Faculty Bibliography

Background: Occasionally, blood samples may be required from thyroid cancer patients after they have been given the therapy dose of (131)I, as part of necessary medical management of comorbidities. Thus, in the days after (131)I administration, medical health professionals may be involved in the withdrawal, handling, and manipulation of radioactive blood samples. The purpose of this study was to quantify the amount of radioactivity in blood samples taken from thyroidectomized thyroid carcinoma patients after the administration of therapeutic activities of (131)I. Methods: For dosimetry purposes, serial blood sampling is performed on thyroidectomized thyroid carcinoma patients prior to therapy with (131)I. The quantities of radioactive material present in these blood samples were expressed as a percentage of the administered activity and then extrapolated to the high levels of (131)I used in therapy for 377 patients in this study. The corresponding radiation exposure rate from the blood samples was then calculated to determine what radiation protection methods were required for staff handling these samples. Results: The average amount of radioactivity in a 1 mL blood sample at 1 hour postadministration of 5.5 GBq (150 mCi) of (131)I was 0.2 +/- 0.15 MBq (5.4 +/- 4.0 muCi). This corresponds to an exposure rate of 1.23 muSv/h (0.123 mrem/h) at 10 cm from the sample. For samples obtained beyond 24 hours after a therapeutic administration of 5.55 GBq (150 mCi), the exposure levels are approximately equal to background radiation. Conclusion: The data in this study indicate that the radiation exposure from blood samples withdrawn from thyroidectomized thyroid cancer patients is low. However, to ensure that staff members are exposed to minimal levels of radiation, it is imperative that staff members who are involved in withdrawing, handling, or manipulating radioactive blood samples adhere to the recommended radiation safety practices

PURPOSE: To assess the accuracy of glomerular filtration rate (GFR) measurements obtained with low-contrast agent dose dynamic contrast material-enhanced magnetic resonance (MR) renography in patients with liver cirrhosis who underwent routine liver MR imaging, with urinary clearance of technetium 99m ((99m)Tc) pentetic acid (DTPA) as the reference standard. MATERIALS AND METHODS: This HIPAA-compliant study was institutional review board approved. Written informed patient consent was obtained. Twenty patients with cirrhosis (14 men, six women; age range, 41-70 years; mean age, 54.6 years) who were scheduled for routine 1.5-T liver MR examinations to screen for hepatocellular carcinoma during a 6-month period were prospectively included. Five-minute MR renography with a 3-mL dose of gadoteridol was performed instead of a routine test-dose timing examination. The GFR was estimated at MR imaging with use of two kinetic models. In one model, only the signal intensities in the aorta and kidney parenchyma were considered, and in the other, renal cortical and medullary signal intensities were treated separately. The GFR was also calculated by using serum creatinine levels according to the Cockcroft-Gault and modification of diet in renal disease (MDRD) formulas. All patients underwent a (99m)Tc-DTPA urinary clearance examination on the same day to obtain a reference GFR measurement. The accuracies of all MR- and creatinine-based GFR estimations were compared by using Wilcoxon signed rank tests. RESULTS: The mean reference GFR, based on (99m)Tc-DTPA clearance, was 74.9 mL/min/1.73 m(2) +/- 27.7 (standard deviation) (range, 10.3-120.7 mL/min/1.73 m(2)). With both kinetic models, 95% of MR-based GFRs were within 30% of the reference values, whereas only 40% and 60% of Cockcroft-Gault- and MDRD-based GFRs, respectively, were within this range. MR-based GFR estimates were significantly more accurate than creatinine level-based estimates (P < .001). CONCLUSION: GFR assessment with MR imaging, which outperformed the Cockcroft-Gault and MDRD formulas, adds less than 10 minutes of table time to a clinically indicated liver MR examination without ionizing radiation. Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1

An 81-year-old woman with renal cell carcinoma (RCC) underwent F-18 FDG PET/CT for staging, which demonstrated intense uptake in a dilated azygos vein, in the inferior vena cava (IVC), and in the known large left RCC. Contrast-enhanced CT of the chest and abdomen obtained in the days following confirmed the presence of tumor thrombus in the dilated azygos system, IVC, and the contiguous left renal vein. This case serves as a reminder that special attention should always be paid to the renal vein, IVC, and adjoining venous drainage pathways for abnormal FDG activity while imaging RCC, as the diagnosis of venous tumor thrombus has important clinical ramifications.

We present the PET/CT findings of hemostatic absorbable gelatin (Gelfoam) in a 41-year-old woman who had hysterectomy and bilateral oophorectomy. CT showed a very low attenuation lesion (-232 HU) in the surgical bed, but PET showed no significant activity.

We present the case of a 61-year-old man who underwent I-123 metaiodobenzylguanidine (MIBG) scintigraphy based on clinical suspicion of pheochromocytoma. The study was nondiagnostic secondary to diffuse muscle uptake. On review of his medications, the patient was found to be taking mirtazapine, a tetracyclic antidepressant (Remeron). We hypothesize that the MIBG biodistribution was altered by mirtazapine-mediated blockade of the presynaptic alpha-2 receptor. To our knowledge, tetracyclic antidepressants have not been previously reported to cause altered biodistribution on I-123 MIBG scans.