Line sources with 177Lu solutions (0.3 MBq/ml) were prepared and measured in air at three different distances (5, 10, and 15 cm) from the gamma camera collimator. The gamma camera used for generating planar and SPECT/CT images was a Millennium VG Hawkeye (General Electric Medical Systems, Milwaukee, WI, USA), equipped with a medium-energy parallel-hole collimator. A 20% energy window over the 208 keV photon peak was used. A 1024 × 1024 matrix was used for the gamma camera measurement of the line sources. The SPECT image acquisition used the same energy setting as above. The clinical SPECT images of patients, injected with 7.4 GBq 177Lu-DOTATATE, were collected 24 h post-injection, with a 30-s frame time duration for 120 projections. The matrix size was 128 × 128 with a pixel size of 4.42 mm and a slice thickness of 4.42 mm. The CT images were acquired using a 140-kV tube voltage, 2.5 mAs, and a rotation speed of 2.6 rpm. The matrix size was 512 × 512 with a pixel size of 0.98 mm and a slice thickness of 5 mm.
The Jaszczak image quality phantom was used to evaluate the performance of the MC OSEM reconstruction (SARec-OSEM) in comparison with standard clinical attenuated corrected OSEM reconstructions (AC-OSEM) and clinical state-of-the-art OSEM reconstructions with resolution recovery corrections (RRC-OSEM). A 256 × 256 matrix was used in this evaluation. The six spheres and the background in the Jaszczak phantom were filled with an activity concentration of 300 and 12 kBq/ml, respectively. Thereby, the activity concentration ratio between the spheres and the background was equal to 25, which is in the order of the tumor-to-normal tissue ratios observed in patients [32 (link)]. The activity recovery, i.e., the normalized signal-to-background ratio (SBR) and signal-to-noise ratio (SNR), were measured. The signal in the different sphere sizes was measured within a volume of interest (VOI) equal in size to the spheres. The mean background and the standard deviation of the background were measured in 19 VOIs, equal in size to the signal VOI, and placed in the central plane of the phantom.
The Jaszczak image quality phantom was used to evaluate the performance of the MC OSEM reconstruction (SARec-OSEM) in comparison with standard clinical attenuated corrected OSEM reconstructions (AC-OSEM) and clinical state-of-the-art OSEM reconstructions with resolution recovery corrections (RRC-OSEM). A 256 × 256 matrix was used in this evaluation. The six spheres and the background in the Jaszczak phantom were filled with an activity concentration of 300 and 12 kBq/ml, respectively. Thereby, the activity concentration ratio between the spheres and the background was equal to 25, which is in the order of the tumor-to-normal tissue ratios observed in patients [32 (link)]. The activity recovery, i.e., the normalized signal-to-background ratio (SBR) and signal-to-noise ratio (SNR), were measured. The signal in the different sphere sizes was measured within a volume of interest (VOI) equal in size to the spheres. The mean background and the standard deviation of the background were measured in 19 VOIs, equal in size to the signal VOI, and placed in the central plane of the phantom.