Three dimensional ultrashort echo time (UTE) MRI for meniscus enhancement

Abstract

There is an increasing need to image meniscus that $T_2$ is very short. The MR signal of this component with short $T_2$ relaxation decays rapidly, meniscus is not detected or poorly detected with conventional magnetic resonance (MR) pulse sequences. In order to detect short $T_2$ components, several ultrashort echo time (UTE) methods were developed. It is appropriate to subtract two echo images out of several methods, because it allows faster scan and requires less shimming effort than other methods. However, this method is vulnerable to edge artifact and contrast may be degraded on short $T_2$ image by residual long $T_2$ tissues. The proposed method uses the spoiled gradient echo based (FLASH UTE) sequence and the balanced steady-state free precession based UTE (balanced UTE) sequence. In the case of the signal obtained by the balanced UTE, the FID signal and the echo signal are combined, which is k times larger than the signal obtained by the FLASH UTE using only the FID signal according to the $T_1$ and $T_2$ values of the material. Therefore, we can obtain a meniscus enhanced image by scaling the k value of the surrounding tissues of the meniscus to the FLASH UTE image and subtracting the balanced UTE image. These sequences are acquired through three-dimensional radial k-space sampling. In-vivo experiments demonstrated that the proposed method can provide better meniscus contrast than conventional method.