COMBINED IMPEDANCE IMAGING AND MAMMOGRAPHY

Abstract: A probe (40) for impedance imaging comprising: a plurality of conductive elements (500) adapted to contact tissue of a subject; a plurality of conductive wires (504) connecting the conductive elements to an external connector (506); and one or more non-conductive materials (502), wherein the x-ray absorbance of the non-conductive materials (502), in at least some of the surface areas of the probe, is a function of the x-ray absorbance of the conductive wires (504) and elements (500) in the same surface area, such that the probe (40) has substantially the same x-ray absorbance over most of the surface area of the probe.

Description: COMBINED IMPEDANCE IMAGING AND MAMMOGRAPHY FIELD OF THE INVENTION The present invention relates generally to medical imaging techniques. In particular the present invention relates to performing impedance imaging in conjunction with mammography. BACKGROUND OF THE INVENTION Early detection of cancerous tumors increases the chances of success in curing breast cancer. Several methods are known to screen the breast in order detect suspicious tumors. Two of these methods are X-ray mammography and impedance imaging, described, for example, in U.S. patent 4,291,708 to Frei and in U.S. patent 5,810,742 to Pearlman, the disclosures of which are incorporated herein by reference. In impedance imaging, a multi-element impedance probe is placed on a breast of a patient and one or more electrodes apply electrical signals to the subject. Each of the elements of the probe senses electrical signals from the breast and accordingly an image of the breast is generated. The multi-element probe comprises a plurality of conductive elements. U.S. patent 6,157,697, the disclosure of which is incorporated herein by reference, describes the use of an appartus for examining a breast by means of X-rays and by electric impedance measurement. The apparatus can be used to generate both X-ray and impedance images of the breast. A fusion image may be formed from a combination of the images. In order to allow easy comparison and fusion of the images, the images are taken during a single session while the breast is in the same position, and from substantially the same direction. That is, the X-ray images are taken while electrodes used for generating an impedance image are positioned on the breast. The '697 patent suggests using an impedance imaging probe which is formed of three layers. A first layer comprises a plurality of electrodes and lead wires, which electrodes are used in the impedance imaging. Although the electrodes are suggested as comprising a material which attenuates X-ray poorly, the difference between the X-ray intensity passing through the electrodes and the intensity passing through areas between the electrodes may cause artifacts on the x-ray images taken while the impedance probe is in place. Therefore, the '697 patent suggests using a second layer, separated from the electrodes by an insulation (third) layer, which comprises the electrode materials in a mirror image to the first layer. The additional layer is not used in any way for the impedance imaging and is provided in order to prevent formation of shadow artifacts on the x-ray images. SUMMARY OF THE INVENTION An aspect of some embodiments of the present invention relates to a multi-element impedance probe which includes conductive materials in one or more layers. At least one of the layers includes an isolating material, which has an x-ray absorption level substantially equal to that of the conductive materials, between the conductive materials of the layer. The isolating material is optionally included throughout an imaging region of the probe. In some embodiments of the invention, the isolating material has substantially the same x-ray absorbency as the conductive material of the same layer. Alternatively, the isolating material of a layer has a different thickness than the conductive material of the layer, such that the x-ray absorption of the conductive and isolating materials of the layer is substantially equal. Further alternatively, the isolating material comprises a mixture of materials which has substantially the same x-ray absorption as the conductive material. In some embodiments of the invention, the impedance probe includes a plurality of layers including, for example, a body contact layer, one or more wire leading layers, a substrate layer and one or more isolating layers. It is noted that the wire leading layers and body contact layer include both conductive materials and the isolating materials between them. In some embodiments of the invention, the conductive and non-conductive materials of a single layer have substantially the same height. In other embodiments of the invention, the substantive conductive and non-conductive materials of a single layer have different heights. The difference in the heights may be left empty (e.g., in the body contact layer), or may be filled in with low x-ray absorbent materials (e.g., low x-ray absorbency plastics) for example of an adjacent isolating layer. Optionally, each of the layers has substantially the same x-ray absorption over its entire surface area within the imaging region. Having each of the layers of the multi-element probe have equal absorption levels over the surface area included in the imaging region prevents formation of artifacts in images taken in an angle relative to the impedance probe. In addition, using an isolating material for equalizing the x-ray absorption level of the layers, allows simple use of a plurality of conductive layers in a single probe. An aspect of some embodiments of the invention relates to a multi-element impedance probe in which the x-ray absorption level of the non-conductive layers of surface regions of the probe are a function of the x-ray absorption level of the conductive layers of the surface regions. In some embodiments of the invention, different surface regions of the probe have substantially different x-ray absorption levels of their non-conductive layers. Optionally, the probe has a substantially equal x-ray absorption level, substantially over its entire imaging region. Optionally, the probe does not include non-functional conductive portions. In some embodiments of the invention, the conductive elements of the impedance probe and the insulation separating the elements are formed of materials which have similar x-ray absorbency. Optionally, the materials are substantially x-ray transparent materials, which have a very low X-ray absorbency. In an exemplary embodiment of the invention, the conductive elements comprise aluminum and the insulation comprises Alumina (i.e., AI2O3) and/or silicone. Alternatively or additionally, the thickness of the probe at different areas is varied according to the X-ray attenuation of the materials in each specific surface area. Optionally, the conductive elements are held by a substrate which has a variable thickness according to the size and shape of the conductive elements. An aspect of some embodiments of the invention relates to an impedance imaging probe which has conductive portions with dimensions substantially smaller than the resolution of x-rays passing through the probe. The x-ray absorbence of conductive portions which cover less than the resolution limit of the x-ray detector reduces with the percentage of the area of the pixel covered by the conductive portions. In some embodiments of the invention, an impedance probe comprises a conductive element layer and a lead wire layer. Lead wires from the lead wire layer are optionally connected to respective conductive elements with vias having a cross-section substantially smaller than the resolution of x-ray imaging techniques. An aspect of some embodiments of the invention relates to a combined X-ray mammography and impedance system in which the compression and support plates comprise respective multi-element impedance probes. Optionally, the probes have the same two- dimensional arrangement of elements but have different physical structures. In some embodiments of the invention, one of the probes comprises a two piece structure including a disposable contact layer and a reusable connector unit, while the other probe comprises a single integral unit. Alternatively or additionally, one of the probes comprises thinner leads, to the conductive elements, than the other. Optionally, the probe associated with the support plate, i.e., closer to the x-ray detectors of the mammograph, is less X-ray absorbent than the probe of the upper compression plate, as X-ray energy absorbed by the support plate already passed through the breast. Alternatively or additionally, the probe associated with the lower support plate is more uniform in its x-ray absorption over its surface. Generally, differences in the x-ray absorption of the probe associated with the upper compression plate cause less severe artifacts in the x-ray images because the x-rays from the upper compression plate pass through the breast where they are anyhow scattered. An aspect of some embodiments of the invention relates to an impedance imaging system including a pair of multi-element probes, each having a plurality of separate conductive elements, which have different numbers and/or sizes of conductive elements. The probes are optionally adapted for placement on opposite sides of an organ. An aspect of some embodiments of the invention relates to a multiple modality examination procedure, including impedance and x-ray imaging, in which results from one modality are used in setting one or