Patent Application
20130037251
The subject matter described herein relates generally to imaging detectors, such as computed tomography (CT) detectors, and more particularly, to a cooling system for CT detectors.
CT detectors may include a detector rail having a plurality of detector components positioned thereon. The detector components also may include a collimator having openings formed therein to direct x-rays emitted from a subject to a scintillator. The collimator separates the x-rays along the scintillator. The x-rays are then converted to light waves with a plurality of photodiodes positioned behind the scintillator. An analog-to-digital convertor converts the analog light waves to digital signals that can be generated into an image of the subject.
Generally, the detector components of the CT detector generate a considerable amount of heat. The detector components may be sensitive to the heat generated by the CT detector. For example, the heat may cause the detector components to shift on the detector rail. As such, the openings of the collimator may become misaligned with openings in the scintillator, leading to scatter or noise in an image generated by the CT detector. Additionally, some detector components are sensitive to changes in temperature. For example, the photodiodes may overheat or become damaged if exposed to large changes in temperature. This is particularly problematic given that large amounts of heat are generated by the analog-to-digital converter which is positioned adjacent to the photodiodes.
Conventional means to cool heat generated by the CT detector include cooling the detector with fans, heat sinks, or the like. However, such methods do not maintain a temperature of the CT detector, but rather, merely supply cooled air to the components. As such, temperature variations still exist within the CT detector, leading to shifting of the detector components and/or sensitivity of the components. Other CT detectors do not attempt to cool the components, but rather, compensate for heat within the detector through software. In particular, the temperature of the CT detector is monitored and data acquisition and image formation are compensated for based on the detected temperature. Such methods may be undesirable as software corrections may lead to error within the data.
In one embodiment, a computed tomography (CT) detector is provided having a detector rail. An x-ray detector is positioned on the detector rail. The x-ray detector includes a plurality of detector components. At least some of the detector components are configured to detect x-rays. A liquid cooled thermal control system is provided having cooling channels in thermal communication with the detector rail. The cooling channels have a cooling fluid flowing therethrough to control a temperature of the detector components in response to one or more disturbances that changes a temperature of the x-ray detector. A control module is provided in the liquid cooled thermal control system to adjust parameters of the liquid cooled thermal control system in response to the disturbances.
In another embodiment, a liquid cooled thermal control system for a computed tomography (CT) detector is provided. One or more cooling channels are provided in thermal communication with a detector rail of the CT detector. The cooling channels have a cooling fluid flowing therethrough to control a temperature of detector components positioned on the detector rail in response to one or more disturbances that changes a temperature of the detector rail. A heat exchanger is provided for receiving heated cooling fluid from the cooling channels. The heat exchanger cools the cooling fluid. A heater is also provided for receiving the cooled cooling fluid from the heat exchanger. The heater heats the cooled cooling fluid from the heat exchanger and discharges the cooling fluid into the cooling channels. A control module is provided for controlling at least one of the heat exchanger, the heater, or a fan of the heat exchanger to control a temperature of the cooling fluid.
In yet another embodiment, a method of cooling detector components of a computed tomography (CT) detector is provided. The method includes controlling a liquid cooled thermal control to control a temperature of a cooling fluid at a predetermined temperature. The cooling fluid is cooled to the predetermined temperature with the liquid cooled thermal control. The cooling fluid is discharged into cooling channels positioned in thermal communication with a detector rail of a CT detector having a plurality of detector components. The cooling fluid in the cooling channels controls a temperature of the detector components at the predetermined temperature.
The presently disclosed subject matter will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:
The foregoing summary, as well as the following detailed description of certain embodiments, will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors, controllers, circuits or memories) may be implemented in a single piece of hardware or multiple pieces of hardware. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
Although the embodiments are described with respect to a computed tomography (CT) detector, it should be noted that the liquid cooled thermal control described herein may be modified for use with other detectors or systems. For example, the liquid cooled thermal control may be utilized at least with a Positron Emission Tomography (PET) system, a Single Photon Emission Computed Tomography (SPECT) system, a Magnetic Resonance Imaging (MRI) system, and/or an X-ray system, among others. In one embodiment, the liquid cooled thermal control may be utilized with detectors formed from different materials.
