Contribution of early systole to total forward flow volume in breath-hold phase-contrast flow measurements

Purpose: To evaluate the contribution of early systole for the assessment of antegrade aortic flow volume by breath-hold velocity-encoded magnetic resonance (MR) flow measurements. Materials and Methods: Expiratory breath-hold fast low-angle shot (FLASH) phase-contrast flow measurements (temporal resolution tRes 61 msec, shared phases) perpendicular to the proximal ascending aorta and short axis true fast imaging with steady-state precession (TrueFISP) cine MR ventriculometry (tRes 34.5 msec) were performed in ten healthy male volunteers on a 1.5 T MR system (Sonata, Siemens Medical Solutions). Antegrade aortic flow volume (AFV) and left ventricular stroke volume (LV-SV) were evaluated using Argus Ventricular Function and Argus Flow Software, version MR 2002B (Siemens Medical Solutions). A beta release of Argus Flow MR 2004A allowed interpolation of the flow up-slope during early systole to the preceding R-wave trigger. The respective intraindividual median differences between the AFV of each flow evaluation and LV-SV as well as between both AFV measurements were calculated and compared using the sign test for paired samples. Results: Non-interpolated AFV significantly deviated from LV-SV (p=0.006), underestimating the latter by 13.1 mL (13%). Interpolating aortic flow during early systole significantly increased AFV by 10.8 mL (13%) compared to the flow evaluation which did not take early systole into account (p=0.006). AFV with interpolation of early systolic flow agreed well with LV-SV (median difference -3.0 mL or -3%, respectively), and no significant difference between these measurements was found (p=1.0). Conclusion: Flow during early systole contributes substantially to total forward flow volume in the ascending aorta. Interpolation of the early systolic up-slope is therefore recommended for the evaluation of breath-hold phase-contrast flow measurements. (orig.)