Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-02-23
2003-06-03
Robinson, Daniel (Department: 3742)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06574493
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of localizing an object, notably in interventional radiology where a volume in which the object to be localized is present is examined by means of digital image processing on the basis of projection images. The invention also relates to a radiological diagnostic apparatus for carrying out the method, to surgical instruments used in interventional radiology, and to a computer program product that is used for digital image processing in interventional radiology.
BACKGROUND OF THE INVENTION
Generally speaking, the exact localization of given three-dimensional objects, for example catheters, needles, endoscopes, etc. is of crucial importance in interventional radiology. For example, in the case of X-ray guided biopsies a volume of possibly less than 1 mm
3
must be targeted by the puncture needle. In image-guided orthopedic surgery the positioning and orientation of, for example screws in the bone tissue must be monitored with a high degree of accuracy. For any type of minimum invasive intervention the surgeon must be capable of accurately determining the spatial position of the relevant instruments relative to the patient.
During a typical image guided intervention the patient is continuously monitored by means of X-rays. A C-arm X-ray apparatus which enables determination of the spatial position of a surgical instrument by carrying out X-ray fluoroscopy in two different, substantially perpendicular projection directions is preferably used for this purpose. The two images are simultaneously available to the surgeon, so that a three-dimensional impression can be obtained regarding the position and orientation of the surgical instrument in the region of surgery. For the monitoring of the surgery it is necessary to repeat the fluoroscopy of the patient at short time intervals so as to track the movement of the surgical instruments. Repeated change-overs may then occur he two projection directions of the C-arm fluoroscopy apparatus. The method is complex and time-consuming and, moreover, implies an excessive exposure to ionizing radiation both for the patient as well as the surgeon.
U.S. Pat. No. 5,772,594 proposes a system for image-guided surgery where the patient, the X-ray apparatus and the part of a surgical instrument that is situated outside the patient are provided with light-emitting diodes (LEDs). The relative spatial position of the patient, the X-ray apparatus and surgical instrument is determined by means of an optical measuring system. The position of the surgical instrument can be correlated to the X-ray images by means of X-ray opaque markers which are also provided on the patient. A digital image processing system serves to superpose an image of the position and the orientation of the surgical instrument on the various X-ray images.
Such a known optically operating system for image-guided surgery has a drawback in that it requires a large amount of additional hardware. The application is limited to surgical apparatus suitably provided with light-emitting diodes which can thus be localized by the image processing system. It is a further drawback that motions of the patient must be excluded during the procedure, as otherwise the spatial position of the surgical instrument can no longer be correctly correlated to the X-ray images.
Therefore, it is an object of the present invention to provide a method of localizing an object which does not require additional apparatus components and enables reliable, continuous and fully automatic determination of the position and the orientation of an object, notably a surgical instrument. The spatial position of an object relative to the patient should thus be visualized in the case of the application in interventional radiology.
This object is achieved by a method of the kind set forth in that projections of the object to be localized, whose geometrical shape is known, are simulated and compared with the projection image of the volume examined.
SUMMARY OF THE INVENTION
The method according to the invention utilizes two-dimensional projection images as they are formed, for example by means of X-ray fluoroscopy, in order to derive therefrom the position and orientation of the object. The digital image processing of the two-dimensional data set imposes comparatively easy requirements as regards the capability of the data processing system used. Therefore, the method according to the invention can be implemented in practically any standard computer system used for image processing in radiological diagnostic apparatus. Thus, exclusively a pure software extension in existing radiological diagnostic apparatus is involved; such an extension can be realized at all times and at low costs.
Most applications in interventional radiology involve the localization of objects whose geometrical shape is known. When a three-dimensional geometrical model, for example a surgical instrument, is presented to the digital image processing, two-dimensional projection images can be calculated therefrom. This simulation is to be based not only on the geometrical object data but also on a respective, apparatus-specific model of the image formation (camera model). Comparison of the calculated projections and the real projection image then simply enables determination of the desired object position and orientation.
The method according to the invention requires in principle only a single two-dimensional image for object localization. This obviates in principle the necessity of changing over between different projection directions for three-dimensional object localization. The three-dimensional information is available at all times, because the processing of the comparatively small amount of data of the two-dimensional image data set can be performed within a very short period of time.
However, the reliability and the accuracy of the method can be enhanced substantially by using a plurality of real projection images with each time different projection directions, if possible, for the localization. The use of two or more projection images is advantageous notably when the two-dimensional projection of the object to be localized does not provide unambiguous information as regards the exact position and orientation.
The simulation of the projections is performed on the basis of the six object degrees of freedom (position and orientation). Because of the small number of parameters taken into account in the simulation, the localization method according to the invention is extremely fast with easy requirements imposed on the computer hardware, very robust and easy to implement.
The object localization is preferably carried out in such a manner that the simulation is iteratively repeated while systematically varying the degrees of freedom of the object until the deviations between calculated simulation and real projection image become minimum. The procedure can be interrupted as soon as the object position and the object orientation have been determined with the predetermined accuracy. The correspondence between the simulated projection and the real image is evaluated by means of image processing and recognition algorithms that are known per se.
The method according to the invention can be advantageously simplified further by providing the object to be localized with one or more markers which are reproduced in the projection image. The markers may have a very simple geometrical shape that can be presented to the image processing system with a minimum expenditure. The simulation of the projections of such markers is even substantially simpler than the calculation of possibly complex three-dimensional objects. The localization method can thus be carried out even faster and more effectively. The determination of the desired object position and object orientation is then performed on the basis of the knowledge of the arrangement of the markers relative to the object to be localized.
Because the localization method according to the invention utilizes a two-dimensional projection image for determining the object position,
Rasche Volker
Sabczynski Jörg
Schmitz Georg
Van Vaals Johannes Jacobus
Zylka Waldemar
Koninklijke Philips Electronics , N.V.
Robinson Daniel
Vodopia John
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