Voxel-Level Comparison of [¹⁸F]CETO and [¹¹C]MTO for Molecular Imaging of Primary Aldosteronism

Primary aldosteronism (PA), which accounts for up to 14% of all hypertension cases and 25% of treatment-resistant hypertension cases, may be caused by unilateral or bilateral adrenal gland pathology. The identification of patients who are most likely to benefit from targeted intervention (i.e., adrenalectomy or nodule ablation) remains a challenge. Adrenal vein sampling is an invasive procedure with restricted availability, and recent studies have found that its accuracy in predicting surgical cure may be lower than previously thought. Molecular imaging with [¹¹C]metomidate ([¹¹C]MTO) PET is a noninvasive alternative, but the short half-life of ¹¹C prevents its widespread use. A novel fluorinated radiotracer, para-chloro-2-[¹⁸F]fluoroethyletomidate ([¹⁸F]CETO), has the potential to address this limitation because of its longer half-life. Initial reports suggest that [¹⁸F]CETO and [¹¹C]MTO have very similar visual (qualitative) appearances in patients with adrenal gland tumors. Methods: Using individual voxel measurements, we compared [¹⁸F]CETO and [¹¹C]MTO uptake in the adrenal glands of 31 patients with PA who were recruited to the extension phase of the MATCH clinical trial. Results: Qualitative comparisons of [¹⁸F]CETO and [¹¹C]MTO images showed comparable adrenal gland uptake, although [¹¹C]MTO demonstrated greater liver uptake, which obscured the right adrenal gland in some patients. Voxelwise comparisons yielded high correlation coefficients for both the left (r = 0.89) and right (r = 0.87) adrenal glands, which were statistically significant (P < 0.001). Bland-Altman analyses revealed mean SUV differences of 0.71 (CI, -6.09 to 7.51) for the left adrenal gland and 2.55 (CI, -5.91 to 11.00) for the right adrenal gland, indicating no significant bias between radiotracers. Conclusion: [¹⁸F]CETO and [¹¹C]MTO show remarkable similarity when used for molecular imaging in patients with PA. Notably, the right adrenal gland is more readily visualized with [¹⁸F]CETO, attributed to lower hepatic uptake. These findings, coupled with the longer half-life of ¹⁸F, should enable wider access to molecular imaging of the adrenal glands.