Method and apparatus for forming energy subtraction images

Claim 1

A method for forming an energy subtraction image, which comprises the steps of: i) after a plurality of radiation images of an object are recorded on recording media by irradiating several kinds of radiation with different energy levels to said object, which is constituted of a plurality of tissues exhibiting different levels of radiation absorptivity with respect to the several kinds of radiation with different energy levels, and a plurality of image signals representing the plurality of said radiation images are then detected, each of the plurality of said image signals being made up of a series of image signal components, selecting an image signal from the plurality of said image signals, or generating an image signal, which represents the mean-level image of the plurality of said radiation images, from the plurality of said image signals, ii) changing the values of parameters, which are used for a subtraction process, in accordance with the values of said image signal, which has been selected from the plurality of said image signals, or in accordance with the values of said image signal, which represents the mean-level image of the plurality of said radiation images, and iii) subtracting the image signal components of the plurality of said image signals from each other, which image signal components represent corresponding picture elements in the plurality of said radiation images, with the value of each said parameter being thus changed for different picture elements in each of the plurality of said radiation images, whereby a subtraction image signal is obtained which represents a subtraction image, in which only the pattern of a specific tissue of said object is formed or emphasized.

Claim 8

An apparatus for forming an energy subtraction image, which comprises: i) a parameter storage means for storing information about functions representing the values of parameters to be used for a subtraction process, in which functions the level of an image signal selected from a plurality of image signals representing a plurality of radiation images of an object or the level of an image signal, which is generated from the plurality of said image signals and represents the mean-level image of the plurality of said radiation images, serves as a variable, the plurality of said radiation images of said object having been recorded on recording media by irradiating several kinds of radiation with different energy levels to said object, which is constituted of a plurality of tissues exhibiting different levels of radiation absorptivity with respect to the several kinds of radiation with different energy levels, each of the plurality of said image signals being made up of a series of image signal components, and ii) a subtracting operation means for subtracting the image signal components of the plurality of said image signals from each other, which image signal components represent corresponding picture elements in the plurality of said radiation images, with the values of said parameters, which have been calculated for the respective picture elements from said functions stored in said parameter storage means, and thereby obtaining a subtraction image signal representing a subtraction image, in which only the pattern of a specific tissue of said object is formed or emphasized.