Table 3. Contrast-to-noise (CNR) and figure of merit (FOM) values of different nodules at the threshold of scanning conditions.
| Kilovolt | Tolerance threshold of subjective perception to image quality | Image quality threshold of −800 HU nodules observed | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Milliampere-second | Volume CT dose index (mGy) | CNR | FOM | Milliampere-second | Volume CT dose index (mGy) | CNR | FOM | ||||||||||||||||
| A | B | C | D | A | B | C | D | A | B | C | D | A | B | C | D | ||||||||
| 120 | 20 | 1.4 | 2.7 | 1.2 | 1.4 | 0.9 | 5.0 | 1.0 | 1.4 | 0.6 | 10 | 0.7 | 1.9 | 0.9 | 1.2 | 0.6 | 5.2 | 1.2 | 2.3 | 0.6 | |||
| 100 | 40 | 1.6 | 3.1 | 1.6 | 1.7 | 1.0 | 6.1 | 1.7 | 1.8 | 0.6 | 20 | 0.8 | 2.5 | 1.0 | 1.5 | 0.6 | 7.9 | 1.1 | 2.7 | 0.5 | |||
| 80 | 80 | 1.6 | 3.0 | 1.4 | 1.0 | 0.8 | 5.7 | 1.3 | 0.6 | 0.4 | 40 | 0.8 | 2.4 | 1.1 | 1.2 | 0.5 | 7.5 | 1.4 | 1.8 | 0.4 | |||
A, −630 HU nodule with 12-mm diameter at right chest wall of right lower lung; B, −800 HU nodule with 8-mm diameter at posterior chest wall of right lower lung, adjacent to spine; C, −630 HU nodule with 8-mm diameter at left costophrenic angle; D, −800 HU nodule with 12-mm diameter at left costophrenic angle.