Dual phase free breathing 3D bSSFP MRA with Preserved Eddy-current Tolerance with Adaptive k-space Lengths (PETAL) acquisition (RF_SA_496)

Accurate aortic annulus measurement is crucial for TAVR procedure planning to prevent complications such as prosthesis dislocation and annulus rupture¹.3D Navigator-assisted SSFP cardiac MRI (CMR) provides the required anatomical assessment to ensure precise prosthesis sizing  as an alternative for patients contraindicated for CT scans². Yet, prospective gating is often hindered by navigator echo positioning, arrhythmia, and breathing pattern variability, leading to unpredictable scan times³. Self-navigated techniques improve scan predictability by acquiring the center of k-space regularly to address respiratory motion. However, these methods can cause fast and high-amplitude gradient-induced eddy-current artifacts, especially in 3T MRI and fast sequences like bSSFP⁴. To mitigate this, we propose a Cartesian-like trajectory that maximizes k-space coverage while minimizing the distance between adjacent readouts, following a pattern that periodically returns to the center of k-space. As multiple navigators can be acquired per heartbeat, respiratory motion can be addressed for longer acquisition windows allowing image acquisition in different cardiac phases.

Methods:

The proposed Cartesian-based trajectory, described in Figure 1-A is referred to as PETAL. Imaging was performed on a 3T MR system (MAGNETOM Cima.X, Siemens Healthineers, Forchheim, Germany) using an ECG-gated, free breathing, T2-prepared, fat saturated, 3D bSSFP sequence, as  shown on the diagram in Figure 1-B using the following imaging parameters: repetition time (TR) / echo time (TE): 3.4 ms / 1.7 ms, field of view: 307 × 307 x 307 mm³; matrix: 192 x 192 × 192; acquired isotropic voxel size of 1.6 mm; flip angle: 45°. The data was retrospectively binned using the navigator’s position at each heartbeat to address respiratory motion, as described in Figure 1-C. The position of each navigator determines if the data acquired before the following navigator is accepted.

Results:

Preliminary results from 3 healthy volunteers demonstrated a comparable aortic annulus (AA) measurement to a conventional navigator-gated free breathing whole-heart SSFP based sequence acquired in diastole, while offering more predictable scan times as detailed in Table 1. The diameter and perimeter of the aortic annulus were measured parallel to the valve plane, along the red line shown in Figure 2. The same metrics were taken for the volume acquired during systole. AA dimensions and their variation throughout the cardiac cycle are similar to those reported in previous studies⁵.

Conclusion:

We demonstrated that the proposed method is a viable alternative for the conventional whole-heart sequence, offering more predictable scan times. Furthermore, it enables the acquisition of systolic volume, allowing for the assessment of AA variation throughout the cardiac cycle without extending scan duration.