title: Utility of respiratory-navigator-rejected k-space lines for improved signal-to-noise ratio in three-dimensional cardiac MR.
abstract: OBJECTIVE
  To develop and evaluate a technique that uses the k-space lines rejected by prospective respiratory navigator (NAV) to improve the signal-to-noise ratio (SNR) without increasing the scan time.
  
  
  METHODS
  In conventional image reconstruction, the motion-corrupted k-space lines rejected by the NAV are not used. In this study, a set of translational motion parameters for the NAV-rejected lines and a phase-corrected average for the k-space line are estimated jointly using a maximum-likelihood approach and the information from the corresponding accepted k-space lines. Left coronary artery images were acquired in 10 healthy adult subjects, and the proposed approach incorporating the NAV-rejected lines was compared with the conventional dataset with NAV-accepted lines only, as well as a simple average of all k-space lines, in terms of SNR, normalized vessel sharpness and qualitative image scores on a four-point scale (1 = poor, 4 = excellent). Late gadolinium enhancement images of the left atrium were also acquired in 21 patients with atrial fibrillation pre- or post-pulmonary vein isolation. Images reconstructed with the proposed, conventional, and simple averaging methods were compared in terms of SNR, and subjective image quality on a four-point scale.
  
  
  RESULTS
  For coronary MRI, there was a significant improvement in SNR with the proposed technique, but no significant difference in normalized vessel sharpness or qualitative image scores were observed with respect to the conventional method. Simple averaging resulted in an SNR gain, but significant loss in vessel sharpness and image quality. For late gadolinium enhancement, there was a significant increase in SNR, but no significant differences were observed in subjective image quality scores between the proposed and conventional methods. There was an SNR gain, but image quality loss for simple averaging, when compared with the conventional technique. In both coronary MRI and late gadolinium enhancement, the SNR gain of the proposed method was not significantly different than the maximum theoretical SNR gain.
  
  
  CONCLUSIONS
  The proposed technique improves SNR using the additional information from NAV-rejected k-space lines, while providing similar image quality to standard reconstruction using motion-free k-space data only, with no increase in scan time.
authors.affiliation: Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Akçakaya
authors.forename: Jaime L
authors.initials: JL
authors.lastname: Shaw
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Hauser
authors.forename: Reza
authors.initials: R
authors.lastname: Nezafat
mesh_terms: D000328:Adult; D000465:Algorithms; D001281:Atrial Fibrillation / Q000473:pathology* / Q000601:surgery; D005260:Female; D006325:Heart Atria / Q000473:pathology* / Q000601:surgery; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D016896:Treatment Outcome