Optimization of Image Reconstruction for ⁹⁰Y Selective Internal Radiotherapy on a Lutetium Yttrium Orthosilicate PET/CT System Using a Bayesian Penalized Likelihood Reconstruction Algorithm

Abstract

Imaging on a γ-camera with Y after selective internal radiotherapy (SIRT) may allow for verification of treatment delivery but suffers relatively poor spatial resolution and imprecise dosimetry calculation.Y PET/CT imaging is possible on 3-dimensional, time-of-flight machines; however, images are usually poor because of low count statistics and noise. A new PET reconstruction software using a Bayesian penalized likelihood (BPL) reconstruction algorithm (termed Q.Clear) was investigated using phantom and patient scans to optimize the reconstruction for post-SIRT imaging and clarify whether BPL leads to an improvement in clinical image quality using Y. Phantom studies over an activity range of 0.5-4.2 GBq were performed to assess the contrast recovery, background variability, and contrast-to-noise ratio for a range of BPL and ordered-subset expectation maximization (OSEM) reconstructions on a PET/CT scanner. Patient images after SIRT were reconstructed using the same parameters and were scored and ranked on the basis of image quality, as assessed by visual evaluation, with the corresponding SPECT/CT Bremsstrahlung images by 2 experienced radiologists. Contrast-to-noise ratio was significantly better in BPL reconstructions when compared with OSEM in phantom studies. The patient-derived BPL and matching Bremsstrahlung images scored higher than OSEM reconstructions when scored by radiologists. BPL with a β value of 4,000 was ranked the highest of all images. Deadtime was apparent in the system above a total phantom activity of 3.3 GBq. BPL with a β value of 4,000 is the optimal image reconstruction in PET/CT for confident radiologic reading when compared with other reconstruction parameters for Y imaging after SIRT imaging. Activity in the field of view should be below 3.3 GBq at the time of PET imaging to avoid deadtime losses for this scanner.

Phantom, clinical, and texture indices evaluation and optimization of a penalized‐likelihood image reconstruction method (Q.Clear) on a BGO PET/CT scanner

“…Results also open the question of the Q.Clear reconstruction optimization for each different radiopharmaceutical and clinical application. For example, it was recently reported that for 90 Y TOF PET imaging a β value of 4000 is the recommended choice, far more elevated than the values considered in the present work. This extreme case is due to the low statistics of 90 Y PET imaging, so different results than those presented in this study can be achieved for other nuclides or pharmaceuticals.…”

Evaluation of a Bayesian penalized likelihood reconstruction algorithm for low-count clinical 18F-FDG PET/CT

“…Finding an optimal β-value in clinical practice depends on finding a balance in counting statistics and resulting image quality. Others have suggested to use β-values of 400-500 for whole-body 18 F-FDG studies [14], 400 or 600 for pulmonary nodules evaluation [16,17], 350-400 for brain studies [18], 300 for 18 F-fluciclovine [19], and 4,000 for low-count 90 Y studies [20].…”

Retrospective PET/CT Imaged Based Dosimetry Following Transarterial Radioembolization

“…Throughout our study we initially performed our analysis on all six reconstruction method variations. However, it became apparent to us that in combination with other's work [10,12] we could focus the presentation of data better as we advanced in this study by eliminating the presentation of results for methods that were inferior. Scott and McGowan concluded based on phantom studies that the optimal β value for the Q.Clear reconstruction method for Y 90 PET imaging was β = 1000 [10].…”

“…The most common post-TARE imaging protocol is 90 Y bremsstrahlung single-photon emission computed tomography (SPECT) to verify treatment deposition in the liver along with no extrahepatic microsphere deposition [1,12]. Due to the noisy nature of these images, they are typically used only for qualitative purposes because quantitative assessment is di cult [1,13].…”