Continuous cooling system for diagnostic medical imaging devices

Abstract

A passive continuous cooling system for continuously absorbing waste heat generated by a diagnostic imaging system during a patient scan when there is a power shortage or interruption in the cooling water supply within the imaging equipment, comprising one or more phase-change materials (PCMs), which maintain the temperature of the cooling system at the melting point of the materials while absorbing the waste heat of the imaging system. This allows the clinician to complete the ongoing imaging scan of the patient within the operating temperature specifications of the scanning system. In some embodiments, the PCMs absorb instantaneous thermal spikes that occur during the patient scan to maintain a relatively constant operating temperature of the cooling system. In some embodiments, a passive continuous cooling system is used to cool a PET / CT, PET, or CT imaging system.

Description

Technical Field

[0001] It relates to a cooling system for a diagnostic medical imaging device. More specifically, it relates to a passive continuous cooling system that continuously absorbs the heat generated by the imaging device in a situation where there is a power shortage or interruption in the cooling water supply within the imaging facility.

Background Art

[0002] Non-exclusive examples of diagnostic imaging devices include computed tomography (CT), digital radiography (DR), positron emission tomography (PET), magnetic resonance imaging (MRI), PET / CT, and PET / MRI modalities. Many of these imaging devices or systems include a donut-shaped (or toroidal) rotating gantry structure into which a patient table is inserted. This gantry surrounds the patient table and is equipped with one or more electromagnetic emission detectors, which emit electrons in response to incident photons of electromagnetic radiation. In some modalities, these incident photons are transmitted X-rays (e.g., CT) or radiation emissions, located at the higher end of the electromagnetic frequency range (e.g., PET), while in others, these incident photons are within the radio frequency range (e.g., MRI). The output electrons of the detector are processed by the detector electronic circuit to generate a detector output signal, which is then processed by an imaging device to generate a patient image. An exemplary electromagnetic radiation detector includes multiple photomultiplier tubes (PMTs) and multiple silicon photomultiplier tubes or silicon photomultipliers (SiPMs). Often, the detector electronic package is housed within a gantry structure along with the detector. To generate usable patient image information during patient scanning, the detector and detector electronic package (collectively referred to as the photon detector assembly (PDA)) are maintained within a relatively narrow maximum operating temperature and acceptable temperature fluctuation bandwidth window. Exceeding the desired temperature fluctuation and operating temperature bandwidth window can lead to inaccurate detector readings and / or excessive noise generation during reading, potentially degrading the quality set of the patient image.Generally, if the PDA temperature exceeds its maximum operating temperature window specification, the scanning system's operation control terminates the scanner operation and initiates a system shutdown.

[0003] During and between patient scans, the gantry and other components of the imaging system generate heat in a periodically fluctuating manner. To maintain the PDA detectors and their electronic components within a desired temperature bandwidth window, the heat generated within the gantry structure is transferred from the gantry to an external cooling system. Some external cooling systems are closed-loop cooling systems, in which waste heat captured by the internal cooler within the scanner is absorbed by a liquid coolant (or coolant fluid) such as glycol or water. The coolant in the closed loop is then cooled by a heat sink (or heat absorber), such as a liquid / liquid heat exchanger, to transfer the heat of the coolant to the water system of the imaging equipment.

[0004] If the water supply (or water supply) of the above equipment to the external heat exchanger of the external cooling system is interrupted, the coolant temperature will rise above the PDA's maximum temperature window specification, leading to a shutdown of the scanning system. The scanning system has a limited run time before it begins to overheat. This run time may vary depending on the operating state of the system, but in many cases, this time is not sufficient to complete a patient scan.

[0005] If the system water supply is interrupted while a patient is being scanned, the scan will be stopped, causing inconvenience to the patient as another scan will need to be scheduled. Patients whose PET scans are stopped have already been injected with relatively expensive radioactive tracers. If a new PET scan is to be rescheduled, another radioactive tracer will need to be injected, resulting in additional time and cost for both the patient and the imaging equipment. If the PET scanner could continue operating for another 10 minutes or so after the water supply interruption, the scan might be completed, eliminating the need to reschedule the procedure. [Overview of the project] [Means for solving the problem]

[0006] The exemplary embodiments described herein relate to a passive, continuous cooling system that, during a patient scan, continues to absorb waste heat generated within the diagnostic imaging system in the event of power shortages or interruptions in the cooling water supply within the associated imaging equipment. This passive, continuous cooling system includes one or more Phase Change Materials (PCMs), which maintain the temperature of the cooling system at the melting point of the material while absorbing waste heat from the imaging system. The cooling system incorporates sufficient thermal mass (or thermal mass) of the PCMs to absorb waste heat from the imaging system in enough time to complete the imaging scan before all of the material melts. This allows the clinician to complete the ongoing imaging scan of the patient within the operating temperature window specification of the scanning system. In some embodiments, multiple PCMs absorb instantaneous (or transient) thermal spikes that occur during the patient scan in order to maintain the operating temperature of the cooling system relatively consistently within the specification window of the imaging system. In exemplary embodiments, the PET / CT scanner includes a passive continuous cooling system incorporating one or more PCMs. In other exemplary embodiments, the PET scanner includes a passive continuous cooling system incorporating one or more PCMs. In other exemplary embodiments, both or either the CT scanner and the PET / CT scanner incorporate a PCM within the sub-cooling system of their X-ray source.

