GAGAN SAHNI , MD, FACC, FACP

Mount Sinai Hospital , New York

CT IN PREGNACY : The tough questions

1. Is it a life saving diagnostic procedure?

2. Is the fetal radiation risk worth it?

3. Is there risk of iodinated contrast?

4. Are there safer alternative modalities?

5. What are the other pitfalls of CT in pregnancy ?

6. What can we do to minimize the radiation risks?

Example: justified use of CT Pregnant female, was in motor vehicle accident

Fetal

skull

ribs Blood

outside

uterus

Fetal dose 20 mGy

INTERNATIONAL

COMMISSION ON RADIOLOGICAL PROTECTION ——————————————————————————————————————

3 minute CT exam and taken to the operating

room. She and the child survived

Free blood

Kidney torn

off aorta (no contrast in it) Splenic laceration

LIFESAVERS Life saving in some situations such as:

1. Trauma

2. Aortic dissection

3. Pulmonary embolism

4. Acute CVA

5. Coronary dissection

LM LAD LCx LM

LAD Intramural hematoma

Cardiac CTA [left] showing coronary intramural hematoma [arrows] in the left main[LM] and left anterior descending [ LAD] artery resulting from a coronary dissection in the tunica media in a 2 weeks post partum woman. The relatively unremarkable angiogram [right] done a few days prior to the CTA missed the diagnosis of coronary dissection. Image Courtesy : Harvey Hecht M.D, Mount Sinai Hospital, New York.

CT IN CORONARY DISSECTION

ED ES

Cardiac CT in a pregnant patient in third trimester of pregnancy showing a Type A dissection involving aortic root and ascending aorta with images in end diastole[left] and end systole [right] showing the dissection flap compressing the left main coronary ostium during systole . Image courtesy: Harvey Hecht M.D , Mount Sinai Hospital , New York.

CT IN AORTIC DISSECTION

CT Angiogram: Pulmonary Arteries

CT scan showing massive bilateral pulmonary embolism [seen as filling defect denoted with arrows ] in a patient presenting with sudden shortness of breath 2 days post partum. Image courtesy: Partho Sengupta M.D, Mount Sinai Hospital , New York

CT IN PULMONARY EMBOLISM

FETAL RISK OF CT SCAN IN PREGNANCY

Radiation risk

1. Teratogenesis

2. Oncogenesis

3. Spontaneous abortion

Iodinated contrast risk

Fetal radiation risk

There are radiation-related risks throughout pregnancy that are related to the stage of pregnancy and absorbed dose

Radiation risks are most significant during organogenesis and in the early fetal period, somewhat less in the 2nd trimester, and least in the 3rd trimester

Less Least

Most

risk

FETAL RADIATION RISK For a fetus, the average dose from naturally occurring

background radiation over the course of a normal gestation is 0.5– 1.0 mGy

According to the National Council on Radiation Protection and Measurements (NCRP), the maximum permissible radiation dose to the fetus of a pregnant radiation worker from occupational exposure (e.g.,

scatter radiation from a patient) is 5 mSv

RADIATION UNITS SIMPLIFIED

mGy= milli GRAY units= Absorbed radiation dose

mSv= milli Sieverts = Effective biological dose

Approximate fetal doses from computed tomography procedures

Data from the UK, 1998

Examination Mean absorbed

dose (mGy)

Maximum

absorbed dose

(mGy)

Head CT <0.005 <0.005

Chest CT 0.06 1.0

Abdomen CT 8.0 49

Pelvis CT 25 80

Radiation-induced malformations

Radiation doses > 100 mGy may result in a 1% combined increased risk of organ malformation and the development of childhood cancer

A fetal radiation exposure of >100 mGy is necessary before pregnancy termination should be considered

Malformations have a threshold of 100-200 mGy or higher and are typically associated with central nervous system problems

Fetal doses of 100 mGy are not reached even with 3 pelvic CT scans or 20 conventional diagnostic x-ray examinations

These levels can be reached with fluoroscopically guided interventional procedures of the pelvis , with radiotherapy and in multiple scans such as in trauma patients

Central nervous system effects

During 8-25 weeks post-conception the CNS is particularly sensitive to radiation

Fetal doses in excess of 100 mGy can result in some reduction of IQ (intelligence quotient)

Fetal doses in the range of 1000 mGy can result in severe mental retardation and microcephaly, particularly during 8-15 weeks and to a lesser xtent at 16-25 weeks

Heterotopic gray matter (arrows) near the ventricles in a

mentally retarded individual occurring as a result of high

dose in-utero radiation exposure

Fetal radiation: The oncogenic risk

Radiation has been shown to increase the risk for leukemia and many types of cancer in adults and children

