Faculty Bibliography

INTRODUCTION: Accurate, reproducible acquisition and interpretation of PET-CT scans can be challenging. As part of an annual quality enhancement exercise for Nuclear Medicine laboratories in the US Department of Veterans Affairs (DVA), we employed a chest imaging phantom designed to test integrated PET-CT imaging and interpretative performance. METHODS: In late 2011, a PET-CT chest phantom was imaged by 88 PET/PET-CT scanners. The phantom, developed by the SNM Quality Assurance Committee (QAC) simulated a stage IIIb lung cancer with 2 "malignant" lung nodules and 3 "metastatic" lymph nodes. Data collection included DICOM images, quality control information, scanner type, imaging parameters (PET and CT) and dose-calibrator information. Interpreting physicians (N=180) reported lesion locations, body-weight-corrected SUVmax and "staged" the simulated lung cancer. We analyzed factors associated with poor performance to assist with remediation of problems identified with image acquisition, processing and interpretation. RESULTS: Based upon QAC-established performance benchmarks 16% (n=14) laboratories failed the exercise. Suboptimal image quality was most often related to short acquisition times (n=6, 6.8%) e.g. 2D mode scanners with imaging time/bed position <3min; suboptimal reconstruction parameters (n=6, 6.8%) e.g. filtered back projection rather than iterative reconstruction; outdated scanners (n=3, 3.4%) e.g. >8y/o without integrated CT; and data entry errors (n=2, 2.3%). SUVmax values varied due to several errors e.g. improper calibration factors or calculation/s. 5% failures (n=4) were related to protocol non-adherence. 33 sites (38%) had not updated dose-calibrators to conform to new NIST standards. 4 sites (5%) used CT tube electrical currents >240 mA for "non-diagnostic" CT. Interpretative performance was negatively impacted by incorrect lesion detection/localization and/or SUV calculations/interpretation. 45 (25%) physicians did not assign Stage IIIb, indicating lack of knowledge of contemporary criteria for lung cancer staging. Other important errors included knowledge of the glucose effect on SUV (n=16, 9% incorrect) and dependence of SUVmean calculations on thresholding techniques (n=38, 21% incorrect). CONCLUSIONS: These "lessons learned" have been used to remediate poor performance and to improve and standardize PET-CT imaging and interpretation in DVA. Our >20yr experience with simulated imaging phantoms continues to demonstrate that strict adherence to standardized NM procedure guidelines is critical for optimal image quality, correct interpretation, longitudinal parametric data comparisons and meaningful participation in clinical trials

Background: Interpreting I-131 whole-body scans (WBSs) after thyroidectomy for thyroid cancer is not simple. There are scans in which interpretation is speculative because of cryptic findings (CF). Complexity is added in scans that are done a week after an ablative or therapeutic dose of I-131 because not only is I-131-labeled thyroxine (T4) distributed throughout the body, but inorganic I-131 that is derived from the de-iodination of T4 may be also detected. We present our observations regarding the analysis of CF on WBS using I-131 single-photon emission computed tomography (SPECT) in fusion with noncontrast computed tomography (CT), referred to here and elsewhere as I-131 SPECT/CT. Methods: Forty of 184 WBSs in 38 thyroidectomized thyroid cancer patients were followed up with I-131 SPECT/CTs. The SPECT/CT images were acquired after a tracer dose of I-131 (n=82) or a week after an ablative or therapeutic dose of I-131 (n=102). Results: Among 184 WBSs, 40 (22%) had CF. In 35 patients the WBS was negative for metastatic disease except for the CF and 5 patients had evidence of thyroid cancer in addition to the CF. There were 49 CF in the planar scans that were localized by SPECT/CT. These were characterized as physiological uptake in gingiva, thymus, gall bladder, menstrual blood, uterine fibroid, recto-sigmoid, colon, and bladder. Also observed was uptake in sites that represented nonthyroidal pathology including dental abscess, hiatal hernia, renal cyst, and struma ovarii. SPECT/CT suggested that 10 of the CF were actually of thyroid origin. In 40 SPECT/CT scans, the images contributed to interpreting the scan. In 15 of 40 patients the SPECT/CT analysis of WBS was performed with tracer doses of I-131 and was important for determining whether to administer ablative I-131 treatment. In another 25 patients, in whom SPECT/CT was performed after ablative or therapeutic doses of 131-I, information regarding the characterization of CF by SPECT/CT was useful in determining if thyroid cancer metastases or thyroid remnants were present. Conclusions: I-131 SPECT/CT is a useful tool to characterize atypical or CF on WBS by differentiating thyroid remnant or cancer from physiologic activity or nonthyroid pathology. In the past, uptake on a WBS that was not explicable as physiologic activity was identified as putative or possible thyroid cancer and generally was treated with I-131. Now, by identifying activity in some possible cancer sites as not thyroid cancer, SPECT/CT can reduce inappropriate treatment with I-131. SPECT/CT of WBS performed after ablative doses of 131-I is useful in determining the nature of CF and therefore likely providing prognostic information

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