Assessing oral glucose and intravenous insulin loading protocol in 18F-fluorodeoxyglucose positron emission tomography cardiac viability studies

Abstract

Oral glucose and intravenous insulin (G/I) loading protocols are commonly used in ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) cardiac viability studies. Although the amount of insulin to be given per blood glucose range has been well described in guidelines, the amount of glucose to be given is not detailed well. In this retrospective study, we aimed to assess if certain parameters, particularly the amount of glucose and insulin given, may affect ¹⁸F-FDG uptake in the hibernating myocardium and also determine the problems with this protocol. ¹⁸F-FDG PET cardiac viability study with G/I loading protocols was performed in 49 patients. Fasting blood glucose (FBG), amount of glucose given, blood glucose level after glucose load, amount of insulin given, and blood glucose level at the time of ¹⁸F-FDG injection were recorded. Statistical analysis was performed to determine if there is any difference in the above values in PET viable and PET nonviable groups and also in subgroups assessing ¹⁸F-FDG uptake also in normal myocardium. For G/I loading, we used our local protocol in 43 patients, and other protocols in six. ¹⁸F-FDG PET showed viability in 31 patients, and it was negative for viability in 18. In 22 patients, mainly in PET viable group, there was varying degree of reduced ¹⁸F-FDG uptake in normal myocardium. There was no significant difference in FBG, amount of glucose given, blood glucose level after glucose load, amount of insulin given, and blood glucose level at the time of ¹⁸F-FDG injection in PET viable and PET nonviable groups and also in subgroups. The problems with G/I loading protocol included deciding on the amounts of glucose and insulin given, maximum amount of insulin to be given, handling diabetics, optimal time to measure blood glucose after insulin administration, and interpretation of findings in cases with diffusely reduced ¹⁸F-FDG uptake. Further improvements in current guidelines are necessary to obtain images in optimal conditions for accurate results.

Keywords: 18F-fluorodeoxyglucose positron emission tomography; myocardial viability; oral glucose and intravenous insulin loading.

Figure 1

Myocardial perfusion single-photon emission computed tomography and ¹⁸F-fluorodeoxyglucose positron emission tomography images of a patient with fasting blood glucose level of 3.9 mmol/L (70.2 mg/dl) who received 50 g oral glucose and 4 unit insulin. Blood glucose at the time of ¹⁸F-fluorodeoxyglucose injection was 8.3 mmol/L (149.4 mg/dl). Single photon emission computed tomography images demonstrate moderate size fixed perfusion defect involving apex, anterior, and anteroseptal walls with mild possible ischemia in inferior wall. ¹⁸F-fluorodeoxyglucose positron emission tomography images demonstrate small area of viability in the anterior and anteroseptal base. ¹⁸F-fluorodeoxyglucose uptake in the rest of the myocardium is near normal with only mild reduction in the inferior wall

Figure 2

Rest myocardial perfusion single photon emission computed tomography and ¹⁸F-fluorodeoxyglucose positron emission tomography short axis and bullseye images of a patient with fasting blood glucose of 7.7 mmol/L (138.6 mg/dl). No oral glucose was given in this patient. One unit insulin was given intravenously. Blood glucose at the time of ¹⁸F-fluorodeoxyglucose injection was 5.5 mmol/L (99 mg/dl). Single photon emission computed tomography images demonstrate a large area of significantly reduced perfusion involving the apex, anterior, and lateral walls and inferolateral region. ¹⁸F-fluorodeoxyglucose positron emission tomography images demonstrate significant viability in these regions but significantly reduced ¹⁸F-fluorodeoxyglucose uptake in normal myocardium (flip-flop pattern)

Figure 3

¹⁸F-fluorodeoxyglucose 1 h and 2 h cardiac images in short axis (top row), vertical long axis (middle row), and horizontal long axis (bottom row) slices in a patient with diabetes. Note the high blood pool activity on early images which significantly reduces with delayed imaging

Figure 4

Illustration of ¹⁸F-fluorodeoxyglucose uptake patterns in fixed perfusion defect and normal myocardium