Assessment of different quantification metrics of [¹⁸F]-NaF PET/CT images of patients with abdominal aortic aneurysm

Background: We aim to assess the spill-in effect and the benefit in quantitative accuracy for [¹⁸F]-NaF PET/CT imaging of abdominal aortic aneurysms (AAA) using the background correction (BC) technique. Methods: Seventy-two datasets of patients diagnosed with AAA were reconstructed with ordered subset expectation maximization algorithm incorporating point spread function (PSF). Spill-in effect was investigated for the entire aneurysm (AAA), and part of the aneurysm excluding the region close to the bone (AAA_exc). Quantifications of PSF and PSF+BC images using different thresholds (% of max. SUV in target regions-of-interest) to derive target-to-background (TBR) values (TBR_max, TBR₉₀, TBR₇₀ and TBR₅₀) were compared at 3 and 10 iterations. Results: TBR differences were observed between AAA and AAA_exc due to spill-in effect from the bone into the aneurysm. TBR_max showed the highest sensitivity to the spill-in effect while TBR₅₀ showed the least. The spill-in effect was reduced at 10 iterations compared to 3 iterations, but at the expense of reduced contrast-to-noise ratio (CNR). TBR₅₀ yielded the best trade-off between increased CNR and reduced spill-in effect. PSF+BC method reduced TBR sensitivity to spill-in effect, especially at 3 iterations, compared to PSF (P-value ≤ 0.05). Conclusion: TBR₅₀ is robust metric for reduced spill-in and increased CNR.