RESUMEN
PET iterative reconstruction algorithms with resolution modelling (RM) can be used to improve spatial resolution in the images. However, RM has a significant impact on quantification, which raises issues for harmonization across multicentre networks or collaborations. This investigation compared quantification from two modern time-of-flight (TOF) PET/CT systems from different manufacturers with RM with the intention to harmonize recovery. Images of a National Electrical Manufacturers Association image quality phantom with a sphere-to-background concentration ratio of 4 : 1 were acquired on a GE Discovery 710 and a Siemens Biograph mCT and reconstructed with RM and TOF. Voxel dimensions and image noise (background coefficient of variation) were matched. One to five iterations were used with 2 and 4 mm Gaussian filters. Mean and maximum contrast recovery (CR) were measured for the 10, 13, 17 and 22 mm hot phantom spheres. Notable differences in CR for images reconstructed with matched reconstruction parameters were observed between the scanners. A set of parameters was found that reduced differences in CR between scanners. Using these parameters, relative differences for the Biograph compared with the Discovery were -8.1, -3.7, +7 and +0.7% for mean CR and -23.1, -6.9, +9.1 and +0.9% for maximum CR in the 10, 13, 17 and 22 mm spheres, respectively. This study has used a technique of harmonizing standardized uptake value recovery on PET/CT systems from different vendors with advanced reconstructions including TOF and RM using phantom data. Considerable quantitative differences may occur in images, which highlights the need to apply methods such as those used in this work for multicentre studies.
Asunto(s)
Procesamiento de Imagen Asistido por Computador , Modelos Teóricos , Tomografía Computarizada por Tomografía de Emisión de Positrones , Transporte Biológico , Factores de TiempoRESUMEN
Imaging on a γ-camera with 90Y after selective internal radiotherapy (SIRT) may allow for verification of treatment delivery but suffers relatively poor spatial resolution and imprecise dosimetry calculation. 90Y 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 90Y. Methods: 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. Results: 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 ß 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. Conclusion: BPL with a ß value of 4,000 is the optimal image reconstruction in PET/CT for confident radiologic reading when compared with other reconstruction parameters for 90Y 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.