Patent Application
20130049151
Non-invasive imaging technologies allow images of the internal structures of a subject (e.g., a patient or object) to be obtained without performing an invasive procedure on the patient or object. Non-invasive imaging systems may operate based on the transmission and detection of radiation through or from a subject of interest (e.g., a patient or article of manufacture). For example, X-ray based imaging techniques (such as mammography, fluoroscopy, computed tomography (CT), and so forth) typically utilize an external source of X-ray radiation that transmits X-rays through a subject and a detector disposed opposite the X-ray source that detects the X-rays transmitted through the subject. Other radiation based imaging approaches, such as positron emission tomography (PET) or single photon emission computed tomography (SPECT) may utilize a radiopharmaceutical that is administered to a patient and which results in the emission of gamma rays from locations within the patient's body. The emitted gamma rays are then detected and the gamma ray emissions localized.
Thus, in such radiation-based imaging approaches, the radiation detector is an integral part of the imaging process and allows the acquisition of the data used to generate the images of interest. In certain radiation detection schemes, the radiation may be detected by use of a scintillating material that converts the higher energy gamma ray or X-ray radiation to optical light photons (e.g., visible light), which can then be detected by photodetector devices, such as photodiodes. In other detection schemes, the X-ray or gamma ray energy may be directly converted to electrical signals in the detector apparatus, and these electrical signals are read-out electronically.
In certain of these direct conversion radiation detectors, the radiation passes through an electrode or other aspects of the detector packaging prior to reaching the sensor component of the detector. In such approaches, the packaging materials may attenuate the radiation being measured prior to the radiation reaching the sensor. In this manner, radiation signal may be lost to the sensor packaging, resulting on a loss or reduction of detector efficiency. As a result, to compensate for this lost signal, higher radiation doses may be employed to maintain the desired signal level reaching the sensing components of the detector.
In accordance with one embodiment, a radiation detector is provided. The radiation detector comprises a plurality of detector elements comprising a direct conversion material that generates electrical signals directly in response to incident radiation. The radiation detector also comprises a respective anode for each detector element. Each anode is positioned over the respective detector element such that incident radiation passes through the anode before reaching the respective detector element. The radiation detector also comprises a flexible circuit structure comprising aluminum or copper interconnect pads in electrical contact with the anodes. The flexible circuit structure comprises one or more layers of a polymeric composition. The radiation detector also comprises an interconnect structure electrically connecting the respective anodes and the flexible circuit structure.
A method for forming a radiation detector is also provided. In accordance with one embodiment of the method, an aluminum or copper anode is formed on each of a plurality of detector elements. Each detector element comprises a direct conversion material that generates electrical signals directly in response to incident radiation. The respective anodes and respective aluminum or copper interconnect pads of a flexible circuit structure comprising one or more layers of a polymeric composition are electrically connected. The flexible circuit structure is electrically connected to readout circuitry suitable for acquiring signals from the plurality of detector elements.
In accordance with one embodiment, an imaging system is provided. The imaging system comprises a direct conversion radiation detector, a data acquisition system in communication with the radiation detector, and a controller controlling operation of the data acquisition system. The radiation detector comprises one or more detector modules. Each detector module comprises a plurality of detector elements that generates electrical signals directly in response to incident radiation; a flexible circuit structure comprising aluminum or copper interconnect pads each in electrical contact with an anode disposed in the radiation path of a respective detector element, wherein the flexible circuit structure comprises one or more layers of a polymeric composition; and an interconnect structure electrically connecting the respective anodes and the flexible circuit structure.
These and other features and aspects of embodiments of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The present disclosure relates to the use of direct conversion detectors in radiation-based imaging applications. In a direct conversion detector, each radiation photon that is absorbed in the sensor material is converted to a number of electron-hole pairs in proportion to the energy of the radiation photon. A voltage applied across the thickness of the sensor drives the electrons to the anode and the holes to the cathode. Because the mobility of electrons is typically greater than holes in semiconductors with good radiation stopping power, the electron charge is collected on an array of anode electrodes. The electron charge is converted by read-out circuit to a digital imaging signal. The holes are collected on a cathode that is common to the whole sensor area and are not converted to an imaging signal. The anode pixel receiving the electrons is spatially correlated to the arrival position of each photon. Typically, the anode electrode is the pixel-array electrode and the cathode contact is a common electrode. The opposite arrangement, that is a pixel cathode, may be appropriate for other semiconductors where the hole signal is collected on an array of pixel cathodes and radiation incident to the cathode face.
