Purpose: Implementation, evaluation and application of a pulse sequence for retrospectively-gated sodium magnetic resonance imaging of the human heart.
Methods: Measurements were conducted at a magnetic field strength of 7.0 Tesla. A 3D projection reconstruction technique using a standard (ST) and a golden angle (GA) acquisition scheme for short echo time (23)Na MR was applied. Data were acquired continuously without cardiac triggering using a free breathing regime. Arbitrary phases of the cardiac cycle were reconstructed using synchronization with a physiological trigger signal and different temporal resolutions. Phantom measurements and examinations of healthy subjects were performed to evaluate the performance of the ST and GA acquisition schemes. A signal-to-background ratio (SBR)--that compromises both the signal-to-noise ratio and artifacts--was calculated for benchmarking the GA and ST scheme.
Results: In phantom measurements, the measured SBR of the GA acquisition scheme was up to 88% higher versus ST. Undersampling artifacts were reduced in GA compared to the ST sampling scheme. Whole heart coverage sodium images could be reconstructed with a nominal spatial resolution of (6 mm)(3) and a temporal resolution of Δt=0.1 s for covering the entire cardiac cycle. Changes in overall heart volume and myocardial wall thickness throughout the cardiac cycle were clearly visible in the reconstructed images. For the in vivo data and the imaging protocol used, GA provided a mean SBR of 38.0±5.5 while ST provided a mean SBR of 37.2±2.2.
Conclusion: Retrospectively-gated CINE (23)Na imaging of the heart at 7.0 T using density-adapted 3D projection reconstruction is feasible. The GA acquisition scheme is superior to the ST acquisition.
Keywords: 3D radial sequence; 7Tesla; Cardiac imaging; Golden angle acquisition; Retrospective gating; Sodium MRI.
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