[0007] Exemplary embodiments of this disclosure disclose features of a passive continuous cooling system for a diagnostic medical imaging scanner. The system includes a diagnostic medical imaging scanner, which is selected from a group of imaging modalities consisting of PET, CT, and combined PET / CT. The scanner has a patient table enclosed by a gantry and a photon detector assembly (PDA) coupled to the gantry. The PDA has a maximum operating temperature window during patient imaging scans. The internal cooler within the scanner is in thermal communication (or thermal transmission) with the gantry and the PDA. This internal cooler has a coolant inlet and a coolant outlet, and captures the internal waste heat generated within the scanner during patient imaging scans to maintain the PDA's temperature below its maximum operating temperature window. The external cooling system outside the scanner circulates liquid coolant in a closed-loop coolant conduit, directing it towards the coolant intake and outlet of the internal cooler. As the circulating coolant flows through the internal cooler, it extracts internal waste heat captured from the internal cooler. The external cooling system includes a liquid / liquid external heat exchanger in a closed-loop conduit upstream of the coolant inlet of the internal cooler, which extracts heat from the circulating coolant and transfers it to the water supply of the equipment's water system. In this case, the heat transfer rate through the external liquid / liquid heat exchanger is sufficient to maintain the temperature of the coolant at the coolant inlet of the internal cooler below the maximum operating temperature window of the PDA. A heat sink is positioned downstream of the external heat exchanger and upstream of the coolant inlet of the internal cooler, within the closed-loop coolant conduit. This heat sink contains a first-phase transition material (PCM), which is oriented outward from the conduit and in conductive thermal communication with the coolant. The melting temperature of the first PCM is below the maximum operating temperature window of the PDA and below the temperature of the coolant flowing out of the liquid / liquid external heat exchanger. When the temperature of the coolant flowing into the heat sink exceeds the melting temperature of the first PCM, the material absorbs latent heat from the coolant to keep the temperature at the coolant inlet below the maximum operating temperature window of the PDA for a specified duration sufficient to perform a complete patient scan.

[0008] In some embodiments, the continuous cooling system further includes a CT scanner equipped with a rotary CT gantry. The rotary CT gantry includes an X-ray source held in a sealed X-ray housing and an oil cooler that is in thermal communication with the internal cooler in the scanner. The oil cooler includes a closed-loop oil conduit, which is coupled to the X-ray housing and includes an inlet and outlet line for flowing oil, an oil pump for circulating oil within the oil conduit to cool the X-ray source, and a second-phase change material (PCM) oriented outside the oil conduit so as to be conductively and thermally in communication with the circulating oil. The second PCM absorbs latent heat from the circulating oil during the solid-to-liquid phase transition, buffering the instantaneous heat spikes generated by the X-ray source during the patient imaging scan. The second PCM then transfers the absorbed latent heat to the scanner's internal cooler during the time intervals between the multiple instantaneous heat spikes that occur.

[0009] In some embodiments, the continuous cooling system further includes a PET / CT scanner, each scanner unit including a gantry having a PDA inside, and each gantry surrounding a patient table. The CT scanner described above includes a second PCM within a rotating gantry, as mentioned above. Both the PET and CT scanner modalities share a common external cooling system, as described above. The PET coolant inlet of the PET internal cooler described above is oriented into the closed-loop coolant conduit downstream of the CT coolant outlet of the CT internal cooler described above. The second PCM of the oil cooler of the CT scanner retains the latent heat absorbed by the X-ray source when the water supply to the external heat exchanger of the external cooling system is interrupted, thereby reducing the latent heat absorbed by the first PCM in the heat sink of the external cooling system.

[0010] Another exemplary embodiment of the present disclosure features a method for passively and continuously cooling a diagnostic medical imaging scanner in the event of an interruption in the supply of cooling water to the equipment's water-cooled external cooling system for the diagnostic medical imaging scanner. This method is performed using a diagnostic imaging scanner selected from a group of imaging modalities consisting of PET, CT, and combined PET / CT. The scanner comprises a patient table surrounded by a gantry and a photon detector assembly (PDA) coupled to the gantry. The PDA has a maximum operating temperature during the patient imaging scan. The scanner has an internal cooler, which is in thermal communication with the gantry and the PDA. The internal cooler has a coolant inlet and a coolant outlet, and captures the internal waste heat generated within the scanner during the patient imaging scan to maintain the temperature of the PDA below its maximum operating temperature window. The external cooling system is positioned outside the scanner, circulating the liquid coolant within a closed-loop coolant conduit, directing it towards the coolant intake and outlet of the internal cooler. As the circulating coolant flows through the internal cooler, it is designed to extract the captured internal waste heat from the internal cooler. More specifically, the external cooling system includes a liquid / liquid external heat exchanger in a closed-loop conduit upstream of the coolant inlet of the internal cooler, which extracts heat from the circulating coolant and transfers it to the feedwater of the equipment's water system. In this case, the heat transfer rate through the external liquid / liquid heat exchanger is sufficient to maintain the temperature of the coolant at the coolant inlet of the internal cooler below the maximum operating temperature window of the PDA. During steady-state operation (or routine operation) of the external cooling system, the external heat exchanger transfers heat from the circulating coolant to the feedwater of the equipment's water system. The external cooling system further includes a heat sink in the closed-loop coolant conduit downstream of the external heat exchanger and upstream of the coolant inlet of the internal cooler, to provide backup, continuous cooling in the event of an interruption in the water supply to the equipment up to the external heat exchanger. The heat sink contains a first phase change material (PCM), which is oriented outward from the conduit and in thermal communication with the coolant. The melting temperature of the first PCM is below the maximum operating temperature of the PDA and below the temperature of the coolant flowing out of the external heat exchanger. When the above scanner is used to initiate an imaging scan of a patient, the above external cooling system circulates the coolant through the coolant loop, transferring heat from the circulating coolant to the water supply of the equipment's water system, thereby maintaining the PDA's temperature below its maximum operating temperature. In the event of an interruption in the water supply from the water system of the above equipment to the liquid / liquid external heat exchanger, the temperature of the coolant flowing into the heat sink is raised above the melting temperature of the first PCM, so that the material absorbs the captured internal waste heat removed from the internal cooler by the coolant as latent heat, instead of the external heat exchanger. The first PCM of the heat sink maintains the temperature at the coolant inlet below the maximum operating temperature of the PDA for a specified duration, sufficient to complete the patient scan. As a result, the patient scan is completed within the specified duration.

