Patent Number: 
Section: description

Referring initially to FIG. 2, an imaging system in accordance with the present invention is shown and generally designated 10. As shown in FIG. 2, the system 10 includes an X-ray source 12 configured to produce a spectrum of X-ray radiation 14. An optional collimator 16 may be provided to collimate the radiation 14 emitted from the X-ray source 12 into one or more beams 18a-c. As such, each beam 18 emanates from the X-ray source 12 in a slightly different direction, and consequently, along a separate path 20a-c. It is to be appreciated that the use of three beams 18 is merely exemplary and that as many beams 18 as desired may be used in accordance with the present invention. In detail, as shown in FIG. 2, beam 18a initially travels substantially along path 20a, beam 18b initially travels substantially along path 20b and beam 18c initially travels substantially along path 20c.  Referring still to FIG. 2, a detector array 22 is shown positioned to receive the beams 18 from the source 12. Specifically, the detector array 22 is shown having three detectors 24a-c, with detector 24 a positioned to receive beam 18a, detector 24b positioned to receive beam 18b and detector 24c positioned to receive beam 18c. For the present invention, an object 26 can be interposed between the X-ray source 12 and the detector array 22 to thereby allow the beams 18 to be modified by passing through the object 26 before reaching the detectors 24. In accordance with the present invention, the detectors 24 can be any type of detector known in the pertinent art capable of receiving radiation and producing an electrical signal that is proportional to the intensity of the radiation received. For example, the detectors 24 can be solid state detectors (separate or having a charge couple detector structure), gas-filled detectors or scintillators with photo-multipliers. Preferably, each detector 24 is a small-area X-ray detector. For the present invention, the output of each detector 24 is electrically wired to a computer (not shown) to allow the signals generated by the detectors 24 to be processed. Also shown in FIG. 2, the X-ray source 12 can be slideably mounted on a circular track 28 that extends around the object 26. Additionally, as shown, each detector 24 or the entire detector array 22 can be slideably mounted on the track 28. As such, the X-ray source 12 and detectors 24 can be moved either continuously or incrementally around the track 28 and relative to the object 26. The dashed lines in FIG. 2 show an exemplary second position for the X-ray source 12 and detectors 24. By moving the X-ray source 12, each radiation beam 18 emanating from the X-ray source 12 can be caused to successively travel on different paths 20 through the object 26. For example, as shown in FIG. 2, when X-ray source 12 is in the initial position represented by the solid lines, beam 18 a travels substantially along path 20a, and when X-ray source 12 is moved to a second position represented by dashed lines, beam 18a travels substantially along path 20d. Similarly, beam 18b travels substantially along path 20e and beam 18c travels substantially along path 20f when the X-ray source 12 is in the position indicated by dashed lines. Accordingly, the detector array 22 can be moved in conjunction with the X-ray source 12 to allow each detector 24 to track a single X-ray beam 18, as that X-ray beam 18 travels on successive paths 20 through the object 26. An important aspect of the present invention is that the X-ray radiation 14 is filtered between the X-ray source 12 and the detectors 24. By cross-referencing FIGS. 2 and 3, it can be seen that a wheel 30 having two attached filters 32, 34 can be used to successively filter each X-ray beam 18a-c on each path 20. As further shown, a motor 40 having a shaft 42 can be used to rotate the wheel 30 and filters 32, 34 to successively filter each beam 18 twice while the beam 18 travels substantially along a single path 20. Thus, for a path 20, the beam 18 is first filtered with filter 32 and then filtered with filter 34. Additionally, each time a beam 18 is moved to a new path 20, the wheel 30 is rotated through one complete revolution to once again successively filter the beam 18 with each filter 32, 34. Alternatively, the wheel 30 can be located between the X-ray source 12 and the collimator 16 (this configuration not shown). As shown, a bracket 44 can be used to attach the motor 40 to the X-ray source 12 to allow the wheel 30, the filters 32, 34, the motor 40 and the shaft 42 to travel with the X-ray source 12 as the source 12 moves along the track 28 relative to the object 26. Each time a beam 18 is successively filtered by filter 32 and filter 34, two different electrical signals are produced by a detector 24 (i.e. one electrical signal for filtration with filter 32 and one electrical signal for filtration with filter 34). For the present invention, a computer processor (not shown) can be configured to manipulate the two electrical signals created for each path 20 to produce an image signal for the path 20. For example, each path 20 can be used to produce an image signal that represents a single pixel in the final image. Or stated another way, a computer processor can be configured to subtract, pixel by pixel, the digital images created by each filter 32, 34 