Magnetic susceptibility differences at air/tissue interfaces induce strong localized static magnetic field (B0) inhomogeneities, which cannot be effectively shimmed with the whole-body spherical harmonic (SH) shim coils onboard clinical MRI scanners, resulting in image artifacts such as distortions, blurring, signal loss, and incomplete fat suppression. These artifacts introduce diagnostic inaccuracies in clinical applications and are particularly severe in body imaging, which suffers from more extensive B0 inhomogeneities than brain imaging, and for techniques based on fast imaging sequences such as echo-planar imaging, which is used in many clinical applications such as diffusion-weighted imaging (DWI). Thus, body DWI is one of the most challenging applications and the development of a new technology that can achieve a high B0 homogeneity in the body is critically needed to improve its spatial fidelity and accuracy and to increase its clinical utility. A novel concept, termed integrated parallel reception, excitation, and shimming (iPRES), was recently proposed, which allows a radiofrequency (RF) current and a direct current (DC) to flow in the same coil, thereby enabling RF reception and localized B0 shimming with a single integrated RF/shim coil array. This new technology can thus effectively shim localized B0 inhomogeneities without reducing the signal-to-noise ratio (SNR) or requiring additional space in the magnet bore, which was demonstrated in the human brain with a 32-channel iPRES head coil array. However, its application to body imaging is more challenging, because of the larger coil elements in body coil arrays and the more extensive B0 inhomogeneities. The goal of this proposal is to develop the next generation of iPRES coil design, termed adaptive iPRES(N), to achieve a high B0 homogeneity in the body. Specifically, each RF coil element of a 32-channel body coil array will be divided into N smaller independent DC loops and switches will be added to distribute the DC currents into the appropriate DC loops as needed, resulting in a much higher flexibility and spatial resolution for localized B0 shimming, without requiring additional power supplies. Simulations will first be performed to optimize the coil design (Aim 1). The coil array will then be implemented by using a novel switch technology and will be integrated into a 3T MRI scanner (Aim 2). Finally, it will be validated by performing bench tests, phantom experiments, and human experiments, including high-resolution abdominal DWI (Aim 3). This new technology will provide an unprecedented B0 homogeneity in the body with no SNR penalty, which will substantially improve the spatial fidelity, image quality, diagnostic accuracy, scan efficiency, and patient comfort for a wide range of clinical applications, including body DWI. It will also enable shimming on wide- bore and PET/MR scanners, which do not have SH shim coils, and will eliminate the need for such coils in future scanners, resulting in lower manufacturing costs and a wider magnet bore to fit larger patients.
/ Public Health Relevance Statement The innovative integrated RF/shim coil array developed in this project will enable a much more effective shimming of localized B0 inhomogeneities in the body than currently achievable, without reducing the RF performance or requiring additional space in the magnet bore. These advantages will directly translate into an improved spatial fidelity, image quality, diagnostic accuracy, scan efficiency, and patient comfort, thereby making a significant and immediate impact on a wide range of clinical MR applications. This new technology will particularly benefit body DWI, which is widely used in clinical practice for the early detection, staging, and treatment response monitoring of many serious diseases such as cancer, including a variety of liver, pancreas, kidney, prostate, breast, spine, and gynecological lesions.
|Darnell, Dean; Ma, Yixin; Wang, Hongyuan et al. (2018) Adaptive integrated parallel reception, excitation, and shimming (iPRES-A) with microelectromechanical systems switches. Magn Reson Med 80:371-379|
|Darnell, Dean; Cuthbertson, Jonathan; Robb, Fraser et al. (2018) Integrated radio-frequency/wireless coil design for simultaneous MR image acquisition and wireless communication. Magn Reson Med :|