Does pregnancy affect vascular enhancement in patients undergoing CT pulmonary angiography?

Abstract

The aim of this study was to evaluate whether pregnancy affects contrast enhancement within the pulmonary arteries during computed tomography pulmonary angiography (CTPA). This was a retrospective analysis of the CTPA examinations of 16 pregnant and 16 non-pregnant female patients, suspected of having an acute pulmonary embolus (PE), during the same time period. Pulmonary vascular enhancement was evaluated by measuring the CT density within the pulmonary arteries. In a blinded evaluation, subjective grading of contrast enhancement within the pulmonary arteries was also performed. There was a significant difference in arterial enhancement between the two groups, with pregnant patients having a mean pulmonary arterial density 112 HU less than patients in the control group [mean attenuation of 259.79 +/- 59.31 HU in pregnant patients versus 371.88 +/- 60.63 HU in non-pregnant patients (p < 0.001)]. The mean subjective pulmonary arterial enhancement score in the pregnant group was 8.19 +/- 2.51 versus 13.69 +/- 3.07 in the control group (p < 0.001). Pregnant women undergoing CTPA have significantly decreased pulmonary arterial enhancement compared to non-pregnant patients, probably due to the increase in cardiac output in pregnancy. We may need to reconsider how we perform CTPA in this group in order to ensure adequate opacification for diagnosis.

CTPA for the diagnosis of acute pulmonary embolism during pregnancy

“…Although the two studies differ with respect to scan speed, examination protocols and methods of image evaluation, the reduction of contrast enhancement (mean 259HU in pregnant vs 371HU in non-pregnant women [17]) and the increase in number of inadequate exams was marked and statistically significant (7.5% vs 27.5% [16]). One study even noted a higher number of segments that could not be properly evaluated (13.3% vs 28.7%, p= 0.0001 [16]), a fact that has a potential influence on the ability of CTA to rule out embolism.…”

“…In clinical practice, however, CTPA in pregnant women appears to be less robust than expected because of variable image quality. This clinical observation has been investigated by two retrospective studies published in this issue of European Radiology [16,17]. Both studies found-by subjective evaluation and objective quantification-a significantly lower enhancement of the pulmonary arteries in pregnant women than in non-pregnant women of comparable age.…”

“…As a consequence, contrast injection protocols for pulmonary CTA have not taken into account the physiological changes occurring during pregnancy, with the result that many routine examinations (7.5% vs 27.5% [16]) are not fully diagnostic. The authors of the two studies published in this issue [16,17] have to be congratulated for drawing attention to the need for adaptating contrast injection protocols in pregnancy. How would such an adaptation look?…”

“…A fixed start delay of 20 s as used by ref. [17] is no longer appropriate: bolus triggering, because of the shorter delay ideally located in the pulmonary trunk, will allow for compensating for the intra-individual variations and guarantee that no extra contrast material needs to be injected to ensure good enhancement with variable contrast arrival times. Iodine delivery rates can be increased by choosing a contrast agent with higher iodine concentration (350-400 mg/ml) or by increasing the flow rate of contrast injection.…”

“…Such an approach should be able to compensate for the 35% decrease in enhancement seen in the study by ref. [17]. An increase in flow rate, however, also requires an increase in contrast volume to ensure that contrast enhancement does not decrease prematurely.…”