more parameters of another modality. In some embodiments of the invention, the results of a first modality and/or combined results of a plurality of modalities are used to determine whether an anomaly is existent within the breast and/or the location of the anomaly. According to the location of the anomaly, one or more parameters of an examination procedure of a second modality are adjusted, in order to determine the type of the anomaly, i.e., whether the anomaly is malignant. Optionally, the second modality comprises impedance imaging. In some embodiments of the invention, the one or more adjusted parameters comprise the specific locations from which electrification signals are applied to the subject, and/or the amplitudes, frequencies and/or phases of the electrification signals. Alternatively or additionally, the one or more adjusted parameters comprise constants of a calculation procedure used to generate the images. In some embodiments of the invention, the parameter adjustment is performed by a human operator. Alternatively or additionally, the parameter adjustment is performed automatically, e.g., by a control processor. Alternatively or additionally, the results of a first modality and/or combined results of a plurality of modalities are used to determine whether an anomaly is existent within the breast and/or the two-dimensional location of the anomaly, while the second modality is used to determine the depth of the anomaly beneath the probe. In some embodiments of the invention, the second modality comprises X-ray imaging and the one or more parameters comprise the volt peak (KNP), X-ray voltage, x-ray current and/or mAs product of the X-ray source. An aspect of some embodiments of the invention relates to a multiple modality examination procedure, including impedance and x-ray imaging, in which the analysis and/or display of results from one modality depends on the results from another modality. In some embodiments of the invention, the type of the parameter of the impedance imaging which is displayed (e.g., critical frequency, phase, capacitance, conductivity) is selected responsive to results from the imaging of another modality. Alternatively or additionally, during the impedance imaging, data is collected for a plurality of stimulation signals and the data displayed is chosen responsive to the imaging results from another modality. There is thus provided, in accordance with an exemplary embodiment of the invention a probe for impedance imaging comprising: a plurality of conductive elements adapted to contact tissue of a subject; a plurality of conductive wires connecting the conductive elements to an external connector; and one or more non-conductive materials, wherein the x-ray absorbance of the non-conductive materials, in at least some of the surface areas of the probe, is a function of the x-ray absorbance of the conductive wires and elements in the same surface area, such that the probe has substantially the same x-ray absorbance over most of the surface area of the probe. In an embodiment of the invention, the one or more non-conductive materials comprise a substrate layer having different thickness at different surface areas of the probe. Optionally, the substrate layer is thinner in surface areas of the probe which include conductive wires. In an embodiment of the invention, the one or more non-conductive materials comprise at least one isolating material which has an x-ray absorbency substantially equal to the x-ray absorbency of the conductive elements or of the conductive wires. Optionally, the plurality of conductive elements comprise an aluminum-based deposit and the at least one isolating material comprises alumina. In an embodiment of the invention, the one or more non-conductive materials comprise at least one isolating material which is deposited between at least some of the conductive elements. In an embodiment of the invention, the x-ray absorption level of at least some of the surface areas including the conductive elements is substantially equal to the absorption level of at least some of the surface areas not including the conductive elements. Optionally, the plurality of lead wires are included in a single layer which has a substantially equal x-ray absorption level over substantially its entire surface area. Optionally, the probe does not include conductive portions which are not included in an electrical path between one of the conductive elements and the external connector. Optionally, the probe has an x-ray absorption level of less than 6%. There is further provided in accordance with an embodiment of the invention, a probe for impedance imaging comprising: a tissue contact layer which includes a plurality of conductive elements adapted to contact tissue of a subject; one or more wire layers which include a plurality of conductive wires connecting the conductive elements to at least one external connector; and a substrate layer, wherein at least one of the tissue contact layer or the wire layers has less than 2% variations in its x-ray absorbance over a surface area including a plurality of the conductive elements. Optionally, at least one of the tissue contact layer or the wire layers has less than 2% variations in its x-ray absorbance over most of the surface area of the probe. Optionally, at least one of the tissue contact layer or the wire layers has less than 0.25% variations in its x-ray absorbance over a surface area including a plurality of the conductive elements. Optionally, the layer with less than 2% variations in its x-ray absorbance comprises the tissue contact layer. Optionally, the tissue contact layer comprises an isolation material between at least some of the conductive elements. Optionally, the isolation material in the tissue contact layer has substantially the same thickness as the conductive elements. Optionally, the isolation material has substantially the same x-ray absorbancy as a material forming the conductive elements. Optionally, the isolation material comprises alumina and the material forming the conductive elements comprises aluminum. Optionally, the isolation material comprises carbon and the material forming the conductive elements comprises a carbon based plastic. In an embodiment of the invention, the isolation material in the tissue contact layer has a different thickness than the conductive elements. In an embodiment of the invention, the isolation material has a different x-ray absorbancy than a material forming the conductive elements. Optionally, the layer with less than 2% variations in its x-ray absorbance comprises the wire layer. Optionally, the wires in the wire layer are separated by an isolation material having substantially the same x-ray absorbancy as a material forming the wires. there is further provided, in accordance with an embodiment of the invention, a breast impedance imaging apparatus, comprising: a first multi-element impedance imaging probe, adapted for placing on a first side of a breast; and a second multi-element impedance imaging probe, having a different structure than the first impedance imaging probe, adapted for placing on a second side of the breast. Optionally, the apparatus includes a mammogram including an x-ray source and an image receptor adapted for taking images of the breast. Optionally, the mammogram is adapted to generate images based on x-ray signals which pass through at least one of the first and second probes. Optionally, the first and second probes have different numbers of elements. Optionally, the first and second probes have elements of different sizes. Optionally, the first and second probes have the same number of elements. Optionally, the first and second probes have the same arrangement of elements. Optionally, the first and second probes have different average x-ray absorption levels. Optionally, the first and second probes have different maximal differences between x-ray absorption levels of different areas of the probe. Optionally, the first and second probes comprise different materials. Optionally, the first probe comprises a single piece and the second probe comprises a plurality of detachable pieces. There is further provided, in accordance with an embodiment of the invention, a breast impedance imaging apparatus, comprising: a mammogram including an x-ray source and an image receptor adapted for taking images of a breast; a first, multi-element, impedance imaging probe, adapted for placing on a first side of a breast; and a second impedance imaging probe, having a different structure than the first impedance imaging probe, adapted for- placing on a second side of the breast. Optionally, the second probe comprises a single element probe. Alternatively, the impedance imaging apparatus comprises a structure according to an embodiment of the invention. There is further provided, in accordance with an embodiment of the invention, a method of imaging a body portion of a subject, comprising: acquiring an x-ray image of the body portion; determining at least one impedance imaging parameter responsive to the acquired x-ray image; and acquiring an impedance image of the body portion using the determined at least one imaging parameter. In an embodiment of the invention, determining the at least one parameter comprises determining at least one parameter of an applied stimulation signal. Optionally, determining the at least one parameter comprises determining an area to be imaged. Alternatively or additionally, determining the at least one parameter optionally comprises determining a position of a suspected anomaly. There is further