Influence of subcutaneous administration of rapid-acting insulin in the quality of (18)F-FDG PET/CT studies

Clinical scenarios of unusual FDG uptake in muscle

Glucose is essential for muscle function and its uptake is influenced by aerobic conditions, hormonal regulations, and exercise. 18F-Fluorodeoxyglucose (FDG), a glucose analog used in PET/CT scans, can show incidental uptake in muscles, and thus careful interpretation is required to avoid misdiagnosis. Proper patient preparation and understanding of the clinical scenarios affecting FDG uptake are crucial for accurate PET/CT interpretation, thus ensuring precise diagnoses and avoiding unnecessary interventions. This review emphasizes the need to consider patient-specific factors in evaluating incidental FDG uptake in muscle.

Optimal Management of Insulin in Patients Undergoing 18F-Fluorodeoxyglucose Positron Emission Tomography Scans

OBJECTIVE

The management of insulin injections and insulin pumps before 18F-fluorodeoxyglucose-positron emission tomography integrated computerized tomography (FDG-PET/CT) scans is an important area to investigate given the rising rate of diabetes, the significant association between diabetes and cancer, and the complex relationship among glucose, insulin, and FDG tumor uptake. The purpose of this study was to determine the recommendations around subcutaneous insulin administration, insulin pumps, and hybrid closed-loop systems before FDG-PET scans.

METHODS

We examined the websites of 100 hospitals selected from the 2022 US News and World Report top cancer hospitals for specific strategies around diabetes medication management before FDG-PET/CT scans.

RESULTS

Of the 100 hospital websites, 61 had instructions addressing patients with diabetes. Of the 61 hospitals, 47.5% (n = 29) referred patients to their provider for further instructions, 18% (n = 11) referred patients to their own internal radiology department for further instructions, 16.4% (n = 10) had instructions on oral diabetic medications, 23% (n = 14) had instructions on insulin, and 3.3% (n = 2) had instructions on insulin pump management. Most commonly, instructions were to stop insulin 3 to 4 hours before the study and direct patients to their referring provider for more detailed instructions (n = 7).

CONCLUSION

There is a lack of guidance and consensus among US cancer hospitals on managing insulin and continuous subcutaneous insulin infusions before FDG-PET/CT studies and a majority rely on referring providers to advise patients. However, society guidelines offer inconsistent recommendations and little research has been carried out to help guide referring providers. A multidisciplinary panel of specialists could help to guide practitioners on optimal management.

Various Aspects of Fasting on the Biodistribution of Radiopharmaceuticals

It is demonstrated that fasting can alter the biodistribution of radiopharmaceuticals in nuclear medicine. Various studies have highlighted that fasting is interpreted to be easy for physicians during PET study, fasting is one of the most important factors determining the usefulness of this protocol. It is well documented that fasting can suppress normal ¹⁸F-FDG PET uptake during nuclear cardiology. However, there is no consensus about the usefulness of fasting on radiopharmaceuticals, especially on ¹⁸F-FDG in PET imaging, but special attention should be paid to the setting of the fasting duration. Nevertheless, it does seem we still need extensive clinical studies in the future. The present study aims to review the various aspects of fasting, especially metabolic alteration on radiopharmaceutical biodistribution. In this study, we focused more on the effect of fasting on ¹⁸F-FDG biodistribution, which alters its imaging contrast in cardiology and cancer imaging. Therefore, shifting substrate metabolism from glucose to free fatty acids during fasting can be an alternative approach to suppress physiological myocardial uptake.

FDG-PET/CT in intensive care patients with bloodstream infection

Background

2-Deoxy-2-[18F]fluoro-D-glucose (FDG) positron emission tomography (PET)/computed tomography (CT) is an advanced imaging technique that can be used to examine the whole body for an infection focus in a single examination in patients with bloodstream infection (BSI) of unknown origin. However, literature on the use of this technique in intensive care patients is scarce. The purpose of this study was to evaluate the diagnostic yield of FDG-PET/CT in intensive care patients with BSI.

