Table 4 Selections of the regularization parameters with different noise levels
|  | Shepp–Logan | Head slice | ||
|---|---|---|---|---|
60 views 2 million photons | 60 views 1 million photons | 180 views 2 million photons | 90 views 2 million photons | |
DL methods | 4.841 × 103 | 8.141 × 103 | 1.451 × 103 | 1.725 × 103 |
GPBB | 0.4 | 0.5 | 0.5 | 0.6 |