Radiation dose indices, noise, and CNR of temporal bone axial scans with different detector collimations
| Detector Collimation (mm) | CTDIvol(mGy) | DLP (mGy · cm) | Noise (HU) | CNR | |
|---|---|---|---|---|---|
| Brain Stem | Sphenoid | ||||
| 2 × 0.625 | 47.2 | 1898.6 | 77.9 | 41.4 | 16.1 |
| 12 × 0.625 | 20.8 | 935.6 | 18.7 | 15.0 | 60.5 |
| 16 × 0.625 | 22.6 | 902.8 | 82.9 | 43.4 | 15.1 |
| 40 × 0.625 | 24.2 | 1211.5 | 75.3 | 34.6 | 17.2 |
| 64 × 0.625 | 19.4 | 775.6 | 80.4 | 49.6 | 14.8 |
Note:—When the 12 × 0.625-mm collimation was selected, the system could not choose 180 mAs/section. The closest tube mAs, 165 mAs/section, was selected. In addition, the 12 × 0.625-mm collimation used the system's “detailed resolution” setting and got substantially different noise and CNR, with no comparability with other collimations. The 12 × 0.625-mm detector collimation was not available in helical mode and was not included in the comparison.