Apparatus and method for registering two medical images

A non-transitory computer readable storage medium storing computer program instructions for execution by a processor in an apparatus for causing the apparatus to implement a method for registering two medical images comprising:

• obtaining a first medical image including a patient-specific representation of a biological organ of an individual subject or a representation of a biological organ for a population;
• identifying the surface of said organ in said first medical image;
• using said surface to obtain a geometric model that represents the three-dimensional shape of said organ for a subject or the representative shape of said organ for a population;
• using said geometric model to obtain a motion model which can be used to predict the physical motion and deformation of said organ;
• obtaining a second medical image including a representation of said organ of said subject or another subject;
• determining an alignment between surface normal vectors of said geometric model, which represent a first vector field, and estimated surface normal vectors of the organ surface derived by filtering said second medical image, which represent a second vector field, wherein determining said alignment includes applying a mathematical transformation to said geometric model to maximise a measure of orientational alignment between the first and second vector fields, and wherein the spatial position, orientation and shape of said geometric model and of said first vector field are changed in accordance with said motion model to achieve said alignment;
• and registering the first and second medical images with one another based on said determined alignment.

Apparatus for registering two medical images, comprising:

• an image processing system for identifying an organ surface in a first medical image that includes a representation of the said organ;
• a modelling system for using the identified surface to construct a 3D geometric model of said organ surface;
• a modelling system for constructing said organ motion model from said 3-D geometric model;
• an image processing system for calculating first and second surface normal vector fields from said geometric model and from said second medical image respectively;
• a numerical optimisation system for determining an alignment between said first vector field and said second vector field, wherein determining said alignment includes applying a mathematical transformation to said geometric model to maximise a measure of orientational alignment between the first and second vector fields, and wherein the spatial position, orientation and shape of said geometric model and of said first vector field are changed in accordance with said motion model to achieve said alignment, thereby accommodating deformation of the geometric model in accordance with said motion model;
• and
• an image registration system for registering the first and second medical images with one another based on said determined alignment.