fig1 illustrates an exemplary injection device for inserting spherical tantalum markers into a bone . the injection device includes a hollow drill 1 having an opening la at its tip . one or more tantalum spherule 5 ( fig2 ) can be dispensed through the opening la once the drill 1 has drilled a recess or hole into a bone 6 ( e . g ., to a depth of about 3mm ). the drill 1 can be detachably fixed on a housing 2 , which includes a handle 3 and a trigger button 4 . the drill 1 can be rotated either by manually operating the handle 3 or by a motor provided in the housing 2 of the instrument . at the desired depth of penetration , the button 4 can be operated , which inserts the tantalum sphere 5 into the bone 6 . fig2 illustrates a cross - sectional view of the drill 1 penetrating an approximately 3 mm thick compact bone layer in order to insert the spherical tantalum marker 5 ( which has a diameter of about 0 . 5 mm ) into the bone 6 . a marker 5 inserted in this way sits securely in the bore formed in the bone 6 via a press or interference fit . if , as shown in fig2 , a number of tantalum markers 5 are inserted into the bone 6 , then these markers 5 can easily be identified in a two - dimensional x - ray image of the bone structure . such a two - dimensional x - ray image is shown in the x - ray recording of the femur 7 in fig3 . the coordinates of the centers of mass of the spherical markers 5 can be calculated and , when a number of calibrated x - ray recordings have been generated , the coordinates can be transformed into a patient coordinate system . if a number of markers 5 are present or if other characteristic points or landmarks on the structure are additionally acquired using known methods , such as for example acquiring points using a pointer , the anatomical structure can be registered as described herein . fig4 a and 4b show an enlarged representation of the mapping of a tantalum marker 5 in the spina iliaca from two different directions , wherein the position of the tantalum marker 5 in three - dimensional space can be determined from the two calibrated recordings shown in fig4 a and 4b . this can be accomplished , for example , by rear - projecting the marker position ascertained in the two two - dimensional recordings . in hip surgery wherein the patient is positioned laterally , it is not possible to reach both sides of the patient with , for example , a mechanical pointer . however , it is possible to ascertain the position of the spina iliaca in the patient coordinate system , including both the accessible portion and the inaccessible healthy side ( on which the patient is lying ) from the two recordings shown in fig4 a and 4b . therefore , it is possible to register the pelvis from the landmark ascertained in this way together with another landmark which , for example , is likewise marked by tantalum markers 5 or acquired by means of a pointer . fig5 shows a flow diagram of an exemplary method in accordance with the invention . a three - dimensional model of the structure , such as for example a hip , is generated by means of a ct recording at block 10 , and the positions of the inserted markers are determined in the three - dimensional model at block 11 . at block 12 , calibrated fluoroscopic shots can be taken of the anatomical structure or pelvis from two different directions so as to obtain two two - dimensional x - ray recordings of the structure . the positions of the markers that are visible in the x - ray recordings are in turn ascertained at block 13 . a known matching method then can be performed at block 14 in order to orientate the three - dimensional model ascertained from the ct recording in three - dimensional space or in the patient coordinate system . the matching method can use the locational information ascertained from the fluoroscopic shots , such that at block 15 the three - dimensional model of the structure matches the actual structure , thus registering the structure or pelvis . moving now to fig6 there is shown a block diagram of an exemplary computer 20 that may be used to implement the method described herein . the computer 20 may include a display 22 for viewing system information , and a keyboard 24 and pointing device 26 for data entry , screen navigation , etc . a computer mouse or other device that points to or otherwise identifies a location , action , etc ., e . g ., by a point and click method or some other method , are examples of a pointing device 26 . alternatively , a touch screen ( not shown ) may be used in place of the keyboard 24 and pointing device 26 . the display 22 , keyboard 24 and mouse 26 communicate with a processor via an input / output device 28 , such as a video card and / or serial port ( e . g ., a usb port or the like ). a processor 30 , such as an amd athlon 64 ® processor or an intel pentium iv ® processor , combined with a memory 32 execute programs to perform various functions , such as data entry , numerical calculations , screen display , system setup , etc . the memory 32 may comprise several devices , including volatile and non - volatile memory components . accordingly , the memory 32 may include , for example , random access memory ( ram ), read - only memory ( rom ), hard