This paper proposed an extraction method of liver regions in three dimensional abdominal CT images of early and late phases using gray features of not only normal liver tissues but also those of lesions. This method consists of two processes; 1) a rough estimation of liver regions based on two CT values of different phases, 2) a level set method so as to sophisticate the roughly extracted surfaces of livers. Here, the rough extraction process employs a unique parallel process which is made up of three local processes followed by integration of the three outputs, each of which focuses on normal tissues, cancer and cysts regions, respectively. This paper also describes experimental results of applying the proposed method to actual 34 images of 17 patients by multi-row detector CT scanners and unknown four images of two patients used in competition of 2003 with discussion on its effectiveness.

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