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Fetal MRI

Metric Optimized Gating

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Cardiac MRI typically requires gating to prevent motion artifacts; however, a suitable fetal gating signal is not available in the in utero MRI environment, precluding fetal cardiac MRI. Self-gating approaches have been suggested for this application but require specialized pulse sequences [1]. 

We have developed an alternative approach using methods first developed for retrospective image correction [2], [3]. This approach acquires ‘oversampled’ data using a conventional pulse sequence without real time cardiac gating, and retrospectively reconstructs the data in an iterative manner until an image metric is optimized. At each iteration, the data are resorted according to a hypothetical ECG waveform, based on a parameterized model of the fetal cardiac cycle (heart rate model), and the image entropy is calculated to detect blurring and ghosting artifacts associated with incorrect gating. 

We call this approach metric optimized gating (MOG) [4]. This approach to gating has been validated through numerical simulations and also experimental testing in adult volunteers (comparing MOG and ECG reconstructions of the same adult volunteer data), and has been successfully applied to phase-contrast MR imaging of fetal blood flow [4,5,6] and cine imaging of the fetal heart [7]. Example images are presented under Dynamic Imaging of the Fetal Heart.

[1] Larson et al. MRM 2004;51(1):93
[2] Atkinson et al. IEEE TMI 1997;16(6):903-10
[3] Manduca et al. Radiology 2000;215(3):904-9
[4] Jansz et al. MRM 2010;64:1304-14
[5] Seed et al. JCMR 2012;14(79) 
[6] Al Nafisi et al. JCMR 2013;15:65
[7] Roy et al. MRM 2013;70(6):1598-1607