Abstract:
A computed tomography detector apparatus includes a substrate defining a recessed area. The computed tomography detector apparatus includes a heat pipe at least partially disposed within the recessed area. The computed tomography detector apparatus also includes an electronic component attached to the substrate.

Description:
BACKGROUND OF THE INVENTION 
   The subject matter disclosed herein relates to a computed tomography (CT) detector apparatus including a heat pipe. 
   Typically, in CT systems, an x-ray source emits an x-ray beam toward a subject or object, such as a patient or a piece of luggage, positioned on a support. The x-ray beam, after being attenuated by the object, impinges upon a detector assembly. The intensity of the attenuated x-ray beam received at the detector assembly is typically dependent upon the attenuation of the x-ray beam by the object. 
   In known third generation CT systems, the x-ray source and the detector assembly are rotated on a rotatable gantry portion around the object to be imaged so that a gantry angle at which the x-ray beam intersects the object constantly changes. The detector assembly typically includes a plurality of detector modules. Each detector module is typically divided into a plurality of detector elements. Data representing the intensity of the received x-ray beam at each of the detector elements are collected across a range of gantry angles. The data are ultimately processed to form an image. 
   The electronic components produce heat that may cause a degradation in image quality through multiple mechanisms. For example, the gain of a photodiode layer within the detector module is highly temperature dependent and operating the photodiode layer at too high of a temperature may lead to image artifacts such as spots or rings. Also, the amount of pixel-to-pixel leakage between photodiodes increases with temperature. A high level of pixel-to-pixel leakage negatively impacts the signal to noise ratio and may result in reduced image quality. Also, an increase in the temperature of the detector module may result in problems with the mechanical alignment of the detector assembly and a collimator. Third generation CT imaging systems rely on an accurately aligned collimator to effectively block scattered x-ray. However, the mechanical alignment of the detector assembly and the collimator may change as the temperature increases outside of an optimal operating range. If the collimator is not properly aligned with the detector assembly, the result may be additional image artifacts. 
   The problem is that excessive heat within the detector assembly may lead to image artifacts from multiple sources, resulting in images of diminished quality. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification. 
   In an embodiment, a computed tomography detector apparatus includes a substrate defining a recessed area. The apparatus includes a heat pipe at least partially disposed within the recessed area and the apparatus also includes an electronic component attached to the substrate. 
   In another embodiment, a computed tomography detector apparatus includes a rail and a substrate defining a recessed area attached to the rail. The apparatus includes an electronic component attached to the substrate. The apparatus also includes a heat pipe secured to the substrate via a thermal interface material and at least partially disposed within the recessed area. 
   In another embodiment, an apparatus for regulating the temperature of a computed tomography detector includes a heat pipe and a substrate in thermal communication with the heat pipe. The substrate is adapted to support an electronic component. The apparatus also includes a rail attached to the substrate and a liquid coolant in thermal communication with the rail. 
   Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram illustrating a computed tomography system in accordance with an embodiment; 
       FIG. 2  is a schematic diagram illustrating a cross-section of a detector assembly attached to a pair of rails in accordance with an embodiment; and 
       FIG. 3  is a schematic diagram illustrating a cross section of a detector assembly in accordance with an embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following detailed description, reference is made to the accompanying drawings that form a part hereof, 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. 
   Referring to  FIG. 1 , a schematic representation of a computed tomography (CT) system  10  according to an embodiment is shown. The CT system  10  includes a gantry  12 , a rotatable gantry portion  14 , and a support  16 . The rotatable gantry portion  14  is adapted to retain an x-ray source  18  and a detector assembly  20 . The x-ray source  18  is configured to emit an x-ray beam  22  towards the detector assembly  20 . The detector assembly  20  is comprised of a plurality of detector modules (not shown). The support  16  is configured to support a subject  24  being scanned. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The support  16  is capable of translating the subject  24  along a z-direction with respect to the gantry  12  as indicated by a coordinate axis  26 . 
