Self‐calibrated through‐time spiral GRAPPA for real‐time, free‐breathing evaluation of left ventricular function

Abstract

Purpose Through‐time spiral GRAPPA is a real‐time imaging technique that enables ungated, free‐breathing evaluation of the left ventricle. However, it requires a separate fully‐sampled calibration scan to calculate GRAPPA weights. A self‐calibrated through‐time spiral GRAPPA method is proposed that uses a specially designed spiral trajectory with interleaved arm ordering such that consecutive undersampled frames can be merged to form calibration data, eliminating the separate fully‐sampled acquisition. Theory and Methods The proposed method considers the time needed to acquire data at all points in a GRAPPA calibration kernel when using interleaved arm ordering. Using this metric, simulations were performed to design a spiral trajectory for self‐calibrated GRAPPA. Data were acquired in healthy volunteers using the proposed method and a comparison electrocardiogram‐gated and breath‐held cine scan. Left ventricular functional values and image quality are compared. Results A 12‐arm spiral trajectory was designed with a temporal resolution of 32.72 ms/cardiac phase with an acceleration factor of 3. Functional values calculated using the proposed method and the gold‐standard method were not statistically significantly different (paired t‐test, p < 0.05). Image quality ratings were lower for the proposed method, with statistically significantly different ratings (Wilcoxon signed rank test, p < 0.05) for two of five image quality aspects rated (level of artifact, blood‐myocardium contrast). Conclusions A self‐calibrated through‐time spiral GRAPPA reconstruction can enable ungated, free‐breathing evaluation of the left ventricle in 71 s. Functional values are equivalent to a gold‐standard cine technique, although some aspects of image quality may be inferior due to the real‐time nature of the data collection.

The future of CMR: All-in-one vs. real-time CMR (Part 2)

“…These techniques also can be paired with non-Cartesian trajectories to enable higher acceleration factors [53] , [54] . The need for additional calibration data can be avoided by using temporal SENSE/GRAPPA approaches, which derive the respective information from a sliding window reconstruction [53] , [55] , or by deploying self-calibration approaches [56] . K-t techniques use spatiotemporal redundancy of the data, where analysis of the frequency components (f) of the temporal evolution of a certain spatial position (x) in so-called x-f space can assist in the removal of respective aliasing artifacts before the data are transformed back into the k-t representation.…”

Comparison of uniform‐density, variable‐density, and dual‐density spiral samplings for multi‐shot DWI

“…[14][15][16] However, given the sensitivity of spiral sampling to B0 field inhomogeneity, the readout duration of single-shot spiral acquisitions is greatly limited, compromising the achievable spatial resolution. To improve the spatial resolution, single-shot spiral acquisitions can be combined with parallel imaging techniques, 17,18 resulting in shortened readout duration and alleviated static B0 off-resonance effects. With such a strategy, single-shot spiral acquisitions have been used to achieve high-resolution diffusion imaging.…”

Self-calibrated through-time spiral GRAPPA for real-time, free-breathing evaluation of left ventricular function

“…The number of arms was then varied from 50 to 3. Preliminary testing 23,24 suggested that acceleration factors of 8 or lower and TRs less than approximately 10 ms may yield acceptable image quality. Simulations of trajectories that met these specifications were performed, and those that resulted in visually similar image quality to the separately-calibrated reconstruction were tested in vivo for initial qualitative assessment.…”