IMAGING DURING PREGNANCY Flashcards
used as adjuncts for diagnosis and therapy during pregnancy which include:
- Radiography
- Sonography
- Magnetic resonance (MR) imaging
refers to energy transmission and often applied not only to x-rays, but also to microwaves, ultrasound, diathermy, and radio waves.
Radiation
have short wavelengths with very high energy and are ionizing radiation forms
x-rays and gamma rays
long wavelengths and low energy
- microwaves
- ultrasound
- diathermy, and
- radio waves.
refers to waves or particles-photons-of significant energy that can
* change the structure of molecules such as those in DNA or
* that can create free radical or ions capable of secondarily damaging tissue
Ionizing radiation
dose is now expressed in
grays (Gy)
relative effective dose is expressed in
sieverts (Sv)
number of ions produced by xrays per kg of air
unit: roentgen (R)
exposure
amount of energy deposited per kg of tissue
modern unit: gray (Gy) (1 Gy=100rad)
traditional unit: rad
dose
amount of energy deposited per kg of tissue normalized for biological effectiveness
modern unit: sievert (Sv) (1 Sv=100 rem)
traditional unit: rem
Relative effective dose
may result in abortion, growth restriction, congenital malformations, microcephaly, or mental retardation
Deterministic effects
threshold level is the NOAEL—No Observed Adverse Effect Level
there is no risk belowa threshold dose which is how much
(0.05 Gyor 5 rad)
0.05 Sv
the threshold for gross fetal malformations is more likely to be
0.2 Gy (20
rad)
or 0.2 Sv
the increased risk of severe mental retardation was greatest between what weeks of gestation
8 and 15 weeks
there may be a lower-threshold dose of
0.3 Gy (30 rad)
the mean decrease in intelligence quotient (IQ) scores was
25 points per Gy or 100 rad
25/1Gy or 1 SV
25/100 rad or 100 rem
fetus is most susceptible to radiation-induced mental retardation during what age?
8-15 weeks
risk of severe mental retardation -how many percent?
- as low as 4% for 0.1 Gy (10 rad)
- as high as 60% for 1.5 Gy (150 rad)
what age of gestation that the risk is less
16-25 weeks
diagnostic x-rays seldom exceed
0.1 Gy (10 rad)
refer to random, presumably unpredictable oncogenic or mutagenic effects of radiation exposure
Stochastic effects
concern with associations between fetal diagnostic radiation exposureand increased risk of childhood cancers or genetic diseases
Stochastic effects
excess cancers can result from in utero exposure to doses as low as
0.01 Sv or 1 rad
or 0.01 Gy
estimated risk of childhood cancer following fetal exposure to 0.03 Gy or 3 rad
doubles the background risk of 1:600 to that of 2:60