[0011] In another embodiment of the method, the second PCM is further oriented within the gantry to thermally communicate with the internal cooler to capture and buffer instantaneous spikes in internal waste heat generated within the scanner during patient imaging scans. In a steady state, the buffered waste heat is transferred from the second PCM to the internal cooler, and at this time, the external heat exchanger of the external cooling system transfers heat from the circulating coolant to the water supply of the water system of the facility. In the event that the water supply to the external heat exchanger is interrupted, the second PCM retains the additional waste heat generated within the scanner as latent heat until it is completely melted. This temporarily reduces the amount of waste heat that would otherwise be transferred to the coolant of the external cooling system, which could otherwise be transferred to the first PCM in the heat sink. Thus, the two PCMs share the load of waste heat transferred by the coolant when the water supply of the equipment to the external heat exchanger is interrupted.

[0012] Each feature of the exemplary embodiments described herein may be applied simultaneously in any combination or subcombination, or separately. The following detailed description, along with the accompanying drawings, further elaborates on exemplary embodiments of the present invention. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic side view of a combination of a PET / CT diagnostic imaging device and its cooling system for generating PET and / or CT images of a patient. [Figure 2] Figure 2 is a cross-sectional view of the PET scanner section of the imaging device and cooling system shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the CT scanner section of the imaging device and cooling system shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram of the first embodiment of the X-ray source and cooling subsystem of the CT scanner unit shown in Figure 3. [Figure 5] FIG. 5 is a schematic diagram of a second embodiment of the X-ray source of the CT scanner unit in FIG. 3 and the cooling subsystem. [Figure 6] FIG. 6 is a graph showing the temperature change over time of the phase change material when absorbing waste heat generated by a diagnostic medical imaging device. [Figure 7] FIG. 7 is a graph showing the periodic generation of waste heat by an exemplary CT scanner when generating CT images continuously five times. [Figure 8] FIG. 8 is a schematic diagram of the passive continuous cooling system of the PET / CT scanner in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] For ease of understanding, the same reference numerals are used to denote the same components common to the drawings, if possible. Note that the drawings are not drawn to an exact scale.

[0015] Exemplary embodiments of the present invention are used in a passive continuous cooling system that, in the event of a power shortage accident or interruption in the cooling water supply within the imaging facility, continues to absorb waste heat generated by a diagnostic medical imaging system, such as a PET, CT, or PET / CT imaging system, during a patient scan. This passive, continuous cooling system includes a "backup" passive heat sink. This passive heat sink incorporates one or more phase change materials (PCMs) that maintain the temperature of the cooling system at the melting temperature of the material while absorbing the waste heat of the imaging system during the melting transition stage (or transition phase) of the material. Thus, the clinician can complete the imaging scan during patient treatment within the operating temperature window specifications of the scanning system. In some embodiments, multiple PCMs absorb momentary (or transient) heat spikes that occur during a patient scan to maintain a relatively consistent cooling system operating temperature.

[0016] Phase-change materials absorb or release a relatively large amount of heat when their state or phase changes. When using a PCM in "standby" mode, the passive heatsink requires a sufficient mass of material to absorb heat from the PET system over a specified duration in order to complete the scan in progress after the interruption of the equipment water supply to the scanner's external cooling system. This period in this standby application is the maximum time required for the PET scan to be completed after the supply of equipment cooling water is interrupted. This period can be set between 7 and 10 minutes, but a longer period may be selected to allow for margin of error. Generally, the requirement for the external cooling system is that the cooling temperature of the equipment water supply is within the range of 4°C to 12°C. For example, the typical heat generated in a PET scanner to complete a PET scan is 3.2KW when the axial field of view (aFoV) of the scan is 25cm, and up to 10KW when the aFoV of the PET system is 1 meter long. The operating temperature of the PET PDA is in the range of 23°C. Based on this input information, it becomes possible to calculate the required mass / volume of PCM needed to maintain such a temperature for the required time.

[0017] Figures 1 to 3 show exemplary embodiments of a PET / CT imaging system 10. This PET / CT imaging system 10 includes a PET modality scanner 12, a coaxially aligned CT modality scanner 14, and a movable patient table 16. An image processing system 18 communicates with the PET scanner 12 via a communication path 20 and with the CT scanner 14 via a communication path 22. Waste heat generated by the PET / CT imaging system 10 is transferred to a cooling system 24 by a circulating coolant (e.g., water or glycol). In these figures, the cooling system 24 is shown as a functional block, showing all components of the cooling system located outside the PET / CT imaging system 10, including all components and interconnections shown in Figure 8. In Figure 1, the PET coolant inlet 26 receives circulating coolant (or recirculating coolant) from the cooling system 24, transfers waste heat generated in the PET scanner 12 to the circulating coolant, and returns the warmer coolant to the cooling system through the PET coolant outlet 28. Similarly, the CT coolant inlet 30 receives circulating coolant from the cooling system 24, transfers waste heat generated in the CT scanner 14 to the circulating coolant, and returns the warmer coolant to the cooling system through the CT coolant outlet 32. In the embodiment shown in Figure 8, the cooling systems of the CT14 and PET12 scanners are connected in series with the external cooling system 24, and the CT coolant outlet 32 ​​is located upstream of the PET coolant inlet 26. However, in other embodiments, the cooling systems of the CT14 and PET12 scanners can be connected in parallel with the external cooling system 24.

[0018] A cross-sectional view of the PET scanner 12 in Figure 2 shows a patient table 16 oriented within a patient tube 34, and a PET gantry 36 surrounding the patient tube. The PET gantry 36 is rotatable, as indicated by arrow C. However, in other embodiments, the PET gantry 36 may not be rotatable. The PET gantry 36 incorporates a detector electronics assembly (DEA) 38 as this PDA, along with a known detector and associated acquisition electronics. For simplicity, other known components within the PET gantry 36 (e.g., the DEA cooling subsystem and power supply) are not shown. Various embodiments of known cooling subsystems for the PET scanner 12 and this PET gantry 36 include an exhaust cooling fan, a liquid coolant channel and conductive heat sink, a radiator, and air / fluid and fluid / fluid heat exchangers called a PET internal cooler (cooler) 40 (shown as schematic blocks in the figure). The PET internal cooler 40 generally operates to maintain the DEA 38 within a predetermined ambient operating temperature bandwidth window (for example, in some embodiments, a window of 23°C ± 2°C; however, the parameter specifications of this window differ in other embodiments of the PET scanner). To this end, it transfers the waste heat generated in the PET scanner 12 to the circulating coolant received from the PET coolant inlet 26, and as a result, the warmer circulating coolant is discharged from the PET coolant outlet 28.

