Slice-selective fat saturation in MR angiography using spatial-spectral selective prepulses

Presaturation of fat signals by frequency-selective radiofrequency (RF) pulses is often applied in MR angiography to improve the visualization of the blood vessels. Unfortunately, standard fat saturation methods might cause a considerable reduction of the blood signal in the measured slices. This effect is caused by an attenuation of blood magnetization in remote tissue regions with water protons showing a similar Larmor frequency as the fat protons in the recorded slice. The affected blood water protons subsequently flow into the recorded slice and provide low signal intensity. Suitable spatial-spectral selective methods for slice-selective fat saturation were developed to avoid this unwanted effect. A spatial-spectral fat saturation technique was compared with a corresponding only spectrally selective approach. Both saturation techniques were included in a standard two-dimensional (2D) cine sequence and applied in angiographic examinations of the thighs. The results indicate that spatial-spectral saturation (acting slice selectively) leads to a clearly higher blood signal intensity in fat-suppressed MR angiography compared with standard techniques, especially in measurements performed during the systolic phase of the cardiac cycle.