A novel center-out 3D trajectory for sampling magnetic resonance data is presented. The trajectory set is based on a single Fermat spiral waveform, which is substantially undersampled in the center of k-space. Multiple trajectories are combined in a ''stacked cone'' configuration to give very uniform sampling throughout a ''hub,'' which is very efficient in terms of gradient performance and uniform trajectory spacing. The fermat looped, orthogonally encoded trajectories (FLORET) design produces less gradient-efficient trajectories near the poles, so multiple orthogonal hub designs are shown. These multihub designs oversample k-space twice with orthogonal trajectories, which gives unique properties but also doubles the minimum scan time for critical sampling of k-space. The trajectory is shown to be much more efficient than the conventional stack of cones trajectory, and has nearly the same signal-to-noise ratio efficiency (but twice the minimum scan time) as a stack of spirals trajectory. As a center-out trajectory, it provides a shorter minimum echo time than stack of spirals, and its spherical k-space coverage can dramatically reduce Gibbs ringing. Magn Reson Med 66:1303-1311,
Purpose
This work proposes the ISMRM Raw Data (ISMRMRD) format as a common MR raw data format, which promotes algorithm and data sharing.
Methods
A file format consisting of a flexible header and tagged frames of k-space data was designed. Application Programming Interfaces were implemented in C/C++, MATLAB, and Python. Converters for Bruker, General Electric, Philips, and Siemens proprietary file formats were implemented in C++. Raw data were collected using MRI scanners from four vendors, converted to ISMRMRD format, and reconstructed using software implemented in three programming languages (C++, MATLAB, Python).
Results
Images were obtained by reconstructing the raw data from all vendors. The source code, raw data, and images comprising this work are shared online, serving as an example of an image reconstruction project following a paradigm of reproducible research.
Conclusion
The proposed raw data format solves a practical problem for the MRI community. It may serve as a foundation for reproducible research and collaborations. The ISMRMRD format is a completely open and community-driven format, and the scientific community is invited (including commercial vendors) to participate either as users or developers.
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