Imaging invisible tissues with Ultrashort Echo Time magnetic resonance
Imaging invisible tissues with Ultrashort Echo Time magnetic resonance lead image
Magnetic resonance imaging (MRI) uses a powerful static magnetic field to align the magnetic spins of protons in water and fat. A receiver detects these spins as they relax back into their equilibrium states. Different tissues have different relaxation times, creating contrast in the images.
MRI can produce crucial information for both the diagnosis and treatment of diseases and injuries. But the technique is limited to tissues with relatively long transverse relaxation times of tens to hundreds of milliseconds.
Ma et al. described how a new approach, known as Ultrashort Echo Time (UTE) sequences, could expand the applicability of MRI technology to include tissues with short transverse relaxation times, such as menisci, ligaments, tendons, bones, and myelin.
The echo time, or time between the radio frequency pulse and signal detection in conventional MRI, is typically on the order of milliseconds. However, so-called short relaxation times can be in the sub-milliseconds, leading to significant signal decay before the MR system is switched to receiver mode. As a result, tissues with short transverse relaxation times show little or no signal in conventional MR images.
“UTE sequences employ a short pulse excitation followed by radial ramp sampling, which significantly shortens the echo times to tens of microseconds or even shorter,” said author Jiang Du. “As a result, UTE sequences can directly detect signals from these tissues before they decay to the noise level.”
The researchers explained how UTE MRI works in tissues with short transverse relaxation times, how to create high-contrast images, and how the technique can be used to determine tissue properties that are important to the diagnosis and characterization of disease states.
Source: “Making the invisible visible - ultrashort echo time magnetic resonance imaging: Technical developments and applications,” by Yajun Ma, Hyungseok Jang, Saeed Jerban, Eric Y. Chang, Christine B. Chung, Graeme M. Bydder, and Jiang Du, Applied Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0086459 .
