1. A system having one or more processors for visualizing medical image data comprising a plurality of member image data, each having a data element membership index, for multi-volume rendering, the system comprising one or more computer processors configured to: control one or more display devices to display a first view of the medical image data on a viewing plane based on the plurality of member image data, wherein the first view shows first member image data obtained through a first modality; indicate a location on the first view displayed on the viewing plane; trigger propagation of a probing ray from the indicated location perpendicular to the viewing plane into the first medical image data; identify an anatomical structure in the first medical image data, based on the indicated location on the displayed first view and based on the data element membership index of the first medical image data, in response to the triggered event, locating a plurality of probing locations along the probing ray which probing ray locations correspond to data elements having an intensity obtained from the first member image data; select a part of the first medical image data comprising the identified anatomical structure, and converting the intensities of the data elements of the identified anatomical structure into opacity values through is direct volume rendering transfer function and comparing the opacity values to an opacity threshold, and if the opacity threshold is exceeded, identifying the data element membership index to select the part of the first member image data and the anatomical structure of the data element; and control the one or more display devices to display a second view of the selected part of the medical image data, wherein the selected part of the medical image data is based on a second set of member image data of the plurality of member image data comprising the identified anatomical structure obtained through a second modality, thereby visualizing the medical image data wherein the second view of the selected part of the medical image data is further based on the indicated location and the identified anatomical structure.