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library:slice_thickness [2025/07/08 17:38] – scottlibrary:slice_thickness [2025/07/08 18:17] (current) – scott
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   - A gradient is imposed perpendicular to the desired slice; this changes the Larmor Frequency along that direction linearly. This is known as the slice select gradient.   - A gradient is imposed perpendicular to the desired slice; this changes the Larmor Frequency along that direction linearly. This is known as the slice select gradient.
-  - Once the Slice Select gradient is activated, a range of frequencies will be excited corresponding to the desired slice thickness. This is known as the RF transmit bandwidth. +  - At the same time as the Slice Select gradient is activated, a radiofrequency pulse will be played out over a few thousand hz, corresponding to the desired slice thickness. This is known as the RF transmit bandwidth. 
-  - Additional gradient or RF pulses may be used to ensure no undesired tissues are excited. These may be called crushers or spoilers.+   
 +By modifying either the transmit bandwidth and the strength of the slice select gradient, different slice thickness may be achieved. Typically the transmit bandwidth is not changed much, rather it is the slice select gradient that is primarily used to determine slice thickness. In the example below, a 2000 hz range of frequencies between 63 and 63.5 MHz is transmitted while a gradient is turned on, exciting a slice of tissue (green) a a little above isocenter; in this process both the slice thickness and location are determined by the RF and gradient combination. 
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 +{{ :library:slice_selection.png?600 |}}