Introduction to Research Seminar

The temporal sequence of radiofrequency (RF) pulses and magnetic field gradients forms the equivalent of a “musical score” in nuclear magnetic resonance experiments. Like the notes in music, the number, duration, and shapes of RF pulses in the pulse sequence can be altered to create different effects. In MRI, for example, the pulse sequence can be “tuned” to maximize contrast for detecting different microscopic and macroscopic properties of tissue. In this way, MR images can be generated to display not only anatomy, but molecular signatures, physiology, and function. Advances in pulse sequence design are leading to improved data quality, as well as greater sensitivity and specificity to differentiate between normal tissues and pathology with MRI.
Traditionally, only the amplitude, and not the frequency of the RF pulse is modulated when it is transmitted in a pulse sequence. Exceptions to this include the class of frequency-modulated (FM) pulses that function “adiabatically” (for review, see (1)). Currently, adiabatic pulses are exploited mostly to avoid deleterious effects from experimental imperfections, such as RF field non-uniformity. However, recently we have demonstrated that FM pulses operating sub-adiabatically can be used to manipulate nuclear spins in new ways and to create unique images with contrast based on spin relaxation never observed previously. Examples include MRI signals that decay too rapidly to be detected by conventional methods.
In this presentation, I will describe methodologies and applications for this fundamentally different approach to MRI. The main technique to be discussed is known as SWIFT (SWeep Imaging with Fourier Transformation) (2). This and other new FM techniques promise to expand the role of MRI in areas such as materials science, neuroscience, molecular imaging, and clinical medicine.

1. Garwood M, DelaBarre L. The return of the frequency sweep: Designing adiabatic pulses for contemporary NMR. J Magn Reson 2001;153:155-177.
2. Idiyatullin D, Corum C, Park J-Y, Garwood M. Fast and quiet MRI using a swept radiofrequency. J Magn Reson 2006;181:342-349.