In certain embodiments, the direct conversion detector is anode-illuminated (i.e., the X-rays or gamma rays passes through an anode-bearing surface of the detector before reaching the radiation sensing material or components of the detector). By illuminating the anode surface, the radiation is absorbed closer to the anode electrode and the electron signal is more readily collected. Faster response and less polarization may be achieved with this configuration. In such an embodiment, the radiation passes through an interconnect structure (such as a flexible or flex circuit and associated conductive contacts) which may attenuate the radiation before reaching the sensor material. In certain implementations, the interconnect structures that route signals from the sensor elements (e.g., pixels) to the readout electronics are formed using polymeric materials, low atomic number materials, low density or reduced thickness structures, and so forth to reduce or minimize radiation attenuation attributable to the interconnect structures. For example, in certain implementations, thin metal contacts on the sensor material and/or flexible circuit can be formed using aluminum or copper, as opposed to nickel, gold, or silver. Likewise, a composite epoxy-type interconnect between the sensor material and the flexible circuit can be filled with electrically conductive graphite (or other suitable materials) as opposed to nickel, silver, or gold. Further, in other implementations the routing substrate (e.g., flexible or flex circuit) may be formed using thin layers of a flexible polyimide (e.g., Kapton®) films and thin (15 μm-50 μm thick) plated copper traces. In yet further embodiments, laser-formed direct flex-trace to sensor contact interconnect structures may be employed as part of the contact structure. In such embodiments as these, radiation attenuation prior to the gamma rays or X-rays reaching the sensor material may be reduced relative to other anode-illuminated structures.
It should be noted that the present approaches may be utilized in a variety of imaging contexts, such as in medical imaging, product inspection for quality control, and for security inspection, to name a few. However, for simplicity, examples discussed herein relate generally to medical imaging, particularly radiation-based imaging techniques, such as: computed tomography (CT), mammography, tomosynthesis, C-arm angiography, conventional X-ray radiography, fluoroscopy, positron emission tomography (PET), and single-photon emission computed tomography (SPECT). However, it should be appreciated that these examples are merely illustrative and may be discussed merely to simplify explanation and to provide context for examples discussed herein. That is, the present approaches may be used in conjunction with any of the disclosed imaging technologies as well other suitable radiation-based approaches and in contexts other than medical imaging. Specifically,
With the foregoing in mind,
The detector 12 generates electrical signals in response to the detected radiation, and these electrical signals are sent through their respective channels to a data acquisition system (DAS) 16. Once the DAS 16 acquires the electrical signals, which may be analog signals, the DAS 16 may digitize or otherwise condition the data for easier processing. For example, the DAS 16 may filter the image data based on time (e.g., in a time series imaging routine), may filter the image data for noise or other image aberrations, and so on. The DAS 16 then provides the data to a controller 20 to which it is operatively connected. The controller 20 may be an application-specific or general purpose computer with appropriately configured software. The controller 20 may include computer circuitry configured to execute algorithms such as imaging protocols, data processing, diagnostic evaluation, and so forth. As an example, the controller 20 may direct the DAS 16 to perform image acquisition at certain times, to filter certain types of data, and the like. Additionally, the controller 20 may include features for interfacing with an operator, such as an Ethernet connection, an Internet connection, a wireless transceiver, a keyboard, a mouse, a trackball, a display, and so on.
Keeping such an approach in mind,
The controller 20 may furnish a variety of control signals, such as timing signals, imaging sequences, and so forth to the X-ray source 32 via a control link 34. In some embodiments, the control link 34 may also furnish power, such as electrical power, to the X-ray source 32 via control link 34. Generally, the controller 20 will send a series of signals to the X-ray source 32 to begin the emission of X-rays 36, which are directed towards a subject of interest, such as a patient 38. Various features within the patient 38, such as tissues, bone, etc., will attenuate the incident X-rays 36. The attenuated X-rays 40, having passed through the patient 38, then strike the X-ray detecting array 42 to produce electrical signals representative of a corresponding data scan (i.e., an image). The X-ray detecting array 42 may be pixilated form discrete or pixilated detector elements such that hundreds or thousands of discrete detecting elements may be present on the X-ray detecting array 42. Each detecting element may correspond a single channel for data transmission.
