title: Metric optimized gating for fetal cardiac MRI.
abstract: Phase-contrast magnetic resonance imaging can be used to complement echocardiography for the evaluation of the fetal heart. Cardiac imaging typically requires gating with peripheral hardware; however, a gating signal is not readily available in utero. No successful application of existing technologies to human fetal phase-contrast magnetic resonance imaging has been reported to date in the literature. The purpose of this work is to develop a technique for phase-contrast magnetic resonance imaging of the fetal heart that does not require measurement of a gating signal. Metric optimized gating involves acquiring data without gating and retrospectively determining the proper reconstruction by optimizing an image metric. The effects of incorrect gating on phase contrast images were investigated, and the time-entropy of the series of images was found to provide a good measure of the level of corruption. The technique was validated with a pulsatile flow phantom, experiments with adult volunteers, and in vivo application in the fetal population. Images and flow curves from these measurements are presented. Additionally, numerical simulations were used to investigate the degree to which heart rate variability affects the reconstruction process. Metric optimized gating enables imaging with conventional phase-contrast magnetic resonance imaging sequences in the absence of a gating signal, permitting flow measurements in the great vessels in utero.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Jansz
authors.forename: Mike
authors.initials: M
authors.lastname: Seed
authors.forename: Joshua F P
authors.initials: JF
authors.lastname: van Amerom
authors.forename: Derek
authors.initials: D
authors.lastname: Wong
authors.forename: Lars
authors.initials: L
authors.lastname: Grosse-Wortmann
authors.forename: Shi-Joon
authors.initials: SJ
authors.lastname: Yoo
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Macgowan
mesh_terms: D000465:Algorithms; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods*; D005260:Female; D006321:Heart / Q000033:anatomy & histology / Q000196:embryology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011296:Prenatal Diagnosis / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity