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"Advancing Next-Generation MR Instrumentation Will Pave the Way for High-Field MRI Applications in the New Era of Precision Medicine"

Hui Han, Ph.D.
Director, MR Engineering
Assistant Professor, Biomedical Sciences
Cedars-Sinai Medical Center
 

ABSTRACT
Our overall research objective is to develop new tools and technologies to improve precision imaging by overcoming the challenges in high-field MRI (from 3T to 11.7T). Since the advent of MRI in the 1970s, major leaps in image quality have come via persistent increases in static magnetic field (B0) strengths: first from 0.5 Tesla and 1.5 Tesla in the 20th century, and now to 3.0 Tesla (3T) and 7.0 Tesla (7T) in the 21st century. One of the major objectives is to deliver improved visualization of brain microstructure changes that may arise in neurological disorders such as epilepsy, Alzheimer’s and Parkinson’s disease. However, an increased B0 field also comes with proportionally increased B0 field inhomogeneity that is more difficult to correct, whereas a homogeneous B0 is imperative for correct spatial representation of the imaged object. Inhomogeneous B0 field, induced by subject-specific magnetic susceptibility changes across organs, remains a tough and fundamental limitation that can compromise the fidelity, sensitivity, resolution, and speed of MRI, especially advanced and quantitative MRI techniques.

Hardware-based B0 shimming is the most direct approach to rectifying B0 inhomogeneity. Modern MR scanners are equipped with low-order shim coils outside the magnet bore (Figure), distant from and incapable of performing high-order shimming of human organs. This setup has remained essentially unchanged for decades. Meanwhile, the same period has seen major advances in RF coil technology, primarily the introduction of multichannel RF phased array. The phased array replaced the volumetric coil with multiple RF surface coils closely surrounding the target organ, enabling high sensitivity and fast ‘parallel imaging’ acquisition. An analogous move from distant, low-order coils to the surface, high-order arrays is long overdue for B0 shim coils as well, but practical solutions have eluded developers. This talk summarizes our work in breaking the convention by combining shim coils into standard RF coils (Figure), thereby maximizing both RF sensitivity and shim efficacy. The development of these tools will pay the way for high-field MRI applications for both animal and human high-field studies for which excellent field homogeneity and high RF sensitivity are a prerequisite.
 

BIOGRAPHY
Hui Han is the Director of MR Engineering who has established an MRI Engineering Program at Cedars-Sinai Medical Center. His research has a longstanding focus on novel MRI hardware and methodologies. His engineering experiences involve a systematic array of MRI hardware components including RF array coil, B0 shim, magnetic field and gradient monitoring, and MR-compatible devices. His research outcome has led to several U.S. patents on MRI instrumentation under licensing negotiations with vendors such as GE Healthcare. In particular, he spearheaded the development of the integrated RF/shim coil technology, known as iPRES (integrated Parallel Reception, Excitation, and Shimming). This is a new concept for combining B0 shimming and RF into a single array coil (i.e., AC/DC coil). It has received considerable attention from the community, highlighted in several plenary lectures, including those hosted by major vendors such as Siemens and GE Healthcare. His research aims to develop new tools and technologies to improve precision imaging by overcoming the challenges in high-field MRI (from 3T to 11.7T).