CT
- Absolute additional cancer risks associated with CT scans (1 additional cancer case for every 2000 people scanned) are small compared to the baseline cancer risk (i.e. 1 in 35 (men) or 1 in 20 (female) risk of cancer before the age of 50, or 1 in 5 lifetime risk).
- Patel 2007
- Radiation induced teratogenesis:
- Fetal radiation doses and different types of radiation imaging
- *Fetal exposure varies with gestational age, maternal body habitus, and exact acquisition parameters.
- Note: Annual average background radiation = 1.1-2.5 mGy
- 18F = 2-[fluorine-1 8]fluoro-2-deoxy-D-glucose
- Foetal radiation doses of less than 50 mGy are not associated with increased foetal anomalies or fetal loss throughout pregnancy;
- radiation doses of all diagnostic imaging examinations using ionizing radiation routinely used in a trauma evaluation should be well below this threshold
- by comparison foetal dose from natural background radiation during pregnancy is 0.5-1.0 mGy
Gestational Period | Effects | Estimated Threshold Dose* |
Before Implantation (0-2 weeks after fertilization) | Death of embryo or no consequence (all or none) | 50-100 mGy |
Organogenesis (2-8 weeks after fertilization) | Congenital anomalies (skeleton, eyes, genitals) Growth restriction | 200 mGy 200-250 mGy |
8-15 weeks | Severe intellectual disability (high risk) Intellectual deficit Microcephaly | 60-310 mGy 25 IQ-point loss per 1,000 mGy 200 mGy |
16-25 weeks | Severe intellectual disability (low risk) | 250-280 mGy* |
Grade | Examination | Fetal Dose** (mGy) | Additional risk of childhood cancer per examination |
Very low-dose examinations (<0.1 mGy) | Cervical spine XR (anteroposterior and lateral views) | <0.001 | <1 in 1,000,000 |
ㅤ | Head or neck CT | 0.001-0.01 | <1 in 1,000,000 |
ㅤ | Skull XR | ㅤ | ㅤ |
ㅤ | XR of any extremity | <0.001 | <1 in 1,000,000 |
ㅤ | Chest radiography (two views) | 0.0005-0.01 | <1 in 1,000,000 |
Low- to moderate-dose examinations (0.1 - 10 mGy) | Abdominal radiography | 0.1-3.0 | 1 in 100,000 ↔ 1 in 10,000 |
ㅤ | Chest CT or CT pulmonary angiography | 0.01-0.66 | 1 in 1,000,000 ↔ 1 in 100,000 |
ㅤ | Technetium-99m bone scintigraphy | 0.1-0.5 | 1 in 100,000 ↔ 1 in 10,000 |
ㅤ | Lumbar spine CT | 1.0-10 | 1 in 10,000 ↔ 1 in 1000 |
ㅤ | Lumbar spine radiography | 1.0-10 | 1 in 10,000 ↔ 1 in 1000 |
ㅤ | Abdominal CT | 1.0-10 | 1 in 10,000 ↔ 1 in 1000 |
Higher-dose examinations (10-50 mGy) | Abdominal-Pelvis CT | 10-50 | 1 in 1000 ↔ 1 in 200 |
ㅤ | 18F PET/CT whole-body scintigraphy | 10-50 | 1 in 1000 ↔ 1 in 200 |
- Children higher risk of radiation side effects because
- longer life expectancy than adults (a larger window of opportunity for expressing radiation damage),
- may receive a higher radiation dose than necessary if CT settings are not adjusted for their smaller body size.
- For a cumulative dose of between 50 and 60 mGy to
Head (i.e. 2-3 CT head scans) | 3x increase in the risk of brain tumors |
Bone marrow (i.e. 5-10 CT head scans) | 3x increase in the risk of leukemia |
- In children, the lifetime extra risk of cancer from a single CT scan was small
- about 1 case of cancer for every 10,000 scans performed on children (baseline 1 in 500 risk of developing some form of cancer before the age of 14).
- CTH in childhood has a 0.5% lifetime risk of fatal cancer in addition to reduce cognitive abilities.
If pregnant pt needs whole body CT examinations for trauma
- Do it with iodinated contrast
- As it improves detection of both maternal and foetal injuries by providing vascular contrast in organs and opacification of vascular structures, including the placenta.
- Iodinated contrast material to obtain one diagnostic CT study is preferable to obtaining a nonenhanced CT study that may be nondiagnostic and necessitate repeat imaging.
- In a seriously injured pregnant patient, multiple or repeat imaging examinations could result in a foetal radiation dose that exceeds 50 mGy.
- In these situations, it is important to recognize the risks of ionizing radiation to the fetus, which depend on the stage of the pregnancy:
Gestation | Fetal Radiation Dose (mGy) | Risks |
Less than 2 weeks | 50-100 mGy | Failure of blastocyst implantation. If the blastocyst survives, no other deleterious effects are expected. |
2-20 weeks | 50-150 mGy | Teratogenesis |
Anytime during gestation | 50 mGy | Carcinogenesis - doubles the risk of fatal childhood cancer (from 1 in 500 to 1 in 250) and increases the overall lifetime risk of cancer by 2% |
- For imaging studies that require the patient to lie flat for an extended time, use of the 30% left lateral decubitus position during imaging should be strongly considered.
