A three-dimensional image representing a patients organ is obtained. The organ is extracted from the three-dimensional image. A treatment portion, at which desirable treatment for the organ is performed, on a surface of the organ is obtained. A pattern model including an outer surface, an inner surface having a surface form along an organs outer surface of the organ, a guide wall connecting, along the treatment portion, the outer surface and the inner surface, and a positioning portion is generated. The positioning portion positions a predetermined imaging probe in such a manner that a tomographic image of a cross section of the organ including a target portion of the organ is imageable when the guide wall is arranged along the treatment portion on the organ.