to produce the contrast enhancement image. Once an image signal is established for each desired path 20, conventional tomography techniques known in the pertinent art can be used to combine all the image signals (one image signal for each path 20) into a composite image that shows the internal features of the object 26. Referring now to FIG. 3, a filter pair having two different filters 32, 34 is mounted on the wheel 30 to allow each beam 18 on each path 20 to be successively filtered twice It is to be appreciated that a plurality of identical filter pairs, with each pair having two different filters 32, 34, can be mounted on the wheel 30 (multiple filter pair not shown). For example, when two identical filter pairs are used, the wheel 30 is rotated through 180 degrees for each path 18. As further detailed below, a unique filter pair is designed for use with a specific contrast agent that is prescribed for introduction into the object 26. Specifically, the chemical constituents and thickness of each filter 32, 34 is determined with reference to the specific contrast agent that is being used. FIG. 4 shows an exemplary filter 32 having layers 46, 48, 50 and 52. Specifically, the filter 32 can include an optional transparent layer 46, a filtering layer 48, an optional additional balance layer 50 and an optional protective layer 52. It is to be appreciated that each filter 32, 34 will have different layers 46, 48, 50, 52, the layers 46, 48, 50, 52 differing in both chemical makeup and thickness. For the present invention, the optional transparent layer 46 can be included to support as well as protect the other layers 48, 50, 52. The optional protective layer 52 can be included to protect the other layers 48, 50 from corrosion or other environmental factors. The function of the filtering layer 48 and the additional balance layer 50 are discussed below. As seen by cross-referencing FIGS. 3 and 4, a metal ring 54 can be used to hold the layers 46, 48, 50, 52 together and attach them to the wheel 30. When used in conjunction with a contrast agent containing a chemical element having a KEDGE CONTRAST AGENT, a filter pair is constructed in accordance with the present invention having a filter 32 with a filtering layer 48 that contains a chemical element having a KEDGE that is greater than KEDGE, CONTRAST AGENT, and a filter 34 with a filtering layer 48 that contains a chemical element having a KEDGE that is less than KEDGE CONTRAST AGENT. The invention includes specific chemical elements and thickness"" sufficient to create filter pairs for various contrast agents as shown in Table 1. Referring back to FIG. 2, in the operation of the present invention, a contrast agent is first introduced into the object 26. Once introduced, the contrast agent will be selectively absorbed or localized in specific regions to thereby establish portions of the object 26 having differing concentrations of contrast agent. Table 1, below, lists a number of suitable contrast agents that are either in current use for imaging portions of the human body or are contemplated for future use. It is to be appreciated that conventional methods of administering the contrast agent that are known in the pertinent art can be employed. Further, it is anticipated that the present invention is applicable to the imaging of a non-human object 26, such as a structural component for a machine or device (not shown). In this case, a material in the structural component can be used as a contrast agent and a suitable filter pair constructed accordingly. Once a contrast agent has been introduced, the object 26 can be placed between the X-ray source 12 and the detector array 22 as shown in FIG. 2. Next, the X-ray source 12 is located at a first position and activated to produce one or more beams 18a-c travelling through the object 26 on a first set of paths 20a-c. Next, the wheel 30 containing the filters 32, 34, is rotated to successively interpose each of the two filters 32, 34, between the X-ray source 12 and the object 26 to filter each of the beams 18 with each of the two filters 32, 34. This results in the production of two intensity-proportional signals by a detector 24 for each beam 18. It is to be appreciated that the two signals will be temporally spaced from each other, the spacing corresponding to the time the beam 18 strikes the wheel 30 between adjacent filters 32, 34. Referring now to FIG. 5A, a typical emission spectrum for a conventional X-ray source 12 that has passed through a portion of the body having no contrast agent is shown by curve 56. When the spectrum represented by curve 56 reaches a detector 24, an electronic signal that is approximately proportional to the area under curve 56 (the intensity of the emission) is produced. Curve 60 in FIG. 5A represents the spectrum that results after radiation produced by a typical X-ray source 12 is passed through a portion of the body having exemplary contrast agent, Gd, in the absence of filters. Referring now to FIG. 5B, curve 58 represents the spectrum that results after radiation producing curve 56 in FIG. 5A is now passed through filter 34 and a portion of the body having no contrast agent. In this case, filter 34 has a filtering layer 48 having a chemical element with a KEDGE of approximately 49 keV. Accordingly, the electronic signal (hereinafter referred to as the filter 