Status of F-18 fluorodeoxyglucose uptake in normal and hibernating myocardium after glucose and insulin loading

Abstract

Objective: F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has been increasingly used in myocardial viability imaging. In routine PET viability studies, oral glucose and intravenous insulin loading is commonly utilized. In an optimal study, glucose and insulin loading is expected to cause FDG uptake both in hibernating and normal myocardium. However, in routine studies it is not uncommon to see absent or reduced FDG uptake in normal myocardium. In this retrospective study we further analyzed our PET viability images to evaluate FDG uptake status in myocardium under the oral glucose and intravenous insulin loading protocol that we use in our hospital.

Methods: Patients who had both myocardial perfusion single photon emission computed tomography (SPECT) and FDG PET cardiac viability studies were selected for analysis. FDG uptake status in normal and abnormal myocardial segments on perfusion SPECT was evaluated. Based on SPECT and PET findings, patients were divided into two main groups and four subgroups. Group 1 included PET viable studies and Group 2 included PET-nonviable studies. Subgroups based on FDG uptake in normal myocardium were 1a and 2a (normal uptake) and 1b and 2b (absent or significantly reduced uptake).

Results: Seventy-one patients met the inclusion criteria. Forty-two patients were PET-viable and 29 were PET-nonviable. In 33 of 71 patients (46.4%) there was absent or significantly reduced FDG uptake in one or more normal myocardial segments, which was identified more in PET-viable than PET-nonviable patients (59.5% vs. 27.5%, p = 0.008). This finding was also more frequent in diabetic than nondiabetic patients (53% vs. 31.8%), but the difference was not significant (p = 0.160).

Conclusions: In nearly half of our patients, one or more normal myocardial segments showed absent or significantly reduced FDG uptake. This finding, particularly if it is diffuse, could be from suboptimal study, inadequacy of current glucose and insulin loading protocols, or various other patient-related causes affecting FDG uptake both in the normal and hibernating myocardium. In cases with significantly reduced FDG uptake in normal myocardium, PET images should be interpreted cautiously to prevent false-negative results for viability.

Keywords: Fluorodeoxyglucose; Glucose loading; Insulin loading; Myocardial viability; Positron emission tomography.

Figure 1

(A) Stress and rest myocardial perfusion SPECT short, vertical, and horizontal long axis slices and polar maps demonstrate anterior and anteroseptal fixed perfusion defect and mild peri-infarct ischemia. (B) FDG PET slices and polar map shows significant viability in the anterior/anteroseptal region. FDG uptake is normal in other normally perfused walls. SPECT = single photon emission computed tomography; FDG = fluorodeoxyglucose; PET = positron emission tomography.

Figure 2

(A) Stress and rest myocardial perfusion SPECT short, vertical, and horizontal long axis slices and polar maps demonstrate a large area of fixed perfusion defect in the LAD distribution (apex, anterior, and anteroseptal). Mild fixed decreased activity in the inferior wall is likely secondary to diaphragm attenuation. (B) FDG PET slices and polar map shows significant viability in the LAD distribution (PET-viable) but markedly decreased FDG uptake in the rest of myocardium. SPECT = single photon emission computed tomography; FDG = fluorodeoxyglucose; LAD = left anterior descending artery; PET = positron emission tomography.

Figure 3

(A) Stress and rest myocardial perfusion SPECT short, vertical, and horizontal long axis slices and polar maps demonstrate a large area of fixed perfusion defect in the apex, extending to mid anterior, inferior, and septal walls, and fixed decreased activity in the anterior base. (B) FDG PET slices and polar map shows no significant FDG uptake in the region of the fixed perfusion defect (PET-nonviable). FDG uptake in the anterior base is higher than the uptake on perfusion images. In the rest of the left ventricle there is normal FDG uptake. SPECT = single photon emission computed tomography; FDG = fluorodeoxyglucose; PET = positron emission tomography.

Figure 4

(A) Stress and rest myocardial perfusion SPECT short, vertical, and horizontal long axis slices and polar maps demonstrate large area of fixed perfusion defect in the inferior, inferolateral, and inferoseptal segments from apex to base. (B) Selected FDG PET/CT transaxial slices show diffusely decreased activity in the left ventricle. FDG uptake is seen in both atria and right ventricle. SPECT = single photon emission computed tomography; FDG = fluorodeoxyglucose; PET/CT = positron emission tomography/computed tomography.