Ultrashort echo time and zero echo time MRI at 7T

Abstract

Object Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences at 7T to assess differences between these methods. Materials and Methods We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast. Our ZTE used the Water- and fat-suppressed solid-state proton projection imaging (WASPI) method to fill the center of k-space. Images from healthy volunteers obtained at 7T were compared qualitatively as well as with SNR and CNR measurements for various ultrashort, short, and long-T2 tissues. Results We measured nearly identical contrast-to-noise and signal-to-noise ratios (CNR/SNR) in similar scan times between the two approaches for ultrashort, short, and long-T2 components in the brain, knee and ankle. In our protocol, we observed gradient fidelity artifacts in UTE, and our chosen flip angle and readout also resulted as well as shading artifacts in ZTE due to inadvertent spatial selectivity. These can be corrected by advanced reconstruction methods or with different chosen protocol parameters. Conclusion The applied ZTE and UTE pulse sequences achieved similar contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components. Several key differences are that ZTE is limited to volumetric imaging but has substantially reduced acoustic noise levels during the scan. Meanwhile, UTE has higher acoustic noise levels and greater sensitivity to gradient fidelity, but offers more flexibility in image contrast and volume selection.

Assessment of different fitting methods for in-vivo bi-component T2* analysis of human patellar tendon in magnetic resonance imaging

“…However, tendon and other musculoskeletal tissues containing abundant highly organized col- @ C I C E d i z i o n i I n t e r n a z i o n a l i lagen fibers are difficult to assess using quantitative MR techniques due to their extremely rapid signal decay. New MR techniques including ultra-short echotime (UTE) imaging 10,37,38 , variable echo time (VTE) imaging 25,39 and zero echo-time (ZTE) imaging 40,41 have been recently developed to capture the rapidly decaying signal within musculoskeletal tissues. The UTE sequence used in our study utilized a center-out twisted 3D cone k-space trajectory which has been shown to increase sampling uniformity, decrease undersampling artifact, and provide better SNR performance when compared to traditional 2D and 3D radial UTE sequences 33 .…”

Ultrashort echo time magnetic resonance fingerprinting (UTE‐MRF) for simultaneous quantification of long and ultrashort T2 tissues

“…However, bone, tendon, meniscus, and myelin sheath tissues, which have short or ultrashort T 2 values (on the order of 1‐10 ms), are barely detectable in conventional MRI . Ultrashort echo time (UTE) and zero echo time imaging techniques have been used to detect these constituents . Due to their long scan time, single‐point and multipoint imaging techniques are rarely used for in vivo studies.…”

Quantification of metal‐induced susceptibility artifacts associated with ultrahigh‐field magnetic resonance imaging of spinal implants

“…We here quantitatively evaluated the magnitude of metal artifacts derived from spinal implants on 7‐T MRI and analyzed the differences between these artifacts based on the ASTM evaluation method . In addition, the zero echo time (ZTE) technique, which is based on the three‐dimensional (3D) radial technique using dedicated software and RF coil technology equipped with ultrahigh‐speed RF switching, has gained attention in recent years. It has been suggested that this method can reduce acoustic noise and motion artifacts.…”