34 signal) produced by a detector 24 when filter 34 is interposed between the X-ray source 12 and the detector 24 will be approximately proportional to the area under curve 58. Similarly, a curve representing the spectrum that results after radiation producing curve 65 in FIG. 5A is now passed through filter 32 and a portion of the body having no contrast agent is shown in FIG. 5C and designated curve 65. Accordingly, the electronic signal (hereinafter referred to as the filter 32 signal) produced by a detector 24 when filter 32 is interposed between the X-ray source 12 and the detector 24 will be approximately proportional to the area under curve 58. The processor subtracts the filter 34 signal produced by the detector 24 with the filter 34 interposed along the path 20 from the filter 32 signal produced by the detector 24 with the filter 32 interposed along the path 20 to produce an image signal for the path 20. It is to be appreciated that the image signal simulates an image signal that would be obtained if a quasi-monochromatic beam having an average energy approximately equal to KEDGE CONTRAST AGENT were to be passed through the object 26. More specifically, the image signal produced for paths 20 having no contrast agent simulates the exemplary quasi-monochromatic spectrum shown in FIG. 6A and designated 66. Similarly, the image signal produced for paths 20 having contrast agent simulates the exemplary quasi-monochromatic spectrum shown in FIG. 6B and designated 68. These image signals constitute the data processed for tomography or angiography. The image signal strongly varies with concentration and thickness of the contrast element due to the variation of absorption. This results in an enhanced contrast image between the region with the contrast agent and the region without. Referring now to FIG. 7, the effect of additional balance layers 50 in a filter pair is shown. Specifically, FIG. 7 compares the quasi-monochromatic signal that is simulated without additional balance layers 50 (curve 70) and the quasi-monochromatic signal that is simulated with additional balance layers 50 (curve 72). The curve 72 was generated for a filter pair having a filter 32 with a filtering layer 48 that includes 140.0 xcexcm of 65Tb and an additional balance layer 50 of 200.0 xcexcm of 65Tb and a filter 34 with a filtering layer 48 that includes 236.0 xcexcm of 63Eu and an additional balance layer 50 of 200.0 xcexcm of 65Tb. With cross reference to Table 1 and FIG. 7, these two filters 32, 34 can be used in a filter pair in conjunction with the contrast agent Gd to generate the image signal. As shown in FIG. 7, the use of additional balance layers 50 reduces the non-zero difference of the filter transmission outside the energy pass band. Of course, this effect is obtained by paying the price of reducing the radiation intensity within the pass band (by a factor of about two, in this case). In practice, the additional balance layer 50 is designed to provide a compromise between the enhancement of the quality of monochromatization (i.e. a thicker additional balance layer 50 providing better balance) and the intensity level within the energy pass band (i.e. a larger number of photons to provide a better Signal-To-Noise ratio). Referring back to FIG. 2, once image signals are obtained for the first set of paths 20a-c, the X-ray source 12 and collimator 16 can be moved to a second position (shown by dashed lines) to cause the beams 18a-c emanating from the collimator 16 to travel along a new set of paths 20d-f. While the X-ray source 12 and collimator 16 are at the second position, the wheel 30 is again rotated to successively interpose each of the filters 32, 34 between the X-ray source 12 and the object 26 to again filter each of the beams 18a-c with each of the two filters 32, 34. Again, two intensity-proportional signals are produced by a detector 24 for each beam 18. For the present invention, these two signals can be manipulated by a processor (not shown) to produce image signals for each new path 20d-f. This process of moving the X-ray source 12 and producing two image signals for each new path 20 can be repeated as desired. Further, it is to be appreciated that the X-ray source 12 can be moved continuously around the object 26. When this technique is used, the wheel 30 containing filter 32 and filter 34 can be rotated continuously as the X-ray source 12 moves. By rotating the wheel 30 very rapidly, each beam 18 can be filtered by each filter 32, 34 before significant movement of the beam 18 occurs. Thus, in effect, each beam 18 remains on a single path 20 while the successive filtration takes place. It is to be appreciated that the image signals described above may also be obtained by first acquiring electrical signals for all paths 18 with the filter 32 interposed along the paths 18, followed by the acquisition of electrical signals for all paths 18 with filter 34 interposed along the paths 18. Once an image signal is produced for all paths 20 of interest, conventional tomography techniques can be used to combine all the image signals (one image signal for each path 20) into a composite image that shows the internal features of the object 26. Referring now to FIGS. 8A-8C, another embodiment of an imaging system in accordance with the present invention is shown and generally designated 