Table 2.
CPU time and speedup for simulated data experiments. Times are reported as the sum of execution time across all processes.
| Average SSDa Time (min) | Average Iteration Time (min) | # EM Iterations | Total CPU Time (hrs) | |
|---|---|---|---|---|
| Simulated 0.05 SNR | ||||
| StandardEM | 4004 | 4022 | 10 | 670 |
| SubspaceEM-1x | 2.8 | 6.1 | 6 | 0.8 |
| SubspaceEM-2x | 4.3 | 7.2 | 6 | 0.9 |
| SubspaceEM-Overall | 3.5 | 6.7 | 12 | 1.7 |
| Simulated 0.02 SNR | ||||
| StandardEM | 3914 | 3924 | 7 | 458 |
| SubspaceEM-1x | 2.6 | 7.1 | 5 | 0.8 |
| SubspaceEM-2x | 3.7 | 6.8 | 6 | 0.9 |
| SubspaceEM-Overall | 3.2 | 7.0 | 11 | 1.6 |
| Speedupb | ||||
| Simulated 0.05 SNR | 1144 | 600 | - | 394 |
| Simulated 0.02 SNR | 1223 | 561 | - | 280 |
a
SSD = Sum of squared differences. In StandardEM, the differences are calculated between images and projections. In SubspaceEM, the differences are between approximated images and approximated projections.
b
Speedup is calculated as (StandardEM time)/(SubspaceEM-Overall time).