A robust ultrashort TE (UTE) imaging method with corrected k-space trajectory by using parametric multiple function model of gradient waveform.

ABSTRACT

Ultra-short TE (UTE) sequences with radial sampling make it possible to visualize tissues with very short T2 decay times. The UTE sequence acquires an echo signal from the central to the outer parts of k-space and is very sensitive to small trajectory errors. Therefore, k-space errors caused by imperfections in the gradient system performance, such as gradient delay and waveform distortion, must be corrected. During normal clinical use, these errors must be corrected to account for any gradient strength, or image obliquity. Because of time limitation on clinical examination, a simple, robust, and time-efficient correction method for use with UTE is needed. We demonstrated image degradation due to k-space errors by simulation and found that uncontrolled gradient time delays were the dominant cause of image degradation. They could be corrected by using a pre-scan calibration that works by comparison of half and full echo signals. Further improvements in image quality were achieved by using a one-time calibration of gradient waveform approximations that were built from multiple exponential functions and were used during image reconstruction. We have developed a robust UTE correction method that consists of a gradient waveform approximation that follows a short pre-scan for estimating gradient time delay errors.