ABSTRACT The aim of this study is to enable high temporal resolution functional cardiac imaging without breathholds or electrocardiogram (ECG) gating. Real‐time MRI is essential for assessing heart function in patients with limited breathhold capacity or arrhythmias that preclude breathheld ECG‐gated cine scans. The Time‐Dependent Deep Image Prior (Time‐DIP) method is a promising reconstruction for dynamic MRI, combining a nonlinear manifold with zero‐shot deep learning. However, while Time‐DIP has been demonstrated for breathheld cine imaging, it employs a helical manifold that assumes quasi‐periodic motion and thus may not be suitable for free‐breathing real‐time scans, particularly in arrhythmia patients. This study proposes a Multifrequency Time‐DIP technique to extend this framework to free‐breathing real‐time cardiac imaging. First, a “multifrequency manifold” is introduced that parameterizes time using multiple sinusoids spanning various frequencies, enabling dynamic imaging without assuming motion periodicity. Second, joint estimation of coil sensitivities using zero‐shot deep learning is used to improve the reconstruction of multichannel data. Simulations and scans of healthy subjects and patients, including those with arrhythmias, were performed using a 2D free‐breathing ungated golden angle spiral bSSFP sequence. Image quality and left ventricular (LV) functional measurements were compared to real‐time scans reconstructed with compressed sensing and the original Time‐DIP implementation, as well as conventional breathheld ECG‐gated cine scans. Multifrequency Time‐DIP outperformed other real‐time techniques in simulations of various motion scenarios. In vivo scans using Multifrequency Time‐DIP exhibited reduced aliasing artifacts, achieving temporal resolutions as high as a single TR (4.2 ms/frame), with no significant differences in LV functional measurements compared to conventional scans. While conventional scans had better edge sharpness and image contrast scores, Multifrequency Time‐DIP exhibited overall higher image quality metrics among real‐time scans. In conclusion, a generalized Time‐DIP reconstruction was shown to enable high temporal resolution free‐breathing real‐time cardiac imaging in healthy subjects and patients, including those with arrhythmias.
Hamilton et al. (Mon,) studied this question.