Short echo-time 3D radial gradient-echo MRI using concurrent dephasing and excitation.

Ultrashort echo-time imaging and sweep imaging with Fourier transformation are powerful techniques developed for imaging ultrashort T(2) species. However, it can be challenging to implement them on standard clinical MRI systems due to demanding hardware requirements. In this article, the limits of what is possible in terms of the minimum echo-time and repetition time with 3D radial gradient-echo sequences, which can be readily implemented on a standard clinical scanner, are investigated. Additionally, a new 3D radial gradient-echo sequence is introduced, called COncurrent Dephasing and Excitation (CODE). The unique feature of CODE is that the initial dephasing of the readout gradient is performed during RF excitation, which allows CODE to effectively achieve echo-times on the order of ∼0.2 ms and larger in a clinical setting. The minimum echo-time achievable with CODE is analytically described and compared with a standard 3D radial gradient-echo sequence. CODE was implemented on a clinical 3 T scanner (Siemens 3 T MAGNETOM Trio), and both phantom and in vivo human knee images are shown for demonstration.