BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an X-ray detector incorporating a method of signal shielding as described in an embodiment of the invention;
FIG. 2 is a flowchart illustrating a method of signal shielding according to an embodiment of the invention;
FIG. 3 is a flowchart illustrating a method of reducing artifacts according to an embodiment of the invention;
FIGS. 4A and 4B illustrate a structural comparison of a detector without shielding and with a shielding as described in an embodiment of the invention; and
FIGS. 5A, 5B and 5C illustrate the effect of shielding in an X-ray detector in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken as limiting the scope of the invention.
Disclosed herein is a shielding method for a digital detector for shielding the detector from electromagnetic noise generated due to any external interference. The shielding effectively shields data lines, which carry the output signals of the detector, the flex layer, which carries the data lines, and the substrate to which the flex layer is bonded. Thus the method offers three different shielding, which will reduce the effect of artifacts in the images significantly. The invention is applicable to any digital detectors including flat panel detectors. The method also suggests achieving the shielding by software as well as hardware means.
FIG. 1 is a schematic diagram of an X-ray detector incorporating a method of signal shielding as described in an embodiment of the invention. The detector 100 has a substrate 110, and at least one flex layer 130 bonded with the substrate 110. The substrate 110 has an outer surface 112 and an inner surface 114. The outer surface 112 of the substrate 110 is provided with an array of X-ray detector elements 120. Each detector element includes a scintillator and a photo sensor. The scintillator converts X-ray energy into light energy. The photo sensor, in turn, is sensitive to the visible light energy. A plurality of data lines 140 is provided for carrying the output signal of the detector elements. The output signal of each detector element is an electrical signal, corresponding to the brightness of a picture element in the X-ray image projected onto the detector. The data lines 140 are associated with the flex layer 130 and may be provided on any part of the flex layer 130. The data lines 140 are provided on both ends of the detector. The array of detector elements 120 is connected to an X-ray imaging system by scan lines 150 and data lines 140. The inner surface of the substrate 110 is connected to the base. The base is, at least in part, a good conductor of electricity, and may be connected to chassis ground, earth ground, or any other acceptable common. The substrate 110 is a poor dissipater of static charge. In an embodiment the substrate 110 is glass. An X-ray imaging system measures an amount of charge or current that recharges each detector element 120 to generate X-ray images. A protection layer 160 is provided above the array of detector elements 120 for shielding the substrate 110. The protective layer 160 should be hermetic and X-ray transmissive. The coefficient of thermal expansion of the protective layer should be compatible with that of the substrate 110. The protective layer may be made of Al-Graphite-Al cover sealed at edges with epoxy. Graphite epoxy layer is provided for stiffness with X-ray transparency and Aluminum layer is provided to reduce permeability to moisture.
In an embodiment of the invention a conductive shielding is provided over the data lines 140. This conductive shielding will act as a data line shield. As mentioned earlier, data lines 140 are provided for carrying output of array of the detector elements 120 and are placed on the flex layer 130. The conductive shielding incorporates a conductive layer of paint or any other coating material that is suitable to pass the signal generated from any external interference to ground. The conductive shield may be a conductive layer of any conducting material coated, laminated, glued, painted or bonded to the data line. Since the conductive shield is applied over the data line, it will maintain signal integrity and there will be no interference from the boundary signal. In an embodiment the conductive layer is an Indium Tin Oxide layer.
In another embodiment of the invention, a flex shield is provided on the flex layer 130. The flex layer 130 is bonded to the substrate 110. Anisotropically conductive film (ACF) bonding is used in bonding the flex layer 130 to the substrate 110. Since the area where the flex layer is bonded to the substrate is very receptive to noise, it is advantageous to shield it separately. To achieve the shielding of the flex layer a flex shield is provided on the interior surface of the flex layer 130. Providing the flex shield includes coating, painting a metal laminate or masking over the flex layer 130. The metal laminate is a copper or any similar conducting material. In an embodiment the metal laminate is a Copper layer.
In an embodiment a substrate shield is provided on the inner surface of the substrate 110. The substrate shield is formed using a conductive layer similar to the conductive shield placed above the data lines. In an example, the substrate shield is an Indium Tin Oxide layer. The substrate shield will act as an additional shield to protect the detector from the external interference.