The relative risk may be as high as 1.4 (40% increase over

normal incidence) due to a fetal dose of 10 mGy

For an individual exposed in utero to 10 mGy, the absolute risk of cancer at ages 0-15 is about 1 excess cancer death per 1,700

Probability of bearing healthy children as a function of radiation dose

Dose to conceptus

(mGy) above

natural background

Probability of no

malformation

Probability of no

cancer (0-19 years)

0 97 99.7

1 97 99.7

5 97 99.7

10 97 99.6

50 97 99.4

100 97 99.1

>100 Possible Higher

THE NUMBERS CHEAT SHEET

0.5-0.1 mGy = Normal background exposure to the fetus

> 10 mGy = Increased oncological risk

>100 mGy = Increased teratogenic risk, decreased IQ

>150 mGY= Abortion recommended

>1000 mGy= Severe mental retardation

Fetal iodinated Contrast risk Maternal ingestion of iodine in gestation may cause neonatal hypothyroidism

but this has NOT been demonstrated due to intravenous contrast use in pregnancy .

One retrospective study followed 115 consecutive patients admitted to a

group of hospitals in the United Kingdom with suspected pulmonary embolism, 73 of whom underwent CT pulmonary angiography; the remaining 43 women had perfusion imaging . After delivery the neonates of all women in both groups underwent thyroid stimulating hormone (TSH) screening. The study found no significant difference in TSH levels among the neonates when assessed based on antenatal exposure to iodinated contrast.

Rajaram S, Exley C, Fairlie F, Matthews S. Effect of antenatal iodinated contrast agent on neonatal thyroid function. Br J Radiol. 2011.

A retrospective study of 344 pregnant women who underwent a CTPA exam

for suspected PE found normal thyroxine levels in all neonates at time of birth. Bourjeily G, Chalhoub M, Phornphutkul C, Alleyne TC, Woodfield CA,Chen KK. Neonatal thyroid function: effect of a

single exposure to iodinated contrast medium in utero. Radiology 2010;256:744–750.

No animal studies have demonstrated teratogenicity to the developing fetus from iodinated contrast. Iodinated contrast agents are classified as category B by the U.S. Food and Drug Administration (FDA)

CT scan vs VQ SCAN in PE during Pregnancy

A recent retrospective management study comparing CTPA (n = 106) to V/ Q scan (n= 99) in the diagnosis of PE in pregnancy has reported negative predictive values of 99% and 100%, respectively .

Shahir K, Goodman LR, Tali A, Thorsen KM, Hellman RS. Pulmonary embolism in pregnancy: CT pulmonary angiography versus perfusion scanning. AJR Am J Roentgenol 2010;195:W214–220

There is however the consideration that CTPA exposes the fetus to lower radiation doses but has a higher maternal exposure compared to V/Q scanning

Ct scan vs vq scan: Fetal & Maternal Radiation

Diagnostic Test Fetal Dose [mGy] Maternal Dose

[Whole body

effective dose in

mSv]

CXR 0.002 0.1

V/Q scan 0.32-0.74 1-2.5

CTPA 0.03-0.66 4-18

V/Q scan carries a slightly higher risk of childhood cancer in offspring than does CTPA (1 case in 280,000 vs <1 in 1 million) BUT CTPA carries a 13% higher lifetime risk of maternal breast cancer compared to VQ scan [ Effective breast dose is 10-70 mGy, much more in pregnancy compared to a mere 3 mGy in a routine mammogram]

CT SCAN VS VQ SCAN Keep in mind that the mortality associated with

untreated PE far outweighs the potential oncogenic and teratogenic risk incurred by fetal exposure to diagnostic imaging for PE .

The ESC recommends CTPA over VQ scanning for diagnosing PE in pregnancy as fetal risk is lower

The ATS is equivocal with the choice of imaging depending on the initial CXR being normal or no

CT VS MRI Although use of MRI has not been shown to have any

deleterious effects on the fetus, the safety of MRI during pregnancy has yet to be definitely established.

The potential risk of heating effects from radiofrequency pulses and effects of acoustic noise on the fetus have not been validated

Gadolinium has been shown in animal studies to have teratogenic effects when administered at high and repeated doses

CT VS ECHO If TEE and operator is available in time , TEE has a

comparable sensitivity and specificity to CT for proximal type A dissections.

