Preparation methods prior to PET/CT scanning that decrease uptake of 18F-FDG by myocardium, brown adipose tissue, and skeletal muscle

Associations of physiologic myocardial 18F-FDG uptake with fasting duration, HbA1c, and regular exercise

OBJECTIVE

The variability of physiologic ¹⁸F-FDG uptake in the myocardium has hampered the accurate evaluation of cardiac glucose metabolism. We investigated the effects of multiple factors, including fasting duration and physical activity, on the physiologic uptake of ¹⁸F-FDG by the myocardium in healthy participants.

METHODS

A total of 446 participants (predominantly male, 91%) in a health screening program were included in this retrospective study. For the visual analysis of myocardial ¹⁸F-FDG uptake, the participants were categorized into three groups according to qualitative visual scales (QVS). For the quantitative analysis, the maximum SUV of the left ventricular myocardium was measured.

RESULTS

Significant differences were observed in fasting duration (p < 0.001), SUV_max (p < 0.001), aspartate aminotransferase (AST) (p < 0.001), alanine aminotransferase (ALT) (p < 0.001), gamma-glutamyl transpeptidase (γ-GTP) (p = 0.001), and uric acid (p = 0.015) among the QVS groups. Participants who regularly exercised with vigorous activity (p = 0.032) and HbA1c > 6% (p = 0.005) showed significant association with myocardial FDG uptake in the Chi-squared test. The median value of fasting duration decreased significantly as the QVS of the myocardium increased. Twenty-nine of the 31 participants (93.5%) who fasted for 21.5 h or more showed a suppressed FDG uptake (mean SUV_max = 2.1). In multivariate logistic regression analysis, fasting duration (OR = 0.74, 95% CI 0.69-0.80, p < 0.001), HbA1c > 6% (OR = 0.29, 95% CI: 0.12 - 0.66, p = 0.004), uric acid (OR = 0.82, 95% CI 0.68-1.00, p = 0.049) and regular exercise with vigorous activity (OR = 1.75, 95% CI 1.13-2.70, p = 0.012) were significant factors for physiologic myocardial FDG uptake.

CONCLUSIONS

Reduced physiologic ¹⁸F-FDG uptake of the myocardium was associated with longer fasting duration, higher level of HbA1c, and less frequency of regular exercise with vigorous activity. For the preparation of cardiac ¹⁸F-FDG PET, inclusion of longer fasting duration (more than 18 h) might be necessary for the adequate suppression of physiologic ¹⁸F-FDG myocardial uptake.

Effect of Propranolol on 18F-Fluorodeoxyglucose Uptake in Brown Adipose Tissue in Children and Young Adults with Neoplastic Diseases

PURPOSE

To evaluate the effectiveness of propranolol at mitigating FDG uptake in brown adipose tissue (BAT) of pediatric patients with known or suspected malignancies.

METHODS

PET/CT scans of 3 cohorts of patients treated from 2005 to 2017 were scored for the presence of FDG uptake by BAT at 7 sites: right or left neck/supraclavicular area, right or left axilla, mediastinum, posterior thorax, and abdomen/pelvis. Uptake was scored as follows: 0, none; 1, mild uptake < liver; 2, moderate uptake = liver; and 3, intense uptake > liver. Group 1 consisted of 323 patients (630 scans) who had no specific preparation to mitigate FDG uptake by BAT. Group 2 consisted of 345 patients (705 scans) who underwent only warming in an uptake room with a fixed temperature at 24 °C. Group 3 consisted of 622 patients (1457 scans) who underwent warming. In group 3, patients 8 years and older, 471 patients (1114 scans), were also pre-medicated with oral propranolol 60 min before injection of FDG. Generalized estimation equation, using the logit link method, was used to model the relationship between the incidence of BAT score > 0, in any site, as a function of age, sex, seasonal effect, and body surface area (BSA).

RESULTS

In patients aged 8 years or older, the incidence of BAT uptake was 35-44 % and declined to 15 % with propranolol. BAT was most frequent in the neck (26 %), axilla (18 %), posterior thorax (18 %), mediastinum (14 %), and abdomen/pelvis (8 %); BAT was less common in warm months (p = 0.001). No substantial benefit was shown with pre-injection warming alone. No significant effect was found for age, sex, or BSA separately. When BAT uptake was present, it was usually intense.

CONCLUSION

Propranolol preparation minimizes FDG uptake by BAT and should be considered routine for pediatric FDG PET/CT cancer-related protocols in children, adolescents, and young adults.

