The influence of flip angle on the magic angle effect

Objective. To assess the impact of flip angle with gradient sequences on th e "magic angle effect". We characterized the magic angle effect in various gradient echo sequences and compared the signal-to-noise ratios present on these sequences with the signal-to-noise ratios of spin echo sequences. Design. Ten normal healthy volunteers were positioned such that the flexor hallucis longus tendon remained at approximately at 55 degrees to the main magnetic field (the magic angle). The tendon was imaged by a conventional s pin echo T1- and T2-weighted techniques and by a series of gradient techniq ues. Gradient sequences were altered by both TE and flip angle. Signal-to-n oise measurements were obtained at segments of the flexor hallucis longus t endon demonstrating the magic angle effect to quantify the artifact. Signal to-noise measurements were compared and statistical analysis performed. Si milar measurements were taken of the anterior tibialis tendon as an interna l control. Results and conclusions. We demonstrated the magic angle effect on all the gradient sequences. The intensity of the artifact was affected by both the TE and flip angle. Low TE values and a high flip angle demonstrated the gre atest magic angle effect. At TE values less than 30 ms, a high flip angle w ill markedly increase the magic angle effect.