Signa pet mri

Pelvic ¹⁸F-FDG PET/MRI scanning was performed 33 ± 12 min after PET/CT scanning. All images were acquired from the scans that were performed using Signa PET/MRI (GE Healthcare, Waukesha, WI, USA), integrating time-of-flight–PET, and 3.0 T MRI (GE Signa 750w) scanners. PET images and MRI images were acquired simultaneously. A 32-channel coil (upper anterior array) served as the cavitary scanning coil. The pelvic axial scan ranged from the vaginal level to the superior iliac boundary. For pelvic MRI scanning, T2-weighted images (T2WI) were acquired in the axial, sagittal, and coronal planes using the following T2WI parameters: repetition time (TR), 2600–3400 ms; echo time (TE), 60–90 ms; section thickness, 5 mm; interval, 1 mm; matrix, 384 × 384; field of view (FOV), 240 × 240 mm. Axial T1-weighted images parameters were as follows: TR, 500 ms; TE, 8 ms; section thickness, 5 mm; interval, 1 mm; matrix, 384 × 384; FOV, 240 × 240 mm. Axial diffusion-weighted imaging (DWI) with b-values of 0 and 800 s/mm² were obtained. For PET scanning, the correction for γ-ray attenuation was performed with the Dixon MRI sequence. PET scanning was conducted under list mode. Images were reconstructed by iterative ordered subset expectation maximization. The pelvic scan time for PET/MRI was approximately 24 min.

⁶⁸Ga-PSMA was synthetized according to the procedure previously described. [12 (link)]
Fasting condition was requested on the day of ⁶⁸Ga-PSMA PET/MRI scan. Images were acquired on a fully hybrid 3 Tesla PET/MRI system (SIGNA PET/MRI; General Electric Healthcare, Waukesha, WI, USA) from the skull base to mid-thigh in the following examined patients.
The ⁶⁸Ga-PSMA PET/MRI scan started approximately 60 min (Mean ± SD, 63 ± 17 min) after injection of 129–288 MBq (mean ± SD, 170.56 ± 36.06 MBq) of ⁶⁸Ga-PSMA [10 (link),14 (link)].
The ⁶⁸Ga-PSMA PET/MR examination protocol included a high statistic (HS) scan of the pelvis (20 min), covering a single bed position, that was simultaneously acquired with the following MRI sequences.
Following the single bed HS acquisition, a total-body (TB) PET scan (5–6 FOVs, 4 min/FOV) was then simultaneously acquired to a MRI TB T1 Lava Flex sequence for anatomical localization, and a TB DWI with b = 50 and b = 1000 s/mm².
PET images were reconstructed using a Bayesian penalized likelihood reconstruction algorithm with a reconstructed FOV of 60 cm and image matrix of 192 × 192. The algorithm includes a Point Spread Function and Time of Flight information.
Attenuation Correction (AC) of PET data was performed using MR-Based AC technique based on the processing of the LAVA-Flex sequences acquired simultaneously with the PET data.

Patients’ preparation, radiotracer injection, and acquisition protocol were performed as previously described [22 (link)]. In relation to the retrospective design of the study, different tomographs were used: (1) a fully hybrid 3T PET/MRI system (SIGNA PET/MRI; General Electric Healthcare, Waukesha, WI, USA), (2) a Discovery ST (General Electric Healthcare), (3) a Discovery STE (General Electric Healthcare), (4) a Gemini-GXL (Philips Medical Systems, Eindhoven, The Netherlands), and (5) a Discovery 690 (General Electric Healthcare). The PET scans were performed in 2-D mode (4 min per bed position) with the Discovery ST, while 3-D mode acquisition was used with the PET/MRI (4 min per bed position), Discovery STE (2.5 min per bed position), Discovery 690 (3 min per bed position), and Gemini GXL (2 min per bed position). PET raw data were corrected for random, scatter and attenuation, and reconstructed. To overcome the impact of PET image acquisition and reconstruction factors (scanner effects) on imaging parameters, the ComBat harmonization method and tool [38 (link)] were used.

All participants underwent a simultaneous PET-MRI examination on a time-of-flight (TOF) PET-MRI scanner (SIGNA PET-MRI; GE Medical Systems, USA). PET scanning took place for the entirety of the 42-min scanning session. A bolus injection of ¹¹C-raclopride was administered 1 min after the PET scan commenced and, at this same time, we began to obtain brain-structural and MRI-based attenuation correction data for 9 min. We then initiated a 32-min-long fMRI scan. Participants were instructed to rest with their eyes open for the first and last 6 minutes of this scan and to complete trials of a reward challenge task—the MID task, described below—for 20 min between these two rest conditions. Minutes 2–17 of PET data were used to estimate basal BP_ND; PET data from Minute 2 onward (baseline plus task) were used to estimate endogenous ligand displacement by the task. See Fig. 1 for a depiction of the timing of data collection, data modelling, and participant behavior.Fig. 1

Schematic of the timing of data collection, data modelling, and participant behavior for our concurrent PET-MRI scanning paradigm

A clinical routine whole-body ⁶⁸Ga-PSMA-11 PET/MRI was performed 60 min after injection on a hybrid scanner (SIGNA PET/MRI, GE Healthcare, Waukesha, WI, USA) used in previous studies at our department with the same protocol for prostate imaging as recently described [13 (link)]. In brief, six bed positions with 2–3 min acquisition time per bed position for the whole-body protocol, and additional specific sequences covering the pelvis, including a high resolution T1-weighted LAVA-FLEX sequence, T2-weighted fast recovery fast spin-echo sequence in at least two planes and DWI was performed.

[⁶⁸Ga]Ga-PSMA-11 was produced under good manufacturing practices (GMP) as previously described [19 (link)] using an ITG germanium-gallium generator and an iQs fluidic labeling module (ITG, Gärching/Munich, Germany). A median of 73 min (range 53–121 min) following intravenous injection of median 207.2 MBq (range 173.9–299.7 MBq, median 5.6 mCi, range 4.7–8.1 mCi) [⁶⁸Ga]Ga-PSMA-11, patients underwent PET/MRI (3.0 T time-of-flight Signa PET/MRI, GE Healthcare, Waukesha, WI). Targeted MR imaging of the neck was performed in two stations (upper and lower neck) using axial pre-gadolinium T1 weighted, T2 weighted, diffusion weighted, and post-gadolinium T1 weighted sequences. Whole-body PET and whole-body MRI were simultaneously acquired for 3 min at each bed position with concurrent axial T1 and T2 weighted sequences, from the vertex to mid-thighs with arms overhead if tolerated. PET data was reconstructed using time-of-flight, OSEM with two iterations and 28 subsets. A matrix size of 256 × 256 was used, with 600 × 250 mm field of view, and 2.8 mm slice thickness. As has been described [20 (link)], attenuation correction with a standard two-point Dixon acquisition converted into an attenuation map was performed.