A Small Surrogate for the Golden Angle in Time-Resolved Radial MRI Based on Generalized Fibonacci Sequences

Abstract

In golden angle radial magnetic resonance imaging a constant azimuthal radial profile spacing of 111.246...(°) guarantees a nearly uniform azimuthal profile distribution in k-space for an arbitrary number of radial profiles. Even though this profile order is advantageous for various real-time imaging methods, in combination with balanced steady-state free precession (SSFP) sequences the large azimuthal angle increment may lead to strong image artifacts, due to the varying eddy currents introduced by the rapidly switching gradient scheme. Based on a generalized Fibonacci sequence, a new sequence of smaller irrational angles is introduced ( 49.750...(°), 32.039...(°), 27.198...(°), 23.628...(°), ... ). The subsequent profile orders guarantee the same sampling efficiency as the golden angle if at least a minimum number of radial profiles is used for reconstruction. The suggested angular increments are applied for dynamic imaging of the heart and the temporomandibular joint. It is shown that for balanced SSFP sequences, trajectories using the smaller golden angle surrogates strongly reduce the image artifacts, while the free retrospective choice of the reconstruction window width is maintained.

Low rank alternating direction method of multipliers reconstruction for MR fingerprinting

“…To demonstrate the impact of the sampling density on the reconstruction quality, a subset of the simulations was repeated with multiple spokes per TR. These additional spokes where distributed using the tiny golden angle of approximately 32.0397 (29). All radial spokes were associated with an extend of k max ¼ ffiffiffi 2 p p=voxel contrary to the usual convention of radial MRI (k max ¼ p=voxel).…”

Free breathing whole-heart 3D CINE MRI with self-gated Cartesian trajectory

“…As data is acquired only in a mid-diastolic phase, the transient effects such as eddy currents originating from the golden step and periphery to centre k-space jump between the consecutive interleaves are expected to be diminished before the mid-diastolic data acquisition for the next interleave. However, for application of cardiac CINE where data is acquired continuously without interruption, in combination with balanced SSFP sequence, the golden angle step can lead to rapidly changing eddy currents, resulting in strong image artefacts [27]. Recently, a new sequence of smaller irrational angles (49.75°, 32.039°, 27.198°, 23.628°) called as tiny golden angle has been introduced for 2D golden radial acquisition [28].…”

Time‐of‐flight MR‐angiography with a helical trajectory and slice‐super‐resolution reconstruction

“…Because the linear ordering scheme has large sampling gaps along the k x – z direction, a modified helical trajectory with a golden angle ordering scheme was proposed. To reduce eddy currents due to large gradient activity in golden angle radial imaging , the projections in this work are arranged by a smaller golden angle surrogate of . The corresponding golden angle helical trajectory (Figure B) allows for a pseudo random sampling along the k y – z and the k x – z direction, which is beneficial for image reconstruction …”