   Referring to  FIG. 2 , a schematic representation of a cross section of the detector assembly  20  attached to a pair of rails  28  is shown in accordance with an embodiment. For purposes of this disclosure, the radially inward direction of the detector assembly  20  is towards the top of  FIG. 2 . The detector assembly  20  comprises a substrate  30 , a scintillator  32 , a photodiode layer  34 , a plurality of electronic components  36 , and a flexible circuit (flex circuit)  38 . The substrate  30  may comprise a ceramic, such as alumina, or another suitably rigid material. The scintillator  32 , the photodiode layer  34 , the plurality of electronic components  36 , and the flexible circuit  38  are mounted to the substrate  30 . The scintillator  32  converts received x-rays into visible light. The photodiode layer  34  is mounted radially outward from the scintillator  32  and converts the visible light from the scintillator  32  into an electric signal. The plurality of electronic components  36  may comprise one or more components from the following nonlimiting list: an analog-to-digital converter (not shown) for converting the analog electrical signals from the photodiode into digital signals, a field-programmable gate array (not shown), and a power regulator (not shown). The analog-to-digital converter, the field-programmable gate array, and the power regulator are all well-known by those skilled in the art. As shown in  FIG. 2 , the plurality of electronic components  36  may be mounted on both a radially inner side  40  and a radially outer side  42  of the substrate  30 . The flexible circuit  38  connects the electronic components  36  such as the analog to digital converter, the power regulator, and the field-programmable gate array. 
   A heat pipe  44  is shown within the substrate of the cross-section of  FIG. 2 . According to one embodiment, the heat pipe  44  includes a sealed hollow tube adapted to retain a working fluid and a wick. The working fluid generally comprises a liquid phase component and a gaseous phase component. The heat pipe  44  transfers heat from a high temperature portion of the heat pipe  44  to a low temperature portion of the heat pipe  44 . The working fluid in the liquid phase component absorbs heat from the high temperature portion of the heat pipe  44  and undergoes a phase change to the gaseous phase component of the working fluid. The gaseous phase component of the working fluid migrates to the low temperature portion of the heat pipe  44  where it condenses back into the liquid phase component, thus giving off heat. The liquid phase component of the working fluid returns back to the high temperature portion of the heat pipe  44  by moving up the wick via capillary action. Heat pipes are well-known by those skilled in the art and may comprise shapes other than those depicted in  FIG. 2  and  FIG. 3 . 
   According to the embodiment depicted in  FIG. 2 , the heat pipe  44  spans between both of the rails  28 . The heat pipe  44  transports heat generated from the electronic components  36  to both of the rails  28 . It should be appreciated that alternate embodiments could use multiple heat pipes  44 , with each heat pipe  44  only transferring heat in a single direction. 
   Since  FIG. 2  is a cross-section, only one heat pipe  44  is visible. However, embodiments may include two or more heat pipes  44  to aid in the cooling of the detector assembly  20 . Since the detector assembly  20  is mounted on the rotatable gantry portion  14  (shown in  FIG. 1 ) and subject to a centrifugal loading when the CT system  10  (shown in  FIG. 1 ) is scanning, it may be advantageous to position the heat pipe  44  so that both the high temperature portion of the heat pipe  44  and the low temperature portion of the heat pipe  44  are generally the same radial distance from the axis of rotation of the rotatable gantry portion  14 . 
   According to an embodiment, the heat pipe  44  may optionally be electrically connected to the rail  28  by a bushing  46  or another form of an electrical conductor. The bushing  46  serves to electrically ground the heat pipe  44 . If an embodiment does not include the bushing  46 , it may still be important to electrically ground the heat pipe  44  in another manner so that the heat pipe  44  does not act as an antenna. 
