Current Clinical Concerns in CT: Results : Modality of Choice for a Specific Disease
Imaging for suspected PE in the pregnant patient
1. Is a CT PE still preferred in general, or just for pregnant females, vs V/Q scan? Is the radiation exposure to breast and gonads also less for CT in nonpregnant females?2. Is CT or NM the modality of choice to rule out PE during pregnancy? If CT is done, what is the protocol? Is the protocol modified? Do you omit the legs and do a Doppler US? (This question submitted by 2 individuals)
| Answer to 1 and 2: We do CT as it is lower dose than V/Q scans. The OB/GYNs have felt that this is the way to go. We do Doppler as well. We do not image the legs for DVT routinely, and surely not in pregnant patients. We do not change our CT protocol, except to try to be even more careful to limit the field of view, particularly at the level of the diaphragm. |
3. Are there any good studies comparing MDCT for PE vs. nuclear medicine V/Q? We are trying to develop a policy towards multi-detector and need some data to back it up.
| Answer: There is one study using single detector helical CT, but I am not aware of a MDCT study. Here are some references. |
References:
Schuster ME, Fishman JE, Copeland JF, Hatabu H, Boiselle PM. Pulmonary embolism in pregnant patients: a survey of practices and policies for CT pulmonary angiography. AJR 2003; 181(6):1495-8.
- Summary: A survey of 57 members of the Society of Thoracic Radiologists is presented in this study. Of those who participated, 43 (75%) reported that they perform CT angiography in pregnant patients suspected of having pulmonary embolism. Slightly more than half of these (53%) typically perform CT angiography as the initial study rather than ventilation-perfusion scanning. In addition, 26 (60%) require informed consent from the patient. With respect to the protocol: 17 (40%) modify the standard protocol when imaging pregnant patients, to decrease the dose. The majority (71%) accomplish this by decreasing the scanning area along the z-axis. Additional means of dose reduction reported include increasing the pitch, decreasing the field of view, eliminating the frontal and lateral scout images, reducing milliampere-seconds or peak kVp, and increasing detector collimation thickness.
Winer-Muram HT, Boone JM, Borwn HL, Jennings SG, Mabie WC, Lombardo GT. Pulmonary embolism in pregnant patients: Fetal radiation dose with helical CT. Radiology 2002; 224: 487-492.
- Summary: The radiation dose to the fetus from thoracic single detector helical CT for PE was estimated in this study. Women in the first, second and third trimester were included, and maternal-fetal geometry was performed, followed by calculations to estimate the radiation dose using the x-ray output data from a GE CT/I single detector helical scanner. The CT protocol for calculations included a kVP of 120, mAs of 100, 2.5 cm section interval, craniocaudal distance of 11 cm and a pitch of 1. The authors determined that "findings in this study show that the average fetal radiation dose with helical CT is less than that with V-P lung scanning during all trimesters."