Image quality and detectability in Siemens Biograph PET/MRI and PET/CT systems—a phantom study

Abstract

Background The technology of modern positron emission tomography (PET) systems continuously improving, and with it the possibility to detect smaller lesions. Since first introduced in 2010, the number of hybrid PET/magnetic resonance imaging (MRI) systems worldwide is constantly increasing. It is therefore important to assess and compare the image quality, in terms of detectability, between the PET/MRI and the well-established PET/computed tomography (CT) systems. For this purpose, a PET image quality phantom (Esser) with hot spheres, ranging from 4 to 20 mm in diameter, was prepared with fluorodeoxyglucose and sphere-to-background activity concentrations of 8:1 and 4:1, to mimic clinical conditions. The phantom was scanned on a PET/MRI and a PET/CT system for both concentrations to obtain contrast recovery coefficients (CRCs) and contrast-to-noise ratios (CNRs), for a range of reconstruction settings. The detectability of the spheres was scored by three human observers for both systems and concentrations and all reconstructions. Furthermore, the impact of acquisition time on CNR and observer detectability was investigated. Results Reconstructions applying point-spread-function modeling (and time-of-flight for the PET/CT) yielded the highest CRC and CNR in general, and PET/CT demonstrated slightly higher values than PET/MRI for most sphere sizes. CNR was dependent on reconstruction settings and was maximized for 2 iterations, a pixel size of less than 2 mm and a 4 mm Gaussian filter. Acquisition times of 97 s (PET/MRI) and 150 s (PET/CT) resulted in similar total net true counts. For these acquisition times, the smallest detected spheres by the human observers in the 8:1 activity concentration was the 6-mm sphere with PET/MRI (CNR = 5.6) and the 5-mm sphere with PET/CT (CNR = 5.5). With an acquisition time of 180 s, the 5-mm sphere was also detected with PET/MRI (CNR = 5.8). The 8-mm sphere was the smallest detected sphere in the 4:1 activity concentration for both systems. Conclusion In this experimental study, similar detectability was found for the PET/MRI and the PET/CT, although for an increased acquisition time for the PET/MRI.

Cross-validation study between the HRRT and the PET component of the SIGNA PET/MRI system with focus on neuroimaging

“…As expected, the highest RCs were observed from PSF reconstructions for both PET/MR and HRRT data (Fig. 2 ) as has been reported by multiple studies for clinical PET systems [ 8 , 16 , 22 – 25 ]. However, since resolution modeling with PSF can cause edge artifacts (Gibbs artifacts), PSF reconstruction is not necessarily always the most quantitatively accurate method and it needs to be carefully evaluated [ 16 , 22 , 26 , 27 ].…”

Hybrid total-body pet scanners—current status and future perspectives

“…A slight delay to the actual product launch is therefore possible. The presented information has been extracted from [6,11,22,25,30,35,38,46,52,53,60,76,86,88,100,107] to a reduced sensitivity of the PET system. However, in a TB PET system, the increased axial coverage may be able to overcome this effect and keep the sensitivity at a level sufficient for fast and low-dose scans.…”

Standardisation of conventional and advanced iterative reconstruction methods for Gallium-68 multi-centre PET-CT trials

“…The NEMA IEC PET Body Phantom™ (Data Spectrum) was scanned on 12 Siemens and GE scanners with Fluorine-18. Local sites were provided with a standardised filling procedure and asked to acquire the phantom using local clinical protocols for FDG and a sphere-to-background ratio of 4.8:1 to approximate the average tumour-to-background ratio as observed in clinical FDG studies [ 23 , 24 ]. A summary of the scanner models and reconstruction parameters are shown in Table 1 .…”

“…The higher sphere-to-background ratio compared to the FDG scans was selected in order to take into account the higher tumour-to-background ratio observed in 68 Ga-PSMA scans. A conservative approach was selected though compared to the published contrast in clinical images, which also enables the results from this study to be compared with the existing literature [ 16 , 23 , 26 , 27 ]. The reconstruction parameters were based on the local clinical protocols for whole-body 68 Ga-PSMA scans.…”