Our laboratory focuses on developing new methodologies for magnetic resonance imaging (MRI) and spectroscopy to enhance sensitivity and contrast specificity.

We place a strong emphasis on manipulating nuclear spin dynamics, both from a physics and engineering standpoint.

 

Nuclear Spin Hyperpolarization

At the core of our research is Nuclear Spin Hyperpolarization – a mean to amplify the weak signals of nuclear spins. Nuclear spin hyperpolarization involves moving nuclear spins out of thermal equilibrium by creating a significant population difference between the nuclear spin energy levels. There are several ways to increase nuclear spin polarization. In the case of nobel gases this is most commonly achieved by spin-exchange optical pumping (SEOP), a process whereby circularly polarized (laser) light is used to optically pump and spin-polarize valence electrons of an alkali-metal vapor. Through the hyperfine interaction, spin polarization is then transferred from the electrons of the alkali metal to the nuclei of the nobel gas. Applications of spin-polarized Nobel gases range from physics, chemistry, material science, and biomedical imaging.  Our lab is interested in the physics of SEOP as well as on its biomedical imaging applications. For additional information on spin exchange optical pumping techniques and its application you can read this review article.

If you are instead interested in the theory of SEOP and the associated challenges, you can read few articles from our lab.

 

 

 

Low and Ultralow field MRI

imageMRI at ultralow field is a rapidly developing area of research that has the potential to revolutionize medical imaging. Unlike traditional MRI, which operates at high magnetic fields of several tesla, ultralow field MRI operates at magnetic fields of only a few millitesla. This has several advantages, including lower costs and reduced safety concerns. However, one of the challenges of ultralow field MRI is that it typically requires longer scan times and lower signal-to-noise ratios compared to high field MRI. This is because the signal from the spins is weaker at lower fields, and the contrast between different tissues is lower. One approach to addressing this challenge is to combine ultralow field MRI with nuclear spin hyperpolarization techniques.

In a recent cover article in ChemPhysChem, we demonstrated the direct detection of polarization transfer from highly polarized 129Xe spins to 1H spins through the nuclear Overhauser effect.  By introducing hyperpolarized 129Xe gas into a solution, we were able to achieve a remarkable enhancement of 1H polarization levels, reaching up to more than 150-fold increase. While the reported enhancements may seem lower than those achieved under extreme Xe gas pressures at high magnetic field strengths, the real value lies in the repeatability and on-demand nature of this approach.
Additionally,  in the mT range, thermal nuclear spin polarization nearly blends with background noise levels, while different nuclei can be simultaneously detected in a single spectrum, enabling one to witness  the intricate dynamics of nuclear spin polarization transfer.

 

 

 

Hardware Development

One of the research efforts in our lab is the development of hardware for magnetic resonance at low and ultralow field strengths. This effort began as an undergraduate research project aimed at developing an Arduino-based NMR spectrometer that operates at the Earth’s magnetic field—necessitating the relocation of our lab to an open field pasture!

Former P&A undergraduate Christian Browning with former graduate student, Michael Antonacci, testing our Arudino-controlled Earth’s field NMR spectrometer in a field pasture outside the main UNC campus

The project has since evolved into a comprehensive graduate research endeavor, focusing on NMR in the milliTesla (mT) regime.

High-field MR instruments are often perceived as black boxes due to their complexity. While the principles of spin dynamics manipulation are relatively straightforward, the intricacies of the hardware involved remain elusive. In contrast, our mT spectrometer, developed from scratch by my graduate students, offers a transparent and hands-on tool to understanding MR technology.

Students in my lab continuously improve this spectrometer. Currently, we are focusing on optimizing the spin detection hardware to enhance performance and sensitivity. By doing so, we aim to push the boundaries of what is possible in low-field regime making significant strides in both fundamental research and practical applications.

In addition to advance the field of MR, this project  provides valuable training opportunities for students at both undergraduate and graduate levels, fostering the next generation of scientists and engineers.

If interested in learning more about our lab, check out this P&A news article!

 

 

 

Biomedical Imaging Applications

One of the applications we have been working on for over 10 years is the detection of brown fat using hyperpolarized xenon MRI and xeno enhanced CT.  Brown fat, also known as brown adipose tissue (BAT), is a special type of body fat that helps regulate body temperature by burning calories to generate heat. Unlike white fat, which stores energy, brown fat is rich in mitochondria, giving it its distinctive color and unique ability to convert energy from food into heat. This process is particularly important in newborns and hibernating animals but also exists in adults, playing a pivotal role in maintaining body temperature in cold conditions and aiding in weight management and metabolic health- including reglating blood glucose level.

Our group was the first to demonstrate the ability of hyperpolarized 129Xe to detect brown adipose tissue and measure its absolute temperature to assess its activity. While quantifying the distribution of xenon before and during the stimulation of thermogenic activity, we realized that the tissue could also be detected using xenon-enhanced computed tomography. Since then, we have used both polarized and unpolarized xenon to detect this tissue with MRI and CT.