Parametric mapping for ¹¹C-metomidate PET-computed tomography imaging in the study of primary aldosteronism

Abstract

Objective 

¹¹C-metomidate (¹¹C-MTO) PET-computed tomography (CT) imaging has shown good sensitivity and specificity for the classification of bilateral or unilateral overexpression of aldosterone. This work seeks to investigate the usefulness of parametric maps via kinetic modeling of ¹¹C-metomidate data into the clinical diagnosis pathway.

Methods 

Twenty-five patients were injected with 172 ± 12 MBq of ¹¹C-metomidate and a dynamic PET scan performed of the adrenal glands. A blood time-activity curve was drawn from a volume of interest in the left ventricle and converted to a plasma time-activity curve. Metabolite correction was performed with a population-based correction. We performed regional-based graphical Patlak analysis to calculate the regional uptake rate constant K_i(REG), and also calculated parametric maps of K_i(VOX) using a voxel-based technique.

Results 

Comparison of K_i(REG), and the maximum lesion voxel from parametric maps K_i(mVOX) demonstrated a high correlation for all subjects (r² = 0.96). K_i(mVOX) allowed differentiation between cases of active and inactive unilateral adenoma when compared to bilateral hyperplasia (P < 0.017), a feature not observed with standardized uptake ratios (SUV_max) analysis. K_i(mVOX) demonstrated a poor correlation of 0.68 with SUV_max, indicating the differences through the use of static and dynamic imaging. Three false-negative cases based on SUV analysis indicated that K_i(mVOX) was able to successfully differentiate the clinical presentation for these cases.

Conclusion 

Our work demonstrates that parametric K_i(VOX) was able to successfully differentiate between patients with bilateral hyperplasia and patients with unilateral adrenal adenoma in our cohort and that K_i may be considered be an additional useful metric to SUV in ¹¹C-metomidate PET-CT imaging.