Comparison of the Biograph Vision and Biograph mCT for quantitative 90Y PET/CT imaging for radioembolisation

Abstract

Background: New digital PET scanners with improved time of flight timing and extended axial field of view such as the Siemens Biograph Vision have come on the market and are expected to replace current generation photomultiplier tube (PMT)-based systems such as the Siemens Biograph mCT. These replacements warrant a direct comparison between the systems, so that a smooth transition in clinical practice and research is guaranteed, especially when quantitative values are used for dosimetry-based treatment guidance. The new generation digital PET scanners offer increased sensitivity. This could particularly benefit ⁹⁰Y imaging, which tends to be very noisy owing to the small positron branching ratio and high random fraction of ⁹⁰Y. This study aims to determine the ideal reconstruction settings for the digital Vision for quantitative ⁹⁰Y imaging and to evaluate the image quality and quantification of the digital Vision in comparison with its predecessor, the PMT-based mCT, for ⁹⁰Y imaging in radioembolisation procedures.

Methods: The NEMA image quality phantom was scanned to determine the ideal reconstruction settings for the Vision. In addition, an anthropomorphic phantom was scanned with both the Vision and the mCT, mimicking a radioembolisation patient with lung, liver, tumour, and extrahepatic deposition inserts. Image quantification of the anthropomorphic phantom was assessed by the lung shunt fraction, the tumour to non-tumour ratio, the parenchymal dose, and the contrast to noise ratio of extrahepatic depositions.

Results: For the Vision, a reconstruction with 3 iterations, 5 subsets, and no post-reconstruction filter is recommended for quantitative ⁹⁰Y imaging, based on the convergence of the recovery coefficient. Comparing both systems showed that the noise level of the Vision is significantly lower than that of the mCT (background variability of 14% for the Vision and 25% for the mCT at 2.5·10³ MBq for the 37 mm sphere size). For quantitative ⁹⁰Y measures, such as needed in radioembolisation, both systems perform similarly.

Conclusions: We recommend to reconstruct ⁹⁰Y images acquired on the Vision with 3 iterations, 5 subsets, and no post-reconstruction filter for quantitative imaging. The Vision provides a reduced noise level, but similar quantitative accuracy as compared with its predecessor the mCT.

Keywords: PET/CT; Radioembolisation; Yttrium-90.

Fig. 1

Total prompts, randoms, and net trues for a range of ⁹⁰Y activities for the Vision and mCT acquisitions of the NEMA phantom (a) and the thorax phantom (b). The solid and dashed lines are linear fits of the data for the Vision and the mCT respectively

Fig. 2

Transverse slice of three Vision reconstructions (1, 2, and 3 iterations with 5 subsets) and mCT reconstruction (2 iterations with 21 subsets) of the NEMA phantom at day 0 (2.5·10³ MBq), centred on the spheres. Images are scaled between 0 and 1 MBq/mL

Fig. 3

Recovery coefficient (a) and percentage background variability (b) of the NEMA phantom spheres with varying diameter at day 0 (2.5·10³ MBq) as a function of iteration number

Fig. 4

Results of the NEMA phantom comparing the mCT (2 iterations, 21 subsets) with the Vision (3 iterations, 5 subsets). BCA, background concentration accuracy

Fig. 5

Performance of the Vision and the mCT for measures concerning radioembolisation treatment planning: a lung shunt fraction (LSF), b tumour to non-tumour ration (T/N), c parenchymal dose (D_parenchymal), and d contrast-to-noise ratio (CNR) of the extrahepatic depositions