Table 3.
Distribution of CT exams in the fetal-exposure cohort and childhood-exposure cohort from 1996–2016
| Fetal-Exposure Cohort | United States | Ontario, Canada | Total | |||
| n | Col % | n | Col % | n | Col % | |
| Total children | 881,205 | 100.0% | 2,592,795 | 100.0% | 3,474,001 | 100.0% |
| Number of CT exams during mother’s pregnancy per child | ||||||
| 0 | 874,579 | 99.2% | 2,580,910 | 99.5% | 3,455,489 | 99.5% |
| 1 | 6,329 | 0.7% | 10,938 | 0.4% | 17,267 | 0.5% |
| 2 | 252 | <0.05% | 853 | <0.05% | 1,105 | <0.05% |
| 3+ | 45 | <0.05% | 94 | <0.05% | 139 | <0.05% |
| Fetal age at each exam | ||||||
| <14 weeks (first trimester) | 3,269 | 36.8% | 4,116 | 31.7% | 7,385 | 33.8% |
| 14 – <27 weeks (second trimester) | 2,647 | 29.8% | 2,440 | 18.8% | 5,087 | 23.3% |
| 27+ weeks (third trimester) | 2,964 | 33.4% | 3,910 | 30.1% | 6,874 | 31.4% |
| Unknown trimester | 0 | <0.05% | 2,516 | 19.4% | 2,516 | 11.5% |
| Total | 8,880 | 100.0% | 12,982 | 100.0% | 21,862 | 100.0% |
| Exams by anatomic region | ||||||
| Abdomen | 1,508 | 21.6% | 2,375 | 18.3% | 3,883 | 19.4% |
| Chest | 2,115 | 30.2% | 2,979 | 22.9% | 5,094 | 25.5% |
| Head and/or Neck | 2,984 | 42.7% | 6,633 | 51.1% | 9,617 | 48.2% |
| Neck and/or C-Spine | 137 | 2.0% | 129 | 1.0% | 266 | 1.3% |
| Other, NOS | 76 | 1.1% | 217 | 1.7% | 293 | 1.5% |
| Multiple areas | 172 | 2.5% | 649 | 5.0% | 821 | 4.1% |
| Total | 6,992 | 100.0% | 12,982 | 100.0% | 19,974 | 100.0% |
| Childhood-Exposure Cohort | United States | Ontario, Canada | Total | |||
| n | Col % | n | Col % | n | Col % | |
| Total children, n | 931,120 | 100.0% | 2,793,512 | 100.0% | 3,724,633 | 100.0% |
| Number of CT exams per child | ||||||
| 0 | 876,047 | 94.1% | 2,628,149 | 94.1% | 3,504,196 | 94.1% |
| 1 | 45,057 | 4.8% | 126,140 | 4.5% | 171,197 | 4.6% |
| 2 | 6,723 | 0.7% | 26,300 | 0.9% | 33,023 | 0.9% |
| 3–10 | 3,142 | 0.3% | 12,275 | 0.4% | 15,417 | 0.4% |
| >10 | 151 | <0.05% | 648 | <0.05% | 799 | <0.05% |
| Total | 931,120 | 100.0% | 2,793,512 | 100.0% | 3,724,632 | 100.0% |
| Age at each exam | ||||||
| <1 year | 15,276 | 27.7% | 41,584 | 17.4% | 56,860 | 19.4% |
| 1–4 years | 17,942 | 32.6% | 53,028 | 22.2% | 70,970 | 24.2% |
| 5–9 years | 11,189 | 20.3% | 46,965 | 19.7% | 58,154 | 19.8% |
| 10 – <21 years | 10,666 | 19.4% | 97,077 | 40.7% | 107,743 | 36.7% |
| Total | 55,073 | 100.0% | 238,654 | 100.0% | 293,727 | 100.0% |
| Exams by anatomic region | ||||||
| Abdomen | 11,392 | 15.5% | 29,156 | 12.2% | 40,548 | 13.0% |
| Chest | 2,218 | 3.0% | 10,827 | 4.5% | 13,045 | 4.2% |
| Head and/or Neck | 53,408 | 72.5% | 168,063 | 70.4% | 221,471 | 70.9% |
| Neck and/or C-Spine | 2,710 | 3.7% | 3,794 | 1.6% | 6,504 | 2.1% |
| Other, NOS | 1,663 | 2.3% | 14,236 | 6.0% | 15,899 | 5.1% |
| Multiple areas | 2,247 | 3.1% | 12,578 | 5.3% | 14,825 | 4.7% |
| Total | 73,638 | 100.0% | 238,654 | 100.0% | 312,292 | 100.0% |