Differences

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--- library:time_to_echo [2025/05/01 01:56] – scott
+++ library:time_to_echo [2025/05/01 01:57] (current) – scott
@@ Line 25: / Line 25: @@
 ==In and Out of Phase TE==
-When utilizing fast 3D gradient echo sequences, a TE time may no longer be selectable, and instead the options are 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 Chemical Shift artifact. 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.
+When utilizing fast 3D gradient echo sequences, a TE time may no longer be selectable, and instead the options are 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 Chemical Shift artifact. 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.
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