# Step 3.3: Segment the lesions

Various segmentation tools are available, from basic manual contouring, to thresholding and more advanced automated tools.

For segmenting the lesion in PET, we will use a specialized automated tool presented by Beichel et al in [this manuscript](http://dx.doi.org/10.1118/1.4948679).

To segment a PET lesion using this tool, first enable it from the list of segmentation tools, and then click within the primary lesion region in the axial slice.

| ![](https://1608672434-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LM8e4_Fqz67WxPLjNdd%2F-LM8eKSItWZRrPH4GuSH%2F-LM8eR0nwMTwMUg6RvRQ%2Fpt-lesion.png?generation=1536686683665708\&alt=media) | ![](https://1608672434-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LM8e4_Fqz67WxPLjNdd%2F-LM8eKSItWZRrPH4GuSH%2F-LM8eR0pNowauY7rvoy2%2Fpet-effect.png?generation=1536686681371822\&alt=media) | ![](https://1608672434-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LM8e4_Fqz67WxPLjNdd%2F-LM8eKSItWZRrPH4GuSH%2F-LM8eR0rJ10WqJac-7b5%2Fpet-segmented.png?generation=1536686681929875\&alt=media) |
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**Try it yourself: Repeat the same sequence of steps to segment the Secondary lesion!**