Table 1.
Reference CT numbers, signal-to-noise-ratios (SNRs), and contrast-to-noise-ratios (CNRs) for filtered back-projection (FBP), iterative reconstruction iDose4 (levels 2, 4, and 6), and iterative model-based reconstruction (IMR; levels 1, 2, and 3) at CT dose indexes (CTDIvol) of 40.0, 32.0, 24.0, 16.0, 8.0, and 4.0 mGy at 120 and 140- kVp without the influence of metal artifacts. Reference values were determined by averaging values of the unaffected pellets L0, L4, R0, and R4
| CTDIvol (mGy) | FBP | iDose4 L2 | iDose4 L4 | iDose4 L6 | IMR L1 | IMR L2 | IMR L3 | |
|---|---|---|---|---|---|---|---|---|
| CT numbers | ||||||||
| 120- kVp | 40.0 | 285 ± 37 | 283 ± 30 | 283 ± 25 | 283 ± 20 | 263 ± 15 | 263 ± 11 | 263 ± 6 |
| 32.0 | 285 ± 43 | 284 ± 34 | 284 ± 29 | 283 ± 22 | 265 ± 16 | 265 ± 11 | 265 ± 7 | |
| 24.0 | 282 ± 41 | 284 ± 30 | 284 ± 25 | 283 ± 20 | 267 ± 14 | 268 ± 9 | 269 ± 5 | |
| 16.0 | 278 ± 60 | 279 ± 42 | 280 ± 35 | 281 ± 28 | 265 ± 17 | 266 ± 12 | 267 ± 6 | |
| 8.0 | 286 ± 79 | 284 ± 42 | 284 ± 36 | 282 ± 28 | 269 ± 17 | 269 ± 11 | 269 ± 5 | |
| 4.0 | 261 ± 114 | 282 ± 56 | 283 ± 48 | 282 ± 38 | 267 ± 20 | 268 ± 13 | 269 ± 6 | |
| 140- kVp | 40.0 | 259 ± 38 | 259 ± 30 | 259 ± 26 | 259 ± 20 | 243 ± 15 | 244 ± 11 | 244 ± 6 |
| 32.0 | 264 ± 33 | 263 ± 26 | 263 ± 22 | 262 ± 17 | 245 ± 12 | 245 ± 8 | 246 ± 5 | |
| 24.0 | 254 ± 43 | 255 ± 33 | 255 ± 28 | 256 ± 22 | 241 ± 15 | 242 ± 10 | 243 ± 6 | |
| 16.0 | 260 ± 57 | 261 ± 37 | 261 ± 32 | 261 ± 25 | 247 ± 15 | 247 ± 10 | 247 ± 5 | |
| 8.0 | 244 ± 82 | 254 ± 42 | 255 ± 36 | 255 ± 27 | 246 ± 16 | 247 ± 11 | 248 ± 6 | |
| 4.0 | 258 ± 118 | 265 ± 56 | 264 ± 47 | 261 ± 37 | 247 ± 20 | 247 ± 13 | 247 ± 6 | |
| SNRs | ||||||||
| 120- kVp | 40.0 | 7.8 ± 1.1 | 9.7 ± 1.4 | 11.5 ± 1.7 | 14.7 ± 2.4 | 17.6 ± 2.1 | 25.3 ± 3.3 | 46.9 ± 14.8 |
| 32.0 | 6.6 ± 0.8 | 8.5 ± 0.9 | 9.9 ± 1.0 | 12.8 ± 1.3 | 17.0 ± 1.5 | 24.1 ± 2.0 | 40.3 ± 4.2 | |
| 24.0 | 7.0 ± 0.9 | 9.6 ± 1.4 | 11.4 ± 1.6 | 14.4 ± 2.2 | 20.1 ± 3.7 | 29.9 ± 5.7 | 53.1 ± 13.0 | |
