Radiography Imaging Techniques

Relative agreement exists on when to recommend termination of pregnancy after radiation exposure. The so-called "Danish rule" was offered in 1959 by Hammer-Jacobsen, who suggested termination was advisable for a fetal dose of over 10 rads [1]. This guideline has been widely followed. Wagner et al suggest termination should only be considered if a radiation dose of over 5 rad occurs between 2 and 15 weeks of gestation, and is probably indicated only for doses over 15 rad. Hall suggests termination may be considered for a radiation of over 10 rad received between a gestational age of 10 days and 26 weeks [2]. In practice, it is exceptionally unlikely that any single radiological study would deliver a radiation dose sufficient to justify termination. Nonetheless, it is helpful to be aware of the expected radiation dose from common procedures [3, 4], and the magnitude of risk to the fetus per unit dose. This information, which is listed below, can be used to counsel pregnant ...

In general, intravascular contrast media should be avoided in pregnancy, in order to avoid any possible hazard to the fetus. In vitro experiments have shown iodinated contrast to be mutagenic to human cells [1]. Reassuringly, animal studies have failed to show an in vivo teratogenic effect [2, 3]. The iodine content of contrast media has the potential to produce neonatal hypothyroidism, and this has been observed after the direct instillation of ionic contrast into the amniotic cavity during amniofetography [4]. The intravascular use of non-ionic contrast media has been reported to have no effect on neonatal thyroid function [5]. It is standard pediatric practice to screen all neonates for hypothyroidism, but it is particularly important to perform this test in the infants of mothers who received iodinated contrast during pregnancy [6]. Key point: Despite in vitro concerns, iodinated contrast seems safe to use in pregnancy.

Pelvimetry is occasionally requested when vaginal delivery is being considered for breech presentation (especially in a primagravida) or for patients with suspected cephalopelvic disproportion, although reports on the utility of pelvimetry are conflicting and the reproducibility of pelvimetry measurements has also been questioned [1-3]. Pelvimetry can be performed by conventional radiography, CT, or MRI [4]. While MRI has the theoretical advantage of not using ionizing radiation, the fetal dose from a limited CT pelvimetry study (low doses lateral and frontal digital radiographs with a single axial slice through the femoral heads to measure interspinous diameter) is under 0.1 rad. Even assuming the worse case scenario that the dose is 0.1 rad and that such a dose is as dangerous as radiation earlier in pregnancy, the risk of fatal childhood cancer would only be increased by 2%, a minimal risk. For such reasons, if pelvimetry is considered appropriate, it is reasonable to perform pelvi...

Trauma and accidental injuries complicate 6-7% of all pregnancies [1], and are usually due to motor vehicle accidents, domestic abuse or assaults, and falls. Common adverse consequences include uterine contractions, preterm labor or delivery, and placental abruption. Fetal or maternal demise is rare. In many cases, external fetal monitoring and ultrasound may be adequate for assessment, including detection of placental abruption or uterine rupture (the most serious complication) and documentation of fetal well being [1-3]. That said, trauma to the pregnant patient must be considered with the utmost seriousness because even minor trauma can cause fetal demise [4]. The cardinal principle in the management of trauma in pregnancy is that there can be no fetal survival without maternal survival, with the rare exception of the gravely injured mother late in pregnancy where urgent Cesarean section may allow for fetal survival. From an imaging perspective, ultrasound is an excellent tool for ...

Organogenesis occurs predominantly between 2 and 15 weeks gestation. This is the period when the fetus is most susceptible to the teratogenic effects of ionizing radiation, which include microcephaly, microphthalmia, mental retardation, growth retardation, behavioral defects, and cataracts. Teratogenic effects are extremely unlikely in fetuses before 2 weeks of gestation and after 15 weeks of gestation [1]. Teratogenesis is considered a non-stochastic effect of radiation (i.e., a threshold dose exists below which there is no risk). The threshold radiation dose below which no teratogenic effects occur is not known, but is estimated to range from 5 to 15 rad [2]. The radiation dose to the fetus from a spiral CT study of the maternal pelvis using typical technical parameters is variable and depends on gestational age and scanning parameters such as slice thickness and mAs. That said, estimated doses range from 2.4 rad in the first trimester to 4.6 rad in the third trimester [3, 4]. An...

We are exposed to radiation from natural sources all the time. According to recent estimates, the average person in the United States receives an effective dose of about 3 milliSieverts (mSv) per year from naturally occurring radioactive materials and cosmic rays, which is radiation that comes from outer space. These natural “background” doses vary throughout the country. Altitude plays a role in the amount of cosmic radiation, so people living on the plateaus of Colorado or New Mexico receive about 1.5 mSv more per year than those living near sea level. The added dose from cosmic rays during a coast-to-coast round trip flight in a commercial airplane is about 0.03 mSv. However, the largest source of background radiation comes from radon gas in our homes (about 2 mSv per year). Like other sources of background radiation, exposure to radon varies widely from one part of the country to another. In simple terms, the radiation exposure from one chest X-ray is equivalent to the amount...

There are many benefits for patients from medical imaging. Images of the human body are created using a variety of means such as ultrasound, magnetic resonance, nuclear medicine and X-rays to allow physicians to see inside the body, to identify and/or rule out medical problems, and to diagnose diseases. Much has recently been written about radiation, so it is important to have some understanding of imaging performed using radiation, especially the benefits to the patient along with the associated risks. Keep in mind that the radiation doses used in medical radiological imaging examinations like computed tomography (CT) and X-ray scans are much lower than those used in radiation oncology, which uses radiation as a therapy to treat cancer. Radiology (imaging) and radiotherapy (cancer treatment) are quite different. We invite you to learn about what we do to ensure your safety when we make images of your body in the UCSF Department of Radiology & Biomedical Imaging.