E soft workstation

Commercially available FDG (185 MBq) in 2 ml of saline solution was purchased from Nihon Medi-phyisics Co. Ltd. (Tokyo, Japan). All patients were examined by whole-body PET with an integrated 16-slice multidetector CT (Siemens Biograph-16 PET/CT, Nashville, TN, USA).
The patients fasted for more than 5 h before receiving an intravenous injection of FDG (185 MBq). Whole-body PET/CT images (head to upper thigh) were acquired after 60 min for each patient in using 5 or 6 bed positions, depending on subject's height. Emission images were acquired for 2 min per bed position. The data was reconstructed using the ordered subsets expectation maximization (OSEM) method using eight subsets, two iterations, and an array size of 256 × 256. For the attenuation correction of PET/CT fusion images, the CT component was performed according to a standard protocol with the following parameters: 140 kV; 50 mAs; tube rotation time, 0.5 s per rotation; slice thickness, 5 mm; and gap, 2 mm. The E-soft workstation (Siemens, Nashville, TN, USA) was used to construct PET/CT fusion images.

For the ⁹⁰Y-PET acquisition, two scanners were used: GEMINI™ 64 TOF by Philips Medical Systems Nederland B.V. Best and DISCOVERY™ 710 TOF by General Electric, Chicago, USA. The acquisition time per bed position was 15 min, with two bed positions in the absence of lung shunt, or 10 min/bed position, with three bed positions covering the lung in the presence of lung shunt at MAA. Patients with lung shunt were preferably scanned on the DISCOVERY 710 to avoid the underestimation by GEMINI reported in the QUEST study [28 (link)]. The reconstruction protocols were the Blob-OS-TF algorithm (3 iterations, 33 subsets, smooth and sharp) for Philips and the QClear penalized likelihood algorithm (26 iterations, 48 subsets, noise regularization parameter β = 1500) in the GE case.
The ⁹⁰Y-PET images were coregistered to ^99mTc-MAA SPECT images on a e.soft workstation (Siemens Medical Solutions, Hoffmann Estates, USA) with automated rigid coregistration (mutual information algorithm). This allowed us to copy previously defined VOIs onto PET images, thus avoiding inaccuracies derived from having a second VOI definition. Coregistration was always visually inspected.

All patients were examined with a whole-body PET scanner, GE Advance (GE Healthcare, Waukesha, WI, USA), or with a whole-body PET/CT scanner, Siemens True Point Biograph 16 (Siemens/CTI, Erlangen, Germany). All subjects received an intravenous injection of MeAIB (513.6 ± 65.6 MBq) or MET (533.9 ± 35.0 MBq). Brain PET/CT images were acquired 20 min after the radiotracer injection in 1 bed position in both study. Emission images were acquired for 5 min per bed position. The data were reconstructed using the ordered subsets expectation-maximization method using eight subsets, two iterations, and an array size of 256 × 256. For the attenuation correction of PET/CT fusion images, the CT component was performed according to a standard protocol with the following parameters: 140 kV; 50 mAs; tube rotation time, 0.5 s per rotation; slice thickness, 5 mm; and gap, 2 mm. An E-soft workstation (Siemens, Nashville, TN, USA) was used to construct PET/CT fusion images.

All reconstructed images were evaluated using the Esoft workstation (Siemens Healthineers, Germany) volumetric analysis application. Volumes of interests (VOIs) defined on the CT image were applied to the SPECT reconstructed data. The total numbers of counts summed over the phantom reconstructed image (a VOI defined about the CT image of the outer boundaries of the phantom) were used to determine the image calibration factor (ICF). The ICF given in cps/MBq was calculated for the entire volume of the phantom using the formula:
where Counts_Phantom denotes the total number of counts in a VOI defined about the CT image of the outer boundaries of the phantom, after background subtraction, A is the activity present in the phantom at the time of acquisition given in MBq, and T denotes the acquisition duration given in s (T = 3840 s, constant for all acquisitions). The counts per mL in the background was calculated by placing eight spherical VOIs randomly in the main cylinder image (also between cylindrical sources at their height in the phantom; see Fig. 2). The standard uncertainty of the ICF (u(ICF)) was calculated as follows:
The standard uncertainty in the counts u(Counts_Phantom), as well as on measured activity u(A) and for acquisition duration u(T) were defined as the standard uncertainty of planar sensitivity calculations.