   According to an embodiment, the CT system  10  (shown in  FIG. 1 ) may use a liquid coolant  48  to remove heat from the rails  28 . For example, each rail  28  may optionally define a passageway  50  for retaining the liquid coolant  48 . The liquid coolant  48  would pass through the passageway  50  absorbing heat from the rail  28 . While not shown in  FIG. 2 , the passageway  50  forms part of a liquid cooling circuit. After absorbing heat from the rail  28 , the liquid coolant  48  travels to a heat exchanger (not shown). The liquid coolant  48  gives off heat to the heat exchanger before cycling back through the passageway  50  defined by the rail. It should be understood that the cooling circuit may be configured differently according to additional embodiments. Additionally, other embodiments may not use the liquid cooling circuit. Instead, they may remove the heat from each rail  28  by another mechanism, such as forced air cooling as is well-known by those skilled in the art. 
   Referring to  FIG. 3 , a schematic cross-sectional view taken along section A-A of  FIG. 2  is shown in accordance with an embodiment. Common components between  FIG. 2  and  FIG. 3  share common reference numbers. 
   The scintillator  32  and the photodiode layer  34  are mounted to the flex circuit  38  on the radially inner side  40  of the substrate  30 . According to an embodiment, the substrate  30  is generally I-shaped in cross section, as shown in  FIG. 3 . The substrate  30  should be stiff in order to minimize motion of the scintillator  32  and the photodiode layer  34  while scanning. Additionally, the substrate  30  should be light due to the high g-loading caused by the rotation of the rotatable gantry portion  14  (shown in  FIG. 1 ). Designing a substrate  30  with a generally I-shaped cross section helps accomplish both of these goals. However, it should be understood that it would be possible to design a substrate  30  meeting the stiffness and weight criteria with either a generally I-shaped cross section that is different from the one shown in  FIG. 3  or with a cross-section of a completely different shape. 
   In the embodiment shown in  FIG. 3 , the substrate defines a recessed area  52  for securing each of the heat pipes  44 . The heat pipes  44  fit completely within the recessed areas  52  defined by the substrate  30  and are held in place with a thermal interface material  54 . The thermal interface material  54  secures the heat pipes  44  to the substrate  30  and conducts heat from the substrate  30  to the heat pipe  44 . According to an embodiment, the thermal interface material  54  may be an epoxy or a solder. It is important to understand that not all embodiments of the invention need to have a thermal interface material  54 . For example, the recessed area  46  may be shaped to retain the heat pipe  44  without the need for a thermal interface material  54  with adhesive qualities. One example of this includes a substrate with a cylindrical recessed area adapted to retain the heat pipe  44  via a press fit. Additional embodiments may include welding or brazing the heat pipe  44  to the substrate  30 . For the purposes of this disclosure, the term recessed area also includes hollow areas of the substrate  30  that would be capable of surrounding the whole circumference of the heat pipe  44 . 
     FIG. 3  schematically illustrates how the flex circuit  38  wraps generally around the perimeter of the substrate  30  according to an embodiment. The flex circuit  38  connects the electronic components  36  on the radially inner side  40  of the substrate  30  to the electronic components  36  on the radially outer side  42  of the substrate  30 . According to an embodiment, the flex circuit  38  fits partially within the recessed area  52  defined by the substrate  30 . According to the embodiment shown in  FIG. 3 , the flex circuit  38  is attached to the thermal interface material  54 . According to other embodiments, the flex circuit  38  may be directly attached to the heat pipe  44 . The recessed area  52  defined by the substrate  30  may provide advantages during the manufacturing of the detector modules. For example, if the flex circuit  38  is attached first to both the radially inner side  40  of the substrate  30  and to the radially outer side  42  of the substrate  30 , the recessed area  52  will accommodate any slack left in the flex circuit  38 . By taking up the slack in the flex circuit  38 , the recessed area  52  relaxes the tolerances needed for both the substrate  30  and the flex circuit  38 . According to other embodiments, the flex circuit  38 , may be electrically connected to the heat pipe  44 , or the flex circuit  38  may be electrically connected to the thermal interface material  54  in order to electrically ground the heat pipe  44 . 
   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. 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 language of the claims.