The Effect Of HYPER Iterative And OSEM Reconstruction Methods On The Image Quality Of ¹⁸F-FDG UEXPLORER Total-body PET/CT With Different Injection Doses And Acquisition Times

Research BackgroundConventional clinical PET scanners typically have an axial field of view(AFOV)of 15-30 cm,resulting in limited coverage and relatively low photon detection efficiency.Taking advantage of the development of long-axial PET/CT,the uEXPLORER PET/CT scanner with an axial coverage of 194 cm increases the effective count rate by approximately 40 times compared to that of conventional PET scanners.Ordered subset expectation maximization(OSEM)is the most widely used iterative algorithm in PET.The major drawback of OSEM is that the iteration process must be stopped before convergence to avoid image degradation due to excessive noise.A new Bayesian penalized-likelihood iterative PET reconstruction,named HYPER Iterative,was developed and is now available on the uEXPLORER total-body PET/CT,which incorporates a noise control component by using a penalty function in each iteration and finds the maximum likelihood solution through repeated iterations.To date,its impact on lesion visibility in patients with a full injected dose or half injected dose is unclear.The goal of this study was to determine a proper protocol for routine 18F-FDG uEXPLORER total-body PET/CT scans.The routine scanning protocol of uEXPLORER total-body PET/CT based on HYPER Iterative has not yet been fully established.Therefore,this subject will carry out research in this aspect.Research purpose1.Can the new reconstruction algorithm HYPER Iterative produce better image quality than OSEM reconstruction for different injection doses and acquisition times.2.What is the effect of HYPER Iterative reconstruction on homogeneous background and lesion.Materials and methods20 tumor patients who underwent uEXPLORER total-body PET/CT scanning in our center were selected.10 were injected with a full dose of 18F-FDG(3.7MBq/kg),and 10 were injected with a half-dose of 18F-FDG(1.85MBq/kg).The image acquisition time is 5 minutes.The PET images were firstly reconstructed using all 5 min data and further split into 10 sec,30 sec,1 min,2 min,3 min,4 min duration groups to simulate fast acquisition scenarios.Two reconstruction methods(OSEM and HYPER Iterative)were used to reconstruct the images,and then subjective and objective semi-quantitative analysis was carried out.The obtained protocol from 20 oncology patients study was subsequently tested and validated in the phantom.ResultsThe quality of the 5 min PET image was excellent(score 5)for all of the dose and reconstruction methods.Using the HYPER Iterative method,the PET images reached excellent quality at 1 min with full-dose PET and at 2 min with half-dose PET.The PET image reached a similar excellent quality at 2 min with a full-dose and at 3 min with a half-dose using OSEM.The noise in the OSEM reconstruction was higher than that in the HYPER Iterative.For large positive lesions(≥ 2 cm),the SUVmax and TBR reconstructed by HYPER Iterative were slightly higher than those reconstructed by OSEM(SUVmax:up to 9.03%higher in full-dose and up to 12.52%higher in halfdose;TBR:up to 8.69%higher in full-dose and up to 23.39%higher in half-dose).For small positive lesions(≤ 10 mm),the SUVmax and TBR reconstructed by HYPER Iterative were obviously higher than those reconstructed by OSEM(SUVmax:up to 45.21%higher in full-dose and up to 74.96%higher in half-dose;TBR:up to 44.91%higher in full-dose and up to 93.73%higher in half-dose).The phantom study confirms the above conclusion.ConclusionsuEXPLORER total-body PET/CT images with HYPER Iterative reconstruction can meet the needs of clinical diagnosis in full-dose scan for 1 minute and half-dose scan for 2 minutes.Clinical and phantom studies have found that for quantification of small lesions or injection of half-dose of 18F-FDG,HYPER Iterative reconstruction can reduce image noise and improve the display clarity of lesions.