Process and apparatus for calibration of a radiological imaging device

#This application claims a benefit of a priority under 35 USC 119(a)–(d) to French Patent Application No. 02 16078 filed Dec. 18, 2002, the entire contents of which are hereby incorporated by reference.

#This invention and embodiments thereof is directed to a medical field, and more particularly the field of radiological imaging devices. These devices comprise means for emitting radiation, such as an X ray source, and means for acquiring an image, such as an image detector, mounted on the end of a C shaped arm, and the object of which the image is to be taken is placed between the two sides of the arm. The images acquired by the detector as the arm rotates around the object, and thus several acquisitions correspond to different points of view of the object. Means for processing allow a three-dimensional model of the object to be reconstructed from the acquired two-dimensional images. This reconstruction supposes that the different positions of the device are known precisely as well as its geometric characteristics.

#The three-dimensional model obtained can be used by a medical practitioner, such as a surgeon, before an operation in order to become familiar with the part of the anatomy for which the operation is intended. The three-dimensional model can also be used during the operation. For this, the medical practitioner disposes of equipment that allows the two-dimensional views of the part of the anatomy to be displayed in real time, these views being calculated from the three dimensional model.

#An embodiment of the invention will be better understood from the following description, which is given purely by way of illustration and is not restrictive, when read in conjunction with the appended figures in which:

#FIG. 1 represents diagrammatically a C shaped arm type-imaging device;

#FIG. 2 represents diagrammatically a C shaped arm supporting a source and a detector;

#In FIG. 1, the imaging device comprises a base 1 fixed to the ground, and upon which a C shaped arm 2 is mounted. The C shaped arms supports at each of its ends a source 3 formed by an X ray tube and an image detector 4. These elements are disposed so that the focus of the source 3 and the plane 6 of the detector 4 are diametrically opposed on the C shaped arm. The device is positioned close to a table 5 on which a patient will be placed. The plane of the table 5 stretches between the two arms of the C shaped arm, which is to say between the source 3 and the detector 4. The C shaped arm 2 can be commanded in rotation around the X or Y axes, these two axes intersecting at a point O, the center of rotation of the C shaped arm.

#During the calibration phase of the device, a ghost image comprising markers is positioned on the table 5 between the source 3 and the detector 4, more or less at the level of point O. During this phase, the C shaped arm is commanded in rotation and the device performs a series of n acquisitions. Each image acquired is a projection of the markers, of the three dimensional space towards the plane 6 of the detector 4.

#In FIG. 2, the C shaped arm 2 is shown schematically, the focal point S of the source 3 and the plane 6 of the detector 4 as well as an object 10 of which a three dimensional model is to be made.