Methods

In this retrospective cohort study, all intensive care patients from our Dutch university medical center who had culture-proven BSI between 2010 and 2020 and underwent FDG-PET/CT to find the focus of infection were included. Diagnostic performance was calculated and logistic regression analysis was performed to evaluate the association between FDG-PET/CT outcome and C-reactive protein level (CRP), leukocyte count, duration of antibiotic treatment, duration of ICU stay, quality of FDG-PET/CT, and dependency on mechanical ventilation. In addition, the impact of FDG-PET/CT on clinical treatment was evaluated.

Results

30 intensive care patients with BSI were included. In 21 patients, an infection focus was found on FDG-PET/CT which led to changes in clinical management in 14 patients. FDG-PET/CT achieved a sensitivity of 90.9% and specificity of 87.5% for identifying the focus of infection. Poor quality of the FDG-PET images significantly decreased the likelihood of finding an infection focus as compared to reasonable or good image quality (OR 0.16, P = 0.034). No other variables were significantly associated with FDG-PET/CT outcome. No adverse events during the FDG-PET/CT procedure were reported.

Conclusion

FDG-PET/CT has a high diagnostic yield for detecting the infection focus in patients with BSI admitted to intensive care. Poor PET image quality was significantly associated with a decreased likelihood of finding the infection focus in patients with BSI. This could be improved by adequate dietary preparation and cessation of intravenous glucose and glucose-regulating drugs. Recent advances in PET/CT technology enable higher image quality with shorter imaging time and may contribute to routinely performing FDG-PET/CT in intensive care patients with BSI of unknown origin.

Quality Assessment in FDG-PET/CT Imaging of Head-and-Neck Cancer: One Home Run Is Better Than Two Doubles

2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) positron emission tomography (PET)/computed tomography (CT) is indicated in head-and-neck cancer for the initial workup when clinically indicated (e. g., large tumors, clinically positive neck, cervical adenopathy from an unknown primary, etc.), for the assessment of treatment response 12 weeks after completion of (chemo)radiotherapy, and during follow-up when there is suspicion of relapse. The successful implementation of FDG-PET/CT in routine clinical practice requires an in-depth understanding of the recent advances in physics and engineering that have significantly improved the imaging capabilities of PET/CT scanners (e.g., digital silicon photomultipliers, point-spread function modeling, and time-of-flight, and Bayesian penalized likelihood reconstruction). Moreover, a coordinated harmonization effort from professional societies (e.g., EANM) and international bodies (e.g., IAEA) has resulted in the creation of quality assurance frameworks (e.g., QUANUM, EARL, GMP) and guidelines that collectively cover the entire spectrum from tracer production, hardware calibration, patient preparation, and scan acquisition, to image interpretation (e.g., PERCIST, Hopkins criteria). The ultimate goal is to standardize the PET/CT technique and to guarantee accurate and reproducible imaging results for every patient. This review summarizes the recent technical breakthroughs in PET/CT scan design and describes the existing quality assessment frameworks with a focus on applications in head-and-neck cancer. Strict adherence to these harmonization efforts will enable leveraging the full potential of PET/CT and translate the proven benefits of this technique into tangible improvements in outcome for patients with head-and-neck cancer in routine clinical care.

Hyperglycemia and 18F-FDG PET/CT, issues and problem solving: a literature review

Positron emission tomography/computed tomography (PET/CT) is a standard procedure for imaging cancer commonly used in the clinical practice for several diseases, in particular for cancer staging, restaging, treatment monitoring and radiation therapy planning. Despite the availability of many radiotracers, 18F-fluoro-2-deoxy-2-D-glucose ([18F]FDG) is the most used. International PET/CT guidelines propose protocols for patients' correct preparation before [18F]FDG injection, in particular with the regard of diabetic patients and therapy management. Hyperglycemic conditions and oral or insulin medication showed advantages and disadvantages on PET/CT scan accuracy: A correct knowledge of effects of these conditions on glucose metabolism assumes a fundamental role on patients management before [18F]FDG PET/CT scan.