An accumulator 106 and a pump 108 are positioned downstream from the cooling channels 104. The accumulator 106 receives cooling fluid from the cooling channels 104. The amount of cooling fluid received in the accumulator 106 may depend on a pressure of the cooling fluid within the thermal control system 100, as described below. The pump 108 is positioned downstream of the accumulator 106 to control a flow of the cooling fluid thorough the thermal control system 100. The pump 108 may be a single speed pump or a variable speed pump.
The pump 108 discharges the cooling fluid downstream to a heat exchanger 110. The heat exchanger 110 may be any suitable heat exchanger, for example, an air-to-liquid heat exchanger or a liquid-to-liquid heat exchanger. In the illustrated embodiment, the heat exchanger 110 is an air-to-liquid heat exchanger having a fan 112. From the heat exchanger 110, the cooling fluid flows downstream to a heater 114. The heater 114 may be an electric heater, a gas heater, or any other suitable heater. The heater 114 discharges the cooling fluid downstream to the cooling channels 104.
During operation, the cool channels 103 receive the cooling fluid from the heater 114. The cooling fluid is provided at a predetermined temperature that is configured to maintain a temperature of the detector rails 102. The cooling fluid in the cooling channels 104 cools the detector rails 102 by receiving heat from the detector rails 102 through at least one of thermal induction or convection. The heated cooling fluid then flows through the hot channels 105 downstream to the accumulator 106. The accumulator 106 stores a portion of the cooling fluid based on a pressure within the thermal control system 100. For example, when the thermal control system 100 is operating at high pressures, the accumulator 106 may store more cooling fluid than when the system 100 is operating at low pressures. The accumulator 106 stores the cooling fluid to maintain a constant operating pressure of the thermal control system 100. The accumulator 106 accounts for expansion of the cooling fluid at high pressures and may be utilized to pressurize the pump 108, thereby, preventing cavitation within the pump 108.
The pump 108 receives cooling fluid from the accumulator 106. The pump 108 may be a variable speed pump that is controlled to adjust an amount of cooling fluid discharged to the heat exchanger 110. By controlling a speed of the pump 108, a temperature of the cooling fluid may be controlled. For example, increasing a speed of the pump 108 increases the liquid flow rate as the cooling fluid travels through the heat exchanger 110, which increases the cooling rate. Conversely, decreasing a speed of the pump 108 decreases the liquid flow rate as the cooling fluid flows through, the heat exchanger 110, which decreases the cooling rate. In one embodiment, the pump 108 discharges the cooling fluid to the heat exchanger 110 at rate configured to achieve the predetermined temperature of the cooling fluid.
In one embodiment, the heat exchanger 110 receives the cooling fluid from the pump 108. The heat exchanger 110 cools the cooling fluid to a temperature below the predetermined temperature. The fan 112 of the heat exchanger 110 may be controlled to adjust the temperature of the cooling fluid. For example, the fan 112 may be operated at a higher speed to increase the amount of cooling of the cooling fluid. Conversely, the fan 112 may be operated at a lower speed to decrease the amount of cooling of the cooling fluid. The speed of the fan 112 is controlled to achieve cooling of the cooling fluid to below the predetermined temperature.
The cooling fluid is discharged from the heat exchanger 110 downstream to the heater 114. The heater 114 heats the cooling fluid from below the predetermined temperature to the predetermined temperature. In particular, the heater 114 is capable of fine tuning the temperature of the cooling fluid, whereas, the heat exchanger 110 may not be capable of providing precise temperatures. Accordingly, the heat exchanger 110 is utilized to reduce the temperature of the cooling fluid to below the predetermined temperature. The heater 114 then fine tunes the temperature of the cooling fluid to achieve the predetermined temperature. The power supplied to the heater 114 may be controlled to adjust the temperature of the cooling fluid. By adjusting the power supplied to the heater 114, the heat produced by the heater is adjusted. For example, the heater 114 may be operated at a higher power to provide additional heating of the cooling fluid. Conversely, the heater 114 may be operated at a lower power to reduce an amount of heating of the cooling fluid. The heater 114 discharges the cooling fluid into the cool channels 103 at the predetermined temperature to maintain a temperature of the detector rails 102.
