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library:time_to_echo [2026/06/12 15:11] – [TE in Gradient Echo] scottlibrary:time_to_echo [2026/06/12 15:11] (current) – scott
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 When utilizing fast 3D gradient echo sequences, a TE time may no longer be selectable, and instead the options may be limited to an 'in-phase' or 'out-of-phase' option. In-phase and out-of-phase describe the relationship between fat and water vectors as they rapidly precess; at certain time points, fat and water vectors may be pointing in the same direction (in-phase) or opposite directions (out-of-phase) and the resulting images will demonstrate characteristic differences. In out-of-phase images, voxels containing both fat and water will will have signals that cancel out, resulting in the 'india ink' artifact that looks like a black line outlining most organs. In-phase images will not have the black outlines. The specific times where fat and water are in and out of phase depend on the field strength, but at 1.5T are approximately 2.2ms, 4.4ms, 6.6ms etc with the out of phase TE occurring earliest. Unless imaging the abdomen, typically select in-phase whenever possible for the highest readability. When utilizing fast 3D gradient echo sequences, a TE time may no longer be selectable, and instead the options may be limited to an 'in-phase' or 'out-of-phase' option. In-phase and out-of-phase describe the relationship between fat and water vectors as they rapidly precess; at certain time points, fat and water vectors may be pointing in the same direction (in-phase) or opposite directions (out-of-phase) and the resulting images will demonstrate characteristic differences. In out-of-phase images, voxels containing both fat and water will will have signals that cancel out, resulting in the 'india ink' artifact that looks like a black line outlining most organs. In-phase images will not have the black outlines. The specific times where fat and water are in and out of phase depend on the field strength, but at 1.5T are approximately 2.2ms, 4.4ms, 6.6ms etc with the out of phase TE occurring earliest. Unless imaging the abdomen, typically select in-phase whenever possible for the highest readability.
  
-==Out of Phase==+===Out of Phase===
  
 {{:library:ax_op_fspgr.gif|}}   {{:library:ax_op_fspgr.gif|}}  
  
-==In Phase==+===In Phase===
  
 {{:library:ax_ip_fspgr_2_.gif|}} {{:library:ax_ip_fspgr_2_.gif|}}