The RODEO technique can also be used to suppress water or silicone by appropriate frequency and timing adjustments. Meanwhile, off-resonance effects of these RF-pulses are sufficient to stimulate water protons and maintain their coherence in the transverse (xy)-plane for generation of a steady-state signal. These pulses first invert and then restore fat magnetization, leaving fat magnetization unaffected and remaining along the z-direction. The sequence begins with a closely-spaced pair of phase-opposed sinusoidal adiabatic pulses tuned to the fat resonance. RODEO is 3D rapid gradient echo sequence that produces T1-weighted images from a refocused FID. Fat protons were chemically shifted so that they received either the 90°- or 180°-pulses, but not both.Ī somewhat different approach to water excitation can be found in the RODEO (ROtating Delivery of Excitation Off resonance) technique, a method developed for contrast-enhanced breast imaging in the 1990's. Because fat protons were shifted out of the slice in different directions between the 90°- and 180°-pulses, only water protons were stimulated by both the 90°- and 180°-pulses. The slice-select gradient was then activated with reversed polarity at the time of the 180°-pulse.
In this clever technique, an accentuated chemical shift misregistration in the slice-select direction was first induced by using a narrow-bandwidth 90°-RF pulse in conjunction with a reduced strength of slice-select gradient. PASTA is actually a modification of a relatively common method of fat suppression in the 1980's known as slice-selective gradient reversal (SSGR). Details can be found in the reference below. PASTA combines chemical shift selective excitation as part of a spin-echo pulse sequence acquisition with both 90°- and 180°-pulses and a gradient reversal. In addition to their conventional Water Excitation Technique (WET), Toshiba also offers a second method named PASTA (Polarity-Altered Spectral and spaTial Acquisition). Additional Notes on Selective Excitation Pulses
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