1121 Increasing the velocity-to-noise ratio in time-resolved 3D blood flow measurements
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BioMed Central
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Meeting abstract
1121 Increasing the velocity-to-noise ratio in time-resolved 3D blood flow measurements Jochen von Spiczak*, Gérard Crelier, Peter Boesiger and Sebastian Kozerke Address: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland * Corresponding author
from 11th Annual SCMR Scientific Sessions Los Angeles, CA, USA. 1–3 February 2008 Published: 22 October 2008 Journal of Cardiovascular Magnetic Resonance 2008, 10(Suppl 1):A246
doi:10.1186/1532-429X-10-S1-A246
Abstracts of the 11th Annual SCMR Scientific Sessions - 2008
Meeting abstracts – A single PDF containing all abstracts in this Supplement is available here. http://www.biomedcentral.com/content/pdf/1532-429X-10-S1-info.pdfThis abstract is available from: http://jcmr-online.com/content/10/S1/A246 © 2008 von Spiczak et al; licensee BioMed Central Ltd.
Introduction
Methods
Time-resolved phase contrast (PC) imaging permits the assessment of volumetric, multi-directional blood flow velocities [1]. The resulting vector field data can be visualized in different ways using streamlines, arrows, and particle traces [2]. These visualization modes allow for an accurate and intuitive analysis of blood flow characteristics in normal and pathological cases [3]. Despite the advantages of the method, wide-spread acceptance in a clinical setting has been hampered by the long scan durations.
Data acquisition Time-resolved 3D PC data covering the left-ventricular outflow tract, ascending and descending aorta were acquired on a Philips 3 T Achieva system (Philips Medical Systems, Best, The Netherlands). Scan parameters of the navigated and retrospectively triggered fast gradient-echo sequence were: FOV = 320 × 260 × 51 mm3, matrix = 128 × 128 × 17, TR = 3.95/3.85ms, flip angle = 5°, cardiac phases = 25. Healthy subjects were scanned twice with Venc1x, y = 200cm/s, Venc1z = 100cm/s avoiding phase wraps and Venc2x, y = 100cm/s, Venc2z = 50cm/s intentionally accepting phase wraps.
In order to reduce the long measurement times, parallel imaging [4] may be employed. Noise amplification from parallel imaging can partly be compensated for by conducting the measurements at high field. Since the velocityto-noise ratio (VNR) is not only dependent on base signalto-noise but also scales inversely with the encoding velocity (Venc), lowering Venc may be considered an alternative approach to improving VNR. If Venc is chosen smaller than the actual blood velocities, phase aliasing arises and needs to be corrected. Phase unwrapping is a well studied field and has been extensively discussed for two [5] and more dimensions [6]. It was the objective of the present work to improve VNR by using low Venc phase contrast imaging in conjunction with an automatic phase unwrapping algorithm suited for time-resolved 3D blood flow measurements.
Phase unwrapping The phase unwrapping algorithm was designed to take into account appropriate prior knowledge about the phase evolution during one heart cycle: a) absence of phas
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