10xe2x80x2. As shown in FIG. 8A, the system 10xe2x80x2 includes an X-ray source 12xe2x80x2 configured to produce a spectrum of X-ray radiation 14xe2x80x2. As further shown, a detector array 22xe2x80x2 is shown positioned to receive the radiation 14xe2x80x2 from the source 12xe2x80x2. For the present invention, an object 26xe2x80x2 is interposed between the X-ray source 12xe2x80x2 and the detector array 22xe2x80x2 to thereby allow the radiation 14xe2x80x2 to be modified by passing through the object 26xe2x80x2 before reaching the detector array 22xe2x80x2. For the present embodiment, the object 26xe2x80x2 can be a human body, suitcase, machine component or any other object that requires internal imaging. As further shown, a filter set 74 is provided to filter the radiation 14xe2x80x2 before the radiation 14xe2x80x2 reaches the detector array 22xe2x80x2. Preferably, in this embodiment, the filter set 74 and detector array 22xe2x80x2 are stationary during the imaging procedure. With cross reference now to FIGS. 8A, 8B and 8C, it can be seen the filter set 74 includes a plurality of filters 32 and a plurality of filters 34. It is to be appreciated that the filters 32a-p and 34a-p (see FIG. 8B) as well as the filters 32q-r and 34q-r (see FIG. 8C) are only exemplary. As best seen in FIG. 8B, the filters 32, 34 are preferably arranged in a planar, two dimensional array. For an object 26xe2x80x2 having a contrast agent containing a chemical element having a KEDGE CONTRAST AGENT, each filter 32 contains a chemical element having a KEDGE that is greater than KEDGE, CONTRAST AGENT, and each filter 34 contains a chemical element having a KEDGE that is less than KEDGE CONTRAST AGENT. It is to be further appreciated that the specific chemical elements and thickness"" shown in Table 1 can be used to prepare the filters 32, 34 in the filter set 74. As best seen in FIG. 8B, within the planar, two dimensional array, the filters 32, 34 are preferably arranged in an alternating, checker board pattern. With this pattern, a plurality of filter pairs is established, with each pair containing one filter 32 and an adjacent filter 34. For example, filter 32a and 34a constitute a filter pair for the present invention. Similarly, filter 32b and 34b constitute a filter pair for the present invention and so on. As best seen with cross reference to FIGS. 8A and 8C, the detector array 22xe2x80x2 includes a planar array of detectors 76, of which detectors 76a-d are exemplary, with one detector 76 for each filter 32, 34. In accordance with the present invention, the detector array 22xe2x80x2 is preferably an amorphous silicon array of digital detectors 76, with each detector 76 producing an electrical signal that is proportional to the intensity of the radiation received. Furthermore, a pair of detectors 76, such as detector 76a and detector 76b, is provided for each filter pair (32, 34). As shown, the detector pair 76a, 76b is positioned to receive filtered radiation from the filter pair (32q, 34q). For the present invention, the output of each detector 76 is electrically wired (via wires 78, of which wires 78a-d are exemplary) to a computer (not shown) to allow the signals generated by the detectors 76 to be processed. It is to be appreciated that for each filter pair (32, 34), a corresponding pair of detectors 76 produces two different electrical signals (i.e. one electrical signal for filtration with filter 32 and one electrical signal for filtration with filter 34). For the present invention, a computer processor (not shown) can be configured to manipulate the two electrical signals created for each filter pair to produce an image signal for the filter pair (32, 34). More specifically, the processor subtracts the electrical signal corresponding to filtration with filter 34 from the electrical signal corresponding to filtration with filter 32 to produce an image signal for the filter pair (32, 34). It is to be appreciated that each filter pair (32, 34) can be used to produce an image signal that represents a single pixel in the final image. Once an image signal is established for each filter pair (32, 34), the processor can be used to combine all the image signals (one image signal for each filter pair (32, 34) into a composite image that shows the internal features of the object 26xe2x80x2. In another embodiment of the present invention, the detector array 22xe2x80x2 and filter set 74 as shown in FIG. 8a are formed as linear arrays. It is to be appreciated that a single filter pair 32, 34 can be used in this embodiment. Preferably, for this embodiment, the X-ray source 12xe2x80x2, linear detector array 22xe2x80x2 and filter set 74 are mounted on a track (such as the track 28 shown in FIG. 2) for movement relative to the object 26xe2x80x2. During imaging, the X-ray source 12xe2x80x2 is moved along the track 28 to successive positions, and an image signal is generated (as described above) from the filter pair (32, 34) for each position of the X-ray source 12xe2x80x2. Once an image signal is produced for each desired position of the X-ray source 12xe2x80x2, conventional tomography techniques can be used to combine all the image signals into a composite image that shows the internal features of the object 26xe2x80x2. While the particular imaging systems and methods as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.