Update on Serum Glucose and Metabolic Management of Clinical Nuclear Medicine Studies: Current Status and Proposed Future Directions

Management of a patient's blood glucose or metabolism in nuclear medicine studies has become an integral aspect of daily work primarily due to the increasing use of F-18 flurodeoxyglucose (FDG) positron emission tomography (PET). Newer tracers such as F-18 Fluciclovine and C-11 Choline, are in theory subject to metabolic shifts and changes based on patients' insulin levels, and also require attention to achieving optimum patient preparation. Metabolic derangements can also affect other studies, such as gastric emptying (GE), the results of which are dependent upon the patient's blood glucose level during the time of imaging. The growing variety of diabetic medications has increased the complexity of the instructions which need to be given to patients. Current guidelines for patient preparation were developed in the past and have only slowly evolved with the introduction of newer oral medications. In addition to older insulin formulations newer formulations with different profiles of onset, duration, and consistency of action are being used. The wide spectrum of newer drugs now in use for treating diabetes has not been accompanied by any updated consensus on how to manage these drugs for imaging studies which require blood glucose level management. In this article we review these newer diabetes medications primarily to raise awareness of the changing landscape. Our focus will be on suggestions to optimize patient preparation and management for these studies. For each scenario, our suggestions will be given as summary proposals for best patient management. Our hope is that this discussion will stimulate multicenter studies to provide data to support new practice guidelines for metabolically dependent nuclear medicine procedures.

Personalised insulin calculator enables safe and effective correction of hyperglycaemia prior to FDG PET/CT

BACKGROUND

Hyperglycaemia can influence ¹⁸F-fluorodeoxyglucose (FDG) uptake due to competition for glucose transport and phosphorylation by hexokinase. Major international nuclear medicine societies recommend blood glucose level (BGL) < 11.1 mmol/L (200 mg/dL) prior to performing FDG positron emission tomography/computed tomography (PET/CT). However, there is no consensus approach and complications of previously proposed insulin guidelines included significant hypoglycaemia, inconvenience and skeletal muscle uptake. This study aims to establish the safety and efficacy of a personalised insulin calculator protocol to estimate the dose of intravenous insulin injection for correction of hyperglycaemia prior to FDG PET/CT.

RESULTS

This is a retrospective audit of all patients treated with insulin for hyperglycaemia (BGL > 10 mmol/L) prior to FDG PET/CT at the Peter MacCallum Cancer Centre over a 2-year period. Cohort 1 comprised a 12-month period (April 1, 2014-March 31, 2015) using the department's established empiric-dose insulin protocol, and Cohort 2 the 12 months (April 1, 2015-March 31, 2016) following introduction of a personalised insulin calculator protocol. Variables including body mass index, insulin-dose calculated and/or administered, BGL at baseline and nadir, and time to FDG injection were analysed. There were 115 and 136 patients treated with insulin in Cohorts 1 and 2 respectively, with similar baseline variables including mean BGL (14.5 vs 14.4 mmol/L) and range (10.5-22.7 vs 10.4-24.3 mmol/L). Use of the new personalised insulin calculator resulted in significantly fewer hypoglycaemic events (0.7% vs 5.2%; P < 0.03), shorter median time from insulin to FDG injections (108 min vs 136 min; P < 0.001) and greater individualised range in insulin prescription (3-32 IU vs 4-20 IU). The majority of patients (88.3%) receiving the personalised insulin calculator prescribed dose achieved BGL < 10.0 mmol/L. All scans obtained were of diagnostic quality.

