Time-of-Flight PET/CT Imaging of Ga-68-Dotatate: Normal Pattern, SUV Quantification, and Differences from Non-Time-of-Flight Imaging.

Purpose The biodistribution of gallium-68-dotatate (Ga-68-dotatate) and standardized uptake values (SUVs) using non-time-of-flight (TOF) positron emission tomography/computed tomography (PET/CT) cameras is well established. However, with the eventual retirement of older PET cameras and their replacement with newer, highly sensitive TOF PET/CT cameras, where SUV max measurements are reportedly higher, updated knowledge of normal SUV max range is needed and, to our knowledge, not previously reported. Our objectives are as follows: To establish normal Ga-68-dotatate TOF SUV max database for common structures and to aid the visual detection of abnormalities objectively. To compare SUV max values using the TOF and non-TOF algorithms. Methods Fifty consecutive patients referred routinely to our nuclear medicine service (20 men, 30 women; median age 55 years) with presumed neuroendocrine tumors underwent Ga-68-dotatate scans on a PET-CT camera having capability of reconstructing both TOF/non-TOF images. Region of interests (ROIs) were drawn around 24 normal structures as well as the primary lesion with abnormal radiotracer uptake and SUV max was measured. The same ROI was analyzed using both algorithms simultaneously and both TOF and non-TOF SUV max values were compared. Results Twelve hundred ROIs were evaluated. Non-TOF Ga-68-dotatate uptake in normal structures was in alignment with previously published studies. As compared to non-TOF, TOF images had better target to background ratios visually. TOF SUV max was higher for all structures except for lung and brain. TOF SUV max was more than double in adrenals/uncinate process of the pancreas; approximately 1.8 times in abnormal lesions, lymph nodes, pineal gland; and greater than 1.5 times in thyroid, breast, and pancreatic head. Conclusion Normal database of Ga-68-dotatate TOF SUV max is provided for common structures to aid visual detection of abnormalities objectively. Overall, TOF SUV max measures higher in identical ROIs, with abnormal lesions measuring approximately 1.8 times higher versus non-TOF technology. These findings need to be taken in consideration when comparing patient scans imaged on different PET/CT technologies.

The effect of body mass index on high versus low administered activity protocol myocardial perfusion imaging scan time and effective dose using a cadmium zinc telluride camera in clinical practice.

Cadmium Zinc Telluride (CZT) crystal-based myocardial perfusion imaging (MPI) cameras have increased count sensitivity compared to Anger cameras and can be used to lower either the injected activity or the image acquisition time. Institutions adopting CZT cameras need to decide whether to lower the injected activity or imaging time or attempt to lower both with a compromise. The aim of our study was to compare the scan time required to obtain similar count images using high activity protocol (HAP) versus low activity protocol (LAP) stratified by body mass index (BMI) and assess the impact on effective dose and our clinic workflow. Using a CZT camera, a cohort of 100 consecutive clinical patients imaged with LAP rest-stress MPI with approximately 185 MBq and 555 MBq activity was retrospectively compared to a similar cohort of 100 consecutive clinical patients imaged with HAP rest-stress MPI using approximately 370 MBq and 1110 MBq. Administered activity and BMI both had a statistically significant effect on scan time and radiation effective dose. LAP scans took an average of 9 min longer than HAP scans overall, P < 0.0001 and larger BMIs took longer than smaller BMIs, P < 0.0001. In addition, scan times were longer in men than women, P = 0.007. Effective dose was inversely proportional to BMI with an overall decrease of approximately 50% comparing LAP to HAP. For the same CZT camera, the LAP increased scan time while lowering the radiation effective dose when compared to HAP. The increase in scan time increased proportionally to BMI. The effective dose was inversely proportional to BMI. This increase in time did not have a significant impact on our local workflow, but its implications should be considered in the setting of LAP implementation, especially in obese or high patient volume practices.

Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects.

A new era of precision diagnostics and therapy for patients with neuroendocrine neoplasms began with the approval of somatostatin receptor (SSTR) radiopharmaceuticals for PET imaging followed by peptide receptor radionuclide therapy (PRRT). With the transition from SSTR-based γ-scintigraphy to PET, the higher sensitivity of the latter raised questions regarding the direct application of the planar scintigraphy-based Krenning score for PRRT eligibility. Also, to date, the role of SSTR PET in response assessment and predicting outcome remains under evaluation. In this comprehensive review article, we discuss the current role of SSTR PET in all aspects of neuroendocrine neoplasms, including its relation to conventional imaging, selection of patients for PRRT, and the current understanding of SSTR PET-based response assessment. We also provide a standardized reporting template for SSTR PET with a brief discussion.

Dynamic Renal Ptosis Demonstrated on 18F-FDG PET/CT.

Renal ptosis, otherwise known as nephroptosis or "floating kidney," is a condition of abnormal descent of the kidney, often asymptomatic with controversy over its clinical and therapeutic significance. The aberrant location of renal and renal collecting system activity associated with this condition may serve as a diagnostic pitfall in PET/CT interpretation. We report a case of dynamic renal ptosis demonstrated on F-FDG PET/CT, identified as right kidney migration from an ectopic location on attenuation correction CT images, obtained immediately after upright positioning, to the right renal fossa on subsequent PET images, obtained after approximately 10 min of supine positioning.

Initial Experience in the Use of Technetium-99 Metastable Hydroxymethylene Diphosphonate as an Alternative Ventilation Agent During Periods of Interim Shortage.

Sporadic supply interruptions of select radiopharmaceuticals on the global market require consideration of alternative agents to support continuity of essential nuclear medicine examinations. During an acute shortage of Xenon-133 and technetium-99 metastable (Tc-99m) diethylene-triamine-pentaacetate (DTPA), our institution used aerosolized Tc-99m hydroxymethylene diphosphonate (HDP), a radiopharmaceutical traditionally used in bone scintigraphy, in lieu of traditional ventilation agents, for two cases of suspected pulmonary embolism. Similar to Tc-99m-DTPA, Tc-99m-HDP was readily available and easily compounded in our pharmacy, and tolerated well by patients. Identical delivery equipment was used for administration of Tc-99m-HDP as that used in Tc-99m-DTPA, and thus, there was no requirement for a negative pressure room. Similar to Tc-99m-DTPA and unlike Xenon-133, Tc-99m-HDP allowed direct comparison of all 8 ventilation-perfusion images. In addition, the cost per dose of Tc-99m-HDP proved to be less than Tc-99m-DTPA. Despite these favorable characteristics of Tc-99m-HDP, our experience identified an important challenge in obtaining an optimal flux override ratio of > 3 in a reasonable time frame while obtaining ventilation and perfusion images sequentially despite reversing the imaging order in an attempt to overcome this limitation. Although our experience with Tc-99m-HDP in these two cases was favorable, more clinical experience and investigation are warranted before Tc-99m-HDP can be incorporated as a standard alternative ventilation agent.