In some imaging contexts, it can be important to transfer information that may be acquired substantially simultaneously, so as to correlate one acquired signal with another. One such imaging context is PET imaging systems, an embodiment of which is illustrated in
The detector 52 detects photons generated from within the patient 38 by a decaying radionuclide. For example, a radionuclide may be injected into the patient 38 and may be selectively absorbed by certain tissues (e.g., tissues having abnormal characteristics such as a tumor). As the radionuclide decays, positrons are emitted. The positrons may collide with complementary electrons (e.g., from atoms within the tissue), which results in an annihilation event. The annihilation event, in PET, results in the emission of a first and second gamma photon 54, 56. The first and second gamma photons 54, 56 may strike the detectors 52 at separate areas approximately 180 degrees from one another. Typically, the first and second gamma photons 54, 56 strike the detectors 52 at approximately the same time (i.e., are coincident), and are correlated with one another. The origin of the annihilation event may then be localized. This is repeated for many annihilation events, which generally results in an image in which the contrast of the abnormal tissues appear enhanced. In this regard, it should be noted that the detector 52 may advantageously include a plurality of discrete detecting elements (e.g., pixilated elements) so as to allow high spatial resolution to produce an image of sufficient quality. For example, by detecting a number of gamma ray pairs, and calculating the corresponding lines traveled by these pairs, the concentration of the radioactive tracer in different parts of the body may be estimated and a tumor, thereby, may be detected. Therefore, accurate detection and localization of the gamma rays forms a fundamental and foremost objective of the PET system 50.
As noted above with respect to the generalized system of
Turning to
Depending on the implementation, the detector elements may be based on cadmium telluride (CdTe), cadmium zinc telluride (CZT or CdZnTe), or any other suitable direct conversion radiation sensing material (such as gallium arsenide, mercury iodine, and so forth). Likewise, the contacts employed with the detecting elements 72 may be any suitable type, such as ohmic or blocking (i.e., Schottky) contacts. Further, as discussed herein, features or structures formed in or between the detecting elements may be scribed, deposited, chemically etched with lithographic masking or laser formed.
In addition to the detector elements 72 that perform the sensing of incident radiation, the depicted detector module 70 includes structural features and/or signal readout components that support or utilize the functionality of the detector elements 72. For example in the depicted example, the detector elements 72 may be positioned on or connected to an interconnect structure 76 (such as a printed circuit board, multilayered ceramics and/or flex circuit backing) that provides structural support for the detector elements and/or may also provide a substrate for the electrical interconnections that allow readout or operation of the detector elements 72.
The structural features and/or electrical interconnections may be described or defined as the package or detector package and various package options may be available, depending on the implementation. For example, package options may include the presence or use of a flex circuit having a suitable pitch or thickness. By way of example, a single layer flex circuit suitable for use with a 128 channels (i.e., one channel per pixilated detector element in the above example) may have a 50 μm pitch and corresponding electrical traces or connections for each channel. Conversely, a multi-layer flex circuit suitable for use with more detector elements (i.e., more channels, such as 256 channels) may have a greater pitch, such as a pitch between 50 μm to 75 μm, and electrical traces or connections for the respective channels. In order to minimize the attenuation of radiation that passes through the packaging structure before impinging on the sensor material, in certain implementations low-atomic number materials and/or thin thicknesses may be used in forming the packaging structure. As such, organic, such as polyimide, and non-inorganic materials, such as Teflon, may be used to form the flexible substrate. Likewise, as discussed herein, graphite, aluminum, or copper may be used in forming electrical interconnect structures or interfaces, such as in combination with an epoxy material, between the detector elements 72 and downstream readout circuitry. Likewise, anisotropic conductive film or other compressive adhesives may be used in forming the electrical connections between the detector elements 72 and interconnect features, as discussed herein.
The detector module 70 may also include or incorporate one or more application-specific integrated circuits (ASICs) 78 for reading out or otherwise operating the detector elements 72. In certain embodiments, an ASIC 78 may be provided on a flex circuit while in other embodiments, the flex circuit may be provided as part of a printed circuit board (PCB) in electrical communication with the detector elements 72. The ASIC 78 may be configured or designed to support a number of channels corresponding to the number of detector elements 72, such as 64 channels, 128 channels, or 256 channels. Likewise, an ASIC 78 may be provided as a one-dimensional or two-dimensional array.
In operation, the generalized detector module 70 of
For example, turning to
In the depicted embodiment, a surface of the sensor component 84 opposite the pixilated surface 86 is in contact with a continuous electrode 94 (such as a high-voltage continuous electrode) which allows application of a bias voltage to the sensor component 84, allowing readout of the detector elements 72 of the sensor component 84. The continuous electrode 94 is also electrically connected (such as via conductive wire, traces, or connections 96) to the downstream circuitry or substrates. In the depicted embodiment, the sensor component 84, along with anode 86 and continuous electrode 94, is mounted or situated on a mechanical substrate 100, such as a ceramic substrate, which may provide mechanical support for the assembly.