[0019] A cross-sectional view of the CT scanner 14 in Figure 3 shows a patient table 16 oriented within a patient tube 34, and a CT gantry 42 surrounding the patient tube. The CT gantry 42 is rotatable, as indicated by arrow C. The CT gantry 42 incorporates a CT Data Measurement System (DMS) 44 as its PDA, along with known detectors and associated acquisition electronics, and further incorporates an X-ray source that generates incident photons to be detected by the DMS. For simplicity, other known components within the CT gantry 42 (e.g., cooling subsystem and power supply) are not shown. Various embodiments of known cooling subsystems for the CT scanner 14 and its CT gantry 42 include exhaust cooling fans, liquid coolant channels and conductive heat sinks, radiators, and air / fluid and fluid / fluid heat exchangers referred to as CT internal coolers 47 (shown as schematic blocks in the figure). The CT internal cooler 47 generally operates to maintain the CT scanner 14 within a predetermined ambient operating temperature bandwidth window (for example, in some embodiments, a window of 23°C ± 2°C; however, this window differs in other embodiments of the CT scanner). To this end, it transfers the waste heat generated within the CT scanner to the circulating coolant received from the CT coolant inlet 30, and as a result, the warmer circulating coolant is discharged from the CT coolant outlet 32.

[0020] Of particular note is that the X-ray source 46 within the CT scanner 14 generates relatively hot waste heat that is periodically and instantaneously ejected during a CT scan, and this waste heat is absorbed into a circulating closed-loop oil cooling subsystem. The oil cooling subsystem includes an X-ray source housing 48, which surrounds the X-ray source 46 in cooling oil with a high flash point. An oil inlet line 52 circulates the cooling oil into the X-ray source housing 48, where it absorbs the heat generated by the X-ray source 46. The heated cooling oil circulates to exit the housing 48 via an oil outlet line 52 and is cooled by exemplary embodiments of an oil cooler 54 or 154 (shown as schematic blocks 54 / 154). Figure 4 shows an air-cooled oil cooler 54 of a first embodiment, while Figure 5 shows a liquid-cooled oil cooler 154 of a second embodiment.

[0021] In Figure 4, the air-cooled oil cooler 54 circulates cooling oil 56 using a cooling pump 58, which flows into the X-ray source housing 48 via an oil inlet 50. While inside the housing 48, the circulating oil 56 absorbs the heat generated by the X-ray source 46. The cooling pump 58 discharges the heated circulating oil 56 through an oil outlet line 52 and directs it into an oil radiator (oil heat sink) 60, where the oil is cooled again for circulation in a closed loop. The oil radiator 60 is a hybrid liquid / air heat transfer device with multiple cooling oil tubes 61 (only one is shown in Figure 4) that transfer heat to multiple cooling fins 62. These cooling fins transfer heat to the ambient air inside the CT gantry 42 by convection. A cooling fan 64 circulates ambient air over the cooling fins 62 to improve the rate of heat transfer by convection. Furthermore, the oil radiator 60 contains the thermal mass (or thermal formula mass) of the phase change material (PCM) 68, which, although it has conductive thermal communication (or heat transfer) with the circulating oil 56, is isolated from the oil and does not circulate with it. The advantage of fluidly isolating the PCM 68 from the cooling oil 56 is that it prevents the disintegration and entrapment of PCM particles in the oil, which can degrade the quality of the oil and potentially cause clogging of the cooling oil pipes 61 in the oil radiator 60. Referring to Figures 6 and 7, the physical properties of the PCM 68 and the performance advantages of the oil cooler 54 and cooling system 24 are described below. Specifically, the PCM 68 buffers the instantaneous temperature spikes generated by the X-ray source 46 during patient scanning. As a result, the waste heat released by the oil radiator 60 to the CT internal cooler 47 is more constant during scanning. In a CT scanner incorporating an oil cooler 54, ambient air in the CT gantry 42, heated by the oil radiator 60, is then cooled by an air / fluid heat exchanger in the CT internal cooler 47, where the waste heat is transferred through the CT coolant outlet 32 ​​and ultimately to the cooling system 24.

[0022] In Figure 5, the liquid-cooled oil cooler 154 uses a cooling pump 58 to circulate cooling oil 56 into the X-ray source housing 48 through the oil inlet 50. While inside the housing 48, the circulating oil 56 absorbs the heat generated by the X-ray source 46. The cooling pump 58 discharges the heated circulating oil 56 through the oil outlet line 52 into the oil / liquid coolant heat exchanger 160, where the oil is cooled for recirculation in a closed loop. The oil heat exchanger 160 is a hybrid liquid / liquid heat transfer device and has multiple cooling oil tubes 161 that conduct heat transfer to multiple coolant tubes 162. In Figure 5, for simplification, only one oil tube 161 and one coolant tube 162 are shown. The oil heat exchanger 160 also contains the thermal mass of a phase change material (PCM) 68, which has conductive thermal communication with the circulating oil 56 but is isolated from the oil and does not flow with it. Fluid isolation of the PCM 68 from the cooling oil 56 is advantageous in that it prevents the disintegration and entrainment of PCM particles in the oil, but these can degrade the quality of the oil and potentially cause clogging of the cooling oil pipes 161 in the oil heat exchanger 160. Referring to Figures 6 and 7, the physical properties of the PCM 68 and the performance advantages of the oil cooler 154 and cooling system 24 are described below. Specifically, the PCM 68 buffers the instantaneous temperature spikes generated by the X-ray source 46 during patient scanning. As a result, the waste heat released by the oil heat exchanger 160 becomes more constant during scanning. In a CT scanner incorporating the oil cooler 154, the coolant circulating in the coolant pipes 162 heated by the oil 56 is then cooled by the internal cooler 47. In this process, the waste heat is transferred through the CT coolant outlet 32 ​​and ultimately to the cooling system 24. In some embodiments of the CT internal cooler 47, the coolant pipe 162 transfers heat to a second fluid / fluid heat exchanger, but it is located between the CT coolant inlet 30 and the CT coolant outlet 32 ​​for further heat transfer to the cooling system 24. In other embodiments of the CT internal cooler 47, the coolant pipe 162 is directly coupled to the CT coolant inlet 30 and the CT coolant outlet 32 ​​for further heat transfer to the cooling system 24.

