Imaging Ultra-short T2 Species in the Brain

The pulse sequence is shown in Figure 1. A half-pulse variable rate excitation is followed by short PR readouts and a spoiler in the slice select direction. The main lobe of the excitation occupies under 500 ps and the total readout occupies 1024 ps. There is a minimum deadtime of 228 ps between excitation and readout due to hardware timing restrictions and RF recovery. Therefore the minimum echo time is also 228 ps. Suppression of long Tz species is essential for getting good dynamic range from short T2 species. Long-T2 suppression is implemented with a 4 to 8 ms nonselective hard 90° excitation followed by a dephaser [5]. This is done before each imaging excitation. Note that this suppression pulse has a limited bandwidth and does not suppress long-T2 lipid signal.