title: Quantification and visualization of cardiovascular 4D velocity mapping accelerated with parallel imaging or k-t BLAST: head to head comparison and validation at 1.5 T and 3 T.
abstract: BACKGROUND
  Three-dimensional time-resolved (4D) phase-contrast (PC) CMR can visualize and quantify cardiovascular flow but is hampered by long acquisition times. Acceleration with SENSE or k-t BLAST are two possibilities but results on validation are lacking, especially at 3 T. The aim of this study was therefore to validate quantitative in vivo cardiac 4D-acquisitions accelerated with parallel imaging and k-t BLAST at 1.5 T and 3 T with 2D-flow as the reference and to investigate if field strengths and type of acceleration have major effects on intracardiac flow visualization.
  
  
  METHODS
  The local ethical committee approved the study. 13 healthy volunteers were scanned at both 1.5 T and 3 T in random order with 2D-flow of the aorta and main pulmonary artery and two 4D-flow sequences of the heart accelerated with SENSE and k-t BLAST respectively. 2D-image planes were reconstructed at the aortic and pulmonary outflow. Flow curves were calculated and peak flows and stroke volumes (SV) compared to the results from 2D-flow acquisitions. Intra-cardiac flow was visualized using particle tracing and image quality based on the flow patterns of the particles was graded using a four-point scale.
  
  
  RESULTS
  Good accuracy of SV quantification was found using 3 T 4D-SENSE (r2 = 0.86, -0.7 ± 7.6%) and although a larger bias was found on 1.5 T (r2 = 0.71, -3.6 ± 14.8%), the difference was not significant (p = 0.46). Accuracy of 4D k-t BLAST for SV was lower (p < 0.01) on 1.5 T (r2 = 0.65, -15.6 ± 13.7%) compared to 3 T (r2 = 0.64, -4.6 ± 10.0%). Peak flow was lower with 4D-SENSE at both 3 T and 1.5 T compared to 2D-flow (p < 0.01) and even lower with 4D k-t BLAST at both scanners (p < 0.01). Intracardiac flow visualization did not differ between 1.5 T and 3 T (p = 0.09) or between 4D-SENSE or 4D k-t BLAST (p = 0.85).
  
  
  CONCLUSIONS
  The present study showed that quantitative 4D flow accelerated with SENSE has good accuracy at 3 T and compares favourably to 1.5 T. 4D flow accelerated with k-t BLAST underestimate flow velocities and thereby yield too high bias for intra-cardiac quantitative in vivo use at the present time. For intra-cardiac 4D-flow visualization, however, 1.5 T and 3 T as well as SENSE or k-t BLAST can be used with similar quality.
authors.affiliation: Dept of Clinical Physiology, Lund University, Lund, Sweden. marcus.carlsson@med.lu.se
authors.forename: Marcus
authors.initials: M
authors.lastname: Carlsson
authors.forename: Johannes
authors.initials: J
authors.lastname: Töger
authors.forename: Mikael
authors.initials: M
authors.lastname: Kanski
authors.forename: Karin Markenroth
authors.initials: KM
authors.lastname: Bloch
authors.forename: Freddy
authors.initials: F
authors.lastname: Ståhlberg
authors.forename: Einar
authors.initials: E
authors.lastname: Heiberg
authors.forename: Håkan
authors.initials: H
authors.lastname: Arheden
mesh_terms: D000328:Adult; D001011:Aorta / Q000502:physiology; D001783:Blood Flow Velocity; D003326:Coronary Circulation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D011237:Predictive Value of Tests; D011652:Pulmonary Circulation; D012016:Reference Values; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D013318:Stroke Volume; D013548:Sweden; D013997:Time Factors; D055815:Young Adult