Diagnostic Accuracy of Cardiac Computed Tomography and 18-F Fluorodeoxyglucose Positron Emission Tomography in Cardiac Masses

OBJECTIVES

This study sought to assess the diagnostic accuracy of cardiac computed tomography (CT) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) with positron emission tomography/computed tomography (PET/CT) in defining the nature of cardiac masses.

BACKGROUND

The diagnostic accuracy of cardiac CT and ¹⁸F-FDG PET/CT in identifying the nature of cardiac masses has been analyzed to date only in small samples.

METHODS

Of 223 patients with echocardiographically diagnosed cardiac masses, a cohort of 60 cases who underwent cardiac CT and ¹⁸F-FDG PET/CT was selected. All masses had histological confirmation, except for a minority of thrombotic formations. For each mass, 8 morphological CT signs, standardized uptake value (SUV_max, SUV_mean), metabolic tumor volume, and total lesion glycolysis in ¹⁸F-FDG PET were used as diagnostic markers.

RESULTS

Irregular tumor margins, pericardial effusion, invasion, solid nature, mass diameter, CT contrast uptake, and pre-contrast characteristics were strongly associated with the malignant nature of masses. The coexistence of at least 5 CT signs perfectly identified malignant masses, whereas the detection of 3 or 4 CT signs did not accurately discriminate the masses' nature. The mean SUV_max, SUV_mean, metabolic tumor volume, and total lesion glycolysis values were significantly higher in malignant than in benign masses. The diagnostic accuracy of SUV, metabolic tumor volume, and total lesion glycolysis ¹⁸F-FDG PET/CT parameters was excellent in detecting malignant masses. Among patients with 3 or 4 pathological CT signs, the presence of at least 1 abnormal ¹⁸F-FDG PET/CT parameter significantly increased the identification of malignancies.

CONCLUSIONS

Cardiac CT is a powerful tool to diagnose cardiac masses as the number of abnormal signs was found to correlate with the lesions' nature. Similarly, ¹⁸F-FDG PET/CT accurately identified malignant masses and contributed with additional valuable information in diagnostic uncertainties after cardiac CT. These imaging tools should be performed in specific clinical settings such as involvement of great vessels or for disease-staging purposes.

A 1-week extension of a ketogenic diet provides a further decrease in myocardial 18F-FDG uptake and a high detectability of myocarditis with FDG-PET

BACKGROUND

Short periods of fasting and/or low-carbohydrate diet have been proven beneficial for decreasing the myocardial uptake of 18F-fluorodeoxyglucose (18F-FDG) and enhancing the detection of inflammatory heart diseases by 18F-FDG positron emission tomography (PET). This study aimed at determining whether this benefit is increased when a low-carbohydrate ketogenic diet is prolonged up to 7 days.

METHODS

Wistar rats underwent serial 18F-FDG-PET imaging after an 18-hour fasting period and after 2, 4 and 7 days of a ketogenic diet (3% carbohydrate) and they were compared to rats submitted to the same protocol but with normal diet (44% carbohydrate). The 18F-FDG-PET/ketogenic protocol was also applied in rats with immune myocarditis (injection of porcine cardiac myosin).

RESULTS

The 7-day ketogenic diet was associated with (1) a sustained increase in circulating ketone bodies at an equivalent level to that reached after 18-hour fasting, (2) a gradual decrease in 18F-FDG uptake within normal myocardium reaching a lower level compared to fasting at the 7th day (myocardium-to-blood ratios: 1.68 ± 1.02 vs 3.25 ± 1.40, P < .05) and (3) a high 18F-FDG-PET detectability of myocarditis areas.

CONCLUSION

One-week extension of a ketogenic diet provides a further decrease in the 18F-FDG uptake of normal myocardium and a high detectability of inflammatory areas.

Variances of dietary preparation for suppression of physiological 18F-FDG myocardial uptake in the presence of cardiac sarcoidosis: A systematic review

BACKGROUND

18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) is used in the diagnosis and management of patients with cardiac sarcoidosis (CS). Various preparation protocols have been proposed to minimise myocardial 18F-FDG uptake and improve scan readability. The aim of this systematic review was to identify the optimal dietary prescription for suppression of physiological 18F-FDG myocardial uptake to enhance clinical diagnosis of CS.

