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

Rationale and Objectives: To investigate four-dimensional (4D) phase-contrast(PC) magnetic resonance (MR) in the evaluation of intracardiac shunts by simultaneous assessment of pulmonary (Q(P)) and systemic (Q(S)) 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 mm(3)) 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 (M), respectively. A prospectively triggered 4D PC GRE technique (2.4 x 1.8 x 3 mm(3)) 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 +/- 0.52 and 2.84 +/- 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-dimeneional PC MR imaging allows for accurate assessment of Q(P):Q(S) 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: