Abstract
BackgroundPositron emission tomography (PET) imaging of 90Y following selective internal radiation therapy (SIRT) is possible, but image quality is poor, and therefore, accurate quantification and dosimetry are challenging. This study aimed to quantitatively optimise 90Y PET imaging using a new Bayesian penalised likelihood (BPL) reconstruction algorithm (Q.Clear, GE Healthcare). The length of time per bed was also investigated to study its impact on quantification accuracy.MethodsA NEMA IQ phantom with an 8:1 sphere-to-background ratio was scanned overnight on a GE Discovery 710 PET/CT scanner. Datasets were rebinned into varying lengths of time (5–60 min); the 15-min rebins were reconstructed using BPL reconstruction with a range of noise penalisation weighting factors (beta values). The metrics of contrast recovery (CR), background variability (BV), and recovered activity percentage (RAP) were calculated in order to identify the optimum beta value. Reconstructions were then carried out on the rest of the timing datasets using the optimised beta value; the same metrics were used to assess the quantification accuracy of the reconstructed images.ResultsA beta value of 1000 produced the highest CR and RAP (76% and 73%, 37 mm sphere) without overly accentuating the noise (BV) in the image. There was no statistically significant increase (p < 0.05) in either the CR or RAP for scan times of > 15 min. For the 5-min acquisitions, there was a statistically significant decrease in RAP (28 mm sphere, p < 0.01) when compared to the 15-min acquisition.ConclusionOur results indicate that an acquisition length of 15 min and beta value of 1000 (when using Q.Clear reconstruction) are optimum for quantitative 90Y PET imaging. Increasing the acquisition time to more than 15 min reduces the image noise but has no significant impact on image quantification.
Highlights
Positron emission tomography (PET) imaging of 90Y following selective internal radiation therapy (SIRT) is possible, but image quality is poor, and accurate quantification and dosimetry are challenging
The purpose of this work was to identify the optimal beta value to use for quantitative 90Y PET imaging and to explore the effect that scan length has on quantification; it was hypothesised that increasing the scan length could potentially improve the quantification of PET imaging
It was demonstrated that a beta value of 1000 provided the best image quantification; it yielded the highest contrast recovery (CR) of 75%, and there was no significant improvement in recovered activity percentage (RAP) for lower beta values
Summary
Positron emission tomography (PET) imaging of 90Y following selective internal radiation therapy (SIRT) is possible, but image quality is poor, and accurate quantification and dosimetry are challenging. The administration and imaging of 99mTc-MAA (microaggregated albumin) particles, an analogue of 90Y microspheres, is carried out. This is to ensure that no extrahepatic migration of the microspheres occurs, and it allows an assessment of microspheres shunting to the lungs to be made [2]; extrahepatic deposition or a high lung shunt can be contraindications for treatment [3,4,5,6]. The validation of the 90Y microsphere distribution post-SIRT is key in order to perform accurate measures of absorbed dose
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