provided, in accordance with an embodiment of the invention, a method of imaging a body portion of a subject, comprising: acquiring impedance image information of the body portion; acquiring x-ray image information of the body portion; and analyzing a first one of the impedance image information and x-ray image information; and displaying at least one image based on information selected, from a second one of the impedance image information and x-ray image information, responsive to the analyzing. In an embodiment of the invention, analyzing the first one of the impedance image information and x-ray image information comprises analyzing the x-ray information. Alternatively or additionally, analyzing the information optionally comprises determining a location of an anomaly. Alternatively or additionally, analyzing the information optionally comprises determining an impedance measure to be displayed. BRIEF DESCRIPTION OF THE DRAWINGS Exemplary non-limiting embodiments of the invention will be described with reference to the following description of embodiments in conjunction with the figures. Identical structures, elements or parts which appear in more than one figure are preferably labeled with a same or similar number in all the figures in which they appear, in which: Fig. 1 is a schematic illustration of a dual-purpose apparatus for mammography and impedance-imaging, in accordance with an embodiment of the present invention; Fig. 2 is a schematic illustration of an impedance probe and a probe housing, in accordance with an embodiment of the present invention; Figs. 3 A and 3B are schematic views of the impedance probe of Fig. 2, in accordance with an embodiment of the present invention; Fig. 4 is a schematic cross-section view of a portion of an impedance probe, in accordance with an embodiment of the present invention; and Fig. 5 is a flowchart of the acts performed in a dual modality imaging procedure, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 is a schematic illustration of a dual-purpose apparatus 30 for mammography and impedance-imaging, in accordance with an embodiment of the present invention. Dual-purpose apparatus 30 comprises an x-ray mammogram of any type known in the art, of which Fig. 1 shows an x-ray tube 14, an image receptor 18 (which may be analog or digital), filters 16, a collimator 12 and an anti-scattering grid 19. In addition, Fig. 1 shows a compression plate 20 and a support plate 22 which are adapted to receive an examined breast 33. For example, the mammogram may comprise a LORAD® M-IN mammogram (manufactured by LORAD, a subsidiary of Trex Medical Corporation, Danbury, CT) which includes a cellular grid system for contrast and visual enhancement. Alternatively or additionally, the mammogram may have stereoscopic capability for obtaining x-ray images from at least two viewing angles. The mammogram may be upright for use with sitting or standing patients. Optionally, the mammogram can be rotated along the horizontal axis so as to obtain x-ray measurements at any angle. Alternatively, the mammogram may have fewer degrees of freedom. Further alternatively, the mammogram is horizontal for use with prone patients. It should be noted that in general, any mammogram may be fitted in accordance with the present invention, including mammograms designed and/or manufactured without intention to be used in accordance with the present invention. One or more multi-element impedance probes (in Fig. 1, probes 40 and 42) for sensing impedance signals, and/or for applying signals, are placed on breast 33. An electrode 56 for applying electrical stimulation signals is positioned on a surface of the subject whose breast 33 is examined. Optionally, electrode 56 is placed remote from the breast or otherwise not in the path of the x-ray beams from x-ray tube 14. Alternatively, electrode 56 is placed on the breast, for example on the nipple. Optionally, electrode 56 comprises x-ray translucent materials, for example, a single thin aluminum electrode. Alternatively, electrode 56 comprises a multielement probe, for example having a similar structure and/or according to the principles described above with relation to probe 40. Optionally, a computer 24 receives the sensed signals from probe 40, from probe 42 and/or from image receptor 18 (when a digital x-ray detector is used, for example), and provides an indication of the state of breast 33. For example, computer 24 may display an image of breast 33 on a monitor 26. In some embodiments of the invention, apparatus 30 comprises an electrical impedance scanning device 58. which controls the sensing of the impedance signals and the applying of electrification signals to the patient. Scanning device 58 may be substantially any suitable electrical impedance scanning device known in the art, for example, a T-Scan™ 2000 Impedance Scanner of TransScan, Israel, or as described in US patents 5,810,742, 4,458,694, PCT application PCT/ILOO/00127, filed March 1, 2000, PCT application PCT/ILOO/00839, filed December 14, 2000 and/or US Patent Application 09/460,699, filed December 14, 1999, the disclosures of which documents are incorporated herein by reference. Alternatively or additionally, some or all of the tasks of scanning device 58 are performed by computer 24. In some embodiments of the invention, each of the elements of probes 40 and/or 42 is controlled separately such that at any single moment some of the elements may sense signals, others may provide excitation (optionally at different phases, frequencies or amplitudes), and still others may be passive. Alternatively or additionally, the elements of one or more of probes 40 and 42 are controlled in groups, for example in lines or circles including a plurality of elements. Further alternatively or additionally, the control of the elements of probes 40 and 42 is as described in any of the above referenced patent documents. In some embodiments of the invention, apparatus 30 comprises only a single probe (e.g., 40), which is attached to compression plate 20. By placing probe 40 within the path of x- rays used in x-ray imaging of the breast, the images generated by probe 40 cover substantially the same area as the images acquired by receptor 18. When impedance probe 40 is located between X-ray tube 14 and breast 33, X-rays absorbed by probe 40 which therefore do not participate in generating an X-ray image by receptor 18, do not impinge on breast 33. Thus, probe 40 may have a certain degree of uniform x-ray absorption without adversely affecting the x-ray image or the amount of x-rays absorbed by breast 33. The x-ray intensity of the beams generated by head 14 may be adjusted responsive to the x-ray absorption of probe 40. In other embodiments of the invention, apparatus 30 comprises a pair of probes 40 and 42 attached, respectively, to compression plate 20 and support plate 22. As described, for example, in the above mentioned U.S. patent 5,810,742 and/or in PCT/ILOO/00839, a pair of impedance probes 40 and 42 can be used in a multitude of impedance imaging procedures which provide additional information on anomalies within breast 33, such as its location (e.g., depth) and/or type. Alternatively, apparatus 30 comprises only probe 42, which is attached to support plate 22. hi some embodiments of the invention, probes 40 and/or 42 are permanently affixed to compression plate 20 and/or support plate 22. Alternatively or additionally, impedance probe 40 serves as compression plate 20 and/or probe 42 serves as support plate 22. Optionally in this alternative, impedance probes 40 and/or 42 are strengthened with a stiff plastic board, or another, preferably radiolucent, stiff material. Alternatively or additionally, impedance probes 40 and/or 42 are detachably attached to a breast side of compression plate, 20 and/or of support plate 22. Having probes 40 and/or 42 detachably connected to plates 20 and/or 22, respectively, allows performing imaging sessions with only x-rays or with only a single impedance probe 40 or 42. For example, in some cases, in order to reduce x-ray exposure, only impedance probe 40 or 42 is used. In other cases, when a high precision level is required, both impedance probes 40 and 42 are used. In addition, having probes 40 and/or 42 detachably connected to plates 20 and/or 22, respectively, allows replacement of probes 40 and/or 42 for each patient. Impedance probes 40 and/or 42 may be affixed to their respective plates using any suitable method, such as tongue-in-grove, male-female snaps, screws, nuts and bolts, adhesives or Nelcro fasteners, and/or any of the methods described in PCT/IL00/00287, the disclosure of which is incorporated herein by reference. It is noted that probes 40 and/or 42 may have the same size as the plates to which they are connected or may have different sizes than the plates. Fig. 2 is a schematic illustration of an impedance probe 40 and a probe housing 200, in accordance with an embodiment of the present invention. Probe housing 200 receives probe 40, providing mechanical support and/or electrical connection. Optionally, probe 40 is disposable, while housing 200 is used for many patients. Probe housing 200 may be connected to support plate 20 using any of the above described methods. In some embodiments of the invention, impedance probe 40 and compression plate 20 are aligned in a precise and repeatable alignment which allows simple registration of images acquired by probe 40 with images acquired by receptor 18. In those embodiments in which impedance probe 40 is removable, the precise and repeatable alignment is