CONCLUSIONS

The use of our personalised insulin calculator protocol effectively lowered BGL to the target range, resulted in significantly fewer hypoglycaemic events and reduced median time between insulin and FDG injection compared to a pre-existing empiric protocol whilst achieving diagnostic scans.

Management of Diabetes Mellitus Before 18F-Fluorodeoxyglucose PET/CT: A Nationwide Patient-Centered Assessment of Approaches to Examination Preparation

PURPOSE

The aim of this study was to perform, from the patient's point of view, a nationwide assessment of nuclear medicine practices regarding diabetic management before ¹⁸F-fluorodeoxyglucose (FDG) PET/CT for oncologic indications.

METHODS

This prospective observational study was exempt from institutional review board oversight. Sixty-five nuclear medicine scheduling lines (33 academic, 32 private practice, 12-17 in each of the five US regions) were called using a prewritten script under the guise of a nonexpert patient's family member about scheduling a patient with diabetes with "cancer" for FDG PET/CT. Each center was called three times on three different days. The following data were collected: (1) blood glucose threshold for rescheduling an examination, (2) when or if to stop various medications, (3) fasting requirements, and (4) time-of-day scheduling preferences. Withheld information was not specifically requested. Descriptive statistics were calculated.

RESULTS

There were 195 phone calls (mean duration, 2.9 min; range, 2-6 min). Relevant information was often withheld; withholding rates were as follows: blood glucose threshold, 71% (138 of 195); short-acting insulin instructions, 30% (59 of 195); long-acting insulin instructions, 99% (193 of 195); metformin instructions, 88% (179 of 195); fasting duration, 37% (72 of 195); and time-of-day scheduling preference, 91% (177 of 195). Mean provided data were as follows: blood glucose threshold, 195 mg/dL (range, 150-210 mg/dL); short-acting insulin withholding, 4.9 hours (range, 4-8 hours); long-acting insulin withholding, 12 hours (range, 12-24 hours); fasting duration, 5 hours (range, 4-8 hours); and preferred examination time, 91% (177 of 195). When specified (n = 18), morning scheduling was preferred (8% [15 of 195] versus 2% [3 of 195]).

CONCLUSIONS

Diabetes-specific information is commonly withheld by nuclear medicine call centers throughout the United States when discussing oncologic FDG PET/CT despite local and national policies indicating its importance.

Optimization of Pediatric PET/CT

PET/CT, the most common form of hybrid imaging, has transformed oncologic imaging and is increasingly being used for nononcologic applications as well. Performing PET/CT in children poses unique challenges. Not only are children more sensitive to the effects of radiation than adults but, following radiation exposure, children have a longer postexposure life expectancy in which to exhibit adverse radiation effects. Both the PET and CT components of the study contribute to the total patient radiation dose, which is one of the most important risks of the study in this population. Another risk in children, not typically encountered in adults, is potential neurotoxicity related to the frequent need for general anesthesia in this patient population. Optimizing pediatric PET/CT requires making improvements to both the PET and the CT components of the procedure while decreasing the potential for risk. This can be accomplished through judicious performance of imaging, the use of recommended pediatric ¹⁸fluorine-2-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) administered activities, thoughtful selection of pediatric-specific CT imaging parameters, careful patient preparation, and use of appropriate patient immobilization. In this article, we will review a variety of strategies for radiation dose optimization in pediatric ¹⁸F-FDG-PET/CT focusing on these processes. Awareness of and careful selection of pediatric-specific CT imaging parameters designed for appropriate diagnostic, localization, or attenuation correction only CT, in conjunction with the use of recommended radiotracer administered activities, will help to ensure image quality while limiting patient radiation exposure. Patient preparation, an important determinant of image quality, is another focus of this review. Appropriate preparative measures are even more crucial in children in whom there is a higher incidence of brown fat, which can interfere with study interpretation. Finally, we will discuss measures to improve the patient experience, the resource use, the departmental workflow, and the diagnostic performance of the study through the use of appropriate technology, all in the context of minimizing procedure-related risks.