Perfusion Scintigraphy Versus 256-Slice CT Angiography in Pregnant Patients Suspected of Pulmonary Embolism: Comparison of Radiation Risks

One aim of the current study was to determine normalized dose data for maternal radiosensitive organs and embryo/fetus from 256-slice CT pulmonary angiography (CTPA) performed on pregnant patients suspected of having pulmonary embolism. A second aim was to provide reliable maternal and fetal doses and associated radiation cancer risk estimates from 256-slice CTPA and lung perfusion scintigraphy (LPS) for comparison. Methods: Mathematic anthropomorphic phantoms were generated to simulate the average woman at early pregnancy and at the third, sixth, and ninth months of gestation. In each phantom, 0-3 additional 1.5-cm-thick fat tissue layers were added to derive 4 phantoms representing pregnant women with different body sizes. Monte Carlo methods were used to simulate low-dose 256-slice CTPA exposures on each of the 16 generated phantoms. Normalized organ and embryo/fetal dose data were derived for exposures at 80, 100, and 120 kV. Maternal effective dose and embryo/fetal dose from 256-slice CTPA and associated lifetime attributable risks of radiation cancer were determined for different body sizes and gestational stages and compared with corresponding data from LPS. Results: For an average-sized pregnant patient at the first trimester, the 256-slice CTPA exposure resulted in a maternal effective dose of 1 mSv and an embryo/fetal dose of 0.05 mGy. However, maternal effective dose considerably increased with body size, whereas embryo/fetal dose increased with both body size and gestational stage. Compared with LPS, low-dose CTPA to an average-sized pregnant patient resulted in a 30% higher maternal effective dose but a 3.4-6 times lower embryo/fetal dose. Nevertheless, LPS was associated with less aggregated radiation risk for an average-sized pregnant patient, with the difference from CTPA being increased further for larger patients. Conclusion: Compared with CTPA performed with a modem wide-area CT scanner, LPS remains comparatively more dose-efficient.