Tailored RF Pulse Modulation for RF Refocussed Variable Flip Angle MRI

Abstract

Advances in Magnetice Resonance Imaging (MRI) techniques have recently made MRI the imaging modality of choice for many applications of clinical imaging. MRI provides the diagnosing clinician a non-invasive method for obtaining soft tissue differentiation with sub-millimeter resolution. Clinical MRI techniques include 3-dimensional imaging, spectroscopic imaging, arterial angiography and cardiac imaging. One MRI technique which has recently gained popularity is a class of protocols known as variable/partial flip angle MRI. Partial flip angle MRI techniques are useful because of their ability to vary contrast between tissues and/or maintain a particular level of contrast with a reduction in acquisition time [1]. Variable flip angle techniques differ from conventional MRI protocols in that the initial RF excitation/rotation pulse is not constrained to a 90 degree rotation of the longitudinal magnetization. Instead, the initial excitation flip angle is calculated to provide improved contrast between two tissues and/or maximize the intensity of a particular tissue. For tissues with reduced TR/T1 ratios, variable flip angle techniques may also be used to increase the image signal to noise within a localized region.