Table 18.
Physical (geometric) diameters and water-equivalent diameters of different body regions of the six phantoms in this studya.
| Male |
Female |
|||||
|---|---|---|---|---|---|---|
| Normal | Obese class I | Obese class II | Normal | Obese class I | Obese class III | |
| Physical (geometric) diameter (cm) | ||||||
| dchest | 26.8 | 32.3 | 34.5 | 27.8 | 30.5 | 35.1 |
| dabdomen | 25.2 | 32.0 | 35.4 | 27.0 | 30.0 | 35.7 |
| dpelvis | 26.7 | 31.4 | 33.7 | 28.5 | 31.3 | 36.6 |
| dabdomen-pelvis | 26.0 | 31.7 | 34.5 | 27.8 | 30.6 | 36.1 |
| dtrunk | 26.3 | 31.9 | 34.4 | 27.9 | 30.6 | 35.8 |
| Water-equivalent diameter (cm) | ||||||
| Mean energy = 62 keV2 | ||||||
| dw, chest | 25.3 (−6%) | 30.6 (−5%) | 32.8 (−5%) | 25.5 (−8%) | 29.2 (−4%) | 33.1 (−6%) |
| dw, abdomen | 25.6 (2%) | 32.4 (1%) | 35.6 (1%) | 27.1 (0%) | 30.4 (1%) | 35.9 (1%) |
| dw, pelvis | 28.2 (5%) | 32.6 (4%) | 35.0 (4%) | 30.0 (5%) | 32.5 (4%) | 37.8 (3%) |
| dw, abdomen-pelvis | 26.9 (4%) | 32.5 (3%) | 35.3 (2%) | 28.5 (3%) | 31.5 (3%) | 36.9 (2%) |
| dw, trunk | 26.4 (0%) | 31.9 (0%) | 34.4 (0%) | 27.6 (−1%) | 30.8 (1%) | 35.8 (0%) |
| Mean energy = 83 keV2 | ||||||
| dw, chest | 25.1 (−7%) | 30.4 (−6%) | 32.6 (−6%) | 25.3 (−9%) | 29.0 (−5%) | 33.0 (−6%) |
| dw, abdomen | 25.5 (1%) | 32.3 (1%) | 35.5 (0%) | 27.0 (0%) | 30.3 (1%) | 35.9 (0%) |
| dw, pelvis | 27.9 (4%) | 32.4 (3%) | 34.8 (3%) | 29.7 (4%) | 32.3 (3%) | 37.6 (3%) |
| dw, abdomen-pelvis | 26.7 (3%) | 32.3 (2%) | 35.2 (2%) | 28.3 (2%) | 31.3 (2%) | 36.8 (2%) |
| dw, trunk | 26.2 (0%) | 31.7 (−1%) | 34.2 (−1%) | 27.4 (−2%) | 30.7 (0%) | 35.6 (−1%) |
1
Percent values in parenthesis equal
2
Sixty-two kilo-electron-volt is the mean energy of the 120 kVp beam at the isocenter of the GE LightSpeed VCT scanner. It was calculated after attenuating the prebowtie spectrum (at the exit of the x-ray tube and before filtration by the bowtie filter) of the 120 kVp beam by the least attenuating section of the bowtie filter (at beam angle of 0°). Eighty-three kilo-electron-volt is the mean energy of the prebowtie spectrum after being attenuated by 40 cm of water (representing an obese patient) and the most attenuating section of the bowtie filter (at beam angle of ∼27.5°).