To segment the liver, I simply utilised the Segment Editor tool. However, after using the grow from seed effect, I observed that there are extra boundaries and regions that do not belong to the liver region. How do I get rid of them so that I can get a clean liver segmentation in 3D slicer? Should I go through each slice or frame manually by moving the views?
I here attached a screen shot for your further reference
From your screenshot it is hard to tell, what you shared might be the preview of the current seeds. Did you actually hit the apply button, which finalizes the segmentation.
After that you might also consider running a smoothing filter (e.g., median filter) to take care of any remaining jagged edges.
You can undo the “Grow from seeds” (so that you see the seeds instead of the grown regions), initialize the region growing (so that you see the preview results), adjust the seeds until everything looks good.
Liver segmentation is quite tedious job, even using semi-automatic segmentation tools. Fortunately, there are freely available fully automatic liver segmentation tools in Slicer. The easiest to use is NVIDIA-AI-assisted annotation.