There are many algorithms that are region based. Kindly google...FCM may also help you 

Is there series of images which are continuously changing for single patient or different tomography images for different patients?

Dear G R Sinha,

Thanks for your suggestion. I will try to learn more about FCM. 

Hengda

Dear Neha Baraiya 

Thanks for your interest. Sequence of images which is continuously changing with time for single patient. 

Hengda 

You can use watershed segmentation, clustering methods like fcm or k-mean.

Or you can get idea for segmentation of dynamic part from below papers:

http://video.ee.ntu.edu.tw/publication/paper/[J][2002][TCSVT][Shao-Yi.Chien][1].pdf

http://www.irisa.fr/vista/Papers/2009_cviu_bugeau.pdf

http://www.irisa.fr/vista/Papers/2007_cvpr_bugeau.pdf

consider below link for medical image segmentation:

http://liu.diva-portal.org/smash/get/diva2:310036/FULLTEXT02.pdf

Dear Neha Baraiya

Thank you so much. You are so nice. :)

Hengda