Radiation dose indices, noise, and CNR of temporal bone helical scans with different detector collimations
| Detector Collimation (mm) | CTDIvol (mGy) | DLP (mGy · cm) | Noise (HU) | CNR | ||||
|---|---|---|---|---|---|---|---|---|
| Axial | Coronal | |||||||
| Brain Stem | Sphenoid | Brain Stem | Air | Axial | Coronal | |||
| 2 × 0.5 | 32.2 | 1296.7 | 186.2 | 60.4 | 76.5 | 27.5 | 7.3 | 18.1 |
| 16 × 0.625 | 25.5 | 1026.9 | 97.8 | 41.8 | 64.5 | 55.8 | 13.0 | 15.8 |
| 20 × 0.625 | 16.3 | 656.4 | 156.6 | 65.4 | 82.8 | 60.7 | 8.1 | 13.2 |
| 40 × 0.625 | 23.3 | 1169.0 | 92.3 | 40.7 | 73.9 | 56.8 | 13.6 | 14.3 |
| 64 × 0.625 | 22.9 | 1836.6 | 99.9 | 45.9 | 62.7 | 60.5 | 12.3 | 15.6 |
Note:—The 2 × 0.5- and 20 × 0.625-mm detector collimations used the system's “ultrahigh resolution” setting and pitches of 0.7 and 0.656, respectively. So, the noise and CNR of axial images were significantly different from the other detector collimations utilizing the system's “high resolution” setting.