| 16.0 | 4.7 ± 0.6 | 6.7 ± 0.5 | 7.9 ± 0.5 | 10.2 ± 0.8 | 15.2 ± 1.0 | 22.9 ± 2.2 | 45.4 ± 5.6 | |
| 8.0 | 3.6 ± 0.2 | 6.7 ± 0.4 | 8.0 ± 0.5 | 10.2 ± 0.5 | 15.9 ± 1.5 | 24.7 ± 2.1 | 53.4 ± 8.2 | |
| 4.0 | 2.3 ± 0.5 | 5.1 ± 0.8 | 6.0 ± 0.9 | 7.5 ± 1.1 | 13.7 ± 0.8 | 21.3 ± 1.6 | 44.1 ± 9.3 | |
| 140-kVp | 40.0 | 7.1 ± 1.3 | 8.8 ± 1.6 | 10.4 ± 1.8 | 13.3 ± 2.4 | 16.4 ± 1.8 | 23.3 ± 2.8 | 41.5 ± 5.8 |
| 32.0 | 8.1 ± 0.6 | 10.3 ± 1.0 | 12.3 ± 1.2 | 15.2 ± 1.7 | 20.7 ± 2.1 | 29.2 ± 2.0 | 50.5 ± 2.3 | |
| 24.0 | 5.9 ± 0.5 | 7.8 ± 0.6 | 9.2 ± 0.5 | 11.6 ± 0.5 | 15.9 ± 0.9 | 23.3 ± 0.8 | 40.3 ± 2.6 | |
| 16.0 | 4.6 ± 0.4 | 7.0 ± 0.5 | 8.3 ± 0.6 | 10.5 ± 0.7 | 16.9 ± 0.8 | 24.7 ± 1.7 | 47.2 ± 9.0 | |
| 8.0 | 3.1 ± 0.8 | 6.1 ± 0.7 | 7.2 ± 0.8 | 9.4 ± 1.2 | 15.0 ± 0.9 | 22.4 ± 0.5 | 45.0 ± 12.0 | |
| 4.0 | 2.2 ± 0.4 | 4.8 ± 0.7 | 5.6 ± 0.8 | 7.0 ± 1.0 | 12.4 ± 1.6 | 19.2 ± 2.4 | 39.7 ± 6.2 | |
| CNRs | ||||||||
| 120- kVp | 40.0 | 7.9 ± 0.6 | 9.8 ± 0.9 | 11.5 ± 1.0 | 14.1 ± 1.4 | 17.7 ± 1.1 | 23.1 ± 1.4 | 32.7 ± 1.9 |
| 32.0 | 7.3 ± 0.8 | 9.3 ± 0.8 | 10.9 ± 0.9 | 13.7 ± 1.0 | 18.1 ± 1.4 | 24.5 ± 1.8 | 35.9 ± 1.9 | |
| 24.0 | 6.0 ± 0.5 | 8.1 ± 0.8 | 9.6 ± 1.0 | 12.1 ± 1.5 | 16.4 ± 1.5 | 23.1 ± 2.3 | 38.0 ± 3.8 | |
| 16.0 | 5.3 ± 0.3 | 7.8 ± 0.3 | 9.2 ± 0.4 | 11.6 ± 0.8 | 17.4 ± 1.3 | 25.4 ± 2.7 | 40.0 ± 7.2 | |
| 8.0 | 3.3 ± 0.7 | 6.0 ± 0.8 | 7.1 ± 1.0 | 8.8 ± 1.0 | 14.8 ± 1.6 | 22.2 ± 2.8 | 41.2 ± 6.6 | |
| 4.0 | 2.1 ± 0.7 | 5.0 ± 0.6 | 6.0 ± 0.7 | 7.6 ± 0.8 | 13.6 ± 0.5 | 21.3 ± 0.9 | 43.3 ± 5.7 | |
| 140- kVp | 40.0 | 7.7 ± 0.5 | 9.5 ± 0.5 | 11.1 ± 0.6 | 14.1 ± 1.2 | 17.3 ± 1.6 | 23.4 ± 2.9 | 34.9 ± 6.3 |
| 32.0 | 6.8 ± 1.0 | 8.5 ± 1.1 | 9.9 ± 1.3 | 12.4 ± 1.8 | 15.9 ± 1.2 | 21.8 ± 1.8 | 33.0 ± 3.3 | |
| 24.0 | 6.1 ± 1.0 | 8.0 ± 1.3 | 9.4 ± 1.6 | 11.9 ± 2.1 | 16.2 ± 3.3 | 22.6 ± 5.4 | 35.1 ± 11.7 | |
| 16.0 | 4.8 ± 0.6 | 7.0 ± 0.6 | 8.3 ± 0.8 | 10.6 ± 0.9 | 16.7 ± 0.4 | 23.8 ± 0.8 | 38.7 ± 1.5 | |
| 8.0 | 3.2 ± 0.7 | 5.6 ± 0.7 | 6.6 ± 0.9 | 8.4 ± 1.0 | 14.8 ± 1.4 | 22.0 ± 2.7 | 38.2 ± 7.3 | |
| 4.0 | 2.3 ± 0.5 | 5.3 ± 0.8 | 6.2 ± 0.9 | 7.7 ± 1.1 | 13.7 ± 2.1 | 21.0 ± 2.9 | 40.8 ± 5.8 | |