[0023] Figure 6 shows the continuous steady-state heating of a hypothetical PCM over time. The temperature of the PCM rises linearly up to time t1, but at that temperature, the PCM reaches its melting temperature T m Upon reaching a certain temperature, the PCM begins absorbing latent heat. The PCM maintains its melting temperature while absorbing the applied heat until all of its material becomes liquid (or liquefied) at time t2. After that, the PCM temperature rises. The time delay Δt at which the PCM maintains its melting temperature despite the continuous application of heat is a function of the applied heat in kilojoules (kJ), the heat storage capacity of the PCM in kJ / kg, and the mass (kg) of the material. For example, various paraffin waxes have a heat storage capacity of approximately 220 to 260 kJ / kg. The composition of the phase change material is selected from a group including, in other examples, positive temperature salt hydrates and / or positive temperature organics and / or high-temperature salts.

[0024] In an exemplary embodiment, the phase change material RT18HC, sold by Rubizerm Technologies GmbH (Berlin, Germany), has a heat storage capacity of 230 kJ / kg and a melting point (melting temperature) T mThe temperature is 18°C. As stated above in this specification, in order to determine the mass of the PCM required during "standby" mode, it is assumed that the cooling temperature of the equipment feedwater for the passive heat sink for the external cooling system is in the range of 4 to 12°C. It is also assumed that the typical heat generated by the PET scanner to complete a PET scan is 3.2KW for a 25cm axial field of view (aFoV) scan, and increases to 10KW for a PET system with a longer aFoV of 1 meter. The maximum temperature of the DEA operating temperature window specification for the PET is assumed to be in the range of 23°C. Assuming a time delay (Δt) of 10 minutes required to complete a PET scan, an exemplary PCM of 7.824 kg will dissipate 3KW of waste heat to keep the temperature below 23°C. Approximately 26 kg of the same material will dissipate 10KW of waste heat over the same period of time. Other exemplary PCM materials that could potentially be suitable for maintaining the DEA operating window temperature of exemplary PETs below 23°C include, but are not limited to, PureTemp18, sold by PureTemp LLC (Minneapolis, Minnesota, USA), CrodaTherm19, sold by Croda International Plc (East Yorkshire, UK), and PLUSICE A17, sold by PCM Products Ltd (Cambridgeshire, UK).

[0025] According to the latent heat absorption characteristics of the PCM68 in embodiments 54 and 154 of the oil cooler shown in Figures 4 and 5, these oil coolers enable buffering of instantaneous thermal spikes generated by the X-ray source 46 in the CT scanner 14 of the PET / CT scanner 10. If the PCM68 is not provided, the heat transfer capacity of the oil cooler must be sufficient to absorb the highest instantaneous temperature generated by the X-ray source 46 during a complete scan cycle. However, this is not concerned with the fact that these high-temperature pulses occur only irregularly and last only for a short time during a complete patient scan cycle. Figure 7 shows the actual heat transfer to the cooling water during five consecutive CT scans. After the second scan, the instantaneous heat transfer exceeds 6.6 kW. The thick line shows the calculated expected heat transferred and buffered by the exemplary PCM68 in the oil cooler. The maximum expected heat transfer buffered from the PCM68 to the rest of the cooling system 24 is 3.5 kW. Accordingly, by incorporating the PCM68 within the embodiment of the oil cooler 54 or 154, the overall cooling capacity required for the cooling system 24 is reduced to less than 3 kW. In some embodiments, the CT internal cooler 47 continuously transfers heat from the PCM68 to cool it, allowing the phase change material to re-solidify between multiple instantaneous heat spikes. In other embodiments, the supply of coolant to the CT internal cooler 47 is completely limited or stopped so that most or all of the heat generated by the X-ray source 46 is absorbed by the PCM68 during all or part of the CT imaging scan. In this other embodiment, the material in the PCM68 regenerates and returns to a solid state at a specified time later when the flow of coolant to the CT internal cooler 47 is sufficiently increased to allow solidification. In an exemplary embodiment, the PCM68 has a melting range around 70°C. In an exemplary embodiment, the PCM68 includes RT70HC material sold by Rubytherm Technology GmbH (Berlin, Germany).

[0026] Figure 8 is a schematic diagram of the passive continuous cooling system 24 of the PET / CT scanner 10, which shows a closed-loop coolant with a continuous flow of fluid circulating a liquid coolant such as water. Generally, the coolant flowing in the coolant loop absorbs heat generated by the PDA and various other components within the PET / CT scanner 10, such as the exemplary DEA 38 of the PET scanner 12, the DMS 44 with associated electronic equipment, and the X-ray source 46 of the CT scanner 14. The coolant circulating in the closed-loop transfers the heat absorbed from the components of the PET / CT scanner 10 to the equipment heat sink.

[0027] In this case, the equipment heat sink is the equipment's water system 80, which provides a flowing chilled water supply 82 into the intake loop of a liquid / liquid heat exchanger 84 at a temperature range between 4 and 12°C, after which warmer return water 86 flows out of the heat exchanger. The already circulated and heated coolant discharged from the PET / CT scanner 10 flows through the corresponding outlet loop of the external heat exchanger 84, transferring heat to the return water 86, typically lowering the temperature of the circulating refreshed coolant to approximately the same temperature as the chilled water supply 82.

[0028] After leaving the outer loop of the external heat exchanger 84, the circulating coolant passes through the PCM heatsink 88 at approximately the same temperature of 4 to 12°C. In some embodiments of the PCM heatsink 88, a phase change material is sealed in a reservoir tank to provide direct heat transfer and convection thermal communication with the circulating coolant. In other embodiments, the PCM heatsink 88 has a structure similar to a radiator, comprising multiple cooling tubes and fins, with the PCM sandwiched between some or all of the fins and cooling tubes, enabling direct conductive thermal communication with them. During steady-state operation of the coolant system 24, the temperature of the circulating coolant passing through the PCM heatsink 88 (approximately 4 to 12°C) is lower than the melting temperature of the phase change material contained therein. In exemplary embodiments, the melting temperature T of the PCM mThe temperature is 16°C. Therefore, during such steady-state operation, the phase change material remains passively in a solid phase at the refrigerant temperature, allowing it to absorb latent heat, and in that case, the refrigerant temperature is T m It will rise above that.

