FID-SPI Technique for Quantitative MRI

A new sequence for effective spin-spin relaxation time T₂* mapping, named FID-SPI (Free Induction Decay Single Point Imaging), which provides accurate 1D, 2D or 3D fluid content distribution maps in porous media [1] is employed for quantitative analyses of various samples. The measurement generates a series of individual T₂* weighted images acquired following RF excitation and pulsed phase-encoding gradients.
The measurement deadtime is limited by the duration of the phase encoding gradient pulses. Fast switched, high quality magnetic field gradient pulses, generated with a recently developed impulse response based gradient pre-equalization technique [2] are required for FID-SPI. The phase-encoding gradient amplitude may be reduced to 250 microseconds through this technique.
The FID-SPI pulse sequence is able to measure spatially resolved T₂* and provides data for calculating fluid content images.

This new imaging technique permits faster and more accurate spin-density mapping by acquiring hundreds of points to fit. It will be faster for water content imaging and T₂* mapping than an analogous SPRITE imaging technique [3], with comparable sensitivities for the same encoding time.
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