optionally defined by a groove designed to receive the probe, e.g., probe housing 200, and/or the positions of the attachment devices. Alternatively or additionally, human identifiable markings, for example felt-tip markings, instructing an operator how to align compression plate 20 and probe 40 are marked on the plate and/or probe. Alternatively or additionally, registration of the images produced by impedance probe 40 with the X-ray images, is performed each time probe 40 and plate 20 are connected and/or for each imaging procedure. In some embodiments of the invention, probe 40 comprises x-ray absorbing markings, which appear in x-ray images acquired by x-ray receptor 18, deposited thereon at predetermined positions. Optionally, the x-ray absorbing markings are not located above sensing elements of probe 40 and/or are outside the region of interest of most images. Alternatively, the absorbing markings are located on probe housing 200 or on any other device having a predetermined spatial relation with probe 40. Further alternatively, the x-ray absorbing markings are removably attached to impedance probe 40. When alignment is required they are put in place and when x-ray images are acquired they are removed. Alternatively or additionally, the imprints of the x-ray absorbing markings are removed from impedance images by image processing methods. Optionally, the absorbing markings identify the orientation of impedance probe 40, for example using a "right" and/or "left" marking. Optionally, the absorbing markings comprise a material that is sufficiently absorbing to show on the x-ray image, but not so absorbing that it can cause serious artifacts, for example a thick layer of aluminum or a thin layer of platinum or gold. In some embodiments of the invention, the absorbing markings comprise at least two perpendicular lines which define at least one junction, optionally two junctions. In some embodiments of the invention, the absorbing markings are visible to humans. Alternatively or additionally, the location of the absorbing markings on impedance probe 40 are known by computer 24, and registration is performed accordingly. It is noted that any of the above described attachment methods of probe 40 and compression plate 20, may be used to attach probe 42 and support plate 22. Fig. 3 A is a schematic top view of impedance probe 40 shown in Fig. 2, in accordance with an embodiment of the present invention. Fig. 3 A also shows lead wires 504 beneath one row of pads 500. The remaining lead wires are not shown, so as not to clutter Fig. 3 A. Fig. 3B is a side cross-sectional view of the impedance probe 40 of Fig. 3A. Probe 40 comprises a plurality of electrode pads 500, for example arranged in a two dimensional array. As shown, probe 40 comprises an 8x8 array of pads 500. It is noted, however, that the present invention may be implemented with substantially any number of pads 500, in substantially any useful arrangement. In an exemplary embodiment of the invention, probe 40 comprises 45x60 pads 500, each pad having a square area of about 4x4 mm. In some embodiments of the invention, electrode pads 500 are isolated from each other by isolating strips 502. Optionally, isolating strips 502 are as narrow as possible, such that most of the area of the top surface of probe 40 is uniform and does not cause artifacts in x-ray images acquired by receptor 18. Alternatively or additionally, isolating strips 502 have a width selected as a compromise between the desire to minimize artifacts on the x-ray images, and the need to minimize cross talk between the electrical signals of pads 500. In an exemplary embodiment of the invention, the width of insulation strips 502 is about 0.2 mm. A layer including pads 500 and isolating strips 502 is referred to herein as a contact layer 516. Beneath electrode pads 500, probe 40 comprises, for each pad 500, a lead wire 504 which connects the pad to an external connector 506 which leads signals from pads 500 to scanning device 58 (Fig. 1). In some embodiments of the invention, external connector 506 is included in probe housing 200 (Fig. 2). An isolating layer 508 separates pads 500 from lead wires 504. In some embodiments of the invention, isolating strips 520 separate between lead wires 504. Respective vias 510 within isolating layer 508 connect each of pads 500 to its respective lead wire 504. Optionally, a substrate layer 512 beneath lead wires 504 provides probe 40 with durability and/or isolates lead wires 504 from the surroundings. In some embodiments of the invention, electrode pads 500 and isolating strips 502 comprise materials which have substantially the same substance X-ray absorbency. Generally, the substance x-ray absorbency is a function of the atomic number Z of the material. Thus, shadows are not formed on X-ray images acquired by receptor 18, due to a difference between the X-ray absorption of different areas of probe 40. In an exemplary embodiment of the invention, electrode pads 500 comprise aluminum (for example 0.1-0.2 μm) and isolating strips 502 comprise alumina and/or silicone. Optionally, electrode pads 500 have a very thin carbon layer (e.g., 0.1 μm) on the surface which contacts the breast. In some embodiments of the invention, isolating strips 502 include, in addition to the alumina, a respective thin layer of a plastic with similar x-ray absorbency to that of the carbon so as to compensate for the carbon. Alternatively, isolating strips 502 include only alumina, as the carbon layer is very thin. Alternatively to electrode pads 500 including aluminum, electrode pads 500 comprise a carbon, e.g., amorphous carbon, and isolating strips 502 comprise a plastic material with similar x-ray absorbency, e.g., polyester, hi an exemplary embodiment of the invention, pads 500 comprise thin carbon layers of between about 0.1- 20μm. Alternatively to having the same x-ray absorbency, isolating strips 502 have a thickness which compensates for the different x-ray absorbencies, such that electrode pads 500 and isolating strips 502 have the same absorption level. Alternatively, the gaps between electrode pads 500 are not filled in, and other methods, such as described below, are used to minimize artifact generation. In some embodiments of the invention, lead wires 504 and the isolating strips 520 therebetween are similarly formed of materials with substantially the same X-ray absorption levels. Alternatively or additionally, strips 520 are formed of the same material as isolating layer 508. Similarly, in some embodiments of the invention, vias 510 and isolating layer 508 comprise materials with substantially the same X-ray absorption levels. Alternatively or additionally, vias 510 have a width and/or length (e.g., 10 μm) substantially smaller than the resolution of the X-ray imaging apparatus, such that the x-ray absorption of the material of vias 510 is very small relative to the amount of x-ray energy influencing a smallest resolution area on receptor 18. In some embodiments of the invention, the x-ray absorption differences over contact layer 516 and/or over the layers including wires 504 are less than 10%, 5%, 2%, 0.5% or even 0.1%. Substrate 512, and/or isolating layer 508 optionally comprise a radiolucent, nonconductive material such as a low x-ray absorbency plastic (for example, Mylar ® , polyamide, polyimide, polyurethane, polycarbonate, or Tyvec ® ) or paper. In some embodiments of the invention, electrode pads 500, lead wires 504 and/or vias 510 are formed of materials which have a relatively high ratio of their conductivity to their x- ray absorbency. Such materials may have a high conductivity and comparatively high x-ray absorbency relative to other low absorbency materials, e.g., aluminum, or may have a relatively low conductivity with a low x-ray absorbency, e.g., graphite based deposits and/or carbon layers. Alternatively, any other material with a comparative ratio between electrical conductivity and x-ray absorbency, such as amorphous carbon or a carbon slightly doped with a conductive material such as silver, may be used. Optionally, the thickness of pads 500 and/or the cross section of lead wires 504 and/or vias 510, are chosen as a trade-off between their x-ray absorbency and their conductance. Vias 510, as they are very short, optionally have a very small cross-section, as described above. Lead wires 504 optionally have a conductance of up to about 100 Ohm in order to minimize voltage drop of the signals sensed by pads 500 as they are provided by connector 506. For low conductance materials, e.g., carbon, such conductance requires a cross section of between about 1000-3000 μm^, while for high conductance materials, e.g., aluminum, such conductance requires a cross section of between about 20-80 μm^. In some embodiments of the invention, lead wires 504 have a circular and/or rectangular cross sectional shape, with a similar width and length. Thus, the dimensions of lead wires 504 are very small, optionally smaller than the resolution of receptor 18, thus decreasing the effect of the wires on the acquired x-ray images. Alternatively or additionally, some or all of lead wires 504 comprise a very thin film with a relatively wide width. The very thin film has a very low x-ray absorption level and therefore does not substantially cause artifacts on images generated by receptor 18. The use of wide lead wires 504 spreads artifacts caused by the lead wires over a large area and therefore the artifacts are different from anomaly imprints on x-ray images. Thus, the artifacts do not substantially interfere with identifying