In various embodiments, the control system 100 is utilized to maintain a temperature of the detector rails 102 at a steady-state temperature. The control system 100 facilitates reducing or preventing changes in the temperature of the detector rails 102. The control system 100 may adjust several parameters to control the temperature of the cooling fluid. For example, any one of a speed of the pump 108, a speed of the fan 112, or a power of the heater 114 may be adjusted to achieve the predetermined temperature of the cooling fluid.
In one embodiment, the control system 100 may also be utilized to reduce a warm-up time of the CT detector. For example, the heat exchanger 110 may be shut-off and the heater 114 may be operated at a higher power to supply heated cooling fluid to the cooling channels 104. The heated cooling fluid may reduce the time required to warm-up the CT detector. In another embodiment, the heater 114 may be used to increase the dynamic range of air temperatures or gantry rotations to maintain the liquid temperature.
In the illustrated embodiment, the cooling channels 104 extend through the detector rail 102. The cooling channels 104 are in thermal contact with and receive heat from the detector rail 102 to maintain the detector rail 102 at a constant or nearly constant temperature, such as within a tolerance or variance range The cooling channels 104 may maintain a temperature of the detector rails 102 within a range for normal detector operation. In particular, if the temperature of the detector rail 102 changes during operation, the detector rail 102 may contract and/or expand. Contraction and/or expansion of the detector rail 102 may result in shifting of the detector components. For example, the collimator 118 and the scintillator 124 may shift, causing the openings 122 of the collimator 118 to become misaligned with the openings 126 of the scintillator 124. Such misalignment may result in scatter and/or noise in the image data. The cooling channels 104 maintain a temperature of the detector rail 102 to reduce the amount of or to prevent contraction and/or expansion of the detector rail 102, thereby reducing or preventing shifting of the detector components. As such, the cooling channels 104 facilitate maintaining alignment of the openings 122 of the collimator 118 and the openings 126 of the scintillator 124.
The cooling channels 104 are also configured to receive heat 134 from the x-ray detector 116. The cooling channels 104 are in thermal contact with and receive heat from the x-ray detector 116 to maintain a constant or nearly constant temperature of the detector components. In particular, some components, for example, the photodiodes 128 may be sensitive to changes in temperature. Changes in temperature may cause the photodiodes 128 to become damaged and/or malfunction. The cooling channels 104 receive heat through thermal induction or convection from the x-ray detector 116 to maintain a temperature of the photodiodes 128 and other detector components to reduce the likelihood of or prevent damage to and/or malfunctioning of the components.
The cooling fluid flows downstream to the heat exchanger 110 and enters the heat exchanger 110 at an input 150 at a temperature that is greater than the predetermined temperature. The heat exchanger 110 operates at a fan speed, for example, based on a fan speed control signal 111, to reduce the temperature of the cooling fluid to an output 152 at a temperature that is below the predetermined temperature. The cooling fluid then travels downstream to the heater 114. The cooling fluid enters the heater 114 at or about at the temperature of the fluid at the output 152. The heater 114 is operated at a power level that defines a heating level, for example, based on a heat control signal 115, to heat the cooling fluid to the predetermined temperature. The heater 114 discharges the cooling fluid to the module 140 as input cooling fluid 142. The flow rate control signal 148 of the pump 108, the fan speed control signal 111 of the heat exchanger 110, and/or the heat control signal 115 of the heater 114 may be adjusted to control a temperature of the input cooling fluid 142.
