Symbia t2 spect ct system

At the first day after ¹³¹I-chTNT injection, the rabbits (in the subgroup C and D) underwent SPECT/CT scanning for acquiring fusion image to observe the distribution of ¹³¹I-chTNT. The acquisition parameters of SPECT/CT (Symbia T2 SPECT/CT system, Siemens Munich, Germany) were used as follows: zoom 1.5, a 128×128 matrix with a pixel acquisition, the fusion CT acquisition used full-circle rotation, 130 kV, 35 mAs, and 5-mm slices.

No specific patient preparation was required except bladder voiding immediately before imaging. All patients were injected intravenously with ^99mTc-MIP-1404 (mean 705 ± 61 MBq). At 2–4 h, SPECT scans were acquired on a Symbia T2 SPECT/CT system (Siemens Healthcare) from midthigh to skull vertex with low-energy high-resolution collimation, a 128 × 128 matrix with 4.8-mm pixel size, and 120 projections over 360° for 15 s per projection. SPECT scans were followed by low-dose CT (130 kV, 30 mAs) using adaptive dose modulation (CAREDose 4D; Siemens Healthcare). CT data were reconstructed with 3- and 5-mm slice thicknesses using B70s and B41s kernels for image analysis. The SPECT dataset was reconstructed using an ordered-subset expectation maximization algorithm with 4 subsets and 8 iterations, including point-spread-function modeling with CT-based attenuation correction and dual-energy window scatter correction as previously described (10 (link)). Both PET and SPECT scanners underwent routine quality control measures.

Dosimetry was performed using quantitative ¹⁷⁷Lu-SPECT scans of the abdomen 24, 48, and 72 h postinjection. The images were acquired over 15 min on a dual-headed Symbia T2 SPECT/CT system (Siemens Healthineers, Erlangen, Germany) as described previously [12 (link),15 (link)]. For attenuation correction, a low-dose CT scan (AC-CT) was acquired together with the first SPECT scan 24 h postinjection. The AC-CT was coregistered on the SPECT scans acquired 48 and 72 h after therapy (rigid body co-registration, PMOD Version 3.609, PMOD Technologies, Zurich, Switzerland). Quantitative SPECT reconstruction employed an in-house maximum a posteriori (MAP) algorithm with 20 iterations, 16 subsets, and a penalty factor of 0.001, as described previously [8 (link),10 (link)]. Scatter correction and resolution decompensation was applied in addition to the mentioned attenuation correction. For each patient, three to five lesions with the highest visual uptake in abdominal SPECT were evaluated. Tumor lesions were segmented semi-manually by placing volumes of interest (VOIs) with an iso-contour of 40% as proposed by Collarino et al. and confirmed by in-house phantom studies [18 (link)]. Lesion dosimetry was based on a mono-exponential fit model and mass-scaled sphere S-values (Figure 2).