For each patient, whole-body (WB) SPECT/CT scans were acquired (three bed positions from the top of the head to the upper thighs; 90 projections and 25 s per projection) on a Symbia T2 scanner (Siemens Healthineers, Erlangen, Germany) at 1.5 ± 0.5 h, 6 ± 1 h, 24 ± 3 h, 48 ± 3 h, and at 7 days p.i. with a lutetium-177 reference-standard of approximately 10 MBq within the field of view. The scanner was equipped with a medium-energy low-penetration collimator. Three energy windows were acquired and used for further processing, a peak window of 20% width centered around the 208 keV energy peak and two adjacent corresponding lower and upper scatter energy windows of 10% width.
The SPECT images were stitched and quantitatively reconstructed using a commercial 3D ordered-subset expectation maximization (OSEM) algorithm (Flash 3D, Siemens Medical Solution, Germany) using 8 iterations and 9 subsets applying uniformity correction, CT-based attenuation correction, energy window-based scatter correction, and collimator-detector response modeling.
To yield quantitative images in units of Bq/mL, a calibration factor was determined from a phantom experiment using an IEC NEMA body phantom filled with 765 MBq lutetium-177 and applied to each patient SPECT dataset.
The SPECT images were stitched and quantitatively reconstructed using a commercial 3D ordered-subset expectation maximization (OSEM) algorithm (Flash 3D, Siemens Medical Solution, Germany) using 8 iterations and 9 subsets applying uniformity correction, CT-based attenuation correction, energy window-based scatter correction, and collimator-detector response modeling.
To yield quantitative images in units of Bq/mL, a calibration factor was determined from a phantom experiment using an IEC NEMA body phantom filled with 765 MBq lutetium-177 and applied to each patient SPECT dataset.