The control module 160 is in communication with the pump 108, the fan 112 of the heat exchanger 110, and the heater 114. The control module 160 is configured to control the operation of any one or more of the pump 108, the fan 112, or the heater 114. For example, the control module 160 may control a speed of the pump 108, a speed of the fan 112, and/or a power level of the heater 114. The control module 160 receives a temperature input signal 162 indicative of the temperature of at least one of the detector rail 102 or the x-ray detector 116 (both shown in
The control module 160 determines a difference between the temperature input signal 162 and the temperature setpoint 164 to determine adjustments to the control system 100. For example, the control module 160 adjusts the operation of the control system 100 to achieve a temperature based on the temperature input signal 162 (which may be a feedback signal) that is substantially equivalent to the temperature setpoint 164. For example, the control module 160 may adjust a speed of the fan 112, a speed of the pump 108, a power level of the heater 114, or any combination thereof to achieve a temperature level that is substantially equivalent or equal to the temperature setpoint 164.
The control system 200 also includes an outer control loop 222. The outer control loop 222 includes a control module 224 that receives a temperature input 226 (e.g. measured temperature or temperature signal) from the x-ray detector 204. The control module 224 also receives an x-ray detector temperature setpoint 228. Based on a comparison of the temperature input 226 and the temperature setpoint 228, the control module 224 may adjust the cooling fluid temperature setpoint 220. Accordingly, the control system 200 includes two feedback loops capable of adjusting at least one of the pump flow rate 214, the fan speed 218 of the heat exchanger 206, or the heater output 221 to control a temperature of the cooling fluid. The inner control loop 201 and the outer control loop 222 may operate independently or separately.
The control system 250 also includes an outer control loop 274 having an outer control module 276. A control module 276 receives a detector module temperature input 278 (e.g. measured temperature or temperature signal) and a detector module temperature setpoint 280. Based on a comparison of the detector module temperature input 278 and the detector module temperature setpoint 280, the control module 276 may adjust the cooling fluid temperature setpoint 264. Accordingly, the control system 250 includes two feedback loops capable of adjusting at least one of the pump flow rate 268 of the pump 258, the fan speed 270 of the heat exchanger 254, or the heater output 272 of the heater 256 to control a temperature of the cooling fluid. The inner control loop 260 and the outer control loop 274 may operate independently or separately.
As illustrated in
The method 500 further includes cooling 504 the cooling fluid to the predetermined temperature with the liquid cooled thermal control system. A control module may adjust 506 parameters of the liquid cooled thermal control system in response to the disturbances. For example, in one embodiment, a control module of the liquid cooled thermal control system may adjust 508 an output of the heat exchanger. In another embodiment, the liquid cooled thermal control system may adjust 510 an output of the heater. In yet another embodiment, the liquid cooled thermal control system may adjust 512 an output of the fan. Moreover, the liquid cooled thermal control system may adjust 514 an output of at least one of an accumulator or a pump. In an exemplary embodiment, the liquid cooled thermal control system may carry out any combination of the adjustment steps 508, 510, 512, and/or 514.
The method 500 also includes discharging 516 the cooling fluid into cooling channels positioned in thermal communication with a detector rail of a CT detector having a plurality of detector components. The cooling fluid in the cooling channels controls a temperature of the detector components at the predetermined temperature.
In one embodiment, an initial conductance of the heat exchanger is defined as:
G=Total Heat load/ITD=Qtotal/(Tliq-hot−Tair)
By Varying an air flow rate (e.g. varying the cubic feet per minute of airflow by adjusting a fan speed within the liquid cooled thermal control system) the conductance may be varied to control a liquid temperature for various air temperature conditions within the gantry. For a heat exchanger design the initial conductance is function of air flow rate (CFM) and liquid flow rate (GPM). Using these two variables, the outlet liquid temperature of the heat exchanger can be controlled. A fan speed control in the heat exchanger may reduce an error from a set-point.
An inline heater may be used in a control loop to fine tune the control of liquid temperature. A heater power may be manipulated to fine tune the liquid temperature outlet at the inline heater that is fed to the detector. In some embodiments, a power could be variable with a convection boundary condition changing along with air temperature changes. In such embodiments, a cascade loop is incorporated, where an inner loop controls the liquid inlet temperature to the detector using the fan, and/or the pump and/or the inline heater while an outer loop feedbacks the detector module temperature and thereby resets the inner loop liquid temperature for control.
