Magnetic Resonance Assessment of Pulmonary (Q_p) to Systemic (Q_s) Flows Using 4D Phase-contrast Imaging: Pilot Study Comparison with Standard Through-plane 2D Phase-contrast Imaging

摘要

Rationale and Objectives: To investigate four-dimensionai (4D) phase-contrast (PC) magnetic resonance (MR) in the evaluation of intra-cardiac shunts by simultaneous assessment of pulmonary (Q_P) and systemic (Qs) flows in a pilot study and to compare results to through-plane two-dimensional (2D) PC MR.Materials and Methods: Institutional review board approval and written informed consent were obtained. Nineteen patients with suspected intracardiac shunts underwent cardiac MR at 1.5T. Assessments of Q_P and Q_s were performed using free-breathing retrospectively gated 2D PC gradient recalled echo (GRE; 1.6 x 1.6 x 5 mm3) imaging with one-dimensional through-plane velocity encoding gradient (v_(enc) = 150 cm/s) in consecutive measurements for the main pulmonary artery (MPA) and ascending aorta (AA), respectively. A prospectively triggered 4D PC GRE technique (2.4 x 1.8 x 3 mm3) with three orthogonal v_(enc) directions was also used with volume coverage of both MPA and AA.Results: Q_P and Q_s assessed by 4D PC correlated with 2D PC acquisitions (r = 0.92 and r = 0.67 respectively; P < .0001 for both) but demonstrated significant underestimation of individual flow volumes (-21.9 ± 12.2 ml_;P<.0001 and —10.7 + 13.1 mL; P = .0023, respectively). Calculated Q_P:Q_s ratios demonstrated high correlation (r = 0.78; P < .0001) and no significant differences between 4D PC and 2D PC acquisitions (-0.09 ± 0.24, P = .14). Image acquisition times for 2D PC assessment of Q_P and Q_s were 2.98 r 0.52 and 2.84 i 0.50 minutes, respectively (P = .038), whereas time to acquire 4D PC images was significantly longer, 18.75 + 4.58 minutes (P < .001).Conclusions: Four-dimensional PC MR imaging allows for accurate assessment of Q_P:QS ratios in the evaluation of intracardiac shunts while absolute flow volumes demonstrate offsets. Further refinement of the technique with improvement in acquisition times may be required before widespread clinical implementation.