title: Cardiac 4D phase-contrast CMR at 9.4 T using self-gated ultra-short echo time (UTE) imaging.
abstract: BACKGROUND
  Time resolved 4D phase contrast (PC) cardiovascular magnetic resonance (CMR) in mice is challenging due to long scan times, small animal ECG-gating and the rapid blood flow and cardiac motion of small rodents. To overcome several of these technical challenges we implemented a retrospectively self-gated 4D PC radial ultra-short echo-time (UTE) acquisition scheme and assessed its performance in healthy mice by comparing the results with those obtained with an ECG-triggered 4D PC fast low angle shot (FLASH) sequence.
  
  
  METHODS
  Cardiac 4D PC CMR images were acquired at 9.4 T in healthy mice using the proposed self-gated radial center-out UTE acquisition scheme (TE/TR of 0.5 ms/3.1 ms) and a standard Cartesian 4D PC imaging sequence (TE/TR of 2.1 ms/5.0 ms) with a four-point Hadamard flow encoding scheme. To validate the proposed UTE flow imaging technique, experiments on a flow phantom with variable pump rates were performed.
  
  
  RESULTS
  The anatomical images and flow velocity maps of the proposed 4D PC UTE technique showed reduced artifacts and an improved SNR (left ventricular cavity (LV): 8.9 ± 2.5, myocardium (MC): 15.7 ± 1.9) compared to those obtained using a typical Cartesian FLASH sequence (LV: 5.6 ± 1.2, MC: 10.1 ± 1.4) that was used as a reference. With both sequences comparable flow velocities were obtained in the flow phantom as well as in the ascending aorta (UTE: 132.8 ± 18.3 cm/s, FLASH: 134.7 ± 13.4 cm/s) and pulmonary artery (UTE: 78.5 ± 15.4 cm/s, FLASH: 86.6 ± 6.2 cm/s) of the animals. Self-gated navigator signals derived from information of the oversampled k-space center were successfully extracted for all animals with a higher gating efficiency of time spent on acquiring gated data versus total measurement time (UTE: 61.8 ± 11.5%, FLASH: 48.5 ± 4.9%).
  
  
  CONCLUSIONS
  The proposed self-gated 4D PC UTE sequence enables robust and accurate flow velocity mapping of the mouse heart in vivo at high magnetic fields. At the same time SNR, gating efficiency, flow artifacts and image quality all improved compared to the images obtained using the well-established, ECG-triggered, 4D PC FLASH sequence.
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Philosophenweg 3, D-07743, Jena, Germany. martinkraemer84@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Krämer
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.
authors.forename: A G
authors.initials: AG
authors.lastname: Motaal
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Philosophenweg 3, D-07743, Jena, Germany.
authors.forename: K-H
authors.initials: KH
authors.lastname: Herrmann
authors.affiliation: Institute of Medical Microbiology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Löffler
authors.affiliation: Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Philosophenweg 3, D-07743, Jena, Germany.|Michael Stifel Center for Data-driven and Simulation Science Jena, Friedrich Schiller University Jena, Jena, Germany.|Abbe School of Photonics, Friedrich Schiller University Jena, Jena, Germany.|Center of Medical Optics and Photonics, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: J R
authors.initials: JR
authors.lastname: Reichenbach
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.|Biomedical Engineering and Physics, Academic Medical Center, Amsterdam, Netherlands.
authors.forename: G J
authors.initials: GJ
authors.lastname: Strijkers
authors.affiliation: Institute of Medical Microbiology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Hoerr
mesh_terms: D000818:Animals; D016477:Artifacts; D001783:Blood Flow Velocity; D055424:Cardiac-Gated Imaging Techniques / Q000295:instrumentation; D003326:Coronary Circulation; D004562:Electrocardiography; D006321:Heart / Q000000981:diagnostic imaging*; D006339:Heart Rate; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D013997:Time Factors
keywords: 4D PC CMR; Blood flow velocity; High Field; Mice; Self-Gating; UTE