anomaly imprints on the x-ray image. In some embodiments of the invention, lead wires 504 are included on a plurality of layers so as to allow room for wide lead wires. Further alternatively or additionally, some or all of lead wires 504 comprise very narrow, optionally relatively thick, wires which cover a very small area of probe 40. In some embodiments of the invention, all the materials included in probe 40 are bio- compatible and bio-stable. Alternatively, the materials of contact layer 516 are bio-compatible and bio-stable while the materials of probe base 514 have lower bio-compatibility. Thus, the materials of probe base 514 may be less x-ray absorbent, lighter, and/or more conductive or isolating (as appropriate). Optionally, some or all of the materials are hypoallergenic. In some embodiments of the invention, during manufacture, a substrate 512 is carved into shape. Thereafter, lead wires 504 are placed on substrate 512 using any available production method, such as methods, e.g., photo-resist and/or etching, used in production of semi-conductors, printed circuit boards (PCBs) and/or flex circuits. The placement of the amorphous carbon may be performed using any method known in the art, such as laser deposition and/or chemical vapor deposition. Strips 520 between lead wires 504 are then optionally filled in with an isolating material, as described above. Alternatively or additionally, lead wires 504 are covered with a uniform thickness layer of the isolating material of strips 520. In this covering, strips 520 are filled in. Lead wires 504 and strips 520 are then optionally covered by isolating layer 508. At the points at which pads 500 are to be placed, holes are optionally drilled in isolating layer 508, in order to receive vias 510. Optionally, the holes of vias 510 are slanted to allow covering of the walls of the holes with a conductive material without filling the holes entirely. Optionally, a conductive material is placed on the walls of the holes, forming vias 510, while the remaining volume of the holes is filled with a low x-ray absorbency material 518, which is optionally non-conductive or a poorer conductor. Alternatively, the holes are filled entirely with a conductive material. Pads 500 are then placed on isolating layer 508. Thereafter, a filling material forming isolating strips 502 is filled in the area between pads 500. Alternatively, a layer of the material of isolating strips 502 is placed substantially on the entire surface area of probe 40, and cavities are formed therein for pads 500. Contact layer 516 is optionally firmly attached to isolating layer 508. Alternatively, contact layer 516 is manufactured separately, as a disposable contact interface which is connected to a probe base 514 which includes the remaining layers of probe 40. Thus, the advantages of using a disposable contact interface for contacting breast 33, are achieved, while, for example, using expensive materials and/or structures, which do not interfere with x-ray imaging, for lead wires 504. Optionally, pads 500 comprise suitable receptacles which fit on vias 510 of base 514. Alternatively or additionally, any other attachment method is used to connect contact layer 516 to probe base 514. It is noted that the above manufacture method is presented by way of example and substantially any other suitable manufacture method may be used to produce probes in accordance with the present invention. Fig. 4 is a schematic cross-section view of a portion of probe 40, in accordance with an embodiment of the present invention. Fig. 4 shows a portion of probe 40 which includes a single pad 500. In order to equalize the X-ray absorption of probe 40 over substantially its entire area which is in the path of x-ray imaging of apparatus 32, substrate 512 has different thickness at different areas, according to the absorption of the remaining elements of the probe above substrate 512. For example, probe 40 may have three different types of areas, namely, beneath pads 500, beneath vias 510 and pads 500, and not beneath pads 500. In such a probe 40, substrate 512 optionally has three respective thickness areas. Beneath via 510, substrate 512 optionally has a first thickness 610, defining a hole 620. Beneath pad 500, but not under via 510, substrate 512 optionally has a second thickness 612, defining a second hole 622, and in all other areas substrate 512 has a third thickness 614. In some embodiments of the invention, substrate 512 comprises a different material than the filling 518 of via 510 and/or pad 500. Therefore, the depth of holes 620 and/or 622 is not necessarily equal to the thiclaiess of pad 500. Although in some embodiments of the invention, as shown in Fig. 4, the walls of holes 620 and 622 are shown as straight lines, in other embodiments of the invention, the walls of one or more of the holes are slanted and/or rounded. The use of slanted and/or rounded holes smoothes out any artifacts which may be caused by a difference in x-ray absorption between the opposite sides of the walls of the hole. In some embodiments of the invention, impedance probe 42 has any of the structures described above with reference to impedance probe 40. Optionally, probes 40 and 42 of an apparatus 30 have the same structure. Alternatively, probes 40 and 42 have different structures. In some embodiments of the invention, probes 40 and 42 comprise different materials, have different layouts of lead wires 504 and/or are formed of different numbers of pieces. Optionally, probes 40 and/or 42 are marked (e.g., "upper", "lower") so that an operator can differentiate between probes 40 and 42. In some embodiments of the invention, impedance probe 40 has a higher x-ray absorption level than probe 42. In an exemplary embodiment of the invention, the x-ray absorption level of probe 42 is allowed to be up to about 1%, while the absorption level of probe 40 is allowed to be up to about 15%. X-ray energy absorbed by either of probes 40 and 42 does not participate in formation of an image by receptor 18. On the other hand, x-ray energy absorbed by probe 40 does not impinge on breast 33, while x-ray energy absorbed by probe 42 does impinge on breast 33. Therefore, it is usually more important to minimize the x- ray absorption of probe 42 than of probe 40. In some embodiments of the invention, impedance probe 42 has a more uniform x-ray absorption level over its surface, than probe 40. In an exemplary embodiment of the invention, the x-ray absorption differences over the area of probe 42 are less than about 0.1%, while the x- ray absorption differences over the area of probe 40 may go up to about 0.5%. This is because the scattering of x-rays within breast 33 alleviates the artifacts caused by probe 40. For example, in some embodiments of the invention, the production process of probe 42 is more accurate than of probe 40. For example, in laying alumina isolating strips 502, the allowed difference in thickness between pads 500 and strips 502 is lower than a first, low, threshold (e.g., 0.1-0.2 μm) in probe 42 and lower than a second, higher, threshold in probe 40. In some embodiments of the invention, probe 40 comprises a single disposable piece formed of inexpensive materials which have a moderate x-ray absorbency. Probe 42, however, comprises two pieces as described above, such that probe base 514 (Fig. 3B) may comprise expensive materials which have a very low x-ray absorbency. Alternatively or additionally, probe 40 comprises lead wires 504 with a higher conductance and higher x-ray absorbency than the lead wires 504 of probe 42. For example, the lead wires of probe 40 may have a greater cross-section area or may comprise a more conductive material. Further alternatively or additionally, the pads 500 and/or the isolating materials of strips 502 and 520, layer 508 and/or substrate 512 of probe 42 are less x-ray absorbent than the respective materials of probe 40. Further alternatively or additionally, layer 508 and/or substrate 512 are thinner in probe 42 than in probe 40. Alternatively or additionally, probe 42 comprises a structure in accordance with any of the above described embodiments, while probe 40 has a structure known in the art, such as described in above mentioned U.S. patents 5,810,742, or 6,157,697. In some embodiments of the invention, probes 40 and 42 have the same pad arrangements. The use of the same pad arrangements for both of probes 40 and 42 allows generating impedance images of substantially the same quality by both of probes 40 and 42 and allows more freedom in planning impedance imaging sessions. Alternatively, probes 40 and 42 have different pad arrangements. For example, probe 42 may have a different element structure, which has a lower x-ray absorption level and/or lower x-ray absorption difference over its surface, than probe 40. In some embodiments of the invention, probe 42 has fewer pads 500 (e.g., an 8x8 array) than probe 40 (e.g., a 45x60 array) and hence requires fewer lead wires 504. Thus, thinner wires may be used for the same impedance levels on a single layer of the probe. Thus, probe 42 has less x-ray absorption differences over its area and/or less x-ray absorption. Alternatively or additionally, probe 42 is smaller than probe 40 and/or has narrower or wider isolating strips 502 between its pads 500. In some embodiments of the invention, images are normally generated based on signals sensed by probe 40. One or more images with lower resolution (due to the fewer pads 500 included in probe 42) may be provided based on signals from probe 42. In other embodiments