referring now to fig1 , a ct machine 10 includes a gantry 12 having a bore 16 extending along an axis 15 to receive a patient ( not shown ) supported on a patient table 18 extending along the axis 15 . inside the gantry 12 , an x - ray tube 20 may project an x - ray beam 17 to an x - ray detector 22 opposed across the bore 16 . the x - ray tube 20 and detector 22 may orbit about the bore 16 ( on a rotation axis aligned with axis 15 ) to obtain projections through the patient on the patient table 18 at a variety of angles in a plane perpendicular to axis 15 . a radio frequency ablation system 24 may be positioned near the bore 16 to provide a source of radio frequency power through a generator 26 connected to leads 28 . in a “ monopolar ” mode , one lead 28 is connected to a radio frequency probe 30 and the other to a conductive ground pad 32 . generally , the invention is equally applicable to a bipolar system where current flows between two probes 30 and 30 ′ or portions of a single probe having two mutually insulated portions ( not shown in fig1 ). referring now to fig2 and 3 , the probe 30 may be inserted into an organ 34 within a patient 36 positioned within the bore 16 for imaging . the probe 30 may have a small cross - section and a pointed tip to be inserted by piercing the skin so that a proximal end 38 of the probe 30 may embed in or near a tumor at an ablation region 40 . the outer surface of the probe 30 in the ablation region 40 is electrically conductive to form an ohmic contact with the region 40 for the introduction of electrical current into the region 40 and heating thereof . a distal end 42 of the probe 30 extends out of the patient 36 to be connected to a center conductor 46 of a shielded cable 44 providing outer shield 48 coaxially around the center conductor 46 . the center conductor 46 of the shielded cable 44 provides electrical communication between the probe 30 and the generator 26 . at the generator 26 , the center conductor 46 is connected to a radio frequency power source 47 , for example , providing 500 khz radio frequency power and , in any case , radio frequency electrical power less than 300 mhz . one end of the shield 48 ( conveniently at the generator 26 ) is connected to ground ( or any low impedance voltage reference ) to create a constant potential shield around conductor 46 reducing the radiation of electromagnetic energy . the shield 48 may be connected to a metallic housing of the generator 26 providing an enclosed faraday shield for the generator 26 which may also be grounded or connected to any low impedance voltage reference . grounding for this purpose refers to a low impedance connection at the frequency of the generator 26 that need not be ohmic . similarly , a ground pad 32 , providing a broad area of contact to the patient 36 , may be attached to a center conductor 52 of a separate shielded cable 50 providing a coaxial outer shield 54 . as is understood in the art , the ground pad 32 provides a broad area of contact to the skin of the patient 36 allowing electrical flow between the probe 30 and the ground pad 32 without significant heating near the ground pad 32 during high heating and ablation in the region 40 . the center conductor 52 of the shielded cable 50 provides electrical communication between the ground pad 32 and the generator 26 , at which the center conductor 52 joins to the generator ground and the shield 54 is connected to a ground or another point of low impedance constant voltage . this configuration may be used in the monopolar mode , described above , with a probe 30 and ground pad 32 , or ( as shown ) used in a bipolar mode with a first probe 30 and similar second probe 30 ′ both placed within the patient 36 with current flowing between them to create the ablation region 40 as described below . referring now to fig4 , in an alternative balanced shielding configuration , the conductors 46 and 52 may be placed in close proximity ( for example , loosely twisted ) so that their countervailing currents tend to cancel . they are then together placed in surrounding coaxial shield 60 attached to a source of constant potential with respect to the patient 36 as described above with respect to shields 54 and 48 . this configuration may be used in the monopolar mode , described above , with a probe 30 and ground pad 32 , or ( as shown ) used in a bipolar mode with a first probe 30 and similar second probe 30 ′ both placed within the patient 36 with current flowing between them to create the ablation region 40 . the probes 30 and 30 ′ may be needle probes as described above or umbrella probes or other types of percutaneous electrodes . referring now to fig5 , in an alternative reduced lead shielding configuration , the conductor 46 is placed in coaxial shield 60 attached to a source of constant potential with respect to the patient 36 as described above with respect to shields 54 and 48 . in this case , the conductor 52 may be integrated with the shield 60 to reduce the need for a separate conductor 52 along the shielded length of the conductor 46 . this configuration may be used in the monopolar mode , described above , with a probe 30 and ground pad 32 , or ( as shown ) used in a bipolar mode with a first probe 30 and similar second probe 30 ′ both placed within the patient 36 with current flowing between them to create the ablation region 40 . the probes 30 and 30 ′ may be needle probes as described above or umbrella probes or other types of percutaneous electrodes . the conductors 46 and 52 may be separated from the shields 48 , 54 or 60 by means of an intervening electrical insulator 49 . in the embodiments of fig3 and 5 , the shield 60 and the conductors 46 may be realized by a standard coaxial cable such as provides a radio frequency transmission line rg type cables or maybe a standard shielded cable without transmission line properties . the shields 48 , 54 and 60 may be braided conductive wire to provide flexibility to the cables 44 . referring now to fig6 a , an example ct image 61 shows streak artifacts 62 emanating from an arbitrary point removed from the ablation of probe 30 reminiscent of beam - hardening artifacts caused by a spectral change in x - ray energy as it passes through a patient . shielding of the conductors 46 and 52 in the embodiment of fig3 produces the image of fig6 b in which the artifacts are substantially eliminated . referring now to fig7 a , an example digital x - ray image shows horizontal banding . shielding of the conductors 46 and 52 in the embodiment of fig3 produces the image of fig6 b in which the banding is substantially eliminated . while the present invention has been described in the context of computed tomography and digital radiography , it will be understood that the same technique may be applicable to other imaging modalities including not only computed tomography , ultrasound , magnetic resonance imaging , and the like , but also , for example , electrically sensitive computer monitors attached to devices such as endoscopes and the like . the fact that limited shielding of cables leading to an unshielded patient can provide pronounced attenuation of electrical interference may also be useful for non - imaging applications such as the acquisition of ecg signals etc . the shielding techniques described could include non - tubular shielding arrangements such as tightly twisted pair were shielding is provided by close proximity of counteracting currents . further , it will be understood that other devices applying electrical energy to the body when concurrent imaging must be conducted using electronic imaging devices , may benefit from the present invention . such devices may include , for example , those providing for cardiac ablation , electrocautery , varicose vein ablation , etc . it should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein . the invention is capable of other embodiments and of being practiced or carried out in various ways . variations and modifications of the foregoing are within the scope of the present invention . it also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and / or drawings . all of these different combinations constitute various alternative aspects of the present invention . the embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention .
at least one electrode lead outside the body and leading between an rf ablation power source and the unshielded probes in the patient is shielded to substantially eliminate artifacts during concurrent electronic imaging and rf ablation .