CT Imaging in Pregnancy

Brian Wells, MS3, MSM, MPH

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Some Facts of Life• Patients worry• Sometimes their worries are real• However, health care providers have to allay fears without prevarication

when such fears are not grounded in evidence

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Today’s Agenda

• Provide a background on radiation and the effects of radiation exposure

• Discuss the appropriate use of CT imaging in pregnancy

• Clinical scenarios

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Why should I listen?

• Knowing types, number and cost of imaging services provided is important

• Imaging is on the rise– Worldwide estimates from 2000-2007 show 3.6

billion medical procedures with ionizing radiation• Deployed guidelines are in place to protect patients,

improve quality of care, and reduce inter-practice practitioner variability

• Synthesize new information with previous knowledge

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KIDS

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Imaging Use Statistics

• In the United States in 2006:– 377 million diagnostic and interventional radiology exams– 18 million nuclear medicine exams– Usage in the U.S. alone accounted for:

• ~12% of the world’s radiologic procedures• ~50% of the world’s nuclear medicine procedures• Some skew in the data, ex: Germany does not perform

nuclear medicine stress testing because it’s not reimbursed

Radiologic and Nuclear Medicine Studies in the United Statesand Worldwide: Frequency, Radiation Dose and Comparisonwith other Radiation Sources 1950-2007. Metler, FA ea al.Radiology 2009; 253:520-531

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CT is not a benign procedure

“On the basis of risk estimates and data on CT use from 1991 to 1996, it has been estimated that about 0.4% of all cancers in the United States may be attributable to the radiation from CT studies. By adjusting this estimate for CT use, this estimate might now be in the range of 1.5 – 2.0%.”

Computed tomography – an increasing source of radiation exposure. Brenner DJ, Hall EJ. NEJM 2007 Nov 29;357(22):2277-2284.

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CT is not a benign procedure

“From an individual standpoint, when a CT is justified by medical need, the associated risk is small relative to the diagnostic information obtained. However, if it is true that one third of all CT scans are not justified by medical need, and it appears to be likely, perhaps 20 million adults and, crucially, more than 1 million children per year in the United States are being irradiated unnecessarily.”

Computed tomography – an increasing source of radiation exposure. Brenner DJ, Hall EJ. NEJM 2007 Nov 29;357(22):2277-2284.

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Average Exposure Amounts by Procedure

Modality Exposure dose

Chest x-ray (AP and lateral) 0.005 mGy

Flat plate of the abdomen 1 mGy

Mammography 0.05 to 0.2 mGy

Barium enema or small bowel series 20 mGy to 40 mGy

Intravenous pyelogram (IVP) 10 mGy to 20 mGy

CT of the head <10 mGy

CT of the chest <10 mGy

CT of the abdomen and lumbar spine 30 to 40 mGy

1 rad = 0.01 gray (Gy) = 0.01 Sievert (Sv) = 1 rem (roentgen-equivalent man)and 0.001 rad = 1 mrad = 0.01 mGy

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Typical Effective Dose Values

Examination mSv

Head CT 1-2

Chest CT 5-8

Abdomen CT 5-8

Pelvis CT 3-6

Abdomen and Pelvis CT 8-14

Coronary Artery Calcium CT 0.1-3

Coronary CT Angiogram 1-18

*The equivalent dose to a tissue is found by multiplying the absorbed dose, in gray, by a dimensionless "quality factor" Q, dependent upon radiation type, and by another dimensionless factor N, dependent on all other pertinent factors.

The Sv attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterized by the absorbed dose, measured in gray.

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“Effective dose is not the risk for any one individual. Due to inherent uncertainties and oversimplifications involved, effective dose should not be used for epidemiologic studies or for estimating population risks.”

How Effective is Radiation Dose as a Predictor of Radiation Risk? McCollough, CH et al. AJR 2010; 194:890-896

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Controversy

Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May (Almost) Be The Best We Can Do? Little MP et al. Radiology 2009; 251:6-12

v.

The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data. Tubiana M et al. Radiology 2009; 251:13-22

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Linearity Model

“In summary, excess cancer risks obtained in the Japanese atomic bomb survivors and in many medically and occupationally exposed groups exposed at low or moderate doses are generally statistically compatible. For most cancer sites, the dose response in these groups is compatible with linearity over the range observed.”

Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May (Almost) Be The Best We Can Do? Little MP et al. Radiology 2009; 251:6-12

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Linearity is inconsistent with reality“Irradiated cells protect themselves (a) by immediate defense, repair and damage removal mechanisms and (b) by delayed and temporary protection also renewed DNA damage, irrespective of its causes – that is through adaptive responses… The fears associated with concept of the linear no-threshold model and the idea that any dose, even the smallest, is carcinogenic lack scientific justification.”

The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data. Tubiana M et al. Radiology 2009; 251:13-22

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Radiation Exposure in Pregnancy• Most common adverse effects seen from high-dose radiation are

intrauterine growth restriction, microcephaly, and mental retardation• The risk of mental retardation appears to take at least a dose of 20 rads.

This risk is 40% following a dose of 100 rads and increases to 60% with a dose of 150 rads.

