Purpose: It is the purpose of this study to compare pulmonary and aortic blood flow measurements obtained in patients after single lung transplantation (SLTX) with those in volunteers.
Methods/material: In nine patients after SLTX (three male, six female) and nine volunteers (seven male, two female), double oblique phase contrast cine-MRI sequences perpendicular to the direction of blood flow were obtained in the ascending aorta, main, right, and left pulmonary artery on a 0.5-T unit (Philips Gyroscan; Best, the Netherlands) (repetition time, 600 to 800 ms; echo time, 8 ms; alpha=30; field of view=280 mm matrix, 128x256, ECG gating, temporal resolution 16 time frames/RR interval). An initial in vitro study using the same sequence on a nonpulsatile flow phantom showed excellent correlation (r=0.99) between MRI measurements of flow velocity and flow volume and true velocity and flow volume. Measurements of blood flow volume (mL/min), peak mean systolic velocity, resistive index, and distensibility index were obtained in each vessel.
Results: We found excellent correlations between left and right cardiac output as measured by velocity encoded cine-MRI (VEC-MRI) in the ascending aorta and main pulmonary artery both in normal volunteers (r=0.95) and in patients (r=0.91). Differential pulmonary blood flow measurements in volunteers showed that 55% of the right cardiac output was directed to the right and 45% to the left lung. Differential pulmonary blood flow in patients showed that most of the blood flow (81%) reaches the transplanted lung and only 19% reaches the patient's own lung (SLTX: 4.5±1.8 L/min, patient's own lung: 1.2±0.8 L/min). There were significant differences (p<0.05) in peak mean systolic velocity and resistive index obtained in the pulmonary arteries, both between normal volunteers and patients and between measurements obtained in the patient's own lung and the transplanted lung.
Conclusion: VEC-MRI blood flow measurements are a promising noninvasive tool to monitor the hemodynamic changes of pulmonary blood flow after SLTX.