A New Short TE 3D Radial Sampling Sequence: SWIFT-LiTE

Introduction: Ultrashort echo-time (UTE) imaging (1) and sweep imaging with Fourier transformation (SWIFT) (2) are techniques for imaging hard tissues with short T2 relaxation times on the order of a few tens to hundreds of microseconds, due to their very short acquisition delays (in the range of 0.01-0.5 ms). Such short T2 components are not easily detected with conventional imaging techniques (e.g., gradient echo sequences) since the shortest achievable TE is typically in the range of 12 ms. However, implementation of UTE and SWIFT on standard clinical MRI systems can be challenging due to unique sequence and hardware requirements. In some cases, achieving short TE < 1 ms (not ultrashort TE) is all that is required. This can be relatively easily accomplished with the new sequence introduced here, which is called SWIFT-LiTE (SWIFT with Limited TE). SWIFT-LiTE is basically a 3D radial sampling sequence and can effectively cover the short TE range of > ~0.5 ms. In this sequence, data are acquired right after excitation, not during excitation as in SWIFT. However, the readout gradient is applied during excitation as in SWIFT, which is different from conventional 3D radial sampling sequences used for human studies, including 3D UTE. Here, SWIFT-LiTE is demonstrated in human brain imaging.