CONTRAST IN VARIABLE FLIP ANGLE FAST MR IMAGING.

Signal intensity in magnetic resonance imaging (MRI) is described by the solution to the Bloch equations. Image behavior is calculated for the variable-angle gradient refocusing and conventional spin-echo techniques. It is found that by proper manipulation of the excitation angle (and echo time in spin-echo sequences), the imaging time can be reduced up to twentyfold for the gradient refocusing technique and fourfold for the conventional spin-echo imaging. The contrast obtained is comparable to that acquired in conventional MRI. Imaging experiments performed on phantoms and human heads are in good agreement with theoretical results.