METHODS AND RESULTS

MEDLINE and PubMed databases identified 13 studies meeting inclusion criteria for review. Articles were assessed using the Australian National Health and Medical Research Council levels of evidence and categorised as sarcoidosis (human) or non-sarcoidosis (human, animal). Visual uptake scales (qualitative) and/or standardised uptake values (SUV) (quantitative) were used in all the studies reviewed. Nine of 11 human studies showed statistically significant improvements in PET scan interpretation with carbohydrate-restricted diets compared with fasting only, and when carbohydrates were restricted for a longer period of time. Two animal studies showed statistically significant improvements following very low carbohydrate diet preparation (0.01% and 0.4% carbohydrate diets) compared with higher carbohydrate diets.

CONCLUSIONS

Variation in measures used, dietary prescriptions, fasting times, species and study quality makes result comparison and applicability difficult. Definitive dietary recommendations are not possible based on current evidence.

The quantitative carbohydrate ingestion ratio for extensive skeletal muscle uptake in 18F-FDG PET/computed tomography

OBJECTIVES

Extensive skeletal muscle accumulation (ESMA) of F-FDG adversely affects the visual interpretation of F-FDG PET/computed tomography (CT) images. We mainly investigated factors related to ESMA that are based on food compositions.

METHODS

From January 2018 to June 2018, a total of 5554 patients underwent F-FDG PET/CT imaging with at least a 4-hour fast. Among them, 49 patients who exhibiting ESMA and 50 sex-matched and age-matched patients without ESMA were included in the study. The following factors were analysed: BMI, plasma glucose, gastric residue, the total energy of food the patient had before F-FDG injection and the percentages of the food ingredients. Multivariate analysis was performed to evaluate related risk factors between two groups.

RESULTS

In brief, 49 cases and 50 controls were identified. The BMI, gross energy, gross energy of protein, gross energy of carbohydrate and proportion of protein of case group were not significantly different from that of the controls (P ≥ 0.05). The plasma glucose was significantly higher in the case group than in the control group (P = 0.002). The positivity of gastric food residue would more easily demonstrate ESMA than those without gastric food residue (P < 0.0001). The fasting time before scan, gross energy of fat, proportion of fat and proportion of carbohydrate in case group were significantly different with control group. After multivariate analysis, fasting time, gastric food residue and proportion of carbohydrate were investigated as independent risk factors.

CONCLUSION

To avoid ESMA, patients should take a lower proportion of carbohydrate before receiving an F-FDG administration.

Teaching Medical Students Optimal Consulting Skills: The Challenge of Generating Better Referring Physicians

Rationale and objectives We sought to incorporate a new teaching module into the traditional medical student radiology clerkship, to improve the necessary skills for future referring physicians. Materials and methods A new required and graded module was introduced in 2014 into the radiology clerkship in year three of medical school: the Mystery Case. Each student was provided a unique and undifferentiated case from a dedicated teaching file containing de-identified images and requisition data. Students were expected to complete three serial tasks over one week: 1) prepare a voice recognition-derived, structured radiological report utilizing appropriate and relevant vocabulary; 2) discuss pertinent additional clinical information; and 3) discuss appropriate follow-up imaging, in addition to information on how to best prepare patients for these potential patient exams (e.g., with or without contrast, bowel preparation, and length of study). Students were provided written examples and dedicated class instruction with interactive discussions covering specific cases and associated related cases through random pairing with radiology resident and attending mentors. At the close of the week, students gave brief oral presentations of their cases and submitted the tasks for a written evaluation. Upon completion of the clerkship, the students completed a Likert-type six-item survey to evaluate the perceived improvement in select skills. Results The survey was completed by 82% (54/66) of the enrolled students, with 85% finding the Mystery Case an effective use of time. Medical students perceived an improved awareness of the patient care process (77%), awareness of the medical imaging resources available (89%), ability to understand a radiology report (74%), and ability to advise patients (69%). Conclusion Introduction of the Mystery Case as a graded exercise in the medical school radiology clerkship was perceived by students as effective use of time, with an improvement in the skills essential for future referring physicians.

Serial FDG-PET/CT Imaging in the Management of Cardiac Sarcoidosis

A 60-year-old woman with biopsy-proven cardiac sarcoidosis status post implantable cardioverter defibrillator placement presented with periodic dizziness and dyspnea on exertion. Myocardial perfusion scan demonstrated a moderate sized, fixed perfusion defect along the mid to proximal anteroseptal wall of the left ventricle, with better perfusion on stress images. FDG-PET/CT demonstrated corresponding focal FDG avidity of the mid to proximal anteroseptal wall, suggestive of active cardiac sarcoidosis. Because of severe side effects, mycophenolate mofetil was discontinued, and the patient received low-dose steroid therapy. At 7-month follow-up FDG PET/CT, there was increased FDG avidity in the same regions, indicating worsening cardiac sarcoidosis.