Contrast in Variable Flip Angle Fast MR Imaging
Signal intensity in magnetic resonance imaging is described by the solution to the Bloch Equations. Image behavior has been calculated for the variable angle gradient refocusing and conventional spin echo techniques. It was found that by proper manipulation of the excitation angle (and echo time in spin echo sequences) that the imaging time can be reduced up to twenty-fold for the gradient refocusing technique and four-fold for 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.