Table 3.
Scan parameters and CTDI of 3 initial CBCT protocols
| Head | Pelvis | Thorax | |
|---|---|---|---|
| Tube voltage (kVp) | 100 | 125 | 110 |
| Tube current (mA) | 20 | 42 | 20 |
| Exposure time per projection (ms) | 20 | 20 | 20 |
| C-ring rotation range (°) | 200 | 360 | 360 |
| Frame rate (fps) | 10 | 10 | 10 |
| Number of projections | 340 | 600 | 600 |
| Fan mode | Full | Half | Half |
| Reconstruction matrix | 512 × 512 | 1024 × 1024 | 1024 × 1024 |
| Bow-tie filter | Full | Half | Half |
| Pixel size (mm) | 0.55 | 0.52 | 0.52 |
| Slice spacing (mm) | 0.6 | 1 | 1 |
| Phantom diameter (cm) | 16 | 32 | 32 |
| CTDI (centre) (mGy) | 3.4 | 6.5 | 2.0 |
| CTDI (top) (mGy) | 1.9 | 9.7 | 3.2 |
| CTDI (right) (mGy) | 4.2 | 9.3 | 3.1 |
| CTDI (bottom) (mGy) | 5.1 | 8.8 | 2.9 |
| CTDI (left) (mGy) | 3.5 | 11.5 | 3.8 |
| Weighted CTDI (mGy) | 3.6 | 8.7 | 2.9 |
CBCT, cone beam CT; CTDI, CT dose index.