CTDIw vs. Beam Collimation
| Total beam collimation (mm) | Detector configuration | CTDIw relative to 10-mm beam |
|---|---|---|
| 5 | 4 × 1.25 mm | 1.22 |
| 10 | 4 × 2.5 mm | 1.00 |
| 15 | 4 × 3.75 mm | 0.93 |
| 20 | 16 × 1.25 mm | 0.89 |
| 40 | 16 × 2.5 mm | 0.83 |
Because discarded penumbra represents smaller fraction of total beam width, CTDI values decrease with increasing beam widths (combined data from GE Healthcare 4-slice and 64-slice MSCT scanners).