[0029] Referring to Figure 6, the thermal properties of an exemplary phase-change material are described. When the temperature of the circulating coolant reaches the melting temperature of the material in the PCM heatsink 88, which is 16°C, the material absorbs heat from the coolant and begins a phase change from solid to liquid. As a result, the temperature of the circulating coolant flowing out of the PCM heatsink 88 is maintained at the melting temperature of the material, 16°C, as long as the material remains inside the heatsink.

[0030] The heat-absorbing material within the PCM heatsink 88 contains sufficient thermal mass to absorb all the waste heat generated by the PET / CT scanner 10 within a specified operating time window, which is necessary to maintain the scanner components within their operating temperature window specifications (e.g., maintaining the DEA 38 of the PET scanner 12 at a maximum temperature of approximately 23°C). In an exemplary embodiment of the cooling system 24, the 26 kg mass of Rubytherm's RTHC 18 phase change material within the PCM heatsink 88 is capable of dissipating 10 kW of waste heat generated by the PET / CT scanner 10 for 10 minutes (approximately the time required to complete a patient diagnostic imaging scan). One non-limiting example of the cooling parameters required for the PET / CT scanner 10 is that the thermal mass within the PCM heatsink 88 is sufficient to maintain the DEA 38 of the PET scanner 12 within a temperature window not exceeding 23°C during the entire imaging cycle. Generally, the heat absorption capacity of the PCM heatsink 88 is equal to or greater than the equivalent heat absorption capacity of the heat exchanger 84, so the former can function as a passive replacement or "standby" heatsink for the cooling system 24 in the event of an interruption in the equipment water supply 82.

[0031] The first circulation pump 90 delivers cooled coolant from the PCM heat sink 88 through the CT internal cooler 47 to the coolant inlet 30 of the CT scanner 14. The heated coolant flows out of the CT coolant outlet 32, where its flow is then divided by the first bypass tee (or T-tube) 92, where some or all of the fluid is returned to the heat exchanger 84 through the second bypass tee 100. Thus, the heat exchanger 84, PCM heat sink 88, CT internal cooler 47, and the first and second bypass tees 92 and 100 form the first coolant loop. A second coolant loop is formed downstream of the first bypass tee 92, which flows through the mixing valve 94 into the PET coolant inlet 26, the PET internal cooler 40, and out through the PET coolant outlet 28, the second circulation pump 96, and the third bypass tee 98. The coolant flow discharged from the second circulation pump 96 is divided at the bypass tee 98, where a portion of the flow is returned to the mixing valve 94. The remainder of the coolant flow discharged from the third bypass tee 98 goes to the second bypass tee 100, which returns to the first cooling loop and back to the heat exchanger 84, refreshing and cooling the flow cycle through the first and second cooling loops and repeating. In an exemplary embodiment, the temperature of the refreshed coolant flowing out of the heat exchanger 84 is approximately 4 to 12°C. The mixing valve 94, as well as the circulation pumps 114 of the first 90 and second 96, adjust the flow rate and mixing ratio of the recirculating coolant, thereby achieving the desired heat absorption from the components within the PET / CT scanner 10. The mixing valve 94 is controlled by a control program running within the image processing system 18 or by another controller in the scanner 12, the latter based on temperature sensors located at the inlet (from tees 92 and 98) and outlet (to the PET coolant inlet 26) of the mixing valve.

[0032] The mixing valve 94 and the first circulation pump 90 circulate the coolant at a first flow rate in the first cooling loop between the CT scanner 14 and the cooling system 24, maintaining a stable temperature bandwidth designated for the components within the CT scanner (including the X-ray source 46). In an exemplary embodiment, the coolant flow rate in the first cooling loop and the heat transfer capacity of the heat exchanger 84 are calculated to maintain the temperature of the coolant flowing out of the CT coolant outlet 32 ​​at a temperature higher than the inlet temperature of 4 to 12°C and lower than 23°C.

[0033] The cooling temperature stability within the CT scanner 14 is enhanced by embodiments of oil coolers 54 and 154 within the CT gantry 42, in which a PCM 68 is incorporated within the oil radiator 60 or fluid / fluid oil cooler 160. As illustrated in Figure 7, the PCM in the oil cooler embodiment 54 or 154 absorbs instantaneous waste heat spikes generated by the X-ray source 46, which buffers and normalizes the average temperature within the CT gantry 42, ultimately distributing the heat absorption burden between the oil cooler and the overall cooling system 24. In some embodiments, the PCM 68 in the oil cooler absorbs much or all of the waste heat generated by the X-ray source 46 during a CT scan, and subsequently releases it to the CT internal cooler 47 to reduce the overall heat load on the external cooling system 24. In contrast, an oil cooler without a PCM requires the CT internal cooler 47, which has a higher heat absorption capacity, to adapt to the instantaneous temperature spikes generated by the X-ray source 46. As a higher heat absorption capacity is required, the overall thermal load on the external cooling system 24 increases, ensuring that the temperature of the coolant flowing out of the CT coolant outlet 32 ​​remains below the 23°C temperature limit for the DEA 38 in the PET scanner 12, in an exemplary embodiment. The increased thermal load on the external cooling system necessitates a larger capacity for the external heat exchanger 84 and a larger capacity for the standby PCM heatsink 88.

