enrolled 100 patients, divided into 2 groups. For both groups, the radiation dose rate was measured with an ionization survey meter immediately after the scan. For group 1, the patients then voided and their dose rate was measured again. For group 2, the patients waited 30 min before voiding, and we measured the dose rate before (group 2A) and after (group 2B) they voided. Results: In total, 74 of the 100 patients exceeded the 20 μSv/h (2 mR/h) threshold immediately after the scan. In group 1, the mean dose rate decreased by 20.0% from the postscan measurement, with 12 of 36 remaining at or above 20 μSv/h. In group 2A, the mean dose rate decreased by 23% from the postscan measurement, with 9 of 38 remaining at or above 20 μSv/h. In group 2B, the mean dose rate decreased by 35% from the postscan measurement, with 1 of 38 remaining at 20 μSv/h. Conclusion: Nearly 75% of patients undergoing an 18 F-FDG PET/CT scan exceed 20 μSv/h when leaving the imaging facility. The most effective method to reduce radiation exposure was to have the patient void 30 min after the examination.
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