Comparison of two commercial whole body PET systems based on LSO and BGO crystals respectively for brain imaging

The prevalence of neurodegenerative diseases is growing in western countries and PET imaging is increasingly frequently used for clinical and research purposes. However, few PET cameras are dedicated to cerebral imaging. The Biograph 6 (Biograph6) (Siemens Medical Solutions) is a PET/CT dedicated to high throughput whole body studies. Its performance for cerebral imaging has not yet been assessed. The aims of this study were to compare the quantification and detectability of the Biograph for cerebral imaging with those of a well-validated PET camera, the ECAT EXACT HR+ (HR+) (Siemens Medical Solutions). A phantom measuring 19 cm long and 20 cm in diameter was filled with a 18F-fluorodeoxyglucose (18F-FDG) solution. Two 5.7 and 20 ml spheres filled with water (cold-spots), three 0.25 ml spheres (sphere-to-background: 3, 6, and 12), one 1.14 ml sphere (sphere-to-background: 3), and one 11.27 ml sphere (sphere-to-background: 2) filled with a radioactive solution were inserted into the phantom. The activity concentration was chosen so that the count rates for the phantom measurements matched those of typical brain studies on both cameras. Images were reconstructed using FORE and OSEM algorithms. The reconstruction parameters were adjusted to obtain a similar signal-to-noise ratio in images acquired with the two cameras. The contrast recovery (CR) coefficients were similar on the two scanners for the 5.7 and 20 ml spheres (cold spheres) and the 1.14 and 11.27 ml spheres (hot spheres). For the 0.25 ml spheres, the CR values were 35% higher for the sphere-to-background ratio of 12 and 39% higher for the sphere-to-background ratio of 6 on the Biograph6 for the 3 min scan. The variability of measurements was lower on the Biograph6 than on the HR+. The detectability for the smallest spheres on the Biograph6 was close to that on the HR+. The Biograph has similar performances as the HR+ reference tomograph for the detection and quantification of small hot spots and cold spots.