Imaging small dynamic lesions using positron emission tomography and computed tomography: an 18F-sodium fluoride valvular phantom study.

Aims: ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) detects active microcalcification and predicts adverse outcomes including bioprosthetic valve deterioration. However, measuring small areas of ¹⁸F-NaF uptake within moving structures remains challenging, requiring further optimization. We developed a representative cardiac phantom to optimize ¹⁸F-NaF imaging of bioprosthetic valves.

Methods and results: We placed a bioprosthetic valve with two pockets sutured to the leaflets mimicking valvular lesions and a subvalvular ring mimicking the valve remnant into the phantom and injected each with ¹⁸F-radionuclide (1 μCi pockets, 4 μCi ring). We injected the cardiac chambers with iohexol and ¹⁸F-radionuclide (0.176 mCi) for background activity. PET and computed tomography (CT) images were acquired using a Siemens Biograph Vision high-resolution digital PET/CT scanner. We analysed target-to-background ratio (TBR) and signal-to-noise ratio (SNR) and subjective measures of image quality. We compared results with a human case of transcatheter aortic valve replacement. Initially the SNR and TBR in the phantom greatly exceeded those from human imaging. We reduced the scan duration used for reconstruction to 30 and 15 s, achieving comparable results (30 s vs. 15 s vs. patient: SNR 45.6 vs. 13.9 vs. 44.3, TBR_max 6.5 vs. 5.4 vs. 4.1, noise 10.2% vs. 8.8% vs. 12.0%). With motion correction, SNR and image quality improved in the phantom (30 s 135.8 vs. 45.6, 15 s 32.9 vs. 13.9) but remained similar in the human case (47.3 vs. 44.3).

Conclusion: A cardiac phantom can mimic clinical ¹⁸F-NaF valve bioprosthesis imaging, providing an opportunity to explore acquisition, reconstruction, and post-processing of ¹⁸F-NaF PET/CT for small mobile cardiac structures.