Extrinsic multiecho phase-contrast SSFP: evaluation on cardiac output measurements Marijn P. Rolf a, ⁎ , Mark B.M. Hofman a , Joost P.A. Kuijer a , Vinay M. Pai b , Andreas Greiser c , Albert C. van Rossum d , Rob M. Heethaar a a Department of Physics and Medical Technology, ICaR-VU, VU University Medical Center, 1007 MB Amsterdam, The Netherlands b Department of Radiology, New York University, New York, NY 10016, USA c Siemens AG Medical Solutions, 91050 Erlangen, Germany d Department of Cardiology, ICaR-VU, VU University Medical Center, 1007 MB Amsterdam, The Netherlands Received 26 May 2008; revised 9 July 2008; accepted 12 July 2008 Abstract Multiecho phase-contrast steady-state free precession (PC-SSFP) is a recently introduced sequence for flow quantification. In this multiecho approach, a phase reference and a velocity-encoded readout were acquired at different echo times after a single excitation. In this study, the sequence is validated in vitro for stationary flow. Subsequently, the sequence was evaluated on cardiac output measurements in vivo for through- plane flow in comparison to regular single gradient echo velocity quantification [phase-contrast spoiled gradient echo (PC-GE)]. In vitro results agreed with regular flow meters (RMS 0.1 cm/s). Cardiac output measurements with multiecho PC-SSFP on 10 healthy subjects gave on average the same results as the standard PC-GE. However, the limits of repeatability of PC-SSFP were significantly larger than those of PC-GE (2 l/min and 0.5 l/min, respectively, P =.001). The multiecho approach introduced some specific problems in vivo. The difference in echo times made the velocity maps sensitive for water- fat shifts and B 0 -drifts, which in turn made velocity offset correction problematic. Also, the addition of a single bipolar gradient cancelled the flow compensated nature of the SSFP sequence. In combination with the prolonged TR, this resulted in flow artifacts caused by high and pulsatile through-plane flow, affecting repeatability. Given the significantly lower repeatability of PC-SSFP, cardiac output in turn is less reliable, thus impairing the use of multiecho PC-SSFP. © 2009 Elsevier Inc. All rights reserved. Keywords: MRI; SSFP; Multiecho; Phase-contrast; Flow quantification; Cardiac output 1. Introduction Flow quantification is an important tool in cardiovascular magnetic resonance imaging (MRI), for example, to measure cardiac output [1–4]. The conventional approach to flow quantification utilizes spoiled gradient echo (GE) imaging technique, which inherently has a limited signal-to-noise ratio (SNR) when applied with short repetition times. With the advent of faster gradient systems flow quantification with steady-state free precession (SSFP) sequences has become feasible, three different approaches were published by Overall et al. [5], Markl et al. [6] and Pai [7]. Advantages of SSFP are shorter acquisition times and higher SNR [8,9]. The most recently published approach to flow quantification with SSFP was using multiecho phase-contrast SSFP (PC- SSFP) by Pai [7]. The multiecho PC-SSFP sequence uses a regular SSFP scheme with a second echo and a fly-back gradient between the two readout echoes. During the fly- back gradient, a bipolar gradient is applied in slice-select direction for through-plane velocity encoding (extrinsic approach). The first echo provides the phase reference while the second echo is flow-encoded. Available online at www.sciencedirect.com Magnetic Resonance Imaging 27 (2009) 385 – 392 ⁎ Corresponding author. Department of Physics and Medical Tech- nology, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, The Netherlands. Tel.: +31 20 44 40 327; fax: +31 20 44 44 147. E-mail address: mp.rolf@vumc.nl (M.P. Rolf). 0730–725X/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2008.07.006