disks , floppy disks , optical disks ( e . g ., cds and dvds ), tapes , flash devices and / or other memory components , plus associated drives , players and / or readers for the memory devices . the processor 30 and the memory 32 are coupled using a local interface ( not shown ). the local interface may be , for example , a data bus with accompanying control bus , a network , or other subsystem . the memory may form part of a storage medium for storing information , such as application data , screen information , programs , etc ., part of which may be in the form of a database 36 . the database 36 may include data pertaining to a three - dimensional model of a structure to be registered . the storage medium may be a hard drive , for example , or any other storage means that can retain data , including other magnetic and / or optical storage devices . a network interface card ( nic ) 34 allows the computer 20 to communicate with other devices . communicatively coupled to the computer 20 is a recording unit 38 , such as a a calibrated x - ray source and a corresponding calibrated detector ( e . g ., a calibrated c - arm ). the recording unit 38 also can include a reference array 40 or the like attached thereto . the reference array 40 enables a spatial location of the recording unit to be ascertain by a navigation system 42 , for example . a person having ordinary skill in the art of computer programming and applications of programming for computer systems would be able in view of the description provided herein to program a computer system 20 to operate and to carry out the functions described herein . accordingly , details as to the specific programming code have been omitted for the sake of brevity . also , while software in the memory 32 or in some other memory of the computer and / or server may be used to allow the system to carry out the functions and features described herein in accordance with the preferred embodiment of the invention , such functions and features also could be carried out via dedicated hardware , firmware , software , or combinations thereof , without departing from the scope of the invention . computer program elements of the invention may be embodied in hardware and / or in software ( including firmware , resident software , micro - code , etc .). the invention may take the form of a computer program product , which can be embodied by a computer - usable or computer - readable storage medium having computer - usable or computer - readable program instructions , “ code ” or a “ computer program ” embodied in the medium for use by or in connection with the instruction execution system . in the context of this document , a computer - usable or computer - readable medium may be any medium that can contain , store , communicate , propagate , or transport the program for use by or in connection with the instruction execution system , apparatus , or device . the computer - usable or computer - readable medium may be , for example but not limited to , an electronic , magnetic , optical , electromagnetic , infrared , or semiconductor system , apparatus , device , or propagation medium such as the internet . note that the computer - usable or computer - readable medium could even be paper or another suitable medium upon which the program is printed , as the program can be electronically captured , via , for instance , optical scanning of the paper or other medium , then compiled , interpreted , or otherwise processed in a suitable manner . the computer program product and any software and hardware described herein form the various means for carrying out the functions of the invention in the example embodiments . although the invention has been shown and described with respect to a certain preferred embodiment or embodiments , it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings . in particular regard to the various functions performed by the above described elements ( components , assemblies , devices , compositions , etc . ), the terms ( including a reference to a “ means ”) used to describe such elements are intended to correspond , unless otherwise indicated , to any element which performs the specified function of the described element ( i . e ., that is functionally equivalent ), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention . in addition , while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments , such feature may be combined with one or more other features of the other embodiments , as may be desired and advantageous for any given or particular application .
a method for registering an anatomical structure using at least one marker attached to the structure includes : obtaining a three - dimensional model of the structure via an imaging method ; obtaining at least two two - dimensional recordings of the structure from different angles ; and ascertaining a spatial position and location of the three - dimensional model or a position and location of the three - dimensional model in a patient coordinate system based on a matching method that uses the position of the at least one marker in the at least two two - dimensional mappings such that the three - dimensional model of the structure matches the structure .