of the invention, one of probes 40 and 42 is used for electrification and the other is used for imaging. Using one of the probes only for electrification allows planning that probe to better suite the electrification task and/or to be less x-ray absorbent or otherwise x-ray interfering. Optionally, probe 42 comprises the electrification probe and has elongated strips of conductors arranged in parallel rows. Such elongated rows may be electrically connected from a side of probe 42 outside of the imaging region, and therefore are much less x-ray interfering. Alternatively, probe 42 comprises elements organized in circles or comprises a single planar conductive electrode. In some embodiments of the invention, additional probes on sides of breast 33 are used in impedance imaging, in addition to probes 40 and 42. For example, two electrification probes on sides of breast 33 may be used in addition to probes 40 and 42 used for imaging on the top and bottom of breast 33. The electrification probes optionally apply electrification voltage and or current signals from opposite sides while probes 40 and 42 sense voltage signals. In some embodiments of the invention, one or both of probes 40 and 42 have one or more holes for inserting a needle (e.g., a biopsy needle) and/or for passing fingers of a surgeon. The probe 40 and/or 42 having the hole or holes is optionally selected as the one which will cause fewer or less troublesome artifacts on the x-ray images due to the hole. Alternatively or additionally, the holes are located on the probe which allows easier access to a physician. In some embodiments of the invention, a probe serving mainly and/or only as an electrification probe includes the holes. Thus, the area of the holes does not interfere with creation of the images. It is noted that a wide range of impedance imaging sessions may be used with the apparatus of the present invention. Impedance imaging sessions are described, for example, in U.S. patent 5,810,742, and/or PCT/ILOO/00839. Electrification signals may be applied from electrode 56, probe 40, probe 42, from other electrodes and/or from any combination of electrodes and probes. As described above, the images may be acquired by one or both of probes 40 and 42 in a single stage or in a plurality of stages. For example, during an imaging session, some of the images are acquired by probe 42 based on electrification from probe 40 and some of the images are acquired by probe 40 based on electrification from probe 42. Alternatively or additionally, electrification signals are applied from specific elements of one or both of probes 40 and 42 and the images are acquired by the remaining elements of one or both of the probes. In an exemplary embodiment of the invention, signals are applied from one or more specific elements of probe 40 and from one or more specific elements of probe 42, while the remaining elements of probes 40 and 42 are used to generate two images from opposite sides. Optionally, the values for the pixels of the images corresponding to the elements used for electrification are calculated using a suitable interpolation method. In some embodiments of the invention, a symbiotic relationship between the imaging modalities takes place. Since each technique relies on different properties of the lesion, impedance imaging enhances the understanding of x-ray imaging and vice versa. In general, coincident detection of features is expected. When anomalies are seen only on one modality, settings and methods may be somewhat altered in the other modality in order to arrive at coincident detection. Optionally, the knowledge of the improved settings and methods may be used in future imaging. An example of an imaging procedure with such a symbiotic process is now described with reference to Fig. 5. Fig. 5 is a flowchart of the acts performed in a dual modality imaging procedure, in accordance with an embodiment of the present invention. Breast 33 is placed (800) between support plate 22 and compression plate 20. Optionally, a conductive gel layer is placed (802) between breast 33 and probe 40 and/or 42. Compression plate 22 is then closed (804) on breast 33 and one or more images are acquired (806) by x-ray tube 14 and receptor 18. Optionally, one or more impedance images are acquired (808) using impedance probes 40 and/or 42. The acquired images are analyzed (810) to detect possible anomalies in breast 33 and/or find unclear regions which require additional imaging. Responsive to the analysis, one or more additional impedance imaging sessions are performed (812) with one or more parameters selected responsive to the detected possible anomalies. The results of the additional impedance session are analyzed to determine (814) the existence, location and/or type (e.g., cancerous or non-cancerous) of the possible anomaly. Optionally, one or more additional x-ray images are acquired (816) with one or more parameters adjusted responsive to the above determination (814). The one or more adjusted parameters, may comprise for example, the angle from which the images are taken and/or the intensity of the x-rays used in the imaging, for example for unclear regions. Referring in more detail to placing (802) the conducting gel layer, the gel may be placed by smearing the gel on the breast 33 or on probe 40, as is known in the art. Alternatively or additionally, the gel may be pre-placed on a disposable probe 40 or surface contact piece thereof, for example inside wells surrounding the pads thereof, as described for example in U.S. patent 5,810742. Further alternatively or additionally, the gel is placed in the form of an interface sheet, such as described in PCT application PCT/ILOO/00287, filed May 21, 2000, and/or in PCT application PCT/ILOO/00127. The use of an interface sheet isolates breast 33 from probe 40, such that a reusable probe 40 may be employed without endangering the patient. Optionally, the gel layer comprises a material with a low x-ray absorbency. Using an interface sheet also allows the use of non-bio-compatible materials for pads 500 and isolating strips 502 and therefore allows using less x-ray absorbent and/or more conductive materials. In some embodiments of the invention, the gel comprises some adhesive properties which connect probe 40 and/or 42 to the breast. Referring in more detail to analyzing (810) the x-ray images and optionally impedance images, in some embodiments of the invention, the analysis is performed automatically by a processor, e.g., computer 24. Alternatively or additionally, the analysis is performed by a human operator. For example, the images may be displayed on monitor 26 for examination by the operator. In some embodiments, both the x-ray apparatus and the impedance probe produce digital images that are displayed on monitor 26. The images may be displayed one after the other, one next to the other and/or overlaid one on top of the other. Alternatively, film images of the two modalities are produced and superimposed on a light box. Alternatively, the impedance image is printed on a transparency for viewing with a film image, on a light box. Alternatively still, a film image is scanned in order to produce a digital image, and the digital images are overlaid and viewed on a computer monitor. In some embodiments of the invention, digital images that are overlaid and viewed on the computer monitor can undergo image processing by the computer. Image processing may comprise changing the dimensions of one image, in order to match the dimensions of the other image; zooming in on an area, removing noise of any kind and other image-enhancement processing as known in the art. Optionally, x-ray images acquired while probes 40 and/or 42 are in place, are processed by a signal processing program, running for example on computer 24, which removes the anticipated pattern of multi-element impedance probe 40. Optionally, computer 24 identifies the artifacts on the acquired x-ray images and removes them accordingly. Alternatively or additionally, computer 24 removes shadowing artifacts expected for the layout of probes 40 and/or 42. Optionally, computer 24 stores one or more known probe layouts and uses for post processing the stored layout which belongs to the probes 40 and/or 42 currently used. Alternatively or additionally, before an imaging session, a blank image is taken with probes 40 and/or 42 in place but without breast 33, and the blank image is analyzed to determine the artifacts caused by the probes. In some embodiments of the invention, the results of the analysis (810) determine the depth of a suspected anomaly and the additional analysis (814) is used to determine the type of the anomaly, e.g., whether the anomaly has the characteristics of a malignant region. The depth may be determined by acquiring x-ray images from two different angles, as is known in the art. Alternatively or additionally, the analysis (810) is used to determine a two dimensional location of an anomaly and the additional analysis (814) is used to determine the depth of the anomaly. Further alternatively or additionally, the results of the analysis (810) indicate an unclear area and the additional analysis (814) is used to carefully scan the unclear area. Further alternatively or additionally, the results of the analysis (810) are used in normalizing the results of the impedance imaging. Optionally, the analysis of the x-ray image and/or the combined image determine an area with a suspected area and a clear area most distinctly without anomalies. The results of the impedance imaging (812) of the clear area are used