Cardiorespiratory‐resolved magnetic resonance imaging: Measuring respiratory modulation of cardiac function

A technique for cardiac‐ and respiratory‐resolved MRI is described. A retrospectively gated‐segmented acquisition scheme similar to that used in conventional cine cardiac imaging was used to collect image data that spanned both the cardiac and respiratory cycles. Raw k‐space data were regridded in a cardiorespiratory phase space to allow image reconstruction at target cardiac and respiratory phases. The approach can be applied with various k‐space trajectories and pulse sequences, and was implemented in this study with both a Cartesian steady‐state free precession (SSFP) sequence and a radial phase‐contrast (PC) pulse sequence. Free‐breathing short‐axis SSFP images of the heart were reconstructed at multiple respiratory and cardiac phases to illustrate separation of cardiac and respiratory motion without artifacts. A respiratory‐resolved radial PC experiment was used to quantify the volumetric flow rates in the inferior vena cava (IVC), pulmonary artery (PA), and aorta (Ao) in five free‐breathing normal volunteers and a positive‐pressure ventilated dog. Total flow (ml/min) in each vessel was quantified as a function of respiratory phase (peak/minimum output = 1.85 ± 0.29 (IVC), 1.36 ± 0.15 (PA), 1.24 ± 0.09 (Ao)). Peak flow occurred during inspiration for the IVC and PA, and during expiration for the Ao, and there was a complete pattern reversal for the positive‐pressure ventilated dog. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.