[0034] Next, regarding the second cooling loop in the cooling system 24, the mixing valve 94 selectively and proportionally mixes the coolant at the first temperature that has passed through the CT internal cooler 47 in the first coolant loop with the relatively high-temperature downstream coolant that has passed through the PET internal cooler 40 from the third bypass tee 98, at a flow rate determined by the second cooling pump 96, thereby obtaining the desired intake coolant temperature at the PET coolant inlet 26. The coolant at the desired temperature then passes through the PET internal cooler 40, where it absorbs heat from the DEA 38 and any other heat-generating parts (heat-producing components) in the PET scanner 12. One of the specific coolant temperature control parameters of interest is to maintain a stable temperature bandwidth window of the detector components in the DEA 38 within the specified parameters, thereby avoiding detector distortion. In some embodiments of the imaging system, the DEA38 incorporates components of a SiPM detector, and the coolant temperature bandwidth window is within 23°C ± 2°C for all detector components within the PET gantry 36.

[0035] Generally, the kilowatts of heat transfer capacity within the cooling system 24 are calculated to maintain specific operating temperature parameters within the PET / CT scanner 10. The waste heat absorbed by the cooling system 24 is ultimately transferred to the facility's water system 80 via an external heat exchanger 84. In the event of a power failure in the imaging facility, a backup continuous (uninterrupted) power supply typically provides power to the PET / CT scanner 10, the associated first and second circulation pumps 90 and 96, and any other powered components of the cooling system 24 (e.g., the control system). This allows for the completion of patient scans that were already underway before the power failure. If the power failure impairs the performance of the facility's water system 80, which supplies cooling water to the external heat exchanger 84, the PCM heatsink 88 serves as a passive alternative heatsink for the heat exchanger. When the temperature of the coolant circulating in the first and second loops of the cooling system 24 rises to the melting temperature of the exemplary phase-change material in the PCM heatsink 88, the material in the PCM heatsink 88 begins to melt and absorbs latent heat until all of the material has melted. The thermal mass of the exemplary PCM in the PCM heatsink 88 is calculated to absorb the kilowatts of heat generated by the CT / PET scanner 12 in the specified time (approximately 10 minutes) required to complete the scan image. The scanner 10 continues to operate until all of the PCM has melted or the scan is complete. During the controlled shutdown of the CT / PET scanner 12, embodiments of the PCM-enhanced oil coolers 54 and 154 in Figures 4 and 5 absorb some or all of the waste heat generated by the X-ray source 46 to reduce the thermal load; otherwise, that heat needs to be absorbed by the PCM heatsink 88. In some embodiments, after an interruption in the equipment water supply 80, the flow of water to the external heat exchanger 84 and the supply of coolant to the CT internal cooler 47 are temporarily shut off or restricted. As a result, the PCM 68 in the oil cooler shares the heat load with the PCM heatsink 88. This reduces the overall heat load of the external cooling system 24 while completing an ongoing imaging scan.

[0036] When water circulation by the equipment's water system 80 is restored, in an exemplary embodiment of the cooling system 24, the external heat exchanger 84 cools the circulating coolant to a temperature below the melting point of the material in the PCM heatsink 88, which is 16°C. This causes the material in the PCM heatsink 88 to solidify again, preparing for future passive and continuous cooling of the cooling system 24, even if the equipment's water system 88 or power supply is interrupted. Similarly, in an embodiment where the PCM 68 in the CT scanner 14 temporarily absorbs the heat load, its material regenerates and solidifies again as the coolant circulates in the CT internal cooler 47.

[0037] While embodiments of passive continuous cooling systems have been described in this specification, they are assumed to be incorporated within a PET / CT combined modality scanner 10. However, other embodiments of the cooling system may be incorporated into single-modality PET or CT scanners.

[0038] This specification has illustrated and described in detail various embodiments. However, many other modified embodiments that similarly fall within the scope of the claimed invention can be readily conceived. Therefore, the invention relating to this application is not limited to the details of the exemplary embodiments relating to configurations and arrangements of components described herein and shown in the drawings. The invention can be carried out in other embodiments and can be further carried out or implemented in various ways. Furthermore, it should be understood that the expressions and terms used herein are for illustrative purposes only and are not limiting. For example, where “including,” “comprising,” and “having,” and similar terms are used herein, they may encompass not only the items listed thereafter but also their equivalents and additional items. Unless otherwise specified or limited, the terms “mounted,” “connected,” “supported,” and “coupled,” and similar terms should be interpreted broadly and may encompass direct and indirect mounting, connection, support, and coupling.

Claims

1. A passive continuous cooling system for a diagnostic imaging scanner, comprising a diagnostic imaging scanner, an internal cooler within the scanner, and an external cooling system outside the scanner, The diagnostic medical imaging scanner is selected from a group of imaging modalities consisting of PET, CT, and combined PET / CT, and the scanner comprises a patient table surrounded by a gantry and a photon detector assembly (PDA) coupled to the gantry, and the PDA has a maximum operating temperature within an operating temperature window during the patient imaging scan. The internal cooler within the scanner is thermally connected to the gantry and the PDA, has a coolant inlet and a coolant outlet, captures the internal waste heat generated within the scanner during patient imaging scans, and maintains the temperature of the PDA below its maximum operating temperature. The external cooling system outside the scanner circulates liquid coolant in a closed-loop coolant conduit, directing it towards the coolant intake and outlet of the internal cooler, and extracting captured internal waste heat from the internal cooler as the circulating coolant flows through it. The external cooling system includes a liquid / liquid external heat exchanger in the closed-loop conduit upstream of the coolant inlet of the internal cooler, extracting heat from the circulating coolant and transferring it to the water supply of the equipment's water system, wherein the heat transfer rate through the external liquid / liquid heat exchanger is sufficient to maintain the temperature of the coolant at the coolant inlet of the internal cooler below the maximum operating temperature of the PDA, and The external cooling system is a continuous cooling system comprising a heat sink in a closed-loop coolant conduit located downstream of the external heat exchanger and upstream of the coolant inlet of the internal cooler, the heat sink comprising a first phase change material (PCM), the first PCM oriented outward from the conduit and in conductive thermal communication with the coolant, the melting temperature of the first PCM being below the maximum operating temperature of the PDA, and when the temperature of the coolant exceeds the melting temperature of the first PCM, the material absorbs latent heat from the coolant to maintain the temperature at the coolant inlet below the maximum operating temperature of the PDA for a specified duration sufficient to perform a complete patient scan.

2. The continuous cooling system according to claim 1, wherein the internal cooler is equipped with an air / fluid heat exchanger to capture internal waste heat from the ambient air inside the scanner in order to extract the coolant that circulates through the coolant inlet and out through the coolant outlet.

3. The continuous cooling system according to claim 1, wherein the internal cooler is equipped with a fluid / fluid heat exchanger to capture internal waste heat generated in the scanner in order to extract the coolant that circulates through the coolant inlet and out through the coolant outlet.

4. The first PCM is, Paraffin wax, and / or, Salt hydrates at positive temperature, and / or, Organic matter at positive temperatures, and / or High-temperature salt A continuous cooling system according to claim 1, selected from a group consisting of the following.

5. The continuous cooling system further includes a CT scanner. The CT scanner is equipped with a rotary CT gantry, the rotary CT gantry having an X-ray source held in a sealed X-ray housing and an oil cooler that is in thermal communication with the internal cooler in the scanner. The oil cooler includes a closed-loop oil conduit, the closed-loop oil conduit comprising, within the closed loop, an inlet line and an outlet line for flowing oil coupled to the X-ray housing, an oil pump for circulating oil within the oil conduit to cool the X-ray source, and a second-phase change material (PCM) oriented outside the oil conduit so as to be conductively thermally in communication with the circulating oil. The second PCM absorbs latent heat from the circulating oil during the phase transition from solid to liquid, buffering the instantaneous heat spikes generated by the X-ray source during the patient imaging scan, and further, the second PCM transfers the absorbed latent heat to the scanner's internal cooler during the time intervals between the resulting instantaneous heat spikes. The continuous cooling system according to claim 1.

6. The continuous cooling system according to claim 5, wherein the oil cooler further comprises an oil radiator coupled to the oil conduit, the oil radiator being in thermal communication with an internal air / liquid cooler in the scanner, and the internal cooler being further coupled to the coolant inlet and the coolant outlet.

7. The continuous cooling system according to claim 5, wherein the oil cooler further comprises an oil / fluid heat exchanger coupled to the oil conduit, the oil / fluid heat exchanger is in fluid and thermal communication with a liquid / liquid internal cooler in the scanner, and the internal cooler is coupled to the coolant inlet and the coolant outlet.

8. The continuous cooling system according to claim 5, wherein the second PCM has a melting range of 70°C.

9. The continuous cooling system further comprises a PET / CT scanner and a PET cooling fluid inlet for the PET internal cooler. The gantry of the PET / CT scanner each has a PDA inside, and each gantry surrounds a patient table. The PET coolant inlet of the PET internal cooler is oriented into the closed-loop coolant conduit downstream of the CT coolant outlet of the CT internal cooler. The second PCM of the CT scanner's oil cooler retains the absorbed latent heat generated by the X-ray source when the water supply to the external heat exchanger of the external cooling system is interrupted, thereby reducing the latent heat absorbed by the first PCM in the heat sink of the external cooling system. The continuous cooling system according to claim 5.

10. In the event that the supply of cooling water to the water-cooled external cooling system of a diagnostic medical imaging scanner is interrupted, a method for passively and continuously cooling the diagnostic medical imaging scanner is provided. The system includes a diagnostic imaging scanner selected from a group of imaging modalities consisting of PET, CT, and combined PET / CT, and in this case, the scanner is: The system comprises a patient table surrounded by a gantry and a photon detector assembly (PDA) coupled to the gantry, wherein the PDA has a maximum operating temperature within an operating temperature window during a patient imaging scan. The scanner has an internal cooler, which is thermally in communication with the gantry and the PDA, and the internal cooler has a coolant inlet and a coolant outlet, which captures the internal waste heat generated in the scanner during patient imaging scans to maintain the temperature of the PDA below its maximum operating temperature. The scanner is equipped with an external cooling system that circulates liquid coolant in a closed-loop coolant conduit, directing it towards the coolant intake and outlet of the internal cooler, and removing captured internal waste heat from the internal cooler as the circulating coolant flows through it. The external cooling system includes a liquid / liquid external heat exchanger in the closed-loop conduit upstream of the coolant inlet of the internal cooler, which extracts heat from the circulating coolant and transfers it to the water supply of the equipment's water system, wherein the heat transfer rate through the external liquid / liquid heat exchanger is sufficient to maintain the temperature of the coolant at the coolant inlet of the internal cooler below the maximum operating temperature of the PDA, and to transfer the heat from the circulating coolant to the water supply of the equipment's water system. Downstream of the external heat exchanger and upstream of the coolant inlet of the internal cooler, a heat sink is provided within the closed-loop coolant conduit, the heat sink contains a first phase change material (PCM), the first PCM is oriented outward from the conduit and is in thermal communication with the coolant, and the melting temperature of the first PCM is below the maximum operating temperature of the PDA. Using the scanner, the imaging scan of the patient is initiated, and at this time, the external cooling system is activated to circulate the coolant through the coolant loop, transferring heat from the circulating coolant to the water supply of the equipment's water system, thereby maintaining the temperature of the PDA below its maximum operating temperature. When the water supply of the equipment's water system to the liquid / liquid external heat exchanger is interrupted, the captured internal waste heat extracted from the internal cooler by the coolant is absorbed as latent heat within the first PCM of the heat sink by melting the first PCM, thereby keeping the temperature at the coolant inlet below the maximum operating temperature of the PDA for a specified duration sufficient to perform a complete patient scan, and During the specified duration, the patient scan is completed. method.

11. Furthermore, the second PCM is oriented within the gantry to be in thermal communication with the internal cooler, thereby capturing and buffering instantaneous spikes in internal waste heat generated within the scanner during patient imaging scans. In a steady state, the buffered waste heat from the second PCM is transferred to the internal cooler, and at this time, the external heat exchanger of the external cooling system transfers heat from the circulating coolant to the water supply of the equipment's water system. When the water supply to the external heat exchanger is interrupted, the additional waste heat within the second PCM is retained as latent heat until the second PCM is completely melted, thereby temporarily reducing the amount of waste heat that would otherwise be transferred to the coolant of the external cooling system, which could otherwise be transferred to the first PCM in the heat sink. The method according to claim 10.

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