Referring to
Rotation of components on the gantry 404 and the operation of the x-ray source 406 are controlled by a control mechanism 416 of the CT imaging system 400. The control mechanism 416 includes an x-ray controller 418 that provides power and timing signals to the x-ray source 406 and a gantry motor controller 420 that controls the rotational speed and position of components on the gantry 404. A data acquisition system (DAS) 422 in the control mechanism 416 samples analog data from the detectors 402 and converts the data to digital signals for subsequent processing. An image reconstructor 424 receives sampled and digitized x-ray data from the DAS 422 and performs high-speed image reconstruction. The reconstructed image is applied as an input to a computer 426 that stores the image in a storage device 428. The image reconstructor 424 can be specialized hardware or computer programs executing on the computer 426.
The computer 426 also receives commands and scanning parameters from an operator via a console 430 that has a keyboard and/or other user input and/or marking devices, such as a mouse, trackball, or light pen. An associated display 432, examples of which include a cathode ray tube (CRT) display, liquid crystal display (LCD), or plasma display, allows the operator to observe the reconstructed image and other data from the computer 426. The display 432 may include a user pointing device, such as a pressure-sensitive input screen. The operator supplied commands and parameters are used by the computer 426 to provide control signals and information to the DAS 422, x-ray controller 418, and gantry motor controller 420. In addition, the computer 426 operates a table motor controller 434 that controls a motorized table 436 to position the patient 412 in the gantry 404. For example, the table 436 moves portions of the patient 412 through a gantry opening 438.
Various embodiments provide a thermal control system that may be mounted to and receives heat from detector rails and/or cold plates to receive heat from the detector components. The thermal control system has a controlled temperature (e.g. substantially constant temperatures) cooling fluid circulating therethrough to maintain the detector rails at constant temperature, for example, in response to one or more disturbances that fluctuates or changes a temperature of the detector rails or an x-ray detector coupled to the detector rails. The cooling fluid temperature is controlled in various embodiments using a heat exchanger, a heater, and a pump that act as actuators for temperature control. A fan speed of the heat exchanger may be controlled using a control module based on error in the cooling fluid temperature required and a measured cooling fluid temperature. The heater power also may be modulated to control the cooling fluid temperature supplied to the detector rails. A pump speed also may be controlled to achieve a required cooling fluid flow rate through the thermal control system.
In various embodiments, the control module parameters are calculated based on a difference in cooling fluid temperature and air temperature to account for the gain differences required to achieve temperature control. In one embodiment, a feedback in a cascade outer loop is provided to change a cooling fluid temperature setpoint to compensate for heat load changes in the detector components. Alternately, a surface heater may be mounted to the cold plate and/or detector rails. A power of the heater is modulated to control the rail temperature where the thermal control system is mounted.
At least one technical effect of some embodiments is maintaining a constant detector electronics temperature.
Various embodiments described herein provide a tangible and non-transitory machine-readable medium or media having instructions recorded thereon for a processor or computer to operate an imaging apparatus to perform an embodiment of a method described herein. The medium or media may be any type of CD-ROM, DVD, floppy disk, hard disk, optical disk, flash RAM drive, or other type of computer-readable medium or a combination thereof.
The various embodiments and/or components, for example, the modules, or components and controllers therein, also may be implemented as part of one or more computers or processors. The computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus. The computer or processor may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as a floppy disk drive, optical disk drive, and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.
As used herein, the term “computer” or “module” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer”.
The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine.
The set of instructions may include various commands that instruct the computer or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments of the subject matter described herein. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to user commands, or in response to results of previous processing, or in response to a request made by another processing machine.
As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments of the described subject matter without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the invention, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to one of ordinary skill in the art upon reviewing the above description. The scope of the various embodiments of the inventive subject matter should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “Wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose the various embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the various embodiments of the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments 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 the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal languages of the claims.