MRI
There exists no evidence of actual harm
- In considering available data and risk of teratogenicity, the American College of Radiology concludes that no special consideration is recommended for the first (versus any other) trimester in pregnancy
- Human study
- Comparing 1st trimester MRI VS no MRI:
- stillbirths or deaths: RR=1.68 for MRI ; 95% CI, 0.97–2.90).
- Risk also was not significantly higher for
- Congenital anomalies
- neoplasm
- Vision or hearing loss
Theoretical concerns for the fetus from:
- Teratogenesis
- With regard to teratogenesis, there are no published human studies documenting harm, and the preponderance of animal studies do not demonstrate risk
- Tissue heating
- Tissue heating is proportional to the tissue’s proximity to the scanner and, therefore, is negligible near the uterus
- Acoustic damage
- Available studies in humans have documented no acoustic injuries to fetuses during prenatal MRI
- there is a theoretical risk of acoustic damage to the fetus from the noise generated by time-varying EMFs during MRI scans, current evidence suggests that the use of MRI up to 3 Tesla is safe for fetal examinations
- Static field:
- Risks:
- Vertigo
- Nausea
- Magnetophosphenes
- Metallic taste
- Projectiles
- Implant malfunction and movement
- Monitoring device malfunction and movement
- Radiofrequency pulse:
- Risks:
- Heating effect (specific energy absorption rate, SAR)
- Induced current burns
- Time-varying electromagnetic fields (EMFs)
- causing acoustic damage to the fetus primarily arises from the potential harmful effects due to the pulsed electromagnetic gradient fields used in MRI scans.
- During an MRI, the rapid switching of the magnetic field can create loud clicking and beeping noises.
- This acoustic noise is generated by the expansion and contraction of the gradient coils in the presence of a strong magnetic field.
- The concern is that these loud noises could potentially cause acoustic damage to the fetus, as the fetus is in a fluid environment which can conduct sound efficiently.
- These effects can include biological effects, acoustic noise damage, and, though rarely, peripheral nerve stimulation, muscle stimulation, and cardiac fibrillation1.
- Risks:
- Acoustic noise damage
- Peripheral nerve stimulation
- Muscle stimulation (arrhythmia in extreme cases)
MRI + C:
- Gadolinium-based agents
- During pregnancy: controversial.
- Mechanism of foetal effects
- Gd is water soluble and can cross the placenta into the foetal circulation and amniotic fluid.
- Free gadolinium is toxic and, therefore, is only administered in a chelated (bound) form.
- Humans,
- Duration of foetal exposure is not known because the contrast present in the amniotic fluid is swallowed by the fetus and reenters the foetal circulation.
- Longer Gd remain in the amniotic fluid, the greater the potential for dissociation from the chelate --> Risk of causing harm to the foetus
- presumably because this allows for gadolinium to dissociate from the chelation agent.
- Animal studies:
- Gd have been found to be teratogenic at high and repeated doses,
- Human study
- Prospective study evaluating the effect of antepartum gadolinium administration reported no adverse perinatal or neonatal outcomes among 26 pregnant women who received gadolinium in the first trimester
- Gadolinium + MRI (n=397) VS no MRI (n=1,418,451),
- Any rheumatologic, inflammatory, or infiltrative skin condition: higher in MRI + C adjusted hazard ratio= 1.36; 95% CI, 1.09–1.69).
- Stillbirths and neonatal deaths also occurred more frequently among in MRI +C (adjusted RR, 3.70; 95% CI, 1.55–8.85).
- Limitations of the study
- Assessing the effect of gadolinium during pregnancy include using a control group who did not undergo MRI (rather than patients who underwent MRI without gadolinium)
- Rarity of detecting rheumatologic, inflammatory, or infiltrative skin conditions
- Given these findings, as well as ongoing theoretical concerns and animal data, gadolinium use should be limited to situations in which the benefits clearly outweigh the possible risks
- During breast feeding
- The water solubility of gadolinium-based agents limits their excretion into breast milk.
- < 0.04% of an intravascular dose of gadolinium contrast is excreted into the breast milk within the first 24 hours.
- Of this amount, the infant will absorb less than 1% from his or her gastrointestinal tract.
- Although theoretically any unchelated gadolinium excreted into breast milk could reach the infant, there have been no reports of harm.
- Therefore, breastfeeding should not be interrupted after gadolinium administration
- Superparamagnetic iron oxide particles.
- No animal or human fetal studies to evaluate the safety of superparamagnetic iron oxide contrast
- No information on its use during pregnancy or lactation.
- Therefore, if contrast is to be used, gadolinium is recommended.
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