Pulse Sequence Design for Magnetic Resonance

MRI is a coherent imaging modality: the magnetization of the imaged nuclear spins can be manipulated via the application of external electromagnetic fields, and retains its state for several hundreds of milliseconds. This is in stark contrast to, e.g., computerized tomography (CT) or positron emission tomography (PET), which are concerned mainly with incoherent radiation processes. This 'memory' property of the system can be exploited to generate a plethora of interesting image contrasts and localization schemes, with the particuar effect depending on the particular sequence of applied fields. The design of a sequence to achieve a certain goal is termed pulse sequence design, and is a major research interest of the lab.

 

Figure 1. The new STRESS localization sequence developed in our lab simultaneously acquires the spin and stimulated echoes from a defined volume in space. This in effect combines the high signal to noise ratios typical of Point-Resolved Spectroscopy (PRESS) acquisitions with the low chemical shift displacement artifacts, low specific absorption rates and short echo times typical of Stimulated Echo Acquisition Mode (STEAM), two widely used acquisition methodologies.