However, entire aortic vasculature cannot be imaged

Also most aortic dissections occur in the final

trimester when the radiation exposure risk is least

harmful to the fetus

Echo is clearly a safer alternative if imaging of complex structural heart disease is in question

PITFALLS OF CT IN PREGNANCY Smaller studies have suggested that VQ Scan was more reliable than

pulmonary CTA in pregnant patients with more inconclusive CT scans Transient interruption of contrast material by unopacified blood from

the inferior vena cava is a common finding at pulmonary CTA of pregnant patients. Factors such as the hyperdynamic state of pregnancy, hemodilution in pregnancy have also been hypothesized as possible causes of inconclusive CT scan results in pregnancy

28 CTA examinations were performed on 25 pregnant patients, and 25 lung scintigraphic studies were performed on 25 pregnant patients. Lung scintigraphy was more frequently adequate for diagnosis than was pulmonary CTA (4% vs 35.7%) (p = 0.0058). Pulmonary CTA had a higher diagnostic inadequacy rate among pregnant than nonpregnant women (35.7% vs 2.1%) (p < 0.001). Transient interruption of contrast material by unopacified blood from the inferior vena cava was identified in eight of 10 nondiagnostic pulmonary CTA studies.

Carole Ridge et al. Pulmonary Embolism in Pregnancy: Comparison of Pulmonary CT Angiography and Lung ScintigraphyAJR 2009; 193:1223–1227

PITFALLS OF CT IN PREGNANCY

GETTING RID OF THE PITFALLS OF CT IN PREGNANCY

Solutions to better imaging in pregnancy include

1. Bolus triggering with shorter scan delay

2. high flow rate of contrast material flow

3. high concentration of contrast medium ie Isovue

4. use of low-kilovoltage techniques.

5. Image acquisition during shallow inspiration or

held expiration after adequate coaching by a technologist

GETTING RID OF THE PITFALLS OF CT IN PREGNANCY

6. Use of 64 slice MDCT :The use of MDCT acquisition, faster injection rates, higher contrast medium concentration,

and higher trigger levels may decrease the number of nondiagnostic studies in this population. No difference in attenuation in pregnant and non pregnant control population with equal diagnostic accuracy and very low diagnostic rate of only 0.8%

Imaging duration decreases to less than 5 seconds in examinations performed with 64-MDCT; therefore, the contrast media volume can be decreased. This could potentially decrease the risk of side effects due to contrast media and also decreases fetal contrast exposure in pregnant women

Ann Browne et al. Evaluation of Imaging Quality of Pulmonary 64-MDCT Angiography in Pregnancy

and Puerperium. AJR 2014; 202:60–64

SO CT MAY BE A WINNER… 1. Lower fetal radiation risk compared to VQ scan 2. Gives other information such as about aortic, pericardial and

lung ds 3. Superior to other modalities if concomitant lung ds with

abnormal CXR or if done with proper techniques and use of newer 64 MDCT scanners

4. Rapid, convenient and easily available in most centers

Approximate fetal doses from computed tomography procedures

Data from the UK, 1998

Examination Mean absorbed

dose (mGy)

Maximum

absorbed dose

(mGy)

Head CT <0.005 <0.005

Chest CT 0.06 1.0

Abdomen CT 8.0 49

Pelvis CT 25 80

REDUCING RISK

1. Abdominal lead shielding during pulmonary CTs can significantly reduce the dose exposure to the fetus

2. The use of bismuth breast shielding can decrease the radiation dose to the breasts but may increase noise and artifacts, resulting in compromised image quality

3. Combined reduction of kilovoltage and milliampere-second settings and z-axis coverage results in a substantial reduction of radiation dose while maintaining diagnostic imaging quality

Litmanovich et al . Dose Reduction in Computed Tomographic Angiography of Pregnant Patients With Suspected Acute

Pulmonary Embolism. J Comput Assist Tomogr 2009;33: 961Y966

4. Use of newer MDCT scanners that allow faster imaging time and hence potentially lesser radiation and contrast exposure

Ann Browne et al. Evaluation of Imaging Quality of Pulmonary 64-MDCT Angiography in Pregnancy and PuerperiumAJR 2014; 202:60–64

REDUCING RISK

SUMMARY OF CT IN PREGNANCY

ANSWER 1 : Exposure to ionizing radiation of pregnancy should be limited to imaging for life saving conditions

ANSWER 2: The teratogenic to the fetus vs oncogenic risk to fetus and mother should be discussed at length with the mother and informed consent taken for any CT imaging

ANSWER 3: The use of iodinated contrast is not teratogenic

ANSWER 4: Alternatives such as TEE, TTE ,VQ scan and MRI should be balanced with their own inherent risks and imaging quality and diagnostic efficacy

ANSWER 5: Newer imaging CT techniques such as MDCT can improve the diagnostic quality

ANSWER 6: MDCT as well as imaging techniques can help minimize radiation exposure

Thank you !!!