FIG. 2 is a high level flowchart illustrating a method of signal shielding according to an embodiment of the present invention. The method of signal shielding for reducing artifacts in an X-ray detector is described in 200. At block 210, a conductive shielding is provided above the data lines in a detector. The data lines carry the output of detector elements built on the detector. The conductive shielding can be provided using a conductive layer of paint or any other coating material that is suitable to be used to prevent any external interference on the data line carrying the pixel charges and passing that signal to ground. The conductive shield may include a conductive layer with a variety of substances, such as indium tin oxide, conductive paint, conductive foil, conductive mesh, conductive fibers, static dissipative paint, or any other conductive material. The various coating methods include automatic sprayer, squeegee, paint brusher, stencil screen, or sputter. The conductive shielding provides immunity to data lines from external electric field as well as magnetic field. Also the conductive shielding provides an increase in signal to noise ratio of the imaging system. The conductive shielding significantly improves data line noise and signal integrity from any interference source that might affect the data line in the Z-direction. At block 220, the flex layer is shielded by providing a flex shield on the interior surface of the flex layer. The flex shield comprises a coating or painting of a metal laminate over the interior surface of the flex layer. Providing the flex shield enhances the efficiency of the conductive layer and acts as an additional shielding. It helps eliminate signal coming from external electrical field and magnetic field. At block 230, a substrate shield is provided below or on the inner surface of the substrate. The substrate shield is a conductive layer, similar to the conductive shield placed above the data lines. The substrate shield is achieved by providing a conductive layer on the interior surface of the substrate. In an embodiment the substrate shield is Indium Tin Oxide layer.
In an embodiment the detector shielding is achieved by software subtraction. In this embodiment, the output signal of the detector with external interference and without external interference is determined. The difference between these two output signals yields an error signal. For shielding the detector or reducing the artifacts effects in the images the error signal is subtracted from the output signal of the detector. Thus the resulting output signal of the detector is free from the effects of external interferences.
FIG. 3 is a flowchart illustrating a method 300 of reducing artifacts according to an embodiment of the present invention. At block 310, a flex layer is bonded to the substrate. In the detectors, detector elements are placed on the substrate. The flex layer is bonded to the substrate through Anisotropically conductive film (ACF) bonding. The data lines are provided on the flex layer for carrying output of the detector elements. At block 320, a conductive shield is provided above the data line. The conductive shield is a conductive layer with a conducting material coated, laminated, glued, painted or bonded to the data line. The conductive shield reduces data line noise and improves signal integrity from any interference source that might affect the data line in the Z-direction. At block 330, a flex shield is provided on the interior surface of the flex layer. The area where the flex layer is bonded to the substrate is very receptive to external noise and hence additional shielding isadvantageous. In certain instances the flex layer is bonded after shielding the detector and hence it need separate shielding. The flex layer is provided as a coating or lamination of a metal laminate on the interior surface of the flex layer. At block 340, a substrate shield is provided on the inner surface of the substrate. The substrate shield is a conductive layer placed on the inner surface of the substrate. The conductive layer is coated, laminated, glued, painted or bonded to the inner surface of the substrate. At block 350, at least a portion of the noise created by an external interface is conducted through the conductive shield, flex shield or the substrate shield and through the base of the detector to the ground.
FIGS. 4A and 4B illustrate a comparison diagram of a detector without shielding and with a shielding as described in an embodiment of the invention. FIG. 4A illustrates a detector with out any shielding applied. The detector includes a plurality of detector elements 440 provided on the substrate. A flex layer bonded to the substrate incorporates a plurality of data lines 410 for carrying output of detector elements 440. FIG. 4A shows flex shield area 420 and data line shield area 430, where flex shielding and data shielding is required. FIG. 4B illustrates a detector with a flex shield 425 placed over the flex layer and a data line shield 435 placed over the data lines 410. The data line shield includes a conductive shield placed over the data line. The conductive shield is a conductive layer with a conducting material coated, laminated, glued, painted or bonded to the data line. The flex layer shield includes a coating or painting of a metal laminate over the flex layer.
FIGS. 5A, 5B and 5C illustrate the effect of shielding in an X-ray detector in accordance with an embodiment of the invention. The figures illustrate the improvement in artifacts reduction using the methods described above. FIG. 5A shows an image taken without any signal shielding. As seen the image is dominated with background fix artifacts. FIG. 5B is an image with a conductive shielding placed over the data line. As noticed there has been a reduction in the artifacts, fixed pattern artifacts have been eliminated. However strong row correlated artifacts remain. FIG. 5C shows an image with a conductive shielding placed over the data line and a flex shielding placed over the flex layer. The image obtained is artifacts free.
Some of the advantages of the invention include: 1) Providing immunity to data lines from EMC; 2) Providing more immunity to data lines from electrical fields; 3) Providing more immunity to data lines from magnetic fields; 4) Improving the signal to noise ratio; and 5) Providing signal robustness.
Various embodiments of this invention provide a method for shielding in an X-ray detector and an X-ray detector incorporating the shielding as herein described. The invention also provides a method for reducing artifacts in X-ray detectors. However, the embodiments are not limited to what is described herein and may be implemented in connection with any digital detector capable of detecting images including medical imaging, industrial imaging etc, but not limited to this.
While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alaterations and omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention as set forth in the following claims.
Patent Application
20080078938
