Imaging in pregnancy TOG 2019 Flashcards
A fetus is exposed to how much background radiation in pregnancy?
1mGy
2 main units to measure radiation, what are they measuring?
Gray (Gy) - measures dose per KG of tissue. 1000mGy = 1Gy. 1Gy = 100 rad
Sievert (Sv) measures relative effective dose, 1000mSv = 1Sv
When gestation if expose to radiation can cause miscarriage? Which dose?
3-4 weeks
>50-100mGy
When gestation if expose to radiation can cause congenital malformation and FGR? Which dose?
5-10 weeks
>200 mGy
When gestation if expose to radiation can cause Risk lower IQ & microcephaly? Which dose?
11-17 weeks
>200mGy
Which examination are consider very low dose examinations <0.1mGy
Cervical spine Xray
Chest XR
XR extremities
Mammogram
Head & Neck CT
Which examination are consider low to moderate 0.1-10mGy)
Which examinations are consider higher dose 10-50mGy
How much can lead shielding reduce the risk of radiation?
50%
What are the risk with USS?
Thermal effects on tissue
Mechanical effects - tissue cavitation.
Fetal CNS most susceptible to thermal injury.
Measured by Thermal Index and Mechanical Index
Which type of USS has lowest risk of temperature elevations? Which have higher?
Lower: B-mode
Higher: Colour Doppler, spectral doppler
Is MRI safe in pregnancy?
Does not use radiation, magnetic fields.
Considered safe, some concerns with use in 1st trimester but not concrete evidence
Can gadolinium be used in pregnancy?
Advised not to use if can be avoided. Some studies showed higher risk inflammation conditions, risk stillbirth.
Gadolinium cross placenta in 2nd & 3rd trimester
How much fetal exposure to radiation in V/Q scan?
<5mGy
Can radioactive iodine be used in pregnancy
No may cause fetal hypothyroidism esecptiall after 12 weeks
Can PET CT be performed
Safety data, radiation low.
Can be used if needed
What proportion go pregnancy with suspected VTE is confirmed on imaging?
2-6%
How often inconclusive result from V/Q scan and CTPA
V/Q 4%
CTPA 6%
Benefits/Disad CTPA
Availability
Low fetal radiation
Better identifying other pathology
Exposure 20mGy to maternal breast tissues - increase risk 13.6% of breast cancer
Benefits/Dis Ad VQ
Benefite - higher NPP, no radiation to breast
Disad: Risk childhood malignancy but very low - 1 in 170000 per mGy and 0.0006% per mGy used
How to assess breast mass in prengnacy
USS + Tissue Bx
If breast cancer suspected - mammogram
Sensitivity of mammogram in pregnancy?
78-90%
Staging of breast cancer in pregnancy
CXR & liver USS
