Magnetic resonance evaluation of pulmonary circulation in children

Aortopulmonary collaterals after bidirectional cavopulmonary connection or Fontan completion: quantification with MRI

BACKGROUND

Aortopulmonary collaterals (APCs) have been associated with increased morbidity after the Fontan operation. We aimed to quantify APC flow after bidirectional cavopulmonary connections and Fontan completions, using phase-contrast MRI, and to identify risk factors for the development of APCs.

METHODS AND RESULTS

APC blood flow was quantifiable in 24 of 36 retrospectively analyzed MRI studies. Sixteen studies were performed after the bidirectional cavopulmonary connections (group A) and 8 after the Fontan operation (group B). APC blood flow was calculated by subtracting the blood flow volume through the pulmonary arteries from that through the pulmonary veins. The ratio of pulmonary to systemic blood flow (Qp/Qs) was 0.93+/-0.26 in group A and 1.27+/-0.16 in group B. APC flow was 1.42 (0.58 to 3.83) L/min/m(2) and 0.82 (0.50 to 1.81) L/min/m(2) in groups A and B, respectively. The mean inaccuracies corresponded to 7.9+/-14.5% and 7.1+/-13.6% of ascending aortic flow in groups A and B, respectively. Qp/Qs was negatively correlated with a younger age at the time of the bidirectional cavopulmonary connections operation (r=0.62, P=0.01) and positively correlated with the age at the time of the Fontan completion (r=0.81, P=0.01). Patients with a previous right-sided modified Blalock-Taussig shunt had more collateral flow to the right lung than those without.

CONCLUSIONS

APC blood flow can be noninvasively measured in bidirectional cavopulmonary connections and Fontan patients, using MRI in the majority of patients and results in a significant left-to-right shunt.

Anatomical and Functional Evaluation of Pulmonary Veins in Children by Magnetic Resonance Imaging

Pulmonary vein pathologies often present a diagnostic challenge. Among the different imaging modalities used for the evaluation of pulmonary veins, magnetic resonance is the most comprehensive in assessing anatomy and pathophysiology at the same time. Bright blood cine sequences and contrast-enhanced magnetic resonance angiography outline the course and connections of the pulmonary veins. Phase-contrast velocity mapping measures flow patterns, velocities, and volumes throughout the pulmonary circulation. This paper reviews contemporary utilization of magnetic resonance in the evaluation of pulmonary venous abnormalities in children, based on our experience over the last 5 years and on that of other investigators. We summarize how magnetic resonance imaging enhances our understanding of pulmonary vein physiology and how it can influence the diagnostic approach to children and adults with a pulmonary venous pathology, and we discuss its limitations.