to normalize the results of the imaging of the suspected area, thus providing a better view of the suspected anomaly and/or more accurate data on the anomaly. In an exemplary embodiment of the invention, one of probes 40 and 42 is used for sensing signals used in forming an image, while the other probe is used to provide electrification signals to breast 33. Optionally, the additional impedance imaging session is performed with specific electrification patterns and/or sensing patterns suitable for examining the suspected anomaly. For example, the electrification signals may be applied to two parallel lines of pads on opposite sides of the suspected anomaly, as described in PCT application PCT/ILOO/00839. In some embodiments of the invention, the distance between parallel lines and a point above the suspected anomaly is substantially equal to the depth of the anomaly. Optionally, the electrification signals to the parallel lines have different phases, optionally opposite phases. Alternatively or additionally, any other impedance imaging methods, such as described, for example, in PCT/ILOO/00839 and/or in U.S. patent 5,810742, are used. Any of the parameters of such imaging methods may be adjusted responsive to the analysis (810). hi some embodiments of the invention, the adjusted parameters comprise the amplitude and/or frequency of the electrification signals. For example, deeper anomalies may require electrification signals with a higher amplitude and/or a different frequency than used for shallow anomalies. Alternatively or additionally, the adjusted parameters comprise a determination of which pads of the electrification probe are used in the electrification, e.g., how many of the pads and/or in which configuration. Further alternatively or additionally, the adjusted parameters comprise a determination of which elements (on one probe or two probes) are used for electrification and which elements are used for sensing. Further alternatively or additionally, the adjusted parameters comprise a determination of whether a remote electrode is to be used. h some embodiments of the invention, in which the applied signals have different phases as described in PCT/ILOO/00839, the adjusted parameter comprises the phase difference between the applied signals. In some embodiments of the invention, after determining the location and/or type of the anomaly, a biopsy needle is directed to the anomaly in order to receive additional information on the anomaly. The guidance of the needle toward the anomaly may be performed using impedance imaging methods, such as described in PCT/ILOO/00839 and/or U.S. patent 5,810,742. Optionally, an electrical signal is applied to the biopsy needle so that its advance is easily detected by probe 40 and/or 42. It is noted that the guidance using impedance imaging is possible even for anomalies which are only detected based on x-ray images, based on the registration of the impedance images and the x-ray images. An additional x-ray image may be taken when the biopsy needle reaches the designated point as an additional verification that the needle is at the correct point. Referring in more detail to acquiring (816) the additional x-ray images, the additional images are acquired from different angles and/or with different x-ray beam intensities. The different angles and/or intensities are optionally selected responsive to an analysis of previously acquired images. For example, additional x-ray images may be acquired from an angle in which probes 40 and/or 42 cause fewer artifacts in a specific area of interest. It is noted that the entire imaging process may be repeated for a different angular view of breast 33, for example, a lateral view, in which the apparatus is rotated, and the breast is compressed from the side. In some embodiments, the symbiotic relationship is further extended to the understanding of what features and types of lesions are better visualized by x-ray, and what features and what types of lesions are better detected by impedance. As such, specificity and sensitivity of each technique to certain features and types of lesions may be studied and compared. Since different sensitivities exist, the use of both modalities together allows for more thorough diagnosis. Alternatively or additionally to adjusting the acquisition of data of one modality responsive to imaging results from another modality, the display of the data acquired for one of the modalities is adjusted responsive to results from another modality. In some embodiments of the invention, the type of the parameter of the impedance imaging which is displayed (e.g., critical frequency, phase, capacitance, conductivity) is selected responsive to results from the imaging of another modality. Alternatively or additionally, during the impedance imaging, data is collected for a plurality of stimulation signals and the data displayed is chosen responsive to the imaging results from another modality. For example, data may be acquired with applied stimulation signals at a plurality of locations, layouts, phase differences, frequencies and/or amplitudes. The displayed image is optionally chosen responsive to data from images of another modality, e.g., the location of a suspected anomaly in acquired x-ray images. For example, for a suspected anomaly at a depth x beneath probe 40, data may be displayed from imaging performed with stimulation signals applied from opposite sides, optionally at distance x, from the surface area above the suspected anomaly. In some embodiments of the invention, combined mammography and impedance imaging procedures are performed for a plurality of patients one after the other using the same apparatus. For safety purposes, before the breast of each patient is placed in the mammogram, a disposable contact surface is placed on compression plate 20 and/or on support plate 22. The contact surface may comprise, as described above, a gel sheet a probe 40 and/or 42 and or a contact layer of a probe, for example including pads 500 without leading wires 502. Changing the contact surface between patients eliminates the need for sterilization and/or cleaning of the apparatus between imaging procedures. Alternatively or additionally to the method of Fig. 5, any other combined impedance imaging and x-ray imaging method may be used. Particularly, the x-ray images and impedance images may be obtained in any order and/or simultaneously. The method of Fig. 5 and/or other imaging methods in which the parameters of one modality are adjusted responsive to results of imaging using another modality, are not limited to the above described apparatus, but rather may be used with substantially any x-ray apparatus known in the art, including apparatus for imaging tissue other than the breast. In some embodiments of the invention, instead of having all of probe 42 in place during the acquisition of the x-ray image, only a body contact portion of probe 42 is in place. After the x-ray image is acquired, the remaining parts of probe 42 are put in place, optionally after removing receptor 18. Optionally, the body contact portion comprises a thick non-conductive substrate of a very low x-ray absorbance, which can serve as a support plate. The contact portion includes a surface facing the breast, pads 500 as described above. Thin conductive vias lead, through the substrate, from pads 500 to an opposite side of the substrate. A second part of probe 42 includes leading wires 504 and ports which connect the vias from the body contact portion to the leading wires. The principles of the present invention are not limited to dual modality apparatus. In some embodiments of the invention, an additional modality, beyond impedance and X-ray, is used in examining breast 33. The third modality may be substantially any suitable imaging method known in the art, such as gamma imaging. For example, a gamma camera may fit onto impedance probe 40 of compression plate 20. It will be appreciated that the above described methods may be varied in many ways, including, changing the order of steps, and/or performing a plurality of steps concurrently. For example, the steps described above of manufacturing probe 40 may be performed in a different order. It should also be appreciated that the above described description of methods and apparatus are to be interpreted as including apparatus for carrying out the methods, and methods of using the apparatus. The present invention has been described using non-limiting detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. It should be understood that features and/or steps described with respect to one embodiment may be used with other embodiments and that not all embodiments of the invention have all of the features and/or steps shown in a particular figure or described with respect to one of the embodiments. Variations of embodiments described will occur to persons of the art. Furthermore, the terms "comprise," "include," "have" and their conjugates, shall mean, when used in the claims, "including but not necessarily limited to." It is noted that some of the above described embodiments may describe the best mode contemplated by the inventors and therefore may include structure, acts or details of structures and acts that may not be essential to the invention and which are described as examples. Structure and acts described herein are replaceable by equivalents which perform the same function, even if the structure or acts are different, as known in the art. Therefore, the scope of the invention is limited only by the elements and limitations as used in the claims.