• Microcephaly and fetal growth restriction have been reported at doses between 10 and 20 rads

• American College of Obstetricians and Gynecologists (ACOG) and the American College of Radiology (ACR) both state that exposures of less than 5 rads do not increase the risk for anomalies (which leaves the range of 5 to 10 rads as being the gray zone)

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So what about risk?

“The risk burden of radiation exposure to the fetus has to be carefully weighed against the benefits of obtaining a critical diagnosis quickly and using a single tailored imaging exam.”

Imaging in Pregnant Patients: Examination Appropriateness. Weisler KM et al. RadioGraphics 2010; 30:1215-1233

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Potential Effects by Radiation Exposure

Gestational Age (weeks)

< 50 mGy 50 – 100 mGy >100 mGy

0-2 None None None

3-4 None Probably none Possible spontaneous abortion

5-10 None Uncertain Possible malformations

11-17 None Uncertain Possible defects in IQ or mental retardation

18-27 None None IQ deficits not detectable at diagnostic doses

>27 None None None applicable to diagnostic radiology

ACR states that theoretical risks are unlikely at doses <100 mGy (1 Gy = 100 rad)17

What about iodinated contrast in the pregnant patient?“Based on neonatal TSH measurements in a small number of patients, we found no ill effect of iodinated contrast agents on neonatal thyroid function after in utero exposure… In conclusion, based on neonatal TSH measurements in a small number of patients, the IV administration of water soluble nonionic iodinated contrast agents to pregnant patients has no subsequent effect on neonatal thyroid function.”

Neonatal Thyroid Function After Administration of IV Iodinated Contrast Agent to 21 Pregnant Patients. Atwell TD et al. AJR 2008; 191:268-271

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When is CT indicated?• The most common indications for urgent CT during pregnancy are:• Appendicitis

– For first and second trimester pregnancies US and/or MR should be performed prior to obtaining a CT

• Pulmonary embolism– CT pulmonary angiogram exposes the fetus to less radiation than a VQ

scan.– CT should be the initial modality.

• Renal colic– US is the initial study of choice.

• Trauma– US may be sufficient for the initial imaging evaluation of a pregnant

patient who has sustained trauma, but CT should be performed if serious injury is suspected.

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Appendicitis

• Appendicitis– Most common cause of surgical abdomen in pregnancy

• 50-70 per 1000 patients– Slightly higher rate in second trimester– Leukocytosis in pregnancy can confound the diagnosis (as high as

16,000 in second trimester)– Ultrasound is typically done first. Some institutions, including

Woodhull, will also perform MRI• Small case series showed appendix not visualized in 22 of 23

pregnant patients in 3rd trimester due to gravid uterus*– If indeterminate or MRI is not available, a CT is done using oral and IV

contrast

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*Abdominal CT during pregnancy for suspected appendicitis: a 5-year experienceat a maternity hospital. Shetty MK et al. Semin US CT MR 2010; 31:8

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Pulmonary embolism• Pulmonary embolism (PE) is the leading cause of maternal

mortality in the developed world• Pregnancy is associated with an increased risk of

pulmonary embolism. • A pregnant patient with symptoms of deep venous

thrombosis (DVT) should undergo compressive ultrasound or impedance plethysmography.

• Diagnostic testing for pulmonary embolism (PE) should include either V/Q scanning or helical computed axial tomographic pulmonary angiography (HCTPA)– Both can be performed safely during pregnancy).

• The greater accuracy of HCTPA, along with findings that the average fetal radiation dose is consistently lower than V/Q scanning for all 3 trimesters, illustrates that HCTPA is more appropriate for evaluating a pregnant patient in whom you suspect acute PE.

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*Pulmonary embolism in pregnancy. Bourjeily, G et al. The Lancet, February 2010, Volume 375, Issue 9713, Pages 500 - 512

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Urolitiasis• Calculi in pregnancy are uncommon (1/200 to 1/2000)• Urolithiasis during pregnancy can be serious, causing preterm labor in up

to 40% of affected women• The frequency of stone localization is twice as higher in the ureter than in

the renal pelvis or calyx, but there is no difference between the left and right kidney or ureter.

• Ultrasound is done first but, if not helpful, CT is done to rule out stone and look for other causes of flank pain.

• If CT is done, low dose, non-contrast CT is sufficient for diagnosis– No difference between 100%, 50% and 25% examinations in detecting

stones > 3 mm (reducing tube charge from 100 -> 30 mAs)– Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect

on Sensitivity. Ciaschini MW et al. – Note that noise increases at low dose and makes detection of stones

< 3 mm easy to miss. However, these stones and not likely to be clinically significant

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Trauma

• The severity of injury determines workup but priority is given to maternal survival

• CT is used as needed in the chest and abdomen• Most common uterine injury is placental abruption, which occurs in up to

40% of patients with severe injury. • Uterine rupture is rare

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Injured placenta s/p MVC

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In Summary

“The risk burden of radiation exposure to the fetus has to be carefully weighed against the benefits of obtaining a critical diagnosis quickly and using a single tailored imaging exam.”

Imaging in Pregnant Patients: Examination Appropriateness. Wieseler KM et al. RadioGraphics 2010; 30:1215-1233

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Thank you!

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