Turning to
Turning to
In one implementation, and as depicted in
Turning to
In the depicted example, the connector 124 is electrically connected (such as via wire, trace, or other electrical connection 128) to a corresponding connector 126 of an interface board 132 for the detector modules 70, such as a high density interface board. The electrical connection 128 may allow digital communication of signals generated by the readout ASIC components 120 to the interface board 132, may provide power from the interface board to the detector modules 70, and/or may provide a ground connection for the detector modules 70.
Turning to
Turning to
A flexible circuit 122 is depicted as overlying the sensor component 84 (i.e., in the path of the radiation). In one embodiment the flexible circuit 122 is formed from one or more layers of a polyimide film, such as a Kapton® film, or other suitable flexible material and has a thickness between about 15 μm and about 50 μm, such as about 25 μm. On the surface of the flexible circuit 122 facing the sensor component 84, respective interconnect pads 150 may be formed at locations corresponding to the anodes 90 on the surface of the sensor component 84. In one embodiment, the interconnect pads 150 may be formed from a low atomic number material, such as aluminum or copper, or may be of low density or of reduced thickness so as to have minimal attenuating effect of radiation passing through the flexible circuit 122 prior to reaching the sensor component 84. In one embodiment, the interconnect pads 150 have a length in the z-direction and x-direction between about 200 μm and about 300 μm.
In the depicted embodiment, the interconnect pads 150 are electrically connected (such as by vias 152) to via pads 154 to the opposing surface of the flexible circuit 122. The respective via pads 154 may in turn be electrically connected via features or traces 160 formed on the surface of the flex circuit 122. In the depicted example, the pitch of the flexible circuit 122 in the x-direction (i.e., x-pitch 166) is the distance from the middle of one via pad 154 to the next (i.e., the period by which via pads 154 are repeated), which determines the number of traces 160 that can be routed on the surface of the flex circuit 122 between the via pads 154. The x-pitch, p, may be given as:
p=(2n−1)w+D (1)
where n is the number of rows of via pads 154 (and, presumably, anodes 90 and detector elements 72), w is the width 162 of each trace 160, and D is the width 164 of each via pad 154.
In one embodiment, where the interconnect structures are formed at high density, the trace width 162 (i.e., w) may be between about 15 μm to about 50 μm, such as about 30 μm, the via pad width 164 (i.e., D) may be about 100 μm, and the pitch of the flexible circuit 122 in the z-direction may be about 700 μm. In such embodiments, the x-pitch (i.e., p) and number of rows (i.e., n) with respect to a CdTe/CdZnTe sensor component may be related as given in Table 1:
Turning now to the interconnection between the flexible circuit 122 and the sensor component 84, in one implementation the interconnect pads 150 and anodes 90 are electrically connected by an electrically conductive connection material 170 disposed between each interconnect pad 150 and respective anode 90. The connection material allows electrical signals to pass from an anode 90 to the respective interconnect pad 150 and, from there, to downstream circuitry. In one implementation, the connection material may be an isotropic conductive adhesive, such as an epoxy material containing graphite particles, as opposed to nickel, silver, or gold particles. In such an implementation, the epoxy material may be dispensed or to a screen printed onto the interconnect pads 150 of the flexible circuit 122. The sensor component 84 may then be aligned and placed in contact with the flexible circuit 122 such that each anode 90 is electrically connected with a corresponding interconnect pad 150 of the flexible circuit 122. The epoxy material may then be cured at a suitable temperature, such as at a temperature from about 25 C to about 120 C.
Turning to
In a further embodiment,
In another implementation (and as depicted in
Technical effects of the invention include the formation and use of anode-illuminated direct conversion radiation detectors. In one embodiment, the anodes of a sensor element are electrically connected to an interconnect structure (e.g., a flex circuit) using an epoxy material that may include graphite or other low atomic number conductive particles. In another embodiment, the anodes of the sensor element are electrically connected to the interconnect structure by laser-formed contact structures. In a further embodiment, the anodes of the sensor element are electrically connected to the interconnect structure using a non-conductive adhesive that is cured or compressively displaced so as to allow electrical connection between conductive bumps or pillars formed on the anodes and/or interconnect pads and the complementary conductive structures. In an additional embodiment, the anodes of the sensor element are electrically connected to the interconnect structure using an anisotropic conductive film or adhesive that includes conductive particles that allow electrical connection between conductive bumps or pillars formed on the anodes and/or interconnect pads and the complementary conductive structures
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should also be understood that the various examples disclosed herein may have features that can be combined with those of other examples or embodiments disclosed herein. That is, the present examples are presented in such as way as to simplify explanation but may also be combined one with another. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