Claims: CLAIMS 1. A probe for impedance imaging comprising: a plurality of conductive elements adapted to contact tissue of a subject; a plurality of conductive wires connecting the conductive elements to an external connector; and one or more non-conductive materials, wherein the x-ray absorbance of the non-conductive materials, in at least some of the surface areas of the probe, is a function of the x-ray absorbance of the conductive wires and elements in the same surface area, such that the probe has substantially the same x-ray absorbance over most of the surface area of the probe. 2. A probe according to claim 1, wherein the one or more non-conductive materials comprise a substrate layer having different thickness at different surface areas of the probe. 3. A probe according to claim 2, wherein the substrate layer is thinner in surface areas of the probe which include conductive wires. 4. A probe according to claim 1, wherein the one or more non-conductive materials comprise at least one isolating material which has an x-ray absorbency substantially equal to the x-ray absorbency of the conductive elements or of the conductive wires. 5. A probe according to claim 4, wherein the plurality of conductive elements comprise an aluminum-based deposit and the at least one isolating material comprises alumina. 6. A probe according to claim 1, wherein the one or more non-conductive materials comprise at least one isolating material which is deposited between at least some of the conductive elements. 7. A probe according to claim 1, wherein the x-ray absorption level of at least some of the surface areas including the conductive elements is substantially equal to the absorption level of at least some of the surface areas not including the conductive elements. 8. A probe according to any of the preceding claims, wherein the plurality of lead wires are included in a single layer which has a substantially equal x-ray absorption level over substantially its entire surface area. 9. A probe according to any of the preceding claims, wherein the probe does not include conductive portions which are not included in an electrical path between one of the conductive elements and the external connector. 10. A probe according to any of the preceding claims, wherein the probe has an x-ray absorption level of less than 6%. 11. A probe for impedance imaging comprising: a tissue contact layer which includes a plurality of conductive elements adapted to contact tissue of a subject; one or more wire layers which include a plurality of conductive wires connecting the conductive elements to at least one external connector; and a substrate layer, wherein at least one of the tissue contact layer or the wire layers has less than 2% variations in its x-ray absorbance over a surface area including a plurality of the conductive elements. 12. A probe according to claim 11, wherein at least one of the tissue contact layer or the wire layers has less than 2% variations in its x-ray absorbance over most of the surface area of the probe. 13. A probe according to claim 11, wherein at least one of the tissue contact layer or the wire layers has less than 0.25% variations in its x-ray absorbance over a surface area including a plurality of the conductive elements. 14. A probe according to any of claims 11-13, wherein the layer with less than 2% variations in its x-ray absorbance comprises the tissue contact layer. 15. A probe according to claim 14, wherein the tissue contact layer comprises an isolation material between at least some of the conductive elements. 16. A probe according to claim 15, wherein the isolation material in the tissue contact layer has substantially the same thickness as the conductive elements. 17. A probe according to claim 15 or claim 16, wherein the isolation material has substantially the same x-ray absorbancy as a material forming the conductive elements. 18. A probe according to claim 17, wherein the isolation material comprises alumina and the material forming the conductive elements comprises aluminum. 19. A probe according to claim 17, wherein the isolation material comprises carbon and the material forming the conductive elements comprises a carbon based plastic. 20. A probe according to claim 15, wherein the isolation material in the tissue contact layer has a different thickness than the conductive elements. 21. A probe according to claim 15 or claim 20, wherein the isolation material has a different x-ray absorbancy than a material forming the conductive elements. 22. A probe according to any of claims 11-21, wherein the layer with less than 2% variations in its x-ray absorbance comprises the wire layer. 23. A probe according to claim 22, wherein the wires in the wire layer are separated by an isolation material having substantially the same x-ray absorbancy as a material forming the wires. 24. A breast impedance imaging apparatus, comprising: a first multi-element impedance imaging probe, adapted for placing on a first side of a breast; and a second multi-element impedance imaging probe, having a different structure than the first impedance imaging probe, adapted for placing on a second side of the breast. 25. Apparatus according to claim 24, comprising a mammogram including an x-ray source and an image receptor adapted for taking images of the breast. 26. Apparatus according to claim 25, wherein the mammogram is adapted to generate images based on x-ray signals which pass through at least one of the first and second probes. 27. Apparatus according to any of claims 24-26, wherein the first and second probes have different numbers of elements. 28. Apparatus according to any of claims 24-27, wherein the first and second probes have elements of different sizes. 29. Apparatus according to any of claims 24-26, wherein the first and second probes have the same number of elements. 30. Apparatus according to claim 29, wherein the first and second probes have the same arrangement of elements. 31. Apparatus according to any of claims 24-30, wherein the first and second probes have different average x-ray absorption levels. 32. Apparatus according to any of claims 24-31, wherein the first and second probes have different maximal differences between x-ray absorption levels of different areas of the probe. 33. Apparatus according to any of claims 24-32, wherein the first and second probes comprise different materials. 34. Apparatus according to any of claims 24-33, wherein the first probe comprises a single piece and the second probe comprises a plurality of detachable pieces. 35. A breast impedance imaging apparatus, comprising: a mammogram including an x-ray source and an image receptor adapted for taking images of a breast; a first, multi-element, impedance imaging probe, adapted for placing on a first side of a breast; and a second impedance imaging probe, having a different structure than the first impedance imaging probe, adapted for placing on a second side of the breast. 36. Apparatus according to claim 35, wherein the second probe comprises a single element probe. 37. Apparatus according to claim 36 wherein the impedance imaging apparatus comprises a structure according to any of claims 24-34. 38. A method of imaging a body portion of a subj ect, comprising: acquiring an x-ray image of the body portion; determining at least one impedance imaging parameter responsive to the acquired x-ray image; and acquiring an impedance image of the body portion using the determined at least one imaging parameter. 39. A method according to claim 38, wherein determining the at least one parameter comprises determining at least one parameter of an applied stimulation signal. 40. A method according to claim 38 or claim 39, wherein determining the at least one parameter comprises determining an area to be imaged. 41. A method according to any of claims 38-40, wherein determining the at least one parameter comprises determining a position of a suspected anomaly. 42. A method of imaging a body portion of a subj ect, comprising: acquiring impedance image information of the body portion; acquiring x-ray image information of the body portion; and analyzing a first one of the impedance image information and x-ray image information; and displaying at least one image based on information selected, from a second one of the impedance image information and x-ray image information, responsive to the analyzing. 43. A method according to claim 42, wherein analyzing the first one of the impedance image information and x-ray image information comprises analyzing the x-ray information. 44. A method according to claim 42 or claim 43, wherein analyzing the information comprises determining a location of an anomaly. 45. A method according to any of claims 42-44, wherein analyzing the information comprises determining an impedance measure to be displayed.

Inventors: MALONEK DOV, NACHALIEL EHUD, STEINBERG SEBASTIAN, WIMISNER YOAV, MALONEK, DOV, NACHALIEL, EHUD, STEINBERG, SEBASTIAN, WIMISNER, YOAV
Applicants: MALONEK DOV, NACHALIEL EHUD, STEINBERG SEBASTIAN, TRANSSCAN MEDICAL LTD, WIMISNER YOAV, MALONEK, DOV, NACHALIEL, EHUD, STEINBERG, SEBASTIAN, TRANSSCAN MEDICAL LTD., WIMISNER, YOAV
Application year: 2001
Main classification: A